AD AD7719 Low voltage, low power Datasheet

a
Low Voltage, Low Power,
Factory-Calibrated 16-/24-Bit Dual - ADC
AD7719
FEATURES
HIGH RESOLUTION - ADCs
2 Independent ADCs (16- and 24-Bit Resolution)
Factory-Calibrated (Field Calibration Not Required)
Output Settles in 1 Conversion Cycle (Single
Conversion Mode)
Programmable Gain Front End
Simultaneous Sampling and Conversion of 2
Signal Sources
Separate Reference Inputs for Each Channel
Simultaneous 50 Hz and 60 Hz Rejection at 20 Hz
Update Rate
APPLICATIONS
Sensor Measurement
Temperature Measurement
Pressure Measurement
Weigh Scales
Portable Instrumentation
4 to 20 mA Transmitters
GENERAL DESCRIPTION
The AD7719 is a complete analog front end for low frequency
measurement applications. It contains two high resolution Σ-∆
ADCs, switchable matched excitation current sources, low-side
power switches, digital I/O port, and temperature sensor. The
24-bit main channel with PGA accepts fully differential, unipolar,
and bipolar input signal ranges from 1.024 × REFIN1/128 to
1.024 × REFIN1. Signals can be converted directly from a transducer without the need for signal conditioning. The 16-bit auxiliary
channel has an input signal range of REFIN2 or REFIN2/2.
ISOURCE Select™
24-Bit No Missing Codes—Main ADC
13-Bit p-p Resolution @ 20 Hz, 20 mV Range
18-Bit p-p Resolution @ 20 Hz, 2.56 V Range
INTERFACE
3-Wire Serial
SPI®, QSPI™, MICROWIRE™, and DSP Compatible
Schmitt Trigger on SCLK
The device operates from a 32 kHz crystal with an on-chip
PLL generating the required internal operating frequency. The
output data rate from the part is software programmable. The
peak-to-peak resolution from the part varies with the programmed
gain and output data rate.
POWER
Specified for Single 3 V and 5 V Operation
Normal: 1.5 mA Typ @ 3 V
Power-Down: 10 A (32 kHz Crystal Running)
The part operates from a single 3 V or 5 V supply. When operating from 3 V supplies, the power dissipation for the part is
4.5 mW with both ADCs enabled and 2.85 mW with only the
main ADC enabled in unbuffered mode. The AD7719 is housed
in 28-lead SOIC and TSSOP packages.
ON-CHIP FUNCTIONS
Rail-Rail Input Buffer and PGA
4-Bit Digital I/O Port
On-Chip Temperature Sensor
Dual Switchable Excitation Current Sources
Low-Side Power Switches
Reference Detect Circuit
FUNCTIONAL BLOCK DIAGRAM
DVDD
REFIN1(+)
DGND
REFIN1(–)
AVDD
IOUT1
IEXC1
200A
IEXC2
200A
XTAL1
REFERENCE
DETECT
AD7719
AIN1
AIN2
AIN3
AIN4
MUX1
MAIN CHANNEL
24-BIT - ADC
PGA
BUF
OSC. AND
PLL
DOUT
DIN
SCLK
CS
RDY
RESET
SERIAL
INTERFACE
AND
CONTROL
LOGIC
IOUT2
AVDD
XTAL2
AVDD
AGND
I/O PORT
AIN5
AIN6
AUXILIARY CHANNEL
16-BIT - ADC
MUX2
MUX
TEMP
SENSOR
AVDD
AGND
REFIN2
PWRGND
P1/SW1 P2/SW2 P3
P4
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2003 Analog Devices, Inc. All rights reserved.
AD7719
TABLE OF CONTENTS
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . 6
ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
TIMING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 7
DIGITAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
PIN CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . 9
TYPICAL PERFORMANCE CHARACTERISTICS . . . . 11
DUAL-CHANNEL ADC CIRCUIT INFORMATION . . . 12
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Main Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Auxiliary Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Both Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
MAIN AND AUXILIARY ADC NOISE
PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
ON-CHIP REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Communications Register
(A3, A2, A1, A0 = 0, 0, 0, 0) . . . . . . . . . . . . . . . . . . . . 19
Status Register (A3, A2, A1, A0 = 0, 0, 0, 0;
Power-On Reset = 0x00) . . . . . . . . . . . . . . . . . . . . . . . 20
Mode Register (A3, A2, A1, A0 = 0, 0, 0, 1;
Power-On Reset = 0x00) . . . . . . . . . . . . . . . . . . . . . . . 21
Operating Characteristics when Addressing the
Mode and Control Registers . . . . . . . . . . . . . . . . . . . . . 22
Main ADC Control Register (AD0CON):
(A3, A2, A1, A0 = 0, 0, 1, 0;
Power-On Reset = 0x07) . . . . . . . . . . . . . . . . . . . . . . . 22
Aux ADC Control Registers (AD1CON):
(A3, A2, A1, A0 = 0, 0, 1, 1;
Power-On Reset = 0x01) . . . . . . . . . . . . . . . . . . . . . . . 23
Filter Register (A3, A2, A1, A0 = 0, 1, 0, 0;
Power-On Reset = 0x45) . . . . . . . . . . . . . . . . . . . . . . . 24
I/O and Current Source Control Register (IOCON):
(A3, A2, A1, A0 = 0, 1, 1, 1;
Power-On Reset = 0x0000) . . . . . . . . . . . . . . . . . . . . . 24
Main ADC Data Result Registers (DATA0):
(A3, A2, A1, A0 = 0, 1, 0, 1;
Power-On Reset = 0x00 0000) . . . . . . . . . . . . . . . . . . . 26
Aux ADC Data Result Registers (DATA1):
(A3, A2, A1, A0 = 0, 1, 1, 0;
Power-On Reset = 0x0000) . . . . . . . . . . . . . . . . . . . . . 26
Main ADC Offset Calibration Coefficient Registers (OF0):
(A3, A2, A1, A0 = 1, 0, 0, 0;
Power-On Reset = 0x80 0000) . . . . . . . . . . . . . . . . . . . 26
Aux ADC Offset Calibration Coefficient Registers (OF1):
(A3, A2, A1, A0 = 1, 0, 0, 1;
Power-On Reset = 0x8000) . . . . . . . . . . . . . . . . . . . . . 26
Main ADC Gain Calibration Coefficient Registers (GNO):
(A3, A2, A1, A0 = 1, 0, 1, 0;
Power-On Reset = 0x5X XXX5) . . . . . . . . . . . . . . . . . 26
Aux ADC Gain Calibration Coefficient Registers (GN1):
(A3, A2, A1, A0 = 1, 0, 1, 1;
Power-On Reset = 0x59XX) . . . . . . . . . . . . . . . . . . . . . 26
ID Register (ID): (A3, A2, A1, A0 = 1, 1, 1, 1;
Power-On Reset = 0x0X) . . . . . . . . . . . . . . . . . . . . . . . 26
User Nonprogrammable Test Registers . . . . . . . . . . . . . . 26
CONFIGURING THE AD7719 . . . . . . . . . . . . . . . . . . . . . 27
MICROCOMPUTER/MICROPROCESSOR
INTERFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
AD7719-to-68HC11 Interface . . . . . . . . . . . . . . . . . . . . . 29
AD7719-to-8051 Interface . . . . . . . . . . . . . . . . . . . . . . . . 29
AD7719-to-ADSP-2103/ADSP-2105 Interface . . . . . . . . 30
CIRCUIT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . 30
Analog Input Channels . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Programmable Gain Amplifier . . . . . . . . . . . . . . . . . . . . . 32
Bipolar/Unipolar Configuration . . . . . . . . . . . . . . . . . . . . 32
Data Output Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Burnout Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Excitation Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Crystal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Reference Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Reference Detect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Reset Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Power-Down Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Idle Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
ADC Disable Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Grounding and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . 36
3-Wire RTD Configurations . . . . . . . . . . . . . . . . . . . . . . 37
Smart Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . 39
REVISION HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
–2–
REV. A
AD7719–SPECIFICATIONS1(AV
DD = 2.7 V to 3.6 V or 4.75 V to 5.25 V, DVDD = 2.7 V to 3.6 V or 4.75 V to 5.25 V,
REFIN(+) = 2.5 V; REFIN(–) = AGND; AGND = DGND = 0 V; XTAL1/XTAL2 = 32.768 kHz Crystal; all specifications TMIN to TMAX, unless otherwise noted.)
Parameter
ADC CHANNEL SPECIFICATION
Output Update Rate
MAIN CHANNEL
No Missing Codes2
Resolution
Output Noise and Update Rates
Integral Nonlinearity
Offset Error3
Offset Error Drift vs. Temperature 4
Full-Scale Error5, 6, 7
Gain Drift vs. Temperature4
Power Supply Rejection (PSR)
ANALOG INPUTS
Differential Input Voltage Ranges
ADC Range Matching
Absolute AIN Voltage Limits
Analog Input Current2
DC Input Current
DC Input Current Drift
Absolute AIN Voltage Limits
Analog Input Current
DC Input Current
DC Input Current Drift
Normal-Mode Rejection2, 8
@ 50 Hz
@ 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz2
@ 60 Hz2
REFERENCE INPUT (REFIN1)
REFIN1 Voltage
REFIN1 Voltage Range2
REFIN1 Common-Mode Range
Reference DC Input Current
Reference DC Input Current Drift
Normal-Mode Rejection2, 8
@ 50 Hz
@ 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz
@ 60 Hz
Reference Detect Levels
AUXILIARY CHANNEL
No Missing Codes2
Resolution
Output Noise and Update Rates
Integral Nonlinearity
REV. A
AD7719B
Unit
Test Conditions
5.4
105
Hz min
Hz max
Both Channels Synchronized
0.732 ms Increments
24
13
18
See Tables II to V
±10
±3
±10
±10
±0.5
80
Bits min
Bits p-p
Bits p-p
20 Hz Update Rate
±20 mV Range, 20 Hz Update Rate
±2.56 V Range, 20 Hz Update Rate
ppm of FSR max
µV typ
nV/°C typ
µV typ
ppm/°C typ
dB min
Typically 2 ppm. FSR =
±1.024 × REFIN1/GAIN
V nom
±2
AGND + 100 mV
AVDD – 100 mV
µV typ
V min
V max
±1
±5
AGND – 30 mV
AVDD + 30 mV
nA max
pA /°C typ
V min
V max
±125
±2
nA/V typ
pA/V/°C typ
100
100
dB min
dB min
50 Hz ± 1 Hz, 16.65 Hz Update Rate, SF = 82
60 Hz ± 1 Hz, 20 Hz Update Rate, SF = 68
90
dB min
100
100
dB min
dB min
Input Range = ±2.56 V, AIN = 1 V.
100 dB typ. 110 dB typ on ±20 mV Range
50 Hz ± 1 Hz, Range = ±2.56 V, AIN = 1 V
60 Hz ± 1 Hz, Range = ±2.56 V, AIN = 1 V
2.5
1
AVDD
AGND – 30 mV
AVDD + 30 mV
0.5
±0.01
V nom
V min
V max
V min
V max
µA/V typ
nA/V/°C typ
REFIN1 = REFIN1(+) – REFIN1(–)
100
100
dB min
dB min
50 Hz ± 1 Hz, SF = 82
60 Hz ± 1 Hz, SF = 68
110
110
110
0.3
0.65
dB typ
dB typ
dB typ
V min
V max
Input Range = ±2.56 V, AIN = 1 V
50 Hz ± 1 Hz, Range = 2.56 V, AIN = 1 V
60 Hz ± 1 Hz, Range = 2.56 V, AIN = 1 V
NOXREF Bit Active if VREF < 0.3 V
NOXREF Bit Inactive if VREF > 0.65 V
16
16
See Tables VI and VIII
±15
Bits min
Bits p-p
±2.5 V Range, 20 Hz Update Rate
2 × 1.024 REFIN 1
Gain
At the Calibrated Conditions
Input Range = ±2.56 V, 100 dB typ.
110 dB typ on ±20 mV Range
REFIN1 = REFIN1(+) – REFIN1(–)
GAIN = 1 to 128.
Input Voltage = 19 mV on All Ranges
BUF = 0; Buffered Mode of Operation
BUF = 0
ppm of FSR max
–3–
BUF = 1; Unbuffered mode of operation.
BUF = 1. Unbuffered Mode of Operation.
Input Current Varies with Input Voltage
AD7719
Parameter
AD7719B
Unit
Test Conditions
AUXILIARY CHANNEL (continued)
Offset Error3
Offset Error Drift vs. Temperature 4
Full-Scale Error6, 7
Gain Drift vs. Temperature4
Negative Full-Scale Error
Power Supply Rejection (PSR)
±3
±10
±0.75
0.5
±1
70
µV typ
nV/°C typ
LSB typ
ppm/°C typ
LSB typ
dB min
Selected Channel = AIN5/AIN6
±REFIN2
±REFIN2/2
AGND – 30 mV
AVDD + 30 mV
V nom
V nom
V min
V max
ARN = 1
ARN = 0
Unbuffered Input
±125
±2
nA/V typ
pA/V/°C typ
Input Current Varies with Input Voltage
100
100
dB min
dB min
50 Hz ±1 Hz, SF = 82
60 Hz ±1 Hz, SF = 68
85
90
90
dB min
dB min
dB min
Input Range = ±2.5 V, AIN = 1 V
50 Hz ±1 Hz, Range = 2.5 V, AIN = 1 V
60 Hz ±1 Hz, Range = 2.5 V, AIN = 1 V
2.5
1
AVDD
0.2
0.003
V nom
V min
V max
µA/V typ
nA/V/°C typ
200
±10
200
±1
µA nom
% typ
ppm/°C typ
% typ
20
2.1
300
AVDD – 0.6
AGND – 30 mV
ppm/°C typ
µA/V max
nA/V typ
V max
V min
5
7
20
Ω max
Ω max
mA max
TEMPERATURE SENSOR
Accuracy
See TPC 5
°C typ
TRANSDUCER BURNOUT
AIN(+) Current
AIN(–) Current
Initial Tolerance @ 25°C
Drift
–100
100
±15
0.03
nA typ
nA typ
% typ
%/°C typ
1.05 × FS10
–1.05 × FS
0.8 × FS
2.1 × FS
V max
V min
V min
V max
ANALOG INPUTS
Differential Input Voltage Ranges
Absolute AIN Voltage Limits
Analog Input Current
DC Input Current
DC Input Current Drift
Normal-Mode Rejection2, 8
@ 50 Hz
@ 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz2
@ 60 Hz2
REFERENCE INPUT (REFIN2)
REFIN2 Voltage
REFIN2 Range2
Reference DC Input Current 2
Reference DC Input Current Drift
EXCITATION CURRENT SOURCES
(IEXC1 and IEXC2)
Output Current
Initial Tolerance at 25°C
Drift
Initial Current Matching at 25°C
Drift Matching
Line Regulation (AVDD)
Load Regulation
Output Compliance
LOW-SIDE POWER SWITCHES
(SW1, SW2)
RON
Allowable Current2
SYSTEM CALIBRATION2, 9
Full-Scale Calibration Limit
Zero-Scale Calibration Limit
Input Span
AIN = 1 V Input Range = ±2.5 V, Typically 80 dB
With Respect to AGND
–4–
Matching between IEXC1 and IEXC2
No Load
AVDD = 5 V ± 5%. Typically 1.25 µA/V
AVDD = 5 V. Typically 3 Ω
AVDD = 3 V. Typically 4.5 Ω
Continuous Current per Switch
REV. A
AD7719
Parameter
LOGIC INPUTS
All Inputs Except SCLK and XTAL1 2
VINL, Input Low Voltage
VINH, Input High Voltage
SCLK Only (Schmitt-Triggered Input) 2
VT(+)
VT(–)
VT(+) – VT(–)
VT(+)
VT(–)
VT(+) – VT(–)
XTAL1 Only2
VINL, Input Low Voltage
VINH, Input High Voltage
VINL, Input Low Voltage
VINH, Input High Voltage
Input Currents
Input Capacitance2
LOGIC OUTPUTS (Excluding XTAL2)
VOH, Output High Voltage2
VOL, Output Low Voltage2
VOH, Output High Voltage2
VOL, Output Low Voltage 2
Floating-State Leakage Current
Floating-State Output Capacitance
Data Output Coding
AD7719B
Unit
Test Conditions
0.8
0.4
2.0
V max
V max
V min
DVDD = 5 V
DVDD = 3 V
DVDD = 3 V or 5 V
1.4/2
0.8/1.4
0.3/0.85
0.95/2
0.4/1.1
0.3/0.85
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
DVDD = 5 V
DVDD = 5 V
DVDD = 5 V
DVDD = 3 V
DVDD = 3 V
DVDD = 3 V
0.8
3.5
0.4
2.5
±10
–70
V max
V min
V max
V min
µA max
µA max
10
pF typ
DVDD = 5 V
DVDD = 5 V
DVDD = 3 V
DVDD = 3 V
VIN = DVDD
VIN = DGND, Typically –40 µA at 5 V
and –20 µA at 3 V
All Digital Inputs
DVDD – 0.6
0.4
4
0.4
±10
±10
Binary
Offset Binary
V min
V max
V min
V max
µA max
pF typ
Unipolar Mode
Bipolar Mode
I/O PORT11
VINL, Input Low Voltage2
VINH, Input High Voltage2
Input Currents
Input Capacitance
VOH, Output High Voltage2
VOL, Output Low Voltage2
VOH, Output High Voltage2
VOL, Output Low Voltage2
Floating-State Output Leakage Current
Floating-State Output Capacitance
START-UP TIME
From Power-On
From Idle Mode
From Power-Down Mode
POWER REQUIREMENTS
Power Supply Voltages
AVDD – AGND
DVDD – DGND
Power Supply Currents
DIDD Current (Normal Mode) 12
REV. A
DVDD = 3 V, ISOURCE = 100 µA
DVDD = 3 V, ISINK = 100 µA
DVDD = 5 V, ISOURCE = 200 µA
DVDD = 5 V, ISINK = 1.6 mA
I/O Port Voltages Are with Respect to
AVDD and AGND
AVDD = 5 V
AVDD = 3 V
AVDD = 3 V or 5 V
VIN = AVDD
VIN = AGND, Typically –40 µA at AVDD = 5 V
and –20 µA at AVDD = 3 V
All Digital Inputs
AVDD = 3 V, ISOURCE = 100 µA
AVDD = 3 V, ISINK = 100 µA
AVDD = 5 V, ISOURCE = 200 µA
AVDD = 5 V, ISINK = 1.6 mA
0.8
0.4
2.0
±10
–70
V max
V max
V min
µA max
µA max
10
AVDD – 0.6
0.4
4
0.4
±10
±10
pF typ
V min
V max
V min
V max
µA max
pF typ
300
1
1
300
ms typ
ms typ
ms typ
ms typ
Osc. Active in Power-Down
Osc. Powered Down
2.7/3.6
4.75/5.25
2.7/3.6
4.75/5.25
V min/max
V min/max
V min/max
V min
AVDD = 3 V nom
AVDD = 5 V nom
DVDD = 3 V nom
DVDD = 5 V nom
0.6
0.75
mA max
mA max
DVDD = 3 V, 0.5 mA typ
DVDD = 5 V, 0.6 mA typ
–5–
AD7719
Parameter
AD7719B
Unit
Test Conditions
1.1
mA max
0.55
mA max
AIDD Current (Aux ADC)
AIDD Current (Main and Aux ADC)
0.3
1.25
mA max
mA max
DIDD (ADC Disable Mode)13
0.35
0.4
0.15
10
2
30
8
1
mA max
mA max
mA max
µA max
µA max
µA max
µA max
µA max
AVDD = 3 V or 5 V, Buffered Mode,
0.85 mA typ
AVDD = 3 V or 5 V, Unbuffered Mode,
0.45 mA typ
AVDD = 3 V or 5 V, 0.25 mA typ
AVDD = 3 V or 5 V, Main ADC Buffered,
1 mA typ
DVDD = 3 V, 0.25 mA typ
DVDD = 5 V, 0.3 mA typ
AVDD = 3 V or 5 V
DVDD = 3 V, 32.768 kHz Osc. Running
DVDD = 3 V, Oscillator Powered Down
DVDD = 5 V, 32.768 kHz Osc. Running
DVDD = 5 V, Oscillator Powered Down
AVDD = 3 V or 5 V
Power Supply Currents (Continued)
AIDD Current (Main ADC)
AIDD (ADC Disable Mode)
DIDD (Power-Down Mode)
AIDD (Power-Down Mode)
NOTES
1
Temperature range –40°C to +85°C.
