AD AD7715AR-5REEL 3 v/5 v, 450 mua 16-bit, sigma-delta adc Datasheet

3 V/5 V, 450 μA
16-Bit, Sigma-Delta ADC
AD7715
FEATURES
FUNCTIONAL BLOCK DIAGRAM
REF IN(–)
AVDD
REF IN(+)
DVDD
CHARGE BALANCING
ADC
Σ-∆
MODULATOR
AIN(+)
AIN(–)
BUFFER
PGA
A = 1 TO 128
DIGITAL
FILTER
CLOCK
GENERATION
MCLK IN
MCLK OUT
RESET
SERIAL
INTERFACE
REGISTER BANK
AD7715
AGND
DGND
SCLK
CS
DIN
DOUT
DRDY
08519-001
Charge-balancing ADC
16-bits no missing codes
0.0015% nonlinearity
Programmable gain front end
Gains of 1, 2, 32 and 128
Differential input capability
Three-wire serial interface
SPI-, QSPI™-, MICROWIRE™-, and DSP-compatible
Ability to buffer the analog input
3 V (AD7715-3) or 5 V (AD7715-5) operation
Low supply current: 450 μA maximum @ 3 V supplies
Low-pass filter with programmable output update
16-lead SOIC/PDIP/TSSOP
Figure 1.
GENERAL DESCRIPTION
The AD7715 is a complete analog front end for low frequency
measurement applications. The part can accept low level input
signals directly from a transducer and outputs a serial digital
word. It employs a Σ-Δ conversion technique to realize up to
16 bits of no missing codes performance. The input signal is
applied to a proprietary programmable gain front end based
around an analog modulator. The modulator output is processed
by an on-chip digital filter. The first notch of this digital filter
can be programmed via the on-chip control register allowing
adjustment of the filter cutoff and output update rate.
The AD7715 features a differential analog input as well as a
differential reference input. It operates from a single supply (3 V
or 5 V). It can handle unipolar input signal ranges of 0 mV to
20 mV, 0 mV to 80 mV, 0 V to 1.25 V and 0 V to 2.5 V. It can
also handle bipolar input signal ranges of ±20 mV, ±80 mV,
±1.25 V and ±2.5 V. These bipolar ranges are referenced to the
negative input of the differential analog input. The AD7715
thus performs all signal conditioning and conversion for a
single channel system.
The AD7715 is ideal for use in smart, microcontroller, or DSPbased systems. It features a serial interface that can be configured
for three-wire operation. Gain settings, signal polarity, and
update rate selection can be configured in software using the
input serial port. The part contains self-calibration and system
calibration options to eliminate gain and offset errors on the
part itself or in the system.
CMOS construction ensures very low power dissipation, and
power-down mode reduces the standby power consumption to
50 μW typical. The part is available in a 16-lead, 0.3 inch-wide,
plastic dual-in-line package (PDIP) as well as a 16-lead 0.3 inch
wide small outline (SOIC_W) package and a 16-lead TSSOP
package.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
The AD7715 consumes less than 450 μA in total supply
current at 3 V supplies and 1 MHz master clock, making it
ideal for use in low-power systems. Standby current is less
than 10 μA.
The programmable gain input allows the AD7715 to accept
input signals directly from a strain gage or transducer
removing a considerable amount of signal conditioning.
The AD7715 is ideal for microcontroller or DSP processor
applications with a three-wire serial interface reducing the
number of interconnect lines and reducing the number
of optocouplers required in isolated systems. The part
contains on-chip registers which allow software control
over output update rate, input gain, signal polarity, and
calibration modes.
The part features excellent static performance specifications
with 16-bits no missing codes, ±0.0015% accuracy, and low
rms noise (<550 nV). Endpoint errors and the effects of
temperature drift are eliminated by on-chip calibration
options, which remove zero-scale and full-scale errors.