2
Guaranteed by design and/or characterization data on production release.
3
System zero calibration will remove this error.
4
A calibration at any temperature will remove this drift error.
5
The main ADC is factory-calibrated with AV DD = DVDD = 4 V, TA = 25°C, REFIN1(+) – REFIN1(–) = 2.5 V. If the user power supplies or temperature conditions
are significantly different from these, internal full-scale calibration will restore this error to the published specification. System calibration can be used to reduce this
error to the order of the noise. Full-scale error applies to both positive and negative full scale.
6
A system full-scale calibration will remove this error.
7
A typical gain error of ±10 µV results following a user self-calibration.
8
Simultaneous 50 Hz and 60 Hz rejection is achieved using 19.8 Hz (SF = 69) update rate. Normal mode rejection in this case is 60 dB min.
9
After a calibration if the analog input exceeds positive full scale, the converter will output all 1s. If the analog input is less than negative full scale, the device will
output all 0s.
10
FS = Full-Scale Input. FS = 1.024 × REFIN1/Gain on the main ADC, where REFIN1 = REFIN1(+) – REFIN1(–). FS = REFIN2 on the aux ADC when ARN = 1
in the aux ADC control register (AD1CON) and REFIN2/2 on the aux ADC when ARN = 0.
11
Input and output levels on the I/O Port are with respect to AV DD and AGND.
12
Normal mode refers to the case where both main and aux ADCs are running.
13
ADC disable is entered by setting both the AD0EN and AD1EN bits in the main and aux ADC control registers to a 0 and setting the mode bits (MD2, MD1,
MD0) in the mode register to non-0.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS 1
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
SOIC Package
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . 71.4°C/W
θJC Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 23°C/W
TSSOP Package
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . 97.9°C/W
θJC Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 14°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
(TA = 25°C, unless otherwise noted.)
AVDD to AGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
AVDD to DGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
DVDD to AGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
DVDD to DGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
AGND to DGND2. . . . . . . . . . . . . . . . . . . –20 mV to +20 mV
PWRGND to AGND . . . . . . . . . . . . . . . . –20 mV to +20 mV
AVDD to DVDD . . . . . . . . . . . . . . . . . . . . . . . . . . –5 V to +5 V
Analog Input Voltage to AGND . . . . –0.3 V to AVDD +0.3 V
Reference Input Voltage to AGND . . –0.3 V to AVDD +0.3 V
Total AIN/REFIN Current (Indefinite) . . . . . . . . . . . . 30 mA
Digital Input Voltage to DGND . . . . –0.3 V to DVDD +0.3 V
Digital Output Voltage to DGND . . . –0.3 V to DVDD +0.3 V
Operating Temperature Range . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
2
AGND and DGND are connected internally within the AD7719.
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
AD7719BR
AD7719BRU
EVAL-AD7719EB
–40°C to +85°C
–40°C to +85°C
SOIC
TSSOP
Evaluation Board
R-28
RU-28
–6–
REV. A
AD7719
TIMING CHARACTERISTICS1, 2 (AV
DD = 2.7 V to 3.6 V or AVDD = 4.75 V to 5.25 V; DVDD = 2.7 V to 3.6 V or DVDD = 4.75 V to 5.25 V;
AGND = DGND = 0 V; XTAL = 32.768 kHz; Input Logic 0 = 0 V, Logic 1 = DVDD, unless otherwise noted.)
Parameter
t1
t2
Read Operation
t3
t4
t5 4
t5A4, 5
t6
t7
t8
t9 6
t10
Write Operation
t11
t12
t13
t14
t15
t16
Limit at TMIN, TMAX
(B Version)
Unit
Conditions/Comments
32.768
50
kHz typ
ns min
Crystal Oscillator Frequency
RESET Pulsewidth
0
0
0
60
80
0
60
80
100
100
0
10
80
100
ns min
ns min
ns min
ns max
ns max
ns min
ns max
ns max
ns min
ns min
ns min
ns min
ns max
ns max
RDY to CS Setup Time
CS Falling Edge to SCLK Active Edge Setup Time3
SCLK Active Edge to Data Valid Delay3
DVDD = 4.75 V to 5.25 V
DVDD = 2.7 V to 3.6 V
CS Falling Edge to Data Valid Delay3
DVDD = 4.75 V to 5.25 V
DVDD = 2.7 V to 3.6 V
SCLK High Pulsewidth
SCLK Low Pulsewidth
CS Rising Edge to SCLK Inactive Edge Hold Time3
Bus Relinquish Time after SCLK Inactive Edge3
0
30
25
100
100
0
ns min
ns min
ns min
ns min
ns min
ns min
CS Falling Edge to SCLK Active Edge Setup Time3
Data Valid to SCLK Edge Setup Time
Data Valid to SCLK Edge Hold Time
SCLK High Pulsewidth
SCLK Low Pulsewidth
CS Rising Edge to SCLK Edge Hold Time
SCLK Active Edge to RDY High3, 7
NOTES
1
Sample tested during initial release to ensure compliance. All input signals are specified with t R = tF = 5 ns (10% to 90% of DV DD) and timed from a voltage level of 1.6 V.
2
See Figures 2 and 3.
3
SCLK active edge is falling edge of SCLK.
4
These numbers are measured with the load circuit of Figure 1 and defined as the time required for the output to cross the VOL or VOH limits.
5
This specification only comes into play if CS goes low while SCLK is low. It is required primarily for interfacing to DSP machines.
6
These numbers are derived from the measured time taken by the data output to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then
extrapolated back to remove effects of charging or discharging the 50 pF capacitor. This means that the times quoted in the Timing Characteristics are the true bus
relinquish times of the part and as such are independent of external bus loading capacitances.
7
RDY returns high after a read of both ADCs. The same data can be read again, if required, while RDY is high, although care should be taken that subsequent reads
do not occur close to the next output update.
Specifications subject to change without notice.
ISINK (1.6mA WITH DVDD = 5V
100A WITH DVDD = 3V)
TO OUTPUT
PIN
1.6V
50pF
ISOURCE (200A WITH DVDD = 5V
100A WITH DVDD = 3V)
Figure 1. Load Circuit for Timing Characterization
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD7719 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. A
–7–
WARNING!
ESD SENSITIVE DEVICE
AD7719
of the output register to indicate when not to read from the device
to ensure that a data read is not attempted while the register is
being updated. CS is used to select the device. It can be used to
decode the AD7719 in systems where a number of parts are
connected to the serial bus.
DIGITAL INTERFACE
As previously outlined, the AD7719’s programmable functions are
controlled using a set of on-chip registers. Data is written to these
registers via the part’s serial interface; read access to the on-chip
registers is also provided by this interface. All communications to
the part must start with a write operation to the Communications
register. After power-on or RESET, the device expects a write to
its Communications register. The data written to this register
determines whether the next operation to the part is a read or a
write operation and also determines to which register this read
or write operation occurs. Therefore, write access to any of the
other registers on the part starts with a write operation to the
Communications register followed by a write to the selected
register. A read operation from any other register on the part
(including the output data register) starts with a write operation
to the Communications register followed by a read operation
from the selected register.
Figures 2 and 3 show timing diagrams for interfacing to the
AD7719 with CS used to decode the part. Figure 3 is for a read
operation from the AD7719’s output shift register while Figure 2
shows a write operation to the input shift register. It is possible
to read the same data twice from the output register even though
the RDY line returns high after the first read operation. Care must
be taken, however, to ensure that the read operations have been
completed before the next output update is about to take place.
The AD7719’s serial interface consists of five signals: CS, SCLK,
DIN, DOUT, and RDY. The DIN line is used for transferring
data into the on-chip registers while the DOUT line is used for
accessing data from the on-chip registers. SCLK is the serial
clock input for the device, and all data transfers (either on DIN
or DOUT) take place with respect to this SCLK signal. The
RDY line is used as a status signal to indicate when data is ready
to be read from the AD7719’s data register. RDY goes low when a
new data-word is available in the output register of either the
main or aux ADCs. It is reset high when a read operation from
the data register is complete. It also goes high prior to the updating
The AD7719 serial interface can operate in 3-wire mode by tying
the CS input low. In this case, the SCLK, DIN, and DOUT lines
are used to communicate with the AD7719, and the status of
RDY bits (RDY0 and RDY1) can be obtained by interrogating
the STATUS register. This scheme is suitable for interfacing to
microcontrollers. If CS is required as a decoding signal, it can
be generated from a port bit. For microcontroller interfaces, it is
recommended that the SCLK idles high between data transfers.
The AD7719 can also be operated with CS used as a frame synchronization signal. This scheme is suitable for DSP interfaces.
In this case, the first bit (MSB) is effectively clocked out by CS
since CS would normally occur after the falling edge of SCLK
in DSPs. The SCLK can continue to run between data transfers
provided the timing numbers are obeyed.
CS
t11
t16
t14
SCLK
t15
t12
t13
DIN
MSB
LSB
Figure 2. Write Cycle Timing Diagram
RDY
t3
t10
CS
t4
t8
t6
SCLK
t5
t7
t6
t9
t5A
DOUT
MSB
LSB
Figure 3. Read Cycle Timing Diagram
–8–
REV. A
AD7719
The serial interface can be reset by exercising the RESET input
on the part. It can also be reset by writing a series of 1s on the
DIN input. If a logic 1 is written to the AD7719 DIN line for at
least 32 serial clock cycles, the serial interface is reset. This ensures
that in 3-wire systems, if the interface gets lost, either via a software
error or by some glitch in the system, it can be reset back to a
known state. This state returns the interface to where the AD7719
is expecting a write operation to its Communications register. This
operation resets the contents of all registers to their power-on
reset values.
Some microprocessor or microcontroller serial interfaces have a
single serial data line. In this case, it is possible to connect the
AD7719’s DATA OUT and DATA IN lines together and connect
them to the single data line of the processor. A 10 kΩ pull-up
resistor should be used on this single data line. In this case, if the
interface gets lost, because the read and write operations share
the same line, the procedure to reset it to a known state is
somewhat different than previously described. It requires a read
operation of 24 serial clocks followed by a write operation where
a logic 1 is written for at least 32 serial clock cycles to ensure
that the serial interface is back in a known state.
PIN CONFIGURATION
IOUT1
1
28 XTAL1
IOUT2
2
27 XTAL2
AVDD
3
26 DVDD
AGND
4
25 DGND
REFIN1(–)
5
REFIN1(+)
6
AD7719
24 DIN
AIN1
TOP VIEW 23 DOUT
7 (Not to Scale) 22 RDY
AIN2
8
21 CS
AIN3
9
20 SCLK
AIN4 10
19 RESET
AIN5 11
18 P1/SW1
AIN6 12
17 PWRGND
REFIN2 13
16 P2/SW2
P4 14
15 P3
PIN FUNCTION DESCRIPTIONS
Pin No. Mnemonic
1
IOUT1
2
IOUT2
3
4
5
AVDD
AGND
REFIN1(–)
6
REFIN1(+)
7
8
9
10
11
12
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
13
REFIN2
14
15
P4
P3
REV. A
Function
Output for Internal 200 µA Excitation Current Source. Current source IEXC1 and/or IEXC2 can be
switched to this output.
Output for Internal 200 µA Excitation Current Source. Current source IEXC1 and/or IEXC2 can be
switched to this output.
Analog Supply Voltage.
Analog Ground.
Negative Reference Input for Main ADC Channel. This reference input can lie anywhere between AGND
and AVDD – 1 V.
Positive Reference Input for Main ADC Channel. REFIN1(+) can lie anywhere between AVDD and
AGND + 1 V. The nominal reference voltage (REFIN1(+) – REFIN1(–)) is 2.5 V, but the part is functional
with a reference range from 1 V to AVDD.
Analog Input. AIN1 is dedicated to the main channel.
Analog Input. AIN2 is dedicated to the main channel.
Analog Input. AIN3 can be multiplexed to either the main or auxiliary channel.
Analog Input. AIN4 can be multiplexed to either the main or auxiliary channel.
Analog Input. AIN5 is dedicated to the auxiliary channel and is referenced to AIN6 or AGND.
Analog Input. AIN6 is dedicated to the auxiliary channel. It forms a differential input pair with AIN5 in
fully differential input mode or is referenced to AGND in pseudodifferential mode.
Single-Ended Reference Input for Auxiliary Channel. The nominal input reference is 2.5 V. The auxiliary
channel will function with an input reference range from 1 V to AVDD.
General-Purpose I/O Bit. The input and output voltage levels are referenced to AVDD and AGND.
General-Purpose I/O Bit. The input and output voltage levels are referenced to AVDD and AGND.
–9–
AD7719
PIN FUNCTION DESCRIPTIONS (continued)
Pin No. Mnemonic
Function
16
P2/SW2
17
18
PWRGND
P1/SW1
19
RESET
20
SCLK
21
CS
22
RDY
23
DOUT
24
DIN
25
26
27
28
DGND
DVDD
XTAL2
XTAL1
Dual-Purpose Pin. It can act as a general-purpose output (P2) bit referenced between AVDD and AGND
or as a low-side power switch (SW2) to PWRGND.
Ground Point for the Low-Side Power Switches SW2 and SW1. PWRGND must be tied to AGND.
Dual-Purpose Pin. It can act as a general-purpose output (P1) bit referenced between AVDD and AGND
or as a low-side power switch (SW1) to PWRGND.
Digital Input Used to Reset the ADC to Its Power-On Reset Status. This pin has a weak pull-up internally
to DVDD.
Serial Clock Input for Data Transfers to and from the ADC. The SCLK has a Schmitt-triggered input,
making the interface suitable for opto-isolated applications. The serial clock can be continuous with all
data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous clock with the
information being transmitted to or from the AD7719 in smaller batches of data. A weak pull-up to DVDD
is provided on the SCLK input.
Chip Select Input. This is an active low logic input used to select the AD7719. CS can be used to select
the AD7719 in systems with more than one device on the serial bus or as a frame synchronization signal in
communicating with the device. CS can be hardwired low, allowing the AD7719 to be operated in 3-wire
mode with SCLK, DIN, and DOUT used to interface with the device. A weak pull-up to DVDD is provided
on the CS input.
RDY is a logic low status output from the AD7719. RDY is low if either the main ADC or auxiliary ADC
channel has valid data in its data register. This output returns high on completion of a read operation
from the data register. If data is not read, RDY will return high prior to the next update, indicating to the
user that a read operation should not be initiated. The RDY pin also returns low following the completion
of a calibration cycle. The RDY pin is effectively the digital NOR function of the RDY0 and RDY1 bits in
the Status register. If one of the ADCs is disabled, the RDY pin reflects the active ADC. RDY does not
return high after a calibration until the mode bits are written to, enabling a new conversion or calibration.
Since the RDY pin provides information on both the main and aux ADCs, when either the main or aux
ADC is disabled, it is recommended to immediately read its data register to ensure that its RDY bit goes
inactive and releases the RDY pin to indicate output data updates on the remaining active ADC.
Serial Data Output Accessing the Output Shift Register of the AD7719. The output shift register can
contain data from any of the on-chip data, calibration, or control registers.
Serial Data Input Accessing the Input Shift Register on the AD7719. Data in this shift register is transferred
to the calibration or control registers within the ADC depending on the selection bits of the Communications
register. A weak pull-up to DVDD is provided on the DIN input.
Ground Reference Point for the Digital Circuitry.
Digital Supply Voltage, 3 V or 5 V Nominal.
Output from the 32 kHz Crystal Oscillator Inverter.
Input to the 32 kHz Crystal Oscillator Inverter.
–10–
REV. A
Typical Performance Characteristics– AD7719
26
8389600
8389400
24
NO MISSING CODES (Min)
CODE READ
8389200
8389000
8388800
8388600
8388400
22
20
18
8388200
8388000
16
0
100
200
300
400 500 600
READING NO.
700
800
900 1000
0
10
20
30
40
50
60
70
80
90
100 110
UPDATE RATE (Hz)
MAIN ADC IN BUFFERED MODE
RMS NOISE = 0.58V rms
TA = 25C
VREF = 2.5V
AVDD = DVDD = 5V
INPUT RANGE = 20mV
REFIN1(+)–REFIN1(–) = 2.5V
UPDATE RATE = 19.79Hz
TPC 4. No-Missing-Codes Performance
TPC 1. Typical Noise Plot on ±20 mV Input Range with
19.79 Hz Update Rate
1400
9
8
1200
7
1000
THE AMBIENT
TEMPERATURE VARIES
FROM 25C TO 30C
WHILE RECORDING
THE DATA FROM
THE DEVICES.
6
HITS
5
4
800
600
3
400
2
200
1
10
8389110
8388985
8389033
8388779
8388805
8388841
8388874
8388906
8388941
8388754
8388687
8388721
8388657
8388382
8388449
8388499
8388547
8388579
8388615
0
8388039
0
20
30
40
TEMPERATURE SENSOR ( C)
50
TPC 5. Temperature Sensor Accuracy
TPC 2. Noise Distribution Histogram
3.0
1200
2.56V RANGE
2.5
1000
800
AVDD = DVDD = 5V
VREF = 2.5V
INPUT RANGE = 2.56V
UPDATE RATE = 19.79Hz
TA = 25C
1.5
1.0
HITS
RMS NOISE (V)
2.0
20mV RANGE
400
0.5
200
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0
–30
5.0
VREF (V)
–20
–10
0
MAIN CAL ACC. @ 4V (V)
10
TPC 6. Full-Scale Error Distribution
TPC 3. RMS Noise vs. Reference Input
REV. A
600
–11–
20
AD7719
AVDD = DVDD = 5V
TA = 25C
VDD
OSCILLATOR
TIME BASE = 100ms/DIV
TRACE 1 = TRACE 2 = 2V/DIV
TPC 7. Typical Oscillator Power-Up
DUAL-CHANNEL ADC CIRCUIT INFORMATION
Overview
The AD7719 incorporates two independent Σ-∆ ADC channels
(main and auxiliary) with on-chip digital filtering intended for
the measurement of wide dynamic range, low frequency signals
such as those in weigh-scale, strain gage, pressure transducer, or
temperature measurement applications.
Main Channel
This channel is intended to convert the primary sensor input.
This channel can be operated in buffered or unbuffered mode, and
can be programmed to have one of eight input voltage ranges
from ±20 mV to ±2.56 V. This channel can be configured as
either two fully differential inputs (AIN1/AIN2 and AIN3/AIN4)
or three pseudodifferential input channels (AIN1/AIN4, AIN2/
AIN4, and AIN3/AIN4). Buffering the input channel means that
the part can accommodate significant source impedances on the
analog input and that R, C filtering (for noise rejection or RFI
reduction) can be placed on the analog inputs if required. Operating in unbuffered mode leads to lower power consumption in low
power applications, but care must be exercised in unbuffered mode
because source impedances can introduce gain errors. The main
ADC also features sensor burnout currents that can be switched
on and off. These currents can be used to check that a transducer
is still operational before attempting to take measurements.
The ADC employs a Σ-∆ conversion technique to realize up to
24 bits of no-missing-codes performance. The Σ-∆ modulator
fCHOP
ANALOG
INPUT
MUX
fIN
BUF
fMOD
PGA
-
converts the sampled input signal into a digital pulse train whose
duty cycle contains the digital information. A Sinc3 programmable
low-pass filter is then employed to decimate the modulator output
data stream to give a valid data conversion result at programmable output rates from 5.35 Hz (186.77 ms) to 105.03 Hz
(9.52 ms). A chopping scheme is also employed to minimize
ADC channel offset errors. A block diagram of the main ADC
input channel is shown in Figure 4. The sampling frequency of
the modulator loop is many times higher than the bandwidth of
the input signal. The integrator in the modulator shapes the
quantization noise (which results from the analog-to-digital
conversion) so that the noise is pushed toward one-half of the
modulator frequency. The output of the Σ-∆ modulator feeds
directly into the digital filter. The digital filter then band-limits
the response to a frequency significantly lower than one-half of
the modulator frequency. In this manner, the 1-bit output of the
comparator is translated into a band-limited, low noise output
from the AD7719 ADC. The AD7719 filter is a low-pass, Sinc3,
or (SIN(x)/x)3 filter whose primary function is to remove the
quantization noise introduced at the modulator. The cutoff
frequency and decimated output data rate of the filter are programmable via the SF word loaded to the filter register.
A chopping scheme is employed where the complete signal chain is
chopped, resulting in excellent dc offset and offset drift specifications, and is extremely beneficial in applications where drift, noise
rejection, and optimum EMI rejection are important factors.
With chopping, the ADC repeatedly reverses its inputs. The
decimated digital output words from the Sinc3 filters therefore
have a positive offset and negative offset term included. As a result,
a final summing stage is included so that each output word from
the filter is summed and averaged with the previous filter output
to produce a new valid output result to be written to the ADC
data register.
Auxiliary Channel
The Auxiliary (Aux) channel is intended to convert supplementary
inputs such as those from a cold junction diode or thermistor.
This channel is unbuffered and has an input range of ±REFIN2
or ±REFIN2/2, determined by the ARN bit in the auxiliary ADC
control register (AD1CON). AIN3 and AIN4 can be multiplexed
into the auxiliary channel as single-ended inputs with respect to
AGND, while AIN5 and AIN6 can operate as a differential
input pair. With AIN6 tied to AGND, AIN5 can be operated as
an additional single-ended input. A block diagram of the auxiliary
ADC channel is shown in Figure 5.
fCHOP
fADC
3
XOR
MOD0
(8 1 SF )
3 (8 SF )
1
2
DIGITAL
OUTPUT
SINC3 FILTER
AIN + V OS
AIN – V OS
Figure 4. Main ADC Channel Block Diagram
–12–
REV. A
AD7719
fCHOP
ANALOG
INPUT
fMOD
fCHOP
fADC
-
MUX
3
(8 1 SF )
XOR
MOD1
3 (8 SF )
1
2
DIGITAL
OUTPUT
SINC3 FILTER
AIN + VOS
AIN – VOS
Figure 5. Auxiliary ADC Channel Block Diagram
Both Channels
The operation of the aux channel is identical to the main
channel with the exception that there is no PGA on the aux
channel. The input chopping is incorporated into the input
multiplexer while the output chopping is accomplished by an
XOR gate at the output of the modulator. The chopped modulator
bit stream is applied to a Sinc3 filter. The programming of the
Sinc3 decimation factor is restricted to an 8-bit register SF; the
actual decimation factor is the register value times 8. The
decimated output rate from the Sinc3 filter (and the ADC
conversion rate) will therefore be
f ADC =
1  1 
×
× f MOD
3  8 × SF 
where:
fADC is the ADC update rate.
at odd integer multiples of fADC/2. The 3 dB frequency for all
values of SF obeys the following equation:
f (3 dB ) = 0.24 × f ADC
The signal chain is chopped as shown in Figures 4 and 5. The
chop frequency is
f

fCHOP =  ADC 
 2 
As shown in the block diagram, the Sinc3 filter outputs alternately
contain +VOS and –VOS, where VOS is the respective channel
offset. This offset is removed by performing a running average
of 2. This average by 2 means that the settling time to any change
in programming of the ADC will be twice the normal conversion
time, while an asynchronous step change on the analog input will
not be fully reflected until the third subsequent output.
 2 
tSETTLE = 
 = 2 × t ADC
 f ADC 
SF is the decimal equivalent of the word loaded to the
filter register.
fMOD is the modulator sampling rate of 32.768 kHz.
Programming the filter register determines the update rate for
both the main and aux ADC. Both ADCs operate with the same
update rate.
The allowable range for SF is 13 to 255, with a default of 69
(0x45). The corresponding conversion rates, conversion times,
and settling times are tabulated in Table I. Note that the conversion time increases by 0.732 ms for each increment in SF.
The chop rate of the channel is half the output data rate.
Table I. ADC Conversion and Settling Times for Various
SF Words
The frequency response of the filter H (f) is as follows:
3
 1 sin (2 × π × f / fOUT ) 
 1
sin (SF × 8 × π × f / f MOD ) 
×

 × ×

sin ( π × f / f MOD )
sin ( π × f / fOUT ) 
2

 SF × 8
where:
fMOD = 32,768 Hz
SF = value programmed into SF SFR.
fOUT = fMOD/(SF × 8 × 3)
The following shows plots of the filter frequency response for
the SF words shown in Table I. The overall frequency response
is the product of a Sinc3 and a sinc response. There are Sinc3
notches at integer multiples of 3 × fADC and there are sinc notches
REV. A
SF
Word
Data Update Rate
fADC (Hz)
Settling Time
tSETTLE (ms)
13
69 (Default)
255
105.3
19.79
5.35
19.04
101.07
373.54
Normal mode rejection is the major function of the digital filter
on the AD7719. The normal mode 50 Hz ± 1 Hz rejection with an
SF word of 82 is typically –100 dB. The 60 Hz ± 1 Hz rejection with SF = 68 is typically –100 dB. Simultaneous 50 Hz and
60 Hz rejection of better than 60 dB is achieved with an SF of
69. Choosing an SF word of 69 places notches at both 50 Hz
and 60 Hz. Figures 6 to 9 show the filter rejection for a selection of SF words.
–13–
AD7719
0
0
–20
–20
–40
–40
ATTENUATION (dB)
ATTENUATION (dB)
–60
–80
–100
–120
–140
–60
–80
–100
–120
–160
–140
–180
–200
0
–160
50 100 150 200 250 300 350 400 450 500 550 600 650 700
0
10
20
30
FREQUENCY (Hz)
50
60
70
80
90
100
SF = 69
OUTPUT DATA RATE = 19.8Hz
INPUT BANDWIDTH = 4.74Hz
FIRST NOTCH = 9.9Hz
50Hz REJECTION = –66dB, 50Hz 1Hz REJECTION = –60dB
60Hz REJECTION = –117dB, 60Hz 1Hz REJECTION = –94dB
SF = 13
OUTPUT DATA RATE = 105Hz
INPUT BANDWIDTH = 25.2Hz
FIRST NOTCH = 52.5Hz
50Hz REJECTION = –23.6dB, 50Hz 1Hz REJECTION = –20.5dB
60Hz REJECTION = –14.6dB, 60Hz 1Hz REJECTION = –13.6dB
Figure 6. Filter Profile with SF = 13
Figure 8. Filter Profile with Default SF = 69 Giving Filter
Notches at Both 50 Hz and 60 Hz
0
0
–20
–20
–40
–40
ATTENUATION (dB)
ATTENUATION (dB)
40
FREQUENCY (Hz)
–60
–80
–100
–60
–80
–100
–120
–120
–140
–140
–160
–160
0
10
20
30
40
50
60
70
80
90
100
0
FREQUENCY (Hz)
30
40
50
60
70
80
90
100
SF = 255
OUTPUT DATA RATE = 5.35Hz
INPUT BANDWIDTH = 1.28Hz
50Hz REJECTION = –93dB, 50Hz 1Hz REJECTION = –93dB
60Hz REJECTION = –74dB, 60Hz 1Hz REJECTION = –68dB
Figure 7. Filter Profile with SF = 82
Tables II to VII show the output rms noise and output peak-topeak resolution in bits (rounded to the nearest 0.5 LSB) for a
selection of output update rates on both the main and auxiliary
ADCs. The numbers are typical and are generated at a differential
input voltage of 0 V. The output update rate is selected via the
SF7 to SF0 bits in the Filter register. It is important to note that
the peak-to-peak resolution figures represent the resolution for
which there will be no code flicker within a six-sigma limit. The
output noise comes from two sources. The first is the electrical
20
FREQUENCY (Hz)
SF = 82
OUTPUT DATA RATE = 16.65Hz
INPUT BANDWIDTH = 4Hz
50Hz REJECTION = –171dB, 50Hz 1Hz REJECTION = –100dB
60Hz REJECTION = –58dB, 60Hz 1Hz REJECTION = –53dB
MAIN AND AUXILIARY ADC NOISE PERFORMANCE
10
Figure 9. Filter Profile with SF = 255
noise in the semiconductor devices (device noise) used in the
implementation of the modulator. Secondly, when the analog
input is converted into the digital domain, quantization noise is
added. The device noise is at a low level and is independent of
frequency. The quantization noise starts at an even lower level but
rises rapidly with increasing frequency to become the dominant
noise source. The numbers in the tables are given for the bipolar
input ranges. For the unipolar ranges, the rms noise numbers
will be the same as the bipolar range, but the peak-to-peak
resolution is now based on half the signal range, which effectively
means losing one bit of resolution.
–14–
REV. A
AD7719
Table II. Typical Output RMS Noise vs. Input Range and Update Rate for Main ADC (Buffered Mode) Output RMS
Noise in V
SF
Word
Data Update
Rate (Hz)
20 mV
40 mV
80 mV
Input Range
160 mV
320 mV
640 mV
1.28 V
2.56 V
13
69
255
105.3
19.79
5.35
1.50
0.65
0.35
1.60
0.65
0.37
1.75
0.65
0.37
4.50
0.95
0.51
6.70
1.40
0.82
11.75
2.30
1.25
1.50
0.60
0.35
3.50
0.65
0.37
Table III. Peak-to-Peak Resolution vs. Input Range and Update Rate for Main ADC (Buffered Mode) Peak-to-Peak
Resolution in Bits
SF
Word
Data Update
Rate (Hz)
20 mV
40 mV
80 mV
Input Range
160 mV
320 mV
640 mV
1.28 V
2.56 V
13
69
255
105.3
19.79
5.35
13
14
15
14
15
16
15
16
17
15.5
17.5
18.5
16
18
18.8
16
18.5
19.2
12
13
14
15
17
18
Table IV. Typical Output RMS Noise vs. Input Range and Update Rate for Main ADC (Unbuffered Mode) Output
RMS Noise in V
SF
Word
Data Update
Rate (Hz)
20 mV
40 mV
80 mV
Input Range
160 mV
320 mV
640 mV
1.28 V
2.56 V
13
69
255
105.3
19.79
5.35
1.27
0.56
0.30
1.35
0.56
0.32
1.48
0.56
0.32
3.82
0.82
0.44
5.69
1.21
0.71
10.2
2.00
1.10
1.27
0.52
0.30
2.95
0.56
0.32
Table V. Peak-to-Peak Resolution vs. Input Range and Update Rate for Main ADC (Unbuffered Mode) Peak-to-Peak
Resolution in Bits
SF
Word
Data Update
Rate (Hz)
20 mV
40 mV
80 mV
Input Range
160 mV
320 mV
640 mV
1.28 V
2.56 V
13
69
255
105.3
19.79
5.35
13
14
15
14
15
16
15
16
17
15.5
17.5
18.5
16
18
19
16
18.5
19.5
12
13
14
15
17
18
Table VI. Typical Output RMS Noise vs. Update
Rate for Auxiliary ADC (Unbuffered Mode)
Table VII. Peak-to-Peak Resolution vs. Update
Rate for Auxiliary ADC (Unbuffered Mode)
SF
Word
Data Update
Rate (Hz)
Input Range
2.5 V
SF
Word
Data Update
Rate (Hz)
Input Range
2.5 V
13
69
255
105.3
19.79
5.35
10.75 µV
2.00 µV
1.15 µV
13
69
255
105.3
19.79
5.35
16 Bits
16 Bits
16 Bits
REV. A
–15–
AD7719
ON-CHIP REGISTERS
Both the main and auxiliary ADC channels are controlled and configured via a number of on-chip registers as shown in Figure 10 and
described in more detail in the following pages. In the following
descriptions, SET implies a logic 1 state and CLEARED implies
a logic 0 state, unless otherwise stated.