Rev. D
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. Specifications subject to change without notice. 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 owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
AD7715
TABLE OF CONTENTS
Features .............................................................................................. 1
Digital Filtering........................................................................... 21
Functional Block Diagram .............................................................. 1
Analog Filtering.......................................................................... 23
General Description ......................................................................... 1
Calibration................................................................................... 23
Product Highlights ........................................................................... 1
Using the AD7715 .......................................................................... 26
Revision History ............................................................................... 2
Clocking and Oscillator Circuit ............................................... 26
Specifications..................................................................................... 3
System Synchronization ............................................................ 26
AD7715-5 ...................................................................................... 3
Reset Input .................................................................................. 27
AD7715-3 ...................................................................................... 5
Standby Mode ............................................................................. 27
Timing Characteristics ................................................................ 8
Accuracy ...................................................................................... 27
Absolute Maximum Ratings............................................................ 9
Drift Considerations .................................................................. 27
ESD Caution.................................................................................. 9
Power Supplies ............................................................................ 28
Pin Configuration And Function Descriptions.......................... 10
Digital Interface.......................................................................... 29
Terminology .................................................................................... 11
Configuring the AD7715............................................................... 31
On-Chip Registers .......................................................................... 12
Microcontroller/Microprocessor Interfacing ............................. 32
Communications Register (RS1, RS0 = 0, 0) .......................... 13
AD7715 to 68HC11 Interface ................................................... 32
Setup Register (RS1, RS0 = 0, 1); Power On/Reset Status:
28 Hex .......................................................................................... 14
AD7715 to 8XC51 Interface...................................................... 33
Test Register (RS1, RS0 = 1, 0).................................................. 15
Code For Setting Up The AD7715............................................... 34
Data Register (RS1, RS0 = 1, 1) ................................................ 15
C Code for Interfacing AD7715 to 68HC11........................... 34
Output Noise ................................................................................... 16
Applications Information .............................................................. 36
AD7715-5 .................................................................................... 16
Pressure Measurement............................................................... 36
AD7715-3 .................................................................................... 17
Temperature Measurement ....................................................... 37
Calibration Sequences.................................................................... 18
Smart Transmitters..................................................................... 38
Circuit Description......................................................................... 19
Outline Dimensions ....................................................................... 39
Analog Input ............................................................................... 19
Ordering Guide .......................................................................... 40
AD7715 to ADSP-2103/ADSP-2105 Interface ....................... 33
Reference Input........................................................................... 21
REVISION HISTORY
12/09—Rev. C to Rev. D
Updated Format..................................................................Universal