COMMUNICATIONS REGISTER
DIN
DOUT
WEN R/W
DOUT
0
0
A3
A2
A1
A0
ADC STATUS REGISTER
DIN
DOUT
MODE REGISTER
DIN
DOUT
MAIN ADC CONTROL REGISTER
DIN
DOUT
AUX ADC CONTROL REGISTER
DIN
DOUT
I/O CONTROL REGISTER
DIN
DOUT
FILTER REGISTER
DOUT
MAIN ADC DATA REGISTER
DOUT
AUX ADC DATA REGISTER
REGISTER
SELECT
DECODER
DIN
DOUT
MAIN ADC OFFSET REGISTER
DIN
DOUT
AUX ADC OFFSET REGISTER
DIN
DOUT
MAIN ADC GAIN REGISTER
DIN
DOUT
AUX ADC GAIN REGISTER
DOUT
ID REGISTER
DIN
DOUT
TEST REGISTER
Figure 10. On-Chip Registers
–16–
REV. A
AD7719
Table VIII. Registers—Quick Reference Guide
Register Name
Type
Size
Power-On/Reset
Default Value
Communications
Write Only
8 Bits
Not Applicable
MSB
WEN
LSB
R/W
0
Status Register
0
Read Only
A3
A2
8 Bits
A1
A0
0x00
MSB
RDY0
LSB
RDY1
CAL
Mode Register
NOREF
Read/Write
ERR0
ERR1
8 Bits
0
0x00
LSB
BUF
0
CHCON
OSCPD
MD2
All operations to other registers are initiated through
the Communications register. This controls whether
subsequent operations are read or write operations
and also selects the register for that subsequent
operation.
Provides status information on conversions, calibrations, error conditions, and the validity of the
reference voltage.
LOCK
MSB
0
Function
MD1
Controls functions such as mode of operation, channel
configuration, and oscillator operation in power-down.
MD0
Main ADC (AD0CON)
Control Register
Read/Write
8 Bits
0x07
MSB
AD0EN
LSB
WL
CH1
CH0
U/B
RN2
RN1
This register is used to enable the main ADC and to
configure the main ADC for range, channel selection,
16-/24-bit operation, and unipolar or bipolar operation.
RN0
Aux ADC (AD1CON)
Control Register
Read/Write
8 Bits
0x01
MSB
LSB
AD1EN ACH2
ACH1
ACH0
U/B
0
0
This register is used to enable the aux ADC and to
configure the Aux ADC for range, channel selection,
unipolar or bipolar operation, and input range.
ARN
I/O (IOCON)
Control Register
Read/Write
16 Bits
0x0000
This register is used to control and configure the
various excitation and burnout current source options
available on-chip along with controlling the I/O port.
MSB
PSW2
PSW1
0
BO
I2PIN
I1PIN
I2EN
I1EN
LSB
P4DIR
P3DIR
Filter Register
P2EN
P1EN
Read/Write
P4DAT P3DAT P2DAT P1DAT
8 Bits
0x45
MSB
SF7
REV. A
LSB
SF6
SF5
SF4
SF3
SF2
SF1
SF0
–17–
This register determines the amount of averaging
performed by the sinc filter and consequently determines the data update rate of the AD7719. The filter
register determines the update rate for both the main
and aux ADCs.
AD7719
Register Name
Power-On/Reset
Default Value
Type
Size
Function
Read Only
16 Bits or 24 Bits 0x00 0000
Provides the most up-to-date conversion result from
the main ADC. Main ADC data register length
can be programmed to be 16-bit or 24-bit.
Read Only
16 Bits
0x0000
Provides the most up-to-date conversion result from
the auxiliary ADC. Aux ADC data register length is
16 bits.
Read/Write
24 Bits
0x80 0000
Contains a 24-bit word that is the offset calibration
coefficient for the part. The contents of this register
are used to provide offset correction on the output
from the digital filter. There are three offset registers
on the part and these are associated with input channel
pairs as outlined in the AD0CON register.
Read/Write
24 Bits
0x5X XXX5
Contains a 24-bit word that is the gain calibration
coefficient for the part. The contents of this register
are used to provide gain correction on the output
from the digital filter. There are three Gain registers
on the part, which are associated with input channel
pairs as outlined in the AD0CON register.
Read/Write
16 Bits
0x8000
Contains a 16-bit word that is the offset calibration
coefficient for the part. The contents of this register
are used to provide offset correction on the output
from the digital filter.
Gain Register
Read/Write
24 Bits
0x59XX
Contains a 16-bit word that is the gain calibration
coefficient for the part. The contents of this register
are used to provide gain correction on the output
from the digital filter.
ID Register
Read
8 Bits
0x0X
Contains an 8-bit byte that is the identifier for the part.
Test Registers
Read/Write
16 Bits
0x0000
Controls the test modes of the part, which are used
when testing the part. The user is advised not to
change the contents of these registers.
Main ADC (DATA0)
Data Register
Aux ADC (DATA1)
Data Register
Main ADC
Offset Register
Main ADC
Gain Register
Aux ADC
Offset Register
Aux ADC
–18–
REV. A
AD7719
register. This is the default state of the interface, and on power-up
or after a RESET, the AD7719 is in this default state waiting for a
write operation to the Communications register. In situations where
the interface sequence is lost, a write operation of at least 32 serial
clock cycles with DIN high returns the AD7719 to this default
state by resetting the part. Table IX outlines the bit designations
for the Communications register. CR0 through CR7 indicate the
bit location, with CR denoting that the bits are in the Communications register. CR7 denotes the first bit of the data stream.
Communications Register (A3, A2, A1, A0 = 0, 0, 2, 0)
The Communications register is an 8-bit write-only register. All
communications to the part must start with a write operation to
the Communications register. The data written to the Communications register determines whether the next operation is a read
or write operation, and to which register this operation takes
place. For read or write operations, once the subsequent read or
write operation to the selected register is complete, the interface
returns to where it expects a write operation to the Communications
CR7
CR6
CR5
CR4
CR3
CR2
CR1
CR0
WEN (0)
R/W (0)
0 (0)
0 (0)
A3 (0)
A2 (0)
A1 (0)
A0 (0)
Table IX. Communications Register Bit Designations
Bit
Location
Bit
Name
CR7
WEN
Write Enable Bit. A 0 must be written to this bit so the write operation to the Communications register
actually takes place. If a 1 is written to this bit, the part will not clock on to subsequent bits in the register.
It will stay at this bit location until a 0 is written to this bit. Once a 0 is written to the WEN bit, the next
seven bits will be loaded to the Communications register.
CR6
R/W
A 0 in this bit location indicates that the next operation will be a write to a specified register. A 1 in this
position indicates that the next operation will be a read from the designated register.
CR5
Zero
A 0 must be written to this bit position to ensure correct operation of the AD7719.
CR4
Zero
A 0 must be written to this bit position to ensure correct operation of the AD7719.
CR3–CR0
A3–A0
Register Address Bits. These address bits are used to select which of the AD7719’s registers is being
accessed during this serial interface communication. A3 is the MSB of the three selection bits.
Description
Table X. Register Selection Table
REV. A
A3
A2
A1
A0
Register
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Communications Register during a Write Operation
Status Register during a Read Operation
Mode Register
Main ADC Control Register (AD0CON)
Aux ADC Control Register (AD1CON)
Filter Register
Main ADC Data Register
Aux ADC Data Register
I/O Control Register
Main ADC Offset Calibration Register
Aux ADC Offset Calibration Register
Main ADC Gain Calibration Register
Aux ADC Gain Calibration Register
Test 1 Register
Test 2 Register
Undefined
ID Register
–19–
AD7719
Status Register (A3, A2, A1, A0 = 0, 0, 0, 0; Power-On
Reset = 0x00)
The ADC Status register is an 8-bit read-only register. To access
the ADC Status register, the user must write to the Communications register selecting the next operation to be a read and loading
bits A3 to A0 with 0, 0, 0, 0. Table XI outlines the bit designations
for the Status register. SR0 through SR7 indicate the bit location,
with SR denoting that the bits are in the Status register. SR7
denotes the first bit of the data stream. The number in parentheses indicates the power-on/reset default status of that bit.
SR7
SR6
SR5
SR4
SR3
SR2
SR1
SR0
RDY0 (0)
RDY1 (0)
CAL (0)
NOXREF (0)
ERR0 (0)
ERR1 (0)
(0)
LOCK (0)
Table XI. Status Register Bit Designations
Bit
Location
Bit
Name
SR7
RDY0
Ready Bit for Main ADC.
Set when data is written to main ADC data registers or on completion of calibration cycle. The RDY0 bit is
cleared automatically after the main ADC data register has been read or after a period of time before the
data register is updated with a new conversion result. This bit is also cleared by a write to the mode bits to
indicate a conversion or calibration.
SR6
RDY1
Ready Bit for Aux ADC.
Set when data is written to aux ADC data registers or on completion of calibration cycle. The RDY1 bit is
cleared automatically after the aux ADC data register has been read or a period of time before the data register
is updated with a new conversion result. This bit is also cleared by a write to the mode bits to indicate a
conversion or calibration.
SR5
CAL
Calibration Status Bit.
Set to indicate completion of calibration. It is set at the same time that the RDY0 and/or RDY1 bits
are set high. Cleared by a write to the mode bits to start another ADC conversion or calibration.
SR4
NOXREF
No External Reference Bit. (Only active if main ADC is active and applies to REFIN1 only.)
Set to indicate that one or both of the REFIN1 pins is floating or the applied voltage is below a specified
threshold. When Set, conversion results are clamped to all 1s.
Cleared to indicate valid reference applied between REFIN1(+) and REFIN1(–).
SR3
ERR0
Main ADC Error Bit.
Set to indicate that the result written to the main ADC data registers has been clamped to all 0s or all 1s.
After a calibration, this bit also flags error conditions that caused the calibration registers not to be written.
Error sources include Overrange, Underrange, and NOXREF.
Cleared by a write to the mode bits to initiate a conversion or calibration.
SR2
ERR1
Aux ADC Error Bit.
Set to indicate that the result written to the Aux ADC data registers has been clamped to all 0s or all 1s.
After a calibration, this bit also flags error conditions that caused the calibration registers not to be written.
Error sources include Overrange, Underrange, and NOXREF.
Cleared by a write to the mode bits to initiate a conversion or calibration.
SR1
0
Reserved for Future Use.
SR0
LOCK
PLL Lock Status Bit.
Set if the PLL has locked onto the 32 kHz crystal oscillator clock. If the user is worried about exact sampling
frequencies, for example, the LOCK bit should be interrogated and the result discarded if the LOCK bit is 0.
Description
–20–
REV. A
AD7719
Mode Register (A3, A2, A1, A0 = 0, 0, 0, 1; Power-On
Reset = 0x00)
The Mode register is an 8-bit register from which data can be
read or to which data can be written. This register configures the
operating modes of the AD7719. Table XII outlines the bit
MR7
MR6
MR5
0 (0)
BUF (0)
0 (0)
designations for the Mode register. MR7 through MR0 indicate
the bit location, with MR denoting the bits are in the Mode register.
MR7 denotes the first bit of the data stream. The number in
parentheses indicates the power-on/reset default status of that bit.
MR4
MR3
CHCON (0) OSCPD (0)
MR2
MR1
MR0
MD2 (0)
MD1 (0)
MD0 (0)
Table XII. MODE Register Bit Designations
Bit
Location
Bit
Name
Description
MR7
0
Reserved for Future Use.
MR6
BUF
Configures the main ADC for buffered or unbuffered mode of operation. If set, the main ADC operates in
unbuffered mode, lowering the power consumption of the AD7719. If cleared, the Main ADC operates
in buffered mode, allowing the user to place source impedances on the front end without contributing gain
errors to the system.
MR5
0
Reserved for Future Use.
MR4
CHCON
Channel Configure Bit.
If this bit is set, the main ADC operates with three pseudodifferential input channels and the aux ADC
does not have AIN3/AIN4 as an input option. If cleared, the main ADC operates with two fully differential
input channels and the aux channel operates as one fully differential input and two single-ended inputs or
as three single-ended inputs.
MR3
OSCPD
Oscillator Power-Down Bit.
If this bit is set, placing the AD7719 in standby mode will stop the crystal oscillator, reducing the power
drawn by the AD7719 to a minimum. The oscillator will require 300 ms to begin oscillating when the
ADC is taken out of standby mode. If this bit is cleared, the oscillator is not shut off when the ADC is put
into standby mode and will not require the 300 ms start-up time when the ADC is taken out of standby.
MR2–MR0 MD2–MD0
Main and Aux ADC Mode Bits.
These bits select the operational mode of the enabled ADC as follows:
MD2
MD1
MD0
Description
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Power-Down Mode (Power-On Default).
The current sources, power switches, and PLL are shut off in Power-Down mode.
Idle Mode.
In Idle mode, the ADC filter and modulator are held in a reset state although the modulator clocks are still
provided.
Single Conversion Mode.
In Single Conversion mode, a single conversion is performed on the enabled channels. On completion of the
conversion, the ADC data registers are updated, the relevant flags in the STATUS register are written, and
idle mode is entered with the MD2–MD0 being written accordingly to 001.
Continuous Conversion.
In continuous conversion mode, the ADC data registers are regularly updated at the selected update rate
(see Filter register).
Internal Zero-Scale Calibration.
Internal short automatically connected to the enabled channel(s). Returns to Idle mode (001) when complete.
Internal Full-Scale Calibration.
External VREF is connected automatically to the ADC input for this calibration. Returns to idle mode when complete.
System Zero-Scale Calibration.
User should connect system zero-scale input to the channel input pins as selected by the CH1/CH0 and
ACH1/ACH0 bits in the control registers.
System Full-Scale Calibration.
User should connect system full-scale input to the channel input pins as selected by the CH1/CH0 and
ACH1/ACH0 bits in the control registers.
REV. A
–21–
AD7719
calibration commences. On completion, the appropriate calibration registers are written, the relevant bits in STATUS are
written, and the MD2–0 bits are reset to 001 to indicate the
ADC is back in Idle mode.
Operating Characteristics when Addressing the Mode and
Control Registers
1. Any change to the MD bits will immediately reset both ADCs.
A write to the MD2–0 bits with no change is also treated as a
reset. (See exception to this in Note 3.)
2. If AD0CON is written when AD0EN = 1, or if AD0EN is
changed from 0 to 1, both ADCs are also immediately reset. In
other words, the main ADC is given priority over the aux ADC
and any change requested on main is immediately responded to.
3. On the other hand, if AD1CON is written to, only the aux
ADC is reset. For example, if the main ADC is continuously
converting when the aux ADC change or enable occurs, the
main ADC continues undisturbed. Rather than allow the aux
ADC to operate with a phase difference from the main ADC,
the aux ADC will fall into step with the outputs of the main
ADC. The result is that the first conversion time for the aux
channel will be delayed up to three outputs while the aux ADC
update rate is synchronized to the main ADC.
4. Once the MODE has been written with a calibration mode,
the RDY0/1 bits (STATUS) are immediately reset and the
5. Any calibration request of the aux ADC while the temperature
sensor is selected will fail to complete.
6. Calibrations are performed with the maximum allowable SF
value. SF register is reset to user configuration after calibration.
Main ADC Control Register (AD0CON): (A3, A2, A1, A0 = 0,
0, 1, 0; Power-On Reset = 0x07)
The main ADC control register is an 8-bit register from which data
can be read or to which data can be written. This register is used to
configure the main ADC for range, channel selection, 16-/24-bit
operation, and unipolar or bipolar coding. Table XIII outlines
the bit designations for the main ADC control register. AD0CON7
through AD0CON0 indicate the bit location, AD0CON denoting
the bits are in the main ADC control register. AD0CON7 denotes
the first bit of the data stream. The number in parentheses
indicates the power-on/reset default status of that bit.
AD0CON7
AD0CON6
AD0CON5
AD0CON4
AD0CON3
AD0CON2
AD0CON1
AD0CON0
AD0EN (0)
WL (0)
CH1 (0)
CH0 (0)
U/B (0)
RN2 (1)
RN1 (1)
RN0 (1)
Table XIII. Main ADC Control Register (AD0CON) Bit Designations
Bit Location
Bit Name
Description
AD0CON7
AD0EN
Main ADC Enable Bit.
Set by user to enable the main ADC. When set, the main ADC operates according to the MD bits in
the mode register.
Cleared by the user to power down the Main ADC.
AD0CON6
WL
16-/24-Bit Operating Mode.
Set by user to enable 16-bit mode. The conversion results from the main ADC will be rounded to
16 bits and the main ADC data register will be 16 bits wide.
Cleared by user to enable 24-bit mode. The conversion results from the main ADC will be rounded to
24 bits and the main ADC data register will be 24 bits wide.
AD0CON5
AD0CON4
CH1
CH0
Main ADC Channel Selection Bits.
Written by the user to select the differential input pairs used by the main ADC as follows:
(Note: The CHCON bit resides in the Mode register.)
CHCON
0
0
0
0
1
1
1
1
CH1
0
0
1
1
0
0
1
1
CH0
0
1
0
1
0
1
0
1
AD0CON3
U/B
Main ADC Unipolar/Bipolar Bit.
Set by user to enable unipolar coding, i.e., zero differential input will result in 0x00 0000 output and
a full-scale differential input will result in 0xFF FFFF output when operated in 24-bit mode.
Cleared by user to enable bipolar coding, Negative full-scale differential input will result in an output
code of 0x00 0000, zero differential input will result in an output code of 0x80 0000, and a
Positive full-scale differential input will result in an output code of 0xFF FFFF.
Positive Input
AIN1
AIN3
AIN2
AIN3
AIN1
AIN3
AIN4
AIN2
Negative Input
AIN2
AIN4
AIN2
AIN2
AIN4
AIN4
AIN4
AIN4
–22–
Calibration Register Pair
0
1
0
1
0
1
0
2
REV. A
AD7719
Table XIII. Main ADC Control Register (AD0CON) Bit Designations (continued)
Bit Location
Bit Name
Description
AD0CON2
AD0CON1
RN2
RN1
Main ADC Range Bits.
Written by the user to select the main ADC input range as follows.
AD0CON0
RN0
RN2
0
0
0
0
1
1
1
1
RN1
0
0
1
1
0
0
1
1
RN0
0
1
0
1
0
1
0
1
Selected Main ADC Input Range (VREF = 2.5 V)
±20 mV
±40 mV
±80 mV
±160 mV
±320 mV
±640 mV
±1.28 V
±2.56 V
for the aux ADC control register. AD1CON7 through AD1CON0
indicate the bit location, with AD1CON denoting that the bits
are in the aux ADC control register. AD1CON7 denotes the
first bit of the data stream. The number in parentheses indicates
the power-on/reset default status of that bit.
Aux ADC Control Registers (AD1CON):
(A3, A2, A1, A0 = 0, 0, 1, 1; Power-On Reset = 0x00)
The aux ADC control register is an 8-bit register from which data
can be read or to which data can be written. This register is used
to configure the aux ADC for range, channel selection, and unipolar or bipolar coding. Table XIV outlines the bit designations
AD1CON7
AD1CON6
AD1CON5
AD1CON4
AD1CON3
AD1CON2
AD1CON1
AD1CON0
AD1EN (0)
ACH2 (0)
ACH1 (0)
ACH0 (0)
U/B (0)
0 (0)
0 (0)
ARN (1)
Table XIV. Aux ADC Control Register (AD1CON) Bit Designations
Bit Location
Bit Name
Description
AD1CON7
AD1EN
AD1CON6
AD1CON5
AD1CON4
ACH2
ACH1
ACH0
Aux ADC Enable Bit.
Set by user to enable the Aux ADC. When set, the aux ADC operates according to the MD bits
in the mode register.
Cleared by the user to power down the aux ADC.
Aux ADC Channel Selection Bits.
Written by the user to select the active input channels used by the aux ADC as follows:
CHCON
0
0
0
0
0
1
1
1
1
1
X
X
X
ACH2
0
0
0
0
1
0
0
0
0
1
1
1
1
ACH1
0
0
1
1
0
0
0
1
1
0
0
1
1
AD1CON3
U/B
AD1CON2
AD1CON1
AD1CON0
0
0
ARN
Aux ADC Unipolar/Bipolar Selection Bit.
Set by user to enable unipolar coding, i.e., zero differential input will result in 0x0000 output.
Cleared by user to enable bipolar coding, zero differential input will result in 0x8000 output.
Must be zero for specified operation.
Must be zero for specified operation.
Auxiliary Channel Input Range Bit.
When set by the user, the input range is ±REFIN2. When cleared by the user, the input range is ±REFIN2/2.
ACH0
0
1
0
1
0
0
1
0
1
0
1
0
1
Positive Input
AIN3
AIN4
AIN5
Temp Sensor
AGND
AIN5
AIN6
AIN5
Temp Sensor
AGND
Not Defined
Not Defined
Not Defined
Negative Input
AGND
AGND
AIN6
(Temp Sensor Routed to the ADC Inputs)
AGND (Internal Short)
AGND
AGND
AIN6
(Temp Sensor Routed to the ADC Inputs)
AGND (Internal Short)
NOTES
1. When the temperature sensor is selected, the AD7719 automatically selects its internal reference. The temperature sensor is not factory calibrated. Temp sensor
is suitable for relative temperature measurements. The temperature sensor yields conversion results where a conversion result of 0x8000 equates to typically 0°C.
2. A 1°C change in temperature will normally result in a 256 LSB change in the AD1 data register (ADC conversion result).
REV. A
–23–
AD7719
FR7
FR6
FR5
FR4
FR3
FR2
FR1
FR0
SF7 (0)
SF6 (1)
SF5 (0)
SF4 (0)
SF3 (0)
SF2 (1)
SF1 (0)
SF0 (1)
Filter Register (A3, A2, A1, A0 = 0, 1, 0, 0; Power-On
Reset = 0x45)
The Filter register is an 8-bit register from which data can be
read or to which data can be written. This register determines
the amount of averaging performed by the sinc filter. Table XV
outlines the bit designations for the Filter register. FR7 through
FR0 indicate the bit location, with FR denoting that the bits are in
the Filter register. FR7 denotes the first bit of the data stream.
The number in parentheses indicates the power-on/reset default
status of that bit. The number in this register is used to set the
decimation factor and thus the output update rate for the main
and aux ADCs. The filter register cannot be written to by the
user while either ADC is active. The update rate is used for both
main and aux ADCs and is calculated as follows:
f ADC =
1
1
×
× f MOD
3 8 × SF
The allowable range for SF is 13dec to 255dec. Examples of SF
values and corresponding conversion rate (fADC) and time (tADC)
are shown in Table XV. It should also be noted that both ADC
input channels are chopped to minimize offset errors. This
means that the time for a single conversion or the time to the
first conversion result is 2 × tADC.
Table XV. Update Rate vs. SF WORD
SF (dec)
SF (Hex)
fADC (Hz)
tADC (ms)
13
69
255
0D
45
FF
105.3
19.79
5.35
9.52
50.34
186.77
I/O and Current Source Control Register (IOCON): (A3, A2,
A1, A0 = 0, 1, 1, 1; Power-On Reset = 0x0000)
where:
The IOCON register is a 16-bit register from which data can be
read or to which data can be written. This register is used to control
and configure the various excitation and burnout current source
options available on-chip along with controlling the I/O port.
Table XVI outlines the bit designations for this register. IOCON15
through IOCON0 indicate the bit location, with IOCON denoting
that the bits are in the I/O and Current Source control register.
IOCON15 denotes the first bit of the data stream. The number
in parentheses indicates the power-on/reset default status of that
bit. A write to the IOCON register has immediate effect and
does not reset the ADCs. Thus if a current source is switched
while the ADC is converting, the user will have to wait for the
full settling time of the filter before getting a fully settled output.
Since the ADC is chopped, this equates to three outputs.
fADC = ADC output update rate
fMOD = Modulator clock frequency = 32.768 kHz
(main and aux ADC)
SF = Decimal value written to SF register
IOCON15
PSW2 (0)
IOCON14
PSW1 (0)
IOCON13
0 (0)
IOCON12
BO (0)
IOCON11
I2PIN (0)
IOCON10
I1PIN (1)
IOCON9
I2EN (0)
IOCON8
I1EN (0)
IOCON7
P4DIR (0)
IOCON6
P3DIR (0)
IOCON5
P2EN (0)
IOCON4
P1EN (0)
IOCON3
P4DAT (0)
IOCON2
P3DAT (0)
IOCON1
P2DAT (0)
IOCON0
P1DAT (0)
–24–
REV. A
AD7719
Table XVI. IOCON (I/O and Current Source Control Register) Bit Designations
Bit
Location
Bit
Name
IOCON15
PSW2
Power Switch 2 Control Bit.
Set by user to enable power switch P2 to PWRGND.
Cleared by user to enable use as a standard I/O pin.
When the ADC is in standby mode, the power switches are open.
IOCON14
PSW1
Power Switch 1 Control Bit.
Set by user to enable power switch P1 to PWRGND.
Cleared by user to enable use as a standard I/O pin.
When ADC is in standby mode, the power switches are open.
IOCON13
0
This bit must be zero for correct operation.
IOCON12
BO
Burnout Current Enable Bit.
Set by user to enable the 100 nA current sources in the main ADC signal path. A 100 nA current source is
applied to the positive input leg while a 100 nA sink is applied to the negative input.
Cleared by user to disable both transducer burnout current sources.
IOCON11
I2PIN
IEXE2, 200 µA Current Source Direction Bit.
Set by user to enable IEXC2 current source to IOUT1.
Cleared by user to enable IEXC2 current source to IOUT2.
IOCON10
I1PIN
IEXE1, 200 µA Current Source Direction Bit.
Set by user to enable IEXC1 current source to IOUT2.
Cleared by user to enable IEXC1 current source to IOUT1.
IOCON9
I2EN
IEXC2 Current Source Enable Bit.
Set by user to turn on the IEXC2 excitation current source.
Cleared by user to turn off the IEXC2 excitation current source.
IOCON8
I1EN
IEXC1 Current Source Enable Bit.
Set by user to turn on the IEXC1 excitation current source.
Cleared by user to turn off the IEXC1 excitation current source.
IOCON7
P4DIR
P4, I/O Direction Control Bit.
Set by user to enable P4 as an output.
Cleared by user to enable P4 as an input. There are weak active pull-ups internally when enabled as an input.
IOCON6
P3DIR
P3, I/O Direction Control Bit.
Set by user to enable P3 as an output.
Cleared by user to enable P3 as an input. There are weak active pull-ups internally when enabled as an input.
IOCON5
P2EN
P2 Digital Output Enable Bit.
Set by user to enable P2 as a regular digital output pin.
Cleared by user to three-state P2 output.
PSW2 takes precedence over P2EN.
IOCON4
P1EN
P1 Digital Output Enable Bit.
Set by user to enable P1 as a regular digital output pin.
Cleared by user to three-state P1 output.
PSW1 takes precedence over P1EN.
IOCON3
IOCON2
IOCON1
IOCON0
P4DAT
P3DAT
P2DAT
P1DAT
Digital I/O Port Data Bits.
The readback values of these bits indicate the status of their respective pin when the I/O port is active as
an input.
The values written to these data bits appear at the output port when the I/O bits are enabled as outputs.
P2 and P1 are outputs only, so reading P2DAT and P1DAT will return what was last written to these bits.
REV. A
Description
–25–
AD7719
Main ADC Data Result Registers (DATA0): (A3, A2, A1, A0 =
0, 1, 0, 1; Power-On Reset = 0x00 0000)
Main ADC Gain Calibration Coefficient Registers (GNO):
(A3, A2, A1, A0 = 1, 0, 1, 0; Power-On Reset = 0x5X XXX5)
The conversion results for the main ADC channel are stored in
the main ADC data register (DATA0). This register is either 16
or 24 bits wide, depending on the status of the WL bit in the
main ADC control register (AD0CON). This is a read-only
register. On completion of a read from this register, the RDY0
bit in the status register is cleared.
The gain calibration registers hold the 24-bit data gain calibration
coefficient for the main ADC. These registers are configured at
power-on with factory calculated internal full-scale calibration
coefficients. Every device will have different coefficients. However,
these bytes will be automatically overwritten if an internal or
system full-scale calibration is initiated by the user via MD2–0 bits
in the Mode register. There are three gain calibration registers
associated with the main ADC channel. In fully differential
operating mode, there are two input channels and a register is
dedicated to each input. When operating in pseudodifferential
mode, the main ADC can be configured for three input channels
and there is a dedicated register for each pseudodifferential
input. These registers are read/write registers. The calibration
registers can only be written to if the ADC is inactive (MD bits
in the mode register = 000 or 001 or both AD0EN and AD1EN
bits in the control registers are cleared). Reading of the
calibration registers does not clear the RDY1 bit.
Aux ADC Data Result Registers (DATA1): (A3, A2, A1, A0 = 0,
1, 1, 0; Power-On Reset = 0x0000)
The conversion results for the aux ADC channel are stored in
the aux ADC data register (DATA1). This register is 16 bits
wide and is a read-only register. On completion of a read from
this register, the RDY1 bit in the status register is cleared.
Main ADC Offset Calibration Coefficient Registers (OF0):
(A3, A2, A1, A0 = 1, 0, 0, 0; Power-On Reset = 0x80 0000)
The offset calibration registers hold the 24-bit data offset
calibration coefficient for the main ADC. There are three
registers associated with the main ADC channel. In fully
differential operating mode, there are two input channels and a
register is dedicated to each input. When operating in
pseudodifferential mode, the main ADC can be configured for
three input channels and there is a dedicated register for each
pseudodifferential input. These registers have a power-on reset
value of 0x80 0000. The channel bits, in association with the
communication register address for the OF0 register, allow
access to these registers. These registers are read/write registers.
The calibration registers can only be written to if the ADC is
inactive (MD bits in the mode register = 000 or 001 or both
AD0EN and AD1EN bits in the control registers are cleared).
Reading of the calibration registers does not clear the RDY0 bit.
Aux ADC Offset Calibration Coefficient Registers (OF1):
(A3, A2, A1, A0 = 1, 0, 0, 1; Power-On Reset = 0x8000)
The offset calibration register OF1 holds the 16-bit data offset
calibration coefficient for the aux ADC. This register has a poweron-reset value of 0x8000. The channel bits, in association with
the communication register address for the OF1 register, allow
access to these registers. These registers are read/write registers.
The calibration registers can only be written to if the ADC is
inactive (MD bits in the mode register = 000 or 001 or both
AD0EN and AD1EN bits in the control registers are cleared).
Reading of the calibration registers does not clear the RDY1 bit.
Aux ADC Gain Calibration Coefficient Registers (GN1): (A3,
A2, A1, A0 = 1, 0, 1, 1; Power-On Reset = 0x59XX)
The gain calibration register GN1 holds the 16-bit data gain
calibration coefficient for the aux ADC. This register is configured
at power-on with factory calculated internal zero-scale calibration
coefficients. Every device will have different coefficients. However,
these coefficients will be automatically overwritten if an internal
or system zero-scale calibration is initiated by the user via the
MD2–0 bits in the Mode register. These registers are read/write
registers. The calibration registers can only be written to if the
ADC is inactive (MD bits in the mode register = 000 or 001 or
both AD0EN and AD1EN bits in the control registers are cleared).
Reading of the calibration registers does not clear the RDY1 bit.
ID Register (ID): (A3, A2, A1, A0 = 1, 1, 1, 1; Power-On
Reset = 0x0X)
This register is a read-only 8-bit register. The contents are used
to determine the die revision of the AD7719. Table XVII
indicates the bit locations.
User Nonprogrammable Test Registers
The AD7719 contains two test registers. The bits in this test
register control the test modes of the AD7719, which are used
for the testing of the device. The user is advised not to change the
contents of these registers.
Table XVII. ID Register Bit Designations
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
0
0
0
0
X
X
X
X
–26–
REV. A
AD7719
CONFIGURING THE AD7719
MICROCOMPUTER/MICROPROCESSOR INTERFACING
All user-accessible registers on the AD7719 are accessed via the
serial interface. Communication with any of these registers is
initiated by first writing to the Communications register.
Figure 11 outlines a flow diagram of the sequence used to configure all registers after a power-up or reset on the AD7719. The
flowchart shows two methods of determining when it is valid to
read the data register or determine when a calibration cycle is
complete. The first method is hardware polling of the RDY
pin and the second method involves software interrogation of
bits in the status and mode registers. The flowchart details all the
necessary programming steps required to initialize the ADC and
read data from the main and aux channel following a power-on or
reset. The steps can be broken down as follows:
The AD7719’s flexible serial interface allows for easy interface
to most microcomputers and microprocessors. The flowchart of
Figure 11 outlines the sequence that should be followed when
interfacing a microcontroller or microprocessor to the AD7719.
Figures 12, 13, and 14 show some typical interface circuits.
1. Configure and initialize the microcontroller or microprocessor
serial port.
Most of the registers on the AD7719 are 8-bit registers, which
facilitates easy interfacing to the 8-bit serial ports of microcontrollers. The main channel data register (AD0) on the AD7719
can be either 16 or 24 bits, the aux ADC data register (AD1) is
16 bits wide and the offset and gain registers are 24-bit registers,
but data transfers to these registers can consist of multiple 8-bit
transfers to the serial port of the microcontroller. DSP processors and microprocessors generally transfer 16 bits of data in a
serial data operation. Some of these processors, such as the
ADSP-2105, have the facility to program the amount of cycles
in a serial transfer. This allows the user to tailor the number of
bits in any transfer to match the register length of the required
register in the AD7719.