Changes to Table 5............................................................................ 9
Updated Outline Dimensions ....................................................... 39
2/00—Rev. B to Rev. C
Rev. D | Page 2 of 40
AD7715
SPECIFICATIONS
AD7715-5
AVDD = 5 V, DVDD = 3 V or 5 V, REF IN(+) = 2.5 V; REF IN(−) = AGND; fCLK IN = 2.4576 MHz, unless otherwise noted. All specifications
TMIN to TMAX, unless otherwise noted.
Table 1.
Parameter 1
STATIC PERFORMANCE
No Missing Codes
Output Noise
Min
Typ
Max
16
See Table 15 to Table 18
±0.0015
See Table 15 to Table 22
0.5
See Table 15 to Table 22
Integral Nonlinearity
Unipolar Offset Error 2
Unipolar Offset Drift 3
Bipolar Zero Error2
Bipolar Zero Drift3
Positive Full-Scale Error2, 4
Full-Scale Drift3, 5
Gain Error2, 6
Gain Drift3, 7
Unit
Bits
Guaranteed by design; filter notch ≤ 60 Hz
% of FSR
Depends on filter cutoffs and selected gain
Filter notch ≤ 60 Hz
μV/°C
0.5
See Table 15 to Table 22
μV/°C
0.5
See Table 15 to Table 22
0.5
μV/°C
Bipolar Negative Full-Scale Error2
±0.0015
Conditions/Comments
ppm of
FSR/°C
% of FSR
Typically ±0.0004%
μV/°C
μV/°C
dB
For gains of 1 and 2
For gains of 32 and 128
Specifications for AIN and REF IN unless noted
At dc; typically 102 dB
98
dB
dB
For filter notches of 25 Hz, 50 Hz, ±0.02 × fNOTCH
For filter notches of 20 Hz, 60 Hz, ±0.02 × fNOTCH
150
dB
For filter notches of 25 Hz, 50 Hz, ±0.02 × fNOTCH
150
AGND
AGND – 0.03
dB
For filter notches of 20 Hz, 60 Hz, ±0.02 × fNOTCH
AVDD
AVDD + 0.03
V
V
AIN for the BUF bit of setup register = 0 and REF IN
AIN for the BUF bit of setup register = 0 and REF IN
AGND + 0.05
AVDD − 1.5
V
BUF bit of setup register = 1
AIN DC Input Current8
1
nA
AIN Sampling Capacitance8
AIN Differential Voltage Range 10
10
Bipolar Negative Full-Scale Drift3
1
0.6
ANALOG INPUTS/REFERENCE INPUTS
Input Common-Mode Rejection
(CMR)
Normal-Mode 50 Hz Rejection 8
Normal-Mode 60 Hz Rejection8
90
98
Common-Mode 50 Hz Rejection8
8
Common-Mode 60 Hz Rejection
Common-Mode Voltage Range 9
Absolute AIN/REF IN Voltage8
Absolute/Common-Mode AIN
Voltage9
AIN Input Sampling Rate, fS
REF IN(+) − REF IN(−) Voltage
REF IN Input Sampling Rate, fS
LOGIC INPUTS
Input Current
All Inputs Except MCLK IN
VINL, Input Low Voltage
VINL, Input Low Voltage
VINH, Input High Voltage
VINH, Input High Voltage
MCLK IN Only
VINL, Input Low Voltage
VINL, Input Low Voltage
VINH, Input High Voltage
VINH, Input High Voltage
pF
0 to +VREF/GAIN 11
nom
Unipolar input range (B/U bit of setup register = 1)
±VREF/GAIN
nom
GAIN × fCLK IN/64
fCLK IN/8
2.5
V nom
Bipolar input range (B/U bit of setup register = 0)
For gains of 1 and 2
For gains of 32 and 128
±1% for specified performance; functional with
lower VREF
fCLK IN/64
±10
μA
0.8
0.4
V
V
V
V
DVDD = 5 V
DVDD = 3.3 V
DVDD = 5 V
0.8
0.4
V
V
V
V
DVDD = 5 V
DVDD = 3.3 V
DVDD = 5 V
DVDD = 3.3 V
2.4
2.0
3.5
2.5
Rev. D | Page 3 of 40
AD7715
Parameter 1
LOGIC OUTPUTS (Including MCLK OUT)
VOL, Output Low Voltage
VOL, Output Low Voltage
Min
Typ
Max
Unit
Conditions/Comments
0.4
V
V
ISINK = 800 μA except for MCLK OUT 12 ; DVDD = 5 V
ISINK = 100 μA except for MCLK OUT12; DVDD = 3.3 V
0.4
VOH, Output High Voltage
4.0
V
ISOURCE = 200 μA except for MCLK OUT12; DVDD = 5 V
VOH, Output High Voltage
DVDD − 0.6
V
μA
pF
ISOURCE = 100 μA except for MCLK OUT12; DVDD = 3.3 V
Floating State Leakage Current
Floating State Output Capacitance 13
Data Output Coding
±10
9
Binary
Offset binary
1
Unipolar mode
Bipolar mode
Temperature range as follows: A version, −40°C to +85°C.
A calibration is effectively a conversion, so these errors are of the order of the conversion noise shown in Table 15 to Table 22. This applies after calibration at the
temperature of interest.
3
Recalibration at any temperature removes these drift errors.
4
Positive full-scale error includes zero-scale errors (unipolar offset error or bipolar zero error) and applies to both unipolar and bipolar input ranges.
5
Full-scale drift includes zero-scale drift (unipolar offset drift or bipolar zero drift) and applies to both unipolar and bipolar input ranges.
6
Gain error does not include zero-scale errors. It is calculated as full-scale error–unipolar offset error for unipolar ranges and full-scale error–bipolar zero error for
bipolar ranges.
7
Gain error drift does not include unipolar offset drift/bipolar zero drift. It is effectively the drift of the part if zero scale calibrations only were performed.
8
These numbers are guaranteed by design and/or characterization.
9
This common-mode voltage range is allowed provided that the input voltage on AIN(+) or AIN(−) does not go more positive than AVDD + 30 mV or go more negative
than AGND − 30 mV.
10
The analog input voltage range on AIN(+) is given here with respect to the voltage on AIN(−). The absolute voltage on the analog inputs should not go more positive
than AVDD + 30 mV or go more negative than AGND − 30 mV.
11
VREF = REF IN(+) − REF IN(−).
12
These logic output levels apply to the MCLK OUT only when it is loaded with one CMOS load.
13
Sample tested at 25°C to ensure compliance.