2. Initialize the AD7719 by configuring the following registers:
a) IOCON to configure the current sources and digital
I/O port.
b) FILTER to configure the update rate for both channels.
c) AD1CON to enable the aux channel, select the analog
input, select unipolar or bipolar operation and input range.
d) AD0CON to enable the main ADC channel and select
16-/24-bit mode, analog input range, and either unipolar
or bipolar operation.
e) MODE to configure the operating mode. Operating mode
consists of calibration or conversion.
All of these operations consist of a write to the communications
register to specify the next operation as a write to a specified
register. Data is then written to this register. When each
sequence is complete, the ADC defaults to waiting for
another write to the Communications register to specify the
next operation.
3. When the operating mode is selected, the user needs to determine when it is valid to read the data in conversion mode or
when the calibration is complete in calibration mode. This is
accomplished either by polling the RDY pin (hardware polling)
or by interrogating the bits in either the Status or Mode
registers (software polling). Both are shown in Figure 11. It is
assumed that both the main and aux ADCs are being used
and calibration is required. If the AD7719 is operated at
the factory-calibrated conditions, a field calibration will not be
required and these steps can be bypassed.
REV. A
The serial interface on the AD7719 is capable of operating from
just three wires and is compatible with SPI interface protocols.
The 3-wire operation makes the part ideal for isolated systems
where minimizing the number of interface lines minimizes the
number of opto-isolators required in the system. The serial
clock input is a Schmitt-triggered input to accommodate slow
edges from optocouplers. The rise and fall times of other digital
inputs to the AD7719 should be no longer than 1 µs.
Even though some of the registers on the AD7719 are only eight
bits in length, communicating with two of these registers in
successive write operations can be handled as a single 16-bit
data transfer, if required. For example, if the Filter register is to
be updated, the processor must first write to the Communications register (saying that the next operation is a write to the
Filter register) and then write eight bits to the Setup register. If
required, this can all be done in a single 16-bit transfer because
once the eight serial clocks of the write operation to the Communications register have been completed, the part immediately
sets itself up for a write operation to the Setup register.
–27–
AD7719
START
POLL RDY PIN
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A
READ FROM THE MODE REGISTER
POWER-ON/RESET FOR AD7719
NO
CONFIGURE AND INITIALIZE C/P SERIAL PORT
RDY
LOW?
READ FROM MODE REGISTER
YES
WRITE TO THE COMMUNICATIONS REGISTER
SELECTING NEXT OPERATION TO BE A WRITE
TO THE IOCON REGISTER
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
WRITE TO MODE REGISTER SELECTING
CONTINUOUS CONVERSION MODE
WRITE TO COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A WRITE TO THE
FILTER REGISTER
WRITE TO THE COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ FROM THE
MAIN ADC DATA REGISTER (AD0)
WRITE TO FILTER REGISTER CONFIRMING
THE REQUIRED UPDATE RATE
POLL RDY PIN
WRITE TO AD1CON REGISTER ENABLING THE AUX
ADC, SELECT THE INPUT CHANNEL BIPOLAR/
UNIPOLAR OPERATION AND INPUT RANGE
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
WRITE TO MODE REGISTER SELECTING
FULL-SCALE CALIBRATION
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
WRITE TO MODE REGISTER SELECTING
CONTINUOUS CONVERSION MODE
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
NO
RDY
LOW?
WRITE TO MODE REGISTER SELECTING
CONTINUOUS CONVERSION MODE
YES
READ FROM DATA REGISTER (AD0)
POLL RDY PIN
WRITE TO COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A WRITE TO THE MAIN
CHANNEL ADC CONTROL REGISTER (AD0CON)
WRITE TO AD1CON REGISTER ENABLING THE MAIN
ADC, SELECT THE INPUT CHANNEL, WORD LENGTH,
BIPOLAR/UNIPOLAR OPERATION, AND INPUT RANGE
MD BITS
= 001?
YES
WRITE TO THE IOCON REGISTER TO CONFIGURE
THE CURRENT SOURCES, DIGITAL I/O PORT,
AND POWER SWITCHES
WRITE TO COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A WRITE TO THE AUX
CHANNEL ADC CONTROL REGISTER (AD1CON)
NO
NO
RDY
LOW?
WRITE TO THE COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ OF
STATUS REGISTER
READ STATUS REGISTER
NO
YES
WRITE TO THE COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ FROM THE
AUX ADC DATA REGISTER (AD1)
RDY0 = 1?
YES
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A READ
OF THE MAIN ADC DATA REGISTER (AD0)
READ FROM DATA REGISTER (AD0)
READ AD0
HARDWARE
POLLING
SOFTWARE
POLLING
HARDWARE
POLLING
POLL RDY PIN
SOFTWARE
POLLING
WRITE TO THE COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ OF
STATUS REGISTER
READ STATUS REGISTER
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A
READ FROM THE MODE REGISTER
NO
READ FROM MODE REGISTER
RDY1 = 1?
YES
NO
RDY
LOW?
YES
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
WRITE TO MODE REGISTER SELECTING
ZERO-SCALE CALIBRATION
NO
MD BITS
= 001?
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A READ
OF THE AUX ADC DATA REGISTER (AD1)
YES
READ AD1
WRITE TO THE COMMUNICATIONS REGISTER
SETTING UP NEXT OPERATION TO BE A WRITE
TO THE MODE REGISTER
WRITE TO MODE REGISTER SELECTING
FULL-SCALE CALIBRATION
Figure 11. Flowchart for Initializing, Calibrating, and Reading Data from the AD7719 Main and Aux Channels
–28–
REV. A
AD7719
AD7719-to-68HC11 Interface
AD7719-to-8xC51 Interface
Figure 12 shows an interface between the AD7719 and the 68HC11
microcontroller. The diagram shows the minimum (3-wire) interface with CS on the AD7719 hardwired low. In this scheme, the
RDY bits of the Status register are monitored to determine
when the Data register is updated. RDY0 indicates the status of
the main ADC channel while RDY1 indicates the status of the
aux channel. An alternative scheme, which increases the number
of interface lines to four, is to monitor the RDY output line
from the AD7719. The monitoring of the RDY line can be done in
two ways. First, RDY can be connected to one of the 68HC11’s
port bits (such as PC0), which is configured as an input. This
port bit is then polled to determine the status of RDY. The
second scheme is to use an interrupt driven system, in which case
the RDY output is connected to the IRQ input of the 68HC11. For
interfaces that require control of the CS input on the AD7719,
one of the port bits of the 68HC11 (such as PC1) that is
configured as an output, can be used to drive the CS input.
An interface circuit between the AD7719 and the 8xC51 microcontroller is shown in Figure 13. The diagram shows the minimum
number of interface connections with CS on the AD7719 hardwired low. In the case of the 8xC51 interface, the minimum
number of interconnects is just two. In this scheme, the RDY
bits of the Status register are monitored to determine when the
Data register is updated. The alternative scheme, which increases
the number of interface lines to three, is to monitor the RDY output
line from the AD7719. The monitoring of the RDY line can be
done in two ways. First, RDY can be connected to one of the
8xC51’s port bits (such as P1.0) that is configured as an input.
This port bit is then polled to determine the status of RDY.
DVDD
8xC51
AD7719
DVDD
RESET
10k
The 68HC11 is configured in the master mode with its CPOL
bit set to a logic 1 and its CPHA bit set to a logic 1. When the
68HC11 is configured like this, its SCLK line idles high between
data transfers. The AD7719 is not capable of full duplex operation. If the AD7719 is configured for a write operation, no data appears
on the DOUT lines even when the SCLK input is active. Similarly, if the AD7719 is configured for a read operation, data
presented to the part on the DIN line is ignored even when
SCLK is active.
P3.0
DOUT
DIN
P3.1
SCLK
CS
VDD
VDD
68HC11
AD7719
SS
RESET
SCK
SCLK
MISO
DOUT
MOSI
DIN
CS
Figure 12. AD7719-to-68HC11 Interface
REV. A
Figure 13. AD7719-to-8XC51 Interface
The second scheme is to use an interrupt-driven system, in which
case the RDY output is connected to the INT1 input of the
8xC51. For interfaces that require control of the CS input on
the AD7719, one of the port bits of the 8xC51 (such as P1.1)
that is configured as an output can be used to drive the CS
input. The 8xC51 is configured in its Mode 0 serial interface
mode. Its serial interface contains a single data line. As a result,
the DOUT and DIN pins of the AD7719 should be connected
together with a 10 kΩ pull-up resistor. The serial clock on the
8xC51 idles high between data transfers. The 8xC51 outputs the
LSB first in a write operation, while the AD7719 expects the
MSB first so the data to be transmitted has to be rearranged
before being written to the output serial register. Similarly, the
AD7719 outputs the MSB first during a read operation while
the 8xC51 expects the LSB first. Therefore, the data read into
the serial buffer needs to be rearranged before the correct data
word from the AD7719 is available in the accumulator.
–29–
AD7719
AD7719-to-ADSP-2103/ADSP-2105 Interface
Figure 14 shows an interface between the AD7719 and the
ADSP-2103/ADSP-2105 DSP processor. In the interface shown,
the RDY bits of the Status register are again monitored to
determine when the Data register is updated. The alternative
scheme is to use an interrupt-driven system, in which case the
RDY output is connected to the IRQ2 input of the ADSP-2103/
ADSP-2105. The serial interface of the ADSP-2103/ADSP-2105
is set up for alternate framing mode. The RFS and TFS pins
of the ADSP-2103/ADSP-2105 are configured as active low
outputs and the ADSP-2103/ADSP-2105 serial clock line, SCLK,
is also configured as an output. The CS for the AD7719 is active
when either the RFS or TFS outputs from the ADSP-2103/
ADSP-2105 are active. The serial clock rate on the ADSP-2103/
ADSP-2105 should be limited to 3 MHz to ensure correct operation with the AD7719.
DVDD
ADSP-2103 /
ADSP-2105
AD7719
RESET
RFS
TFS
CS
DR
DOUT
DT
DIN
SCLK
SCLK
as not to introduce gain errors. On-chip burnout currents are
available and can be used to check that a transducer on the
selected channel is still operational before attempting to take
measurements.
The second or auxiliary ADC is intended to convert secondary
inputs such as those from a cold junction diode or thermistor.
This ADC is unbuffered and has a fixed input range of 0 V
to REFIN2 (ARN bit = 1) or 0 to REFIN2/2 (ARN bit = 0).
Again, this ADC can be configured for differential or pseudodifferential inputs via the ACH2, ACH1, and ACH0 bits in the
auxiliary ADC control register (AD1CON). The auxiliary ADC
is specified for 16-bit performance and, since its analog inputs
are unbuffered, care must be exercised when placing filtering on
the front end to avoid introducing gain errors into the measurement system.
The basic connection diagram for the AD7719 is shown in
Figure 15. This shows both the AVDD and DVDD pins of the
AD7719 being driven from the analog 5 V supply. Some applications will have AVDD and DVDD driven from separate supplies.
AVDD and DVDD can be operated independently of each other,
allowing the device to be operated with 5 V analog supply and
3 V digital supply or vice versa. An AD780/REF195 precision
2.5 V reference provides the reference source for the part. A
quartz crystal or ceramic resonator provides the 32 kHz master
clock source for the part. In some cases, it will be necessary to
connect capacitors on the crystal or resonator to ensure that it
does not oscillate at overtones of its fundamental operating
frequency. The values of capacitors will vary depending on the
manufacturer’s specifications.
ANALOG 5V
SUPPLY
Figure 14. AD7719-to-ADSP-2103/ADSP-2105 Interface
10F
CIRCUIT DESCRIPTION
AVDD
The AD7719 is a Σ-∆ A/D converter incorporating two independent Σ-∆ A/D converters with on-chip digital filtering, intended
for the measurement of wide dynamic range, low frequency
signals such as those in weigh scale, pressure, temperature,
industrial control, or process control applications.
The main ADC is intended to convert the primary sensor input.
The main ADC employs a Σ-∆ conversion technique to realize up
to 24 bits of no-missing-codes performance. The Σ-∆ modulator
converts the sampled input signal into a digital pulse train whose
duty cycle contains the digital information. A Sinc3 programmable
low-pass filter is then employed to decimate the modulator output
data stream to give a valid data conversion result at programmable output rates from 5.35 Hz (186.77 ms) to 105.03 Hz
(9.52 ms). A Chopping scheme is also employed to minimize
ADC offset and offset and gain drift errors. The analog input
to the main ADC can be operated in buffered or unbuffered
mode and can be programmed for one of eight input ranges from
±20 mV to ±2.56 V. The input channels can be configured for
either fully differential inputs or pseudodifferential input
channels via the CH1 and CH0 bits in the main ADC control
register (AD0CON) and the CHCON bit in the mode register.
When configured for buffered mode (BUF = 0), the input channels
are internally buffered, allowing the part to handle significant
source impedances on the analog input, allowing R/C filtering
(for noise rejection or RFI reduction) to be placed on the analog
inputs if required. When operating in unbuffered mode, care has
to be exercised when selecting front end source impedances so
–30–
0.1F
0.1F
5V
DVDD
RESET
IOUT1
CS
IOUT2
AD7719
AIN1
DOUT
AIN2
RECEIVE
(READ)
DIN
SERIAL
DATA
(WRITE)
SCLK
SERIAL
CLOCK
AIN3
AIN4
CHIP
SELECT
P1/SW1
AIN5
P2/SW2
AIN6
ANALOG 5V
SUPPLY
P3
REFIN2
10F
P4
REFIN1(+)
XTAL1
0.1F
XTAL2
VIN
VOUT
AD780/
REF195
32kHz
CRYSTAL
REFIN1(–)
PWRGND
AGND
DGND
GND
Figure 15. Basic Connection Diagram
REV. A
AD7719
Analog Input Channels
The main ADC has four associated analog input pins (labeled
AIN1 to AIN4) that can be configured as two fully differential
input channels or three pseudodifferential input channels.
Channel selection bits CH1 and CH0 in the ADC0CON
register, along with the CHCON bit of the mode register,
detail the different configurations.
The auxiliary ADC has four external input pins (labeled AIN3
to AIN6) as well as an internal connection to the internal on-chip
temperature sensor. Channel selection bits ACH2, ACH1, and
ACH0 in the ADC1CON register, along with the CHCON
bit in the mode register, detail the various configurations on
these input channels.
Figure 17 shows the analog input channel configurations available to the user when the CHCON bit in the mode register is
set to 1. In this case, the main ADC is configured as three
pseudodifferential input channels (AIN1/AIN4, AIN2/AIN4, and
AIN3/AIN4) and the aux can be configured as two single-ended
inputs with respect to AGND (AIN5/AGND and AIN6/AGND)
and one fully differential input (AIN5/AIN6). The temp sensor
is available as an internal connection.
AIN1
AIN(+)
AIN2
AIN2
AIN3
AIN3
MAIN CHANNEL
AIN(–)
FULLY DIFFERENTIAL
AIN4
AIN4
(MAIN ADC)
SINGLEENDED
INPUT
SINGLEENDED
INPUT
AIN5
MUX2
AIN3
AIN4
AIN5
FULLY DIFFERENTIAL
AIN6
AIN(+)
AUX CHANNEL
AIN(–)
AIN6
AGND
(AUX ADC)
Figure 16. Input Channel Configurations with CHCON = 0
REV. A
MAIN CHANNEL
AIN3
AIN3
AIN(–)
AIN3/AIN4
AIN4
AIN4
PSEUDODIFFERENTIAL
INPUT
(MAIN ADC)
MUX2
AIN3
AIN5
SINGLEENDED
INPUT
AIN4
AIN5
FULLY DIFFERENTIAL
AIN(+)
AUX CHANNEL
AIN(–)
AIN6
AIN6
AGND
SINGLEENDED
INPUT
(AUX ADC)
Figure 17. Input Channel Configurations with CHCON = 1
AIN1
FULLY DIFFERENTIAL
AIN(+)
AIN2
AIN2/AIN4
Figure 16 shows the analog input channel configurations available
to the user when the CHCON bit in the mode register is set to a
zero. In this case, the main ADC can be configured as one or two
fully differential input channels (AIN1/AIN2 and AIN3/AIN4)
and the aux can be configured as two single-ended inputs with
respect to AGND (AIN3/AGND and AIN4/AGND) and one fully
differential input AIN5/AIN6). The aux can also be configured as
three single-ended inputs with respect to AGND (AIN3/AGND,
AIN4/AGND, and AIN5/AGND) by tying AIN6 externally to
AGND. The temp sensor is available as an internal connection.
MUX1
MUX1
AIN1
AIN1/AIN4
AIN2
Two input multiplexers (MUX1 and MUX2) switch the selected
input channel to the on-chip buffer amplifier in the case of the
main ADC when operated in buffered mode, and directly to the
Σ-∆ modulator input in the case of the auxiliary ADC and when
the main ADC is operated in unbuffered mode. When the analog
input channel is switched, the settling time of the part must elapse
before a new valid word is available from the ADC.
AIN1
PSEUDODIFFERENTIAL
INPUT
In buffered mode (BUF = 0), the output of the main ADC multiplexer feeds into a high impedance input stage of the buffer
amplifier. As a result, the main ADC inputs can handle significant
source impedances and are tailored for direct connection to
external resistive-type sensors like strain gages or resistance
temperature detectors (RTDs).
The auxiliary ADC and the main ADC when operated with
BUF = 1, however, are unbuffered, resulting in higher analog
input current. It should be noted that these unbuffered input
paths provide a dynamic load to the driving source. Therefore,
resistor/capacitor combinations on the input pins can cause dc
gain errors, depending on the output impedance of the source
that is driving the ADC inputs. Table XVIII and XIX show the
allowable external resistance/capacitance values for unbuffered
mode such that no gain error at the 16- and 20-bit level,
respectively, is introduced.
The absolute input voltage range on the main ADC when operated in buffered mode is restricted to a range between AGND +
100 mV and AVDD – 100 mV. Care must be taken in setting up
the common-mode voltage and input voltage range so that these
limits are not exceeded; otherwise there will be a degradation in
linearity and noise performance.
–31–
AD7719
Table XVIII. Max Resistance for No 16-Bit Gain Error (Unbuffered Mode)
External Capacitance
Gain
0 pF
50 pF
100 pF
500 pF
1000 pF
5000 pF
1
2
4
8–128
111.3K
53.7K
25.4K
10.7K
27.8K
13.5K
6.4K
2.9K
16.7K
8.1K
3.9K
1.7K
4.5K
2.2K
1.0K
480
2.58K
1.26K
600
270
700
360
170
75
Table XIX. Max Resistance for No 20-Bit Gain Error (Unbuffered Mode)
External Capacitance
Gain
0 pF
50 pF
100 pF
500 pF
1000 pF
5000 pF
1
2
4
8–128
84.9K
42.0K
20.5K
8.8K
21.1K
10.4K
5.0K
2.3K
12.5K
6.1K
2.9K
1.3K
3.2K
1.6K
790K
370
1.77K
880
430
195
440
220
110
50
The absolute input voltage range on the auxiliary ADC and the
main ADC in unbuffered mode includes the range between
AGND – 30 mV to AVDD + 30 mV as a result of being unbuffered. The negative absolute input voltage limit does allow
the possibility of monitoring small true bipolar signals with
respect to AGND.
19.372
ADC INPUT VOLTAGE (mV)
19.371
Programmable Gain Amplifier
Typical matching across ranges is shown in Figure 18. Here, the
primary ADC is configured in fully differential, bipolar mode
with an external 2.5 V reference, while an analog input voltage
of just greater than 19 mV is forced on its analog inputs. The
ADC continuously converts the dc voltage at an update rate of
5.35 Hz, i.e., SF = 0xFF. In total, 800 conversion results are
gathered. The first 100 results are gathered with the primary ADC
operating in the ±20 mV range. The ADC range is then switched
to ±40 mV and 100 more results are gathered; this continues
until the last 100 samples are gathered with the ADC configured
in the ±2.5 V range. From Figure 18, the variation in the sample
mean through each range, i.e., the range matching, is seen to
be on the order of 2 µV.
The auxiliary ADC does not incorporate an eight range PGA.
The aux ADC operates at a gain of 1 or a gain of 2 as determined
by the ARN bit in the AD1CON register.
19.369
19.368
19.367
19.366
19.365
600
700
800
2.56V
500
1.28V
400
640mV
300
320mV
200
160mV
100
40mV
ADC RANGE
80mV
19.364
SAMPLE COUNT 0
20mV
The output from the buffer on the main ADC is applied to the
input of the on-chip programmable gain amplifier (PGA). The
PGA can be programmed through eight different unipolar and
bipolar ranges. The PGA gain range is programmed via the
range bits in the ADC0CON register. With an external 2.5 V
reference applied, the unipolar ranges are 0 mV to 20 mV, 0 mV
to 40 mV, 0 mV to 80 mV, 0 mV to 160 mV, 0 mV to 320 mV,
0 mV to 640 mV, 0 V to 1.28 V and 0 V to 2.56 V while bipolar
ranges are ±20 mV, ±40 mV, ±80 mV, ±160 mV, ±320 mV,
±640 mV, ±1.28 V, and ±2.56 V. These are the ranges that
should appear at the input to the on-chip PGA. The ADC range
matching specification of 2 µV (typ) across all ranges means that
calibration need only be carried out on a single range and does
not have to be repeated when the PGA range is changed. This is
a significant advantage when compared with similar ADCs
available on the market.
19.370
Figure 18. Main ADC Range Matching
Bipolar/Unipolar Configuration
The analog inputs on the AD7719 can accept either unipolar or
bipolar input voltage ranges. Bipolar input ranges do not imply that
the part can handle negative voltages with respect to system
AGND. Unipolar and bipolar signals on the AIN(+) input on
the main ADC are referenced to the voltage on the respective
AIN(–) input. AIN(+) and AIN(–) refer to the signals seen by
the modulator that come from the output of the multiplexer, as
shown in Figures 16 and 17.
For example, if AIN(–) is 2.5 V and the main ADC is configured for an analog input range of 0 mV to 20 mV, the input
voltage range on the AIN(+) input is 2.5 V to 2.52 V. If AIN(–)
is 2.5 V and the AD7719 is configured for an analog input range
of ±1.28 V, the analog input range on the AIN(+) input is 1.22 V
to 3.78 V (i.e., 2.5 V ± 1.28 V). Bipolar or unipolar options are
chosen by programming the main and auxiliary U/B bit in the
ADC0CON and ADC1CON registers, respectively. This programs the relevant ADC for either unipolar or bipolar operation.
Programming for either unipolar or bipolar operation does not
change any of the input signal conditioning; it simply changes the
data output coding and the points on the transfer function
where calibrations occur.
–32–
REV. A
AD7719
turned off by writing a 0 to the BO bit in the IOCON register.
The current sources work over the normal absolute input voltage
range specifications with buffers on.
Data Output Coding
When the ADC is configured for unipolar operation, the output
coding is natural (straight) binary with a zero differential input
voltage resulting in a code of 000 . . . 000, a midscale voltage
resulting in a code of 100 . . . 000, and a full-scale input voltage
resulting in a code of 111 . . . 111. The output code for any analog
input voltage on the main ADC can be represented as follows:
(
Code = AIN × GAIN × 2N
Excitation Currents
The AD7719 also contains two matched, software configurable
200 µA constant current sources. Both source current from
AVDD that is directed to either the IOUT1 or IOUT2 pins of
the device. These current sources are controlled via bits in the
IOCON register. The configuration bits enable the current
sources and can be configured to source 200 µA individually to
both pins or a combination of both currents, i.e., 400 µA to
either of the selected output pins. These current sources can be
used to excite external resistive bridge or RTD sensors.
) (1.024 × V )
REF
Where AIN is the analog input voltage, GAIN is the PGA gain,
i.e., 1 on the 2.56 V range and 128 on the 20 mV range, and
N = 16 in 16-bit mode and N = 24 in 24-bit mode of operation.
The output code for any analog input voltage on the aux ADC
can be represented as follows:
(
Crystal Oscillator
The AD7719 is intended for use with a 32.768 kHz watch crystal. A PLL internally locks onto a multiple of this frequency to
provide a stable 4.194304 MHz clock for the ADC. The modulator sample rate is the same as the crystal oscillator frequency.
)
Code = AIN × GAIN × 2N VREF
Where AIN is the analog input voltage, GAIN is 1 or 2, determined by the ARN bit in the aux ADC control register, i.e., 1 on
the VREF range and 2 on the VREF/2 range, and N = 16.
When an ADC is configured for bipolar operation, the coding is
offset binary with a negative full-scale voltage resulting in a code
of 000 . . . 000, a zero differential voltage resulting in a code of
100 . . . 000, and a positive full-scale voltage resulting in a code
of 111 . . . 111. The output code from the main ADC for any
analog input voltage can be represented as follows:
The start-up time associated with 32 kHz crystals is typically
300 ms. The OSPD bit in the mode register can be used to
prevent the oscillator from powering down when the AD7719 is
placed in power-down mode. This avoids having to wait 300 ms
after exiting power-down to start a conversion at the expense of
raising the power-down current.
Reference Input
The main ADC on the AD7719 contains two 100 nA constant
current generators, one sourcing current from AVDD to AIN(+),
and one sinking current from AIN(–) to AGND. The currents
are switched to the selected analog input pair. Both currents are
either on or off, depending on the Burnout Current Enable (BO)
bit in the IOCON register. These currents can be used to verify
that an external transducer is still operational before attempting
to take measurements on that channel. Once the burnout currents
are turned on, they will flow in the external transducer circuit,
and a measurement of the input voltage on the analog input
channel can be taken. If the resultant voltage measured is full-scale,
the user needs to verify why this is the case. A full-scale reading
could mean that the front end sensor is open circuit; it could
also mean that the front end sensor is overloaded and is justified
in outputting full-scale, or that the reference may be absent and
the NOXREF bit is set, thus clamping the data to all 1s.
The AD7719 has a fully differential reference input capability
for the main channel while the auxiliary channel accepts only a
single-ended reference. On the main channel, the reference inputs
REFIN1(+) and REFIN1(–) provide a differential reference
input capability. The common-mode range for these differential
inputs is from AGND to AVDD. The reference input is unbuffered,
and therefore excessive R-C source impedances will introduce
gain errors. The nominal reference voltage, VREF, (REFIN1(+)
– REFIN1(–), for specified operation is 2.5 V, but the AD7719
is functional with reference voltages from 1 V to AVDD. In applications where the excitation (voltage or current) for the transducer
on the analog input also drives the reference voltage for the part,
the effect of the low frequency noise in the excitation source
will be removed as the application is ratiometric. If the AD7719
is used in a nonratiometric application, a low noise reference
should be used. Recommended reference voltage sources for
the AD7719 include the AD780, REF43, and REF192. It should
also be noted that the reference inputs provide a high impedance,
dynamic load. Because the input impedance of each reference
input is dynamic, resistor/capacitor combinations on these inputs
can cause dc gain errors, depending on the output impedance
of the source that is driving the reference inputs. Reference
voltage sources like those recommended (e.g., AD780) will typically have low output impedances and are therefore tolerant to
having decoupling capacitors on the REFIN1(+) without
introducing gain errors in the system. Deriving the reference
input voltage across an external resistor, as shown in Figure 19,
will mean that the reference input sees a significant external
source impedance. External decoupling on the REFIN1(+)
and REFIN1(–) pins would not be recommended in this type
of circuit configuration.
When reading all 1s from the output, the user needs to check
these three cases before making a judgment. If the voltage
measured is 0 V, it may indicate that the transducer has short
circuited. For normal operation, these burnout currents are
The auxiliary channel conversion results are based on the voltage applied to REFIN2. This is a single-ended reference input
specified for 2.5 V operation but functional with input voltages
from 1 V to AVDD.
Code = 2
N –1
[(
) ]
× AIN × GAIN (1.024 × VREF ) + 1
Where AIN is the analog input voltage, GAIN is the PGA gain,
i.e., 1 on the ±2.56 V range and 128 on the ±20 mV range,
N = 16 in 16-bit mode, and N = 24 in 24-bit mode of operation.
The output code from the aux ADC for any analog input voltage can be represented as follows:
[
]
Code = 2N –1 × ( AIN × GAIN VREF ) + 1
Where AIN is the analog input voltage, GAIN is 1 or 2, determined
by the ARN bit in the aux ADC control register, i.e., 1 on the
±VREF range, 2 on the ±VREF/2 range, and N = 16.
Burnout Currents
REV. A
–33–
AD7719
Reference Detect
ADC Disable Mode
The AD7719 includes on-chip circuitry to detect if the part has a
valid reference on the main ADC for conversions or calibrations.
If the voltage between the external REFIN1(+) and REFIN1(–)
pins goes below 0.3 V or either the REFIN1(+) or REFIN1(–)
inputs are open circuit, the AD7719 detects that it no longer
has a valid reference. In this case, the NOXREF bit of the Status
register is set to 1. If the AD7719 is performing normal conversions and the NOXREF bit becomes active, the conversion results
revert to all 1s. Therefore, it is not necessary to continuously
monitor the status of the NOXREF bit when performing
conversions. It is only necessary to verify its status if the
conversion result read from the ADC data register is all 1s. If the
AD7719 is performing either an offset or gain calibration and
the NOXREF bit becomes active, the updating of the respective
calibration registers is inhibited to avoid loading incorrect
coefficients to these registers, and the ERR0 bit in the Status
register is set. If the user is concerned about verifying that a
valid reference is in place every time a calibration is performed,
the status of the ERR0 bit should be checked at the end of the
calibration cycle.
This mode is entered by setting both the AD0EN and AD1EN
bits in the main and max ADC control registers to 0 and setting
the Mode bits (MD2, MD1, MD0) in the Mode register to non-0.
In this mode, the internal PLL is enabled and the user can
activate the current sources and power switches, but the power
consumption of the ADC is reduced as both ADCs are disabled.
In this mode, the AIDD is reduced to 0.15 mA and the DIDD is
reduced to 0.35 mA max at 3 V and to 0.4 mA max with DVDD = 5 V.
Reset Input
The RESET input on the AD7719 resets all the logic, the digital filter, and the analog modulator while all on-chip registers are
reset to their default state. RDY is driven high and the AD7719
ignores all communications to any of its registers while the
RESET input is low. When the RESET input returns high, the
AD7719 operates with its default setup conditions and it is
necessary to set up all registers and carry out a system calibration
if required after a RESET command.
Power-Down Mode
Loading 0, 0, 0 to the MD2, MD1, MD0 bits in the ADC mode
register places the AD7719 in device power-down mode. Device
power-down mode is the default condition for the AD7719 on
power-up. Individual ADCs (main or auxiliary) can be put in
power-down mode using the AD0EN in the main ADC control
register (AD0CON) to power off the main ADC or the AD1EN
in the auxiliary ADC control register (AD1CON) to power off
the auxiliary ADC. The AD7719 retains the contents of all its
on-chip registers (including the data register) while in powerdown or ADC disable mode.
The device power-down mode does not affect the digital interface, and it does affect the status of the RDY pin. Putting the
AD7719 into power-down or idle mode will reset the RDY line
high. Placing the part in power-down mode reduces the total
current (AIDD + DIDD) to 31 µA max when the part is operated
at 5 V and the oscillator is allowed to run during power-down
mode. With the oscillator shuts down, the total IDD is 3 µA max
at 3 V and 9 µA max at 5 V.
Idle Mode
The AD7719 also contains an idle mode. The ADC defaults
to this mode on completion of a calibration sequence and on
the completion of a conversion when operating in single conversion mode. In idle mode, the power consumption of the
AD7719 is not reduced below the normal mode dissipation.
Calibration
The AD7719 provides four calibration modes that can be programmed via the mode bits in the mode register. One of the
major benefits of the AD7719 is that it is factory-calibrated as
part of the final test process with the generated coefficients
stored within the ADC. At power-on, the factory gain calibration coefficients are automatically loaded to the gain calibration
registers on the AD7719. Each ADC (primary and auxiliary) has
dedicated calibration register pairs as outlined in the AD0CON
and AD1CON register descriptions. Given that the ADC is
factory-calibrated and a chopping scheme is employed that gives
excellent offset and drift performance, it is envisaged that in the
majority of applications the user will not need to perform any
field calibrations.
However, the factory calibration values in the ADC calibration
registers will be overwritten if any one of the four calibration
options are initiated. Even though an internal offset calibration
mode is described below, it should be recognized that both
ADCs are chopped. This chopping scheme inherently minimizes
offset and means that an internal offset calibration should never
be required. Also, because factory 25°C gain calibration coefficients are automatically present at power-on, an internal full-scale
calibration will only be required if the part is being operated at
temperatures significantly different from 25°C or away from the
calibration conditions. The AD7719 offers internal or system
calibration facilities. For full calibration to occur on the selected
ADC, the calibration logic must record the modulator output
for two different input conditions. These are zero-scale and fullscale points derived by performing a conversion on the different
input voltages provided to the input of the modulator during
calibration. The result of the zero-scale calibration conversion is
stored in the offset calibration registers for the appropriate ADC.
The result of the full-scale calibration conversion is stored in the
gain calibration registers for the appropriate ADC. With these
readings, the calibration logic can calculate the offset and the gain
slope for the input-to-output transfer function of the converter.
During an internal zero-scale or full-scale calibration, the respective zero input and full-scale input are automatically connected
to the ADC input pins internally to the device. A system
calibration, however, expects the system zero-scale and system
full-scale voltages to be applied to the external ADC pins before
the calibration mode is initiated. In this way, external ADC errors
are taken into account and minimized as a result of system
calibration. It should also be noted that to optimize calibration
accuracy, all AD7719 ADC calibrations are automatically
carried out at the slowest update rate.
–34–
REV. A
AD7719
Internally in the AD7719, the coefficients are normalized before
being used to scale the words coming out of the digital filter. The
offset calibration coefficient is subtracted from the result prior
to the multiplication by the gain coefficient.