2
Rev. D | Page 4 of 40
AD7715
AD7715-3
AVDD = 3 V, DVDD = 3 V, REF IN (+) = 1.25 V; REF IN(−) = AGND; fCLK IN = 2.4576 MHz, unless otherwise noted. All specifications TMIN
to TMAX, unless otherwise noted.
Table 2.
Parameter 1
STATIC PERFORMANCE
No Missing Codes
Output Noise
Min
Typ
Max
16
See Table 18 to Table 22
±0.0015
See Table 15 to Table 22
0.2
See Table 15 to Table 22
0.2
Integral Nonlinearity
Unipolar Offset Error 2
Unipolar Offset Drift 3
Bipolar Zero Error2
Bipolar Zero Drift3
Positive Full-Scale Error2, 4
See Table 15 to Table 22
0.2
Full-Scale Drift3, 5
Gain Error2, 6
See Table 15 to Table 22
0.2
Gain Drift3, 7
Conditions/Comments
Bits
Guaranteed by design; filter notch ≤ 60 Hz
Depends on filter cutoffs and selected gain
% of FSR
Filter notch ≤ 60 Hz
μV/°C
μV/°C
μV/°C
ppm of
FSR/°C
% of FSR
Typically ±0.0004%
1
μV/°C
For gains of 1 and 2
0.6
μV/°C
Bipolar Negative Full-Scale Error2
±0.003
Bipolar Negative Full-Scale Drift3
Unit
90
dB
For gains of 32 and 128
Specifications for AIN and REF IN unless noted
At dc; tpically 102 dB
98
98
dB
dB
For filter notches of 25 Hz, 50 Hz, ±0.02 × fNOTCH
For filter notches of 20 Hz, 60 Hz, ±0.02 × fNOTCH
Common-Mode 50 Hz Rejection8
150
dB
For filter notches of 25 Hz, 50 Hz, ±0.02 × fNOTCH
Common-Mode 60 Hz Rejection8
Common-Mode Voltage Range 9
Absolute AIN/REF IN Voltage8
Absolute/Common-Mode AIN
Voltage9
150
dB
For filter notches of 20 Hz, 60 Hz, ±0.02 × fNOTCH
ANALOG INPUTS/REFERENCE INPUTS
Input Common-Mode Rejection
(CMR)
Normal-Mode 50 Hz Rejection 8
Normal-Mode 60 Hz Rejection8
AGND
AGND − 0.03
AVDD
AVDD + 0.03
V
V
AIN for BUF bit of setup register = 0 and REF IN
AIN for BUF bit of setup register = 0 and REF IN
AGND + 0.05
AVDD − 1.5
V
BUF bit of setup register = 1
AIN DC Input Current8
1
nA
AIN Sampling Capacitance8
AIN Differential Voltage Range 10
10
0 to
+VREF/GAIN 11
±VREF/GAIN
AIN Input Sampling Rate, fS
REF IN Input Sampling Rate, fS
LOGIC INPUTS
Input Current
All Inputs Except MCLK IN
VINL, Input Low Voltage
VINH, Input High Voltage
MCLK IN Only
VINL, Input Low Voltage
VINH, Input High Voltage
nom
GAIN × fCLK IN/64
fCLK IN/8
1.25
REF IN(+) − REF IN(−) Voltage
pF
nom
V nom
fCLK IN/64
±10
μA
0.8
V
V
0.4
V
V
2.0
2.5
Rev. D | Page 5 of 40
Unipolar input range (B/U bit of setup register = 1)
Bipolar input range (B/U bit of setup register = 0)
For gains of 1 and 2
For gains of 32 and 128
±1% for specified performance; functional with
lower VREF
AD7715
Parameter 1
LOGIC OUTPUTS (Including MCLK OUT)
VOL, Output Low Voltage
VOH, Output High Voltage
Floating State Leakage Current
Floating State Output Capacitance 13
Data Output Coding
Min
Typ
Max
Unit
Conditions/Comments
0.4
V
V
ISINK = 100 μA except for MCLK OUT 12
ISOURCE = 100 μA except for MCLK OUT12
±10
μA
pF
DVDD − 0.6
9
Binary
Offset binary
1
Unipolar mode
Bipolar mode
Temperature range as follows: A version, −40°C to +85°C.
A calibration is effectively a conversion, so these errors are of the order of the conversion noise shown in Table 15 to Table 22. This applies after calibration at the
temperature of interest.
3
Recalibration at any temperature removes these drift errors.
4
Positive full-scale error includes zero-scale errors (unipolar offset error or bipolar zero error) and applies to both unipolar and bipolar input ranges.
5
Full-scale drift includes zero-scale drift (unipolar offset drift or bipolar zero drift) and applies to both unipolar and bipolar input ranges.
6
Gain error does not include zero-scale errors. It is calculated as full-scale error–unipolar offset error for unipolar ranges and Full-Scale Error–Bipolar Zero Error for
bipolar ranges.
7
Gain error drift does not include unipolar offset drift/bipolar zero drift. It is effectively the drift of the part if zero scale calibrations only were performed.
8
These numbers are guaranteed by design and/or characterization.
9
This common-mode voltage range is allowed provided that the input voltage on AIN(+) or AIN(−) does not go more positive than AVDD + 30 mV or go more negative
than AGND − 30 mV.
10
The analog input voltage range on AIN(+) is given here with respect to the voltage on AIN(−). The absolute voltage on the analog inputs should not go more positive
than AVDD + 30 mV or go more negative than AGND − 30 mV.
11
VREF = REF IN(+) − REF IN(−).
12
These logic output levels apply to the MCLK OUT only when it is loaded with one CMOS load.
13
Sample tested at 25°C to ensure compliance.
2
Rev. D | Page 6 of 40
AD7715
AVDD = 3 V to 5 V, DVDD = 3 V to 5 V, REF IN(+) = 1.25 V (AD7715-3) or 2.5 V (AD7715-5); REF IN(−) = AGND; MCLK IN = 1 MHz to
2.4576 MHz, unless otherwise noted. All specifications TMIN to TMAX, unless otherwise noted.
Table 3.
Parameter
SYSTEM CALIBRATION
Positive Full-Scale Calibration Limit 1
Min
Negative Full-Scale Calibration Limit1
Offset Calibration Limit 2
Input Span2
POWER REQUIREMENTS
Power Supply Voltages
AVDD Voltage (AD7715-3)
AVDD Voltage (AD7715-5)
DVDD Voltage
Power Supply Currents
AVDD Current
Typ
Max
Unit
Conditions/Comments
(1.05 ×
VREF)/GAIN
−(1.05 ×
VREF)/GAIN
−(1.05 ×
VREF)/GAIN
V
GAIN Is the selected PGA gain (1, 2, 32, or 128)
V
GAIN Is the selected PGA gain (1, 2, 32, or 128)
V
GAIN Is the selected PGA gain (1, 2, 32, or 128)
V
GAIN Is the selected PGA gain (1, 2, 32, or 128)
(2.1 × VREF)/GAIN
V
GAIN Is the selected PGA gain (1, 2, 32, or 128)
3.6
5.25
5.25
V
V
V
For specified performance
For specified performance
For specified performance
0.8 ×
VREF/GAIN
3
4.75
3
0.27
0.6
mA
mA
0.5
1.1
mA
mA
DVDD Current 4
Power Supply Rejection 5
Normal-Mode Power Dissipation4
0.18
0.4
0.5
0.8
Depends on gain 6
mA
mA
mA
mA
dB
1.5
2.65
3.3
5.3
mW
mW
mW
mW
3.25
5
6.5
9.5
20
10
mW
mW
mW
mW
μA
μA
Normal-Mode Power Dissipation4
Standby (Power-Down) Current 7
Standby (Power-Down) Current7
1
AVDD = 3.3 V or 5 V. gain = 1 to 128 (fCLK IN = 1 MHz) or
gain = 1 or 2 (fCLK IN = 2.4576 MHz)
Typically 0.2 mA; BUF bit of the setup register = 0
Typically 0.4 mA; BUF bit of the setup register = 1, AVDD
= 3.3 V or 5 V; gain = 32 or 128 (fCLK IN = 2.4576 MHz) 3
Typically 0.3 mA; BUF bit of the setup register = 0
Typically 0.8 mA; BUF bit of the setup register = 1
Digital inputs = 0 V or DVDD; external MCLK IN
Typically 0.15 mA. DVDD = 3.3 V. fCLK IN = 1 MHz
Typically 0.3 mA. DVDD = 5 V. fCLK IN = 1 MHz
Typically 0.4 mA. DVDD = 3.3 V. fCLK IN = 2.4576 MHz
Typically 0.6 mA. DVDD = 5 V. fCLK IN = 2.4576 MHz
AVDD = DVDD = 3.3 V; digital inputs = 0 V or DVDD; external
MCLK IN
BUF bit = 0. all gains 1 MHz clock
BUF bit = 1. all gains 1 MHz clock
BUF bit = 0. Gain = 32 or 128 @ fCLK IN = 2.4576 MHz
BUF bit = 1. Gain = 32 or 128 @ fCLK IN = 2.4576 MHz
AVDD = DVDD = 5 V. digital inputs = 0 V or DVDD; external
MCLK IN
BUF bit = 0; all gains 1 MHz clock
BUF bit = 1; all gains 1 MHz clock
BUF bit = 0; gain = 32 or 128 @ fCLK IN = 2.4576 MHz
BUF bit = 1; gain = 32 or 128 @ fCLK IN = 2.4576 MHz
External MCLK IN = 0 V or DVDD. typically 10 μA; VDD = 5 V
External MCLK IN = 0 V or DVDD. typically 5 μA; VDD = 3.3 V
After calibration, if the analog input exceeds positive full scale, the converter outputs all 1s. If the analog input is less than negative full scale, then the device outputs
all 0s.
These calibration and span limits apply provided the absolute voltage on the analog inputs does not exceed AVDD + 30 mV or go more negative than AGND − 30 mV.
The offset calibration limit applies to both the unipolar zero point and the bipolar zero point.
3
Assumes CLK Bit of setup register is set to correct status corresponding to the master clock frequency.
4
When using a crystal or ceramic resonator across the MCLK pins as the clock source for the device, the DVDD current and power dissipation will vary depending on the
crystal or resonator type (see the Clocking and Oscillator Circuit section).
5
Measured at dc and applies in the selected pass-band. PSRR at 50 Hz exceeds 120 dB with filter notches of 25 Hz or 50 Hz. PSRR at 60 Hz exceeds 120 dB with filter
notches of 20 Hz or 60 Hz.
6
PSRR depends on gain. Gain of 1:85 dB typical; gain of 2:90 dB typical; gains of 32 and 128:95 dB typical.
7
If the external master clock continues to run in standby mode, the standby current increases to 50 μA typical. When using a crystal or ceramic resonator across the
MCLK pins as the clock source for the device, the internal oscillator continues to run in standby mode and the power dissipation depends on the crystal or resonator
type (see the Standby Mode section).
2
Rev. D | Page 7 of 40
AD7715
TIMING CHARACTERISTICS
DVDD = 3 V to 5.25 V; AVDD = 3 V to 5.25 V; AGND = DGND = 0 V; fCLKIN = 2.4576 MHz; Input Logic 0 = 0 V, Logic 1 = DVDD, unless
otherwise noted.
Table 4.
Parameter
fCLKIN 3, 4
1, 2
tCLK IN LO
tCLK IN HI
t1
t2
Read Operation
t3
t4
t5 5
t6
t7
t8
t9 6
t10
Write Operation
t11
t12
t13
t14
t15
t16
Limit at TMIN, TMAX
(A Version)
400
2.5
0.4 × tCLK IN
0.4 × tCLK IN
500 × tCLK IN
100
Unit
kHz min
MHz max
ns min
ns min
ns nom
ns min
Master clock frequency: crystal oscillator or externally supplied for specified
performance
Master clock input low time; tCLK IN = 1/fCLK IN
Master clock input high time
DRDY high time
RESET pulsewidth
Conditions/Comments
0
120
0
80
100
100
100
0
10
60
100
100
ns min
ns min
ns min
ns max
ns max
ns min
ns min
ns min
ns min
ns max
ns max
ns max
DRDY to CS setup time
CS falling edge to SCLK rising edge setup time
SCLK falling edge to data valid delay
DVDD = 5 V
DVDD = 3.3 V
SCLK high pulsewidth
SCLK low pulsewidth
CS rising edge to SCLK rising edge hold time
Bus relinquish time after SCLK rising edge
DVDD = +5 V
DVDD = +3.3 V
SCLK falling edge to DRDY high 7
120
30
20
100
100
0
ns min
ns min
ns min
ns min
ns min
ns min
CS falling edge to SCLK rising edge setup time
Data valid to SCLK rising edge setup time
Data valid to SCLK rising edge hold time
SCLK high pulsewidth
SCLK low pulsewidth
CS rising edge to SCLK rising edge hold time
1
Sample tested at +25°C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of DVDD) and timed from a voltage level of 1.6 V.
See Figure 8 and Figure 9.
CLKIN Duty Cycle range is 45% to 55%. CLKIN must be supplied whenever the AD7715 is not in standby mode. If no clock is present in this case, the device can draw
higher current than specified and possibly become uncalibrated.
4
The AD7715 is production tested with fCLKIN at 2.4576 MHz (1 MHz for some IDD tests). It is guaranteed by characterization to operate at 400 kHz.
5
These numbers are measured with the load circuit of Figure 2 and defined as the time required for the output to cross the VOL or VOH limits.
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 2. 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 DRDY
returns high after the first read from the device after an output update. The same data can be read again, if required, while DRDY is high although take care that
subsequent reads do not occur close to the next output update.
2
3
ISINK (800µA AT DV DD = 5V
100µA AT DVDD = 3.3V)
+1.6V
50pF
ISOURCE (200µA AT DV DD = 5V
100µA AT DV DD = 3.3V)
08519-002
TO
OUTPUT
PIN
Figure 2. Load Circuit for Access Time and Bus Relinquish Time
Rev. D | Page 8 of 40
AD7715
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 5.
Parameter
AVDD to AGND
AVDD to DGND
AVDD to DVDD
DVDD to AGND
DVDD to DGND
DGND to AGND
Analog Input Voltage to AGND
Reference Input Voltage to AGND
Digital Input Voltage to DGND
Digital Output Voltage to DGND
Operating Temperature Range
Commercial (A Version)
Storage Temperature Range
Junction Temperature
Plastic DIP Package, Power Dissipation
θJA Thermal Impedance
Lead Temperature, (Soldering, 10 sec)
SOIC Package, Power Dissipation
θJA Thermal Impedance
Lead Temperature, Reflow Soldering
TSSOP Package, Power Dissipation
θJA Thermal Impedance
Lead Temperature, Reflow Soldering
Power Dissipation (Any Package) to +75°C
ESD Rating
Rating
−0.3 V to +7 V
−0.3 V to +7 V
−0.3 V to +7 V
−0.3 V to +7 V
−0.3 V to +7 V
−0.3 V to +7 V
−0.3 V to AVDD + 0.3 V
−0.3 V to AVDD + 0.3 V
−0.3 V to DVDD + 0.3 V
−0.3 V to DVDD + 0.3 V
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 indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
−40°C to +85°C
−65°C to +150°C
150°C
450 mW
105°C/W
260°C
450 mW
75°C/W
260°C
450 mW
128°C/W
+260°C
450 mW
>4000 V
Rev. D | Page 9 of 40
AD7715
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
SCLK 1
16 DGND
MCLK IN 2
15 DVDD
14 DIN
MCLK OUT 3
AD7715
13 DOUT
TOP VIEW
RESET 5 (Not to Scale) 12 DRDY
AVDD 6
11 AGND
AIN(+) 7
10 REF IN(–)
AIN(–) 8
9 REF IN(+)
08519-003
CS 4
Figure 3. Pin Configuration
Table 6. Pin Function Descriptions
Pin
No.
1
Mnemonic
SCLK
2
MCLK IN
3
MCLK OUT
4
CS
5
RESET
6
7
8
9
AVDD
AIN(+)
AIN(−)
REF IN(+)
10
REF IN(−)
11
AGND
12
DRDY
13
DOUT
14
DIN
15
16
DVDD
DGND
Description
Serial Clock. Logic input. An external serial clock is applied to this input to access serial data from the AD7715. This
serial clock can be a continuous clock with all data transmitted in a continuous train of pulses. Alternatively, it can be a
noncontinuous clock with the information being transmitted to the AD7715 in smaller batches of data.
Master Clock Signal for the Device. This can be provided in the form of a crystal/resonator or external clock. A
crystal/resonator can be tied across the MCLK IN and MCLK OUT pins. Alternatively, the MCLK IN pin can be driven
with a CMOS-compatible clock and MCLK OUT left unconnected. The part is specified with clock input frequencies of
both 1 MHz and 2.