From an operational point of view, a calibration should be treated
like another ADC conversion. A zero-scale calibration (if required)
should always be carried out before a full-scale calibration. System
software should monitor the relevant ADC RDY0/1 bit in the
Status register to determine end of calibration via a polling
sequence or interrupt driven routine.
Grounding and Layout
Since the analog inputs and reference input on the main ADC
are differential, most of the voltages in the analog modulator are
common-mode voltages. The excellent common-mode rejection
of the part will remove common-mode noise on these inputs.
The analog and digital supplies to the AD7719 are independent
and separately pinned out to minimize coupling between the
analog and digital sections of the device. The AD7719 can be
operated with 5 V analog and 3 V digital supplies, or vice versa.
The digital filter will provide rejection of broadband noise on
the power supplies, except at integer multiples of the modulator
sampling frequency. The digital filter also removes noise from
the analog and reference inputs provided these noise sources do
not saturate the analog modulator. As a result, the AD7719 is
more immune to noise interference than a conventional high
resolution converter. However, because the resolution of the
AD7719 is so high, and the noise levels from the AD7719 are so
low, care must be taken with regard to grounding and layout.
The printed circuit board that houses the AD7719 should be
designed such that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be easily separated. A minimum
etch technique is generally best for ground planes as it gives the
best shielding.
Although the AD7719 has separate pins for analog and digital
ground, the AGND and DGND pins are tied together within
the device via the substrate. The user must not tie these pins
external to separate ground planes unless the ground planes are
connected together near the AD7719.
In systems where the AGND and DGND are connected somewhere else in the system, i.e., the system power supply, they should
not be connected again at the AD7719 as a ground loop will
result. In these situations, it is recommended that the AD7719’s
AGND and DGND pins be tied to the AGND plane. In any
layout, it is important that the user keep in mind the flow of
currents in the system, ensuring that the return paths for all
currents are as close as possible to the paths the currents took to
reach their destinations. Avoid forcing digital currents to flow
through the AGND sections of the layout.
The PWRGND pin is tied internally to AGND on the AD7719.
The PWRGND pad internally has a resistance of less then 50 mΩ
to the PWRGND pin, while the resistance back to the AGND
pad is >3 Ω. This means that 19.5 mA of the maximum specified current (20 mA) will flow to PWRGND with the remaining
0.5 mA flowing to AGND. PWRGND and AGND should be
tied together at the AD7719 and it is important to minimize the
resistance on the ground return lines.
REV. A
Avoid running digital lines under the device as these will couple
noise onto the die. The analog ground plane should be allowed
to run under the AD7719 to prevent noise coupling. The power
supply lines to the AD7719 should use as wide a trace as possible
to provide low impedance paths and reduce the effects of glitches
on the power supply line. Fast switching signals like clocks
should be shielded with digital ground to avoid radiating noise
to other sections of the board, and clock signals should never be
run near the analog inputs. Avoid crossover of digital and analog
signals. Traces on opposite sides of the board should run at right
angles to each other. This will reduce the effects of feedthrough
through the board. A microstrip technique is by far the best, but is not
always possible with a double-sided board. In this technique, the
component side of the board is dedicated to ground planes while
signals are placed on the solder side.
Good decoupling is important when using high resolution ADCs.
All analog supplies should be decoupled with 10 µF tantalum in
parallel with 0.1 µF capacitors to AGND. To achieve the best from
these decoupling components, they have to be placed as close as
possible to the device, ideally right up against the device. All logic
chips should be decoupled with 0.1 µF ceramic capacitors to
DGND. In systems where a common supply voltage is used to
drive both the AVDD and DVDD of the AD7719, it is recommended that the system’s AVDD supply be used. This supply
should have the recommended analog supply decoupling capacitors between the AVDD pin of the AD7719 and AGND, and the
recommended digital supply decoupling capacitor between the
DVDD pin of the AD7719 and DGND.
APPLICATIONS
The AD7719 provides a low cost, high resolution analog-todigital function. Because the analog-to-digital function is provided
by a Σ-∆ architecture, it makes the part more immune to noisy
environments, making it ideal for use in sensor measurement and
industrial and process control applications. Given the architecture
used in the AD7719, where the signal chain is chopped and
the device is factory-calibrated at final test, field calibration
can be avoided due to the extremely low offset and gain drifts
exhibited by this converter. It also provides a programmable
gain amplifier, a digital filter, and system calibration options. Thus,
it provides far more system-level functionality than off-the-shelf
integrating ADCs without the disadvantage of having to supply a
high quality integrating capacitor. In addition, using the AD7719
in a system allows the system designer to achieve a much higher
level of resolution because noise performance of the AD7719 is
significantly better than that of integrating ADCs.
The on-chip PGA allows the AD7719 to handle an analog input
voltage range as low as 10 mV full-scale with VREF = 1.25 V. The
differential inputs of the part allow this analog input range to
have an absolute value anywhere between AGND + 100 mV and
AVDD – 100 mV. It allows the user to connect the transducer
directly to the input of the AD7719. The programmable gain
front end on the AD7719 allows the part to handle unipolar
analog input ranges from 0 mV to 20 mV to 0 V to 2.5 V and
bipolar inputs of ±20 mV to ±2.5 V. Because the part operates
from a single supply, these bipolar ranges are with respect to a
biased-up differential input. Another key advantage of the AD7719 is
that it contains two Σ-∆ converters operating in parallel; thus the
user does not need to interrupt the main channel when a secondary measurement on a different variable needs to be performed.
–35–
AD7719
The circuit in Figure 20 shows a method that utilizes all three
pseudodifferential input channels on the AD7719 main channel
to temperature-compensate a pressure transducer.
Pressure Measurement
One typical application of the AD7719 is pressure measurement. Figure 19 shows the AD7719 used with a pressure
transducer, the BP01 from Sensym.
5V
The pressure transducer is arranged in a bridge network and
gives a differential output voltage between its OUT(+) and
OUT(–) terminals. With rated full-scale pressure (in this case
300 mmHg) on the transducer, the differential output voltage is
3 mV/V of the input voltage (i.e., the voltage between its IN(+)
and IN(–) terminals).
AVDD
IOUT1
I1
I2
Assuming a 5 V excitation voltage, the full-scale output range
from the transducer is 15 mV. The excitation voltage for the
bridge can be used to directly provide the reference for the ADC
as the reference input range includes the supplies. Alternatively,
a suitable resistor divider can be implemented that allows the
full dynamic range of the input to be utilized in these application. This implementation is fully ratiometric, so variations in
the excitation voltage do not introduce errors in the system.
Choosing resistor values of 20 kΩ and 12 kΩ as per Figure 19
give a 1.875 V reference voltage for the AD7719 when the excitation voltage is 5 V.
REFIN(+)
6.25k
REFIN(–)
OUT(+)
OUT(–)
PRESSURE
BRIDGE
AIN1
AIN4
IN(–)
AIN3
XTAL2
AGND
250
20k
OUT+
OUT–
XTAL1
AD7719
EXCITATION VOLTAGE = 5V
IN+
AIN2
IN(+)
AVDD
Figure 20. Temperature-Compensating a Pressure
Transducer
DVDD
AIN1
AIN2
In this application, pseudodifferential input channel AIN1/AIN4
is used to measure the bridge output while pseudodifferential
channels AIN2/AIN4 and AIN3/AIN4 measure the voltage
across the bridge. The voltage measured across the bridge will
vary proportionally with temperature, and the delta in this voltage can be used to temperature-compensate the output of the
pressure bridge.
IN–
REFIN1(+)
12k
REFIN2(–)
AD7719
P1
Temperature Measurement
DGND
AGND
PWRGND
Figure 19. Pressure Measurement Using AD7719
Using the part with a programmed gain of 128 results in the
full-scale input span of the AD7719 being 15 mV, which corresponds with the output span from the transducer.
A second key advantage to using the AD7719 in transducer
based applications is that the on-chip low-side power switch can
be fully utilized in low power applications. The low-side power
switch is connected in series with the cold side of the bridge. In
normal operation, the switch is closed and measurements can be
taken from the bridge. In applications where power is of concern, the AD7719 can be put in low power mode, substantially
reducing the power burned in the application. In addition to
this, the power switch can be opened while in low power mode
thus avoiding the unnecessary burning of power in the front end
transducer. When the AD7719 is taken back out of power-down
and the power switch is closed, the user should ensure that the
front end circuitry is fully settled before attempting a read from
the AD7719.
The AD7719 is also useful in temperature measurement applications; Figure 21 shows an RTD temperature measurement
application. In this application, the transducer is an RTD (resistive
temperature device), a PT100. The arrangement is a 4-lead RTD
configuration. There are voltage drops across the lead resistances
RL1 and RL4, but these simply shift the common-mode voltage.
There is no voltage drop across lead resistances RL2 and RL3 as
the input current to the AD7719 is very low, looking into a high
input impedance buffer. RCM is included to shift the analog input
voltage to ensure that it lies within the common-mode range
(AGND + 100 mV to AVDD – 100 mV) of the ADC. In the
application shown, the on-chip 200 µA current source provides the
excitation current for the PT100 and also generates the reference
voltage for the AD7719 via the 12.5 kΩ resistor. Variations in
the excitation current do not affect the circuit as both the input
voltage and the reference voltage vary ratiometrically with the
excitation current. However, the 12.5 kΩ resistor must have a low
temperature coefficient to avoid errors in the reference voltage
over temperature.
–36–
REV. A
AD7719
The switched polarity current source is developed using the
on-chip current sources and external phase control switches
(A and A) driven from the controller. During the conversion
process, the AD7719 takes two conversion results, one on each
phase. During Phase 1, the on-chip current source is directed to
IOUT1 and flows top to bottom through the sensor and switch
controlled by A. In Phase 2, the current source is directed to
IOUT2 and flows in the opposite direction through the sensor
and through switch controlled by A. In all cases, the current
flows in the same direction through the reference resistor to
develop the reference voltage for the ADC. All measurements are
ratiometrically derived. The results of both conversions are
combined within the microcontroller to produce one output
measurement representing the resistance or temperature of the
transducer. For example, if the RTD output during Phase 1 is
10 mV, a 1 mV circuit-induced dc error exists due to parasitic
thermocouples, and the ADC measures 11 mV. During the
second phase, the excitation current is reversed and the ADC
measures –10 mV from the RTD and again sees 1 mV dc error,
giving an ADC output of –9 mV during this phase. These measurements are processed in the controller (11 mV – (–9 mV)/2 =
10 mV), thus removing the dc-induced errors within the system.
5V
AVDD DVDD
REFIN(–)
XTAL1
REFIN(+)
RREF
RL1
IOUT1
XTAL2
12.5k
200A
IOUT2
RL2
AIN1
DRDY
RTD
AD7719
SCLK
AIN2
RL3
DIN
CONTROLLER
DOUT
RCM
CS
RL4
DGND
AGND
PWRGND
Figure 21. 4-Wire RTD Temperature Measurement
Using the AD7719
Figure 22 shows a further enhancement to the circuit shown in
Figure 21. Generally, dc excitation has been accepted as the
normal method of exciting resistive-based sensors like RTDs
(resistance temperature detectors) in temperature measurement
applications.
In the circuit shown in Figure 22, the resistance measurement is
made using ratiometric techniques. Resistor RREF, which develops the ADC reference, must be stable over temperature to
prevent reference-induced errors in the measurement output.
With dc excitation, the excitation current through the sensor
must be large enough so that the smallest temperature/resistance
change to be measured results in a voltage change that is larger
than the system noise, offset, and drift of the system. The purpose
of switching the excitation source is to eliminate dc-induced
errors. DC errors (EMF1 and EMF2) due to parasitic thermocouples produced by differential metal connections (solder and
copper track) within the circuit are also eliminated when using
this switching arrangement. This excitation is a form of synchronous detection where the sensor is excited with an alternating
excitation source and the ADC only measures information in the
same phase as the excitation source.
3-Wire RTD Configurations
To fully optimize a 3-wire RTD configuration, two identically
matched current sources are required. The AD7719, which
contains two well-matched current sources, is ideally suited to
these applications. One possible 3-wire configuration using the
AD7719 is outlined in Figure 23.
5V
AVDD DVDD
IOUT1
XTAL1
200A
REFIN(+)
AVDD
EMF1
IOUT1
REFIN(–)
I1
IOUT2
RL1
AIN1
200A
AIN2
AIN3
A
A
SCLK
IOUT2
DIN
BUF
AND
PGA
AIN1
DRDY
AIN2
RTD
RL2
RESISTIVE
TRANSDUCER
EMF2
XTAL2
12.5k
RL3
200A
CS
RCM
MUX1
AGND
AIN4
CONTROLLER
DOUT
AD7719
DGND
REFIN(+)
RREF
REFIN(–)
AD7719
Figure 23. 3-Wire RTD Configuration Using the AD7719
Figure 22. Low Resistance Measurement AD7719
REV. A
–37–
AD7719
In this 3-wire configuration, the lead resistances will result in
errors if only one current source is used because the 200 µA will
flow through RL1, developing a voltage error between AIN1 and
AIN2. In the scheme outlined below, the second RTD current
source is used to compensate for the error introduced by the
200 µA flowing through RL1. The second RTD current flows
through RL2. Assuming RL1 and RL2 are equal (the leads
would normally be of the same material and of equal length),
and IOUT1 and IOUT2 match, the error voltage across RL2
equals the error voltage across RL1, and no error voltage is
developed between AIN1 and AIN2. Twice the voltage is
developed across RL3, but since this is a common-mode voltage,
it will not introduce errors. RCM is included so the current
flowing through the combination of RL3 and RCM develops enough
voltage that the analog input voltage seen by the AD7719 is
within the common-mode range of the ADC. The reference
voltage for the AD7719 is also generated using one of these
matched current sources. This reference voltage is developed
across the 12.5 kΩ resistor as shown, and applied to the differential
reference inputs of the AD7719. This scheme ensures that the analog
input voltage span remains ratiometric to the reference voltage.
Any errors in the analog input voltage due to the temperature drift
of the RTD current source is compensated for by the variation
in the reference voltage. The typical drift matching between the
two RTD current sources is less than 1 ppm/°C. The voltage on
either IOUT pin can go to within 0.6 V of the AVDD supply.
Smart Transmitters
Smart transmitters are another key design-in area for the AD7719.
The dual Σ-∆ converter, single-supply operation, 3-wire interface
capabilities, and small package size are all of benefit in smart
transmitters. Here, the entire smart transmitter must operate
from the 4 to 20 mA loop. Tolerances in the loop mean that the
amount of current available to power the transmitter is as low as
3.5 mA. Figure 24 shows a block diagram of a smart transmitter,
which includes the AD7719.
Not shown in Figure 24 is the isolated power source required to
power the front end. The advantages of the AD7719 in these
applications is the dual-channel operation, meaning that the
user does not have to interrupt the main channel when measuring secondary variables, and therefore does not have the latency
associated with the settling times of the digital filter. The fact
that the AD7719 is factory-calibrated means that in the majority
of applications, the user will not have to perform any field calibration given the excellent offset and gain drift performance of
the device as a result of the signal chain chopping employed in
the signal chain.
DN25D
3.3V
10F
0.1F
0.01F
10F
1.25V
AVDD
DVDD
MAIN
VARIABLES
AIN1
AIN2
REFIN2
REFIN(+)
AIN3
AIN4
REF OUT1
AD7719
REF IN
DRIVE
0.01F
1k
VCC
CLOCK
MICROCONTROLLER
1000pF
LATCH
AD421
DATA
AIN5
SECONDARY
VARIABLES
LV
COMP
4.7F
0.1F
REFIN(–)
BOOST VCC
REF OUT2
GND
AIN5 COM
CS
LOOP
POWER
DOUT
LOOP
RTN
SCLK
COM
DIN
C1
DGND
C2
C3
AGND
Figure 24. Smart Transmitter Employing the AD7719
–38–
REV. A
AD7719
OUTLINE DIMENSIONS
28-Lead Standard Small Outline Package [SOIC]
Wide Body
(R-28)
Dimensions shown in millimeters and (inches)
18.10 (0.7126)
17.70 (0.6969)
28
15
7.60 (0.2992)
7.40 (0.2913)
1
10.65 (0.4193)
10.00 (0.3937)
14
2.65 (0.1043)
2.35 (0.0925)
0.75 (0.0295)
ⴛ 45ⴗ
0.25 (0.0098)
0.30 (0.0118)
0.10 (0.0039)
8ⴗ
0ⴗ
1.27 (0.0500) 0.51 (0.0201) SEATING
0.32 (0.0126)
PLANE
BSC
0.33 (0.0130)
0.23 (0.0091)
COPLANARITY
0.10
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-013AE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
28-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-28)
Dimensions shown in millimeters
9.80
9.70
9.60
28
15
4.50
4.40
4.30
1
6.40 BSC
14
PIN 1
0.65
BSC
0.15
0.05
COPLANARITY
0.10
0.30
0.19
1.20
MAX
SEATING
PLANE
0.20
0.09
COMPLIANT TO JEDEC STANDARDS MS-153AE
REV. A
–39–
8ⴗ
0ⴗ
0.75
0.60
0.45
AD7719
Revision History
Location
Page
4/03—Data Sheet changed from REV. 0 to REV. A.
Changes to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
–40–
REV. A
C02460–0–4/03(A)
Updated format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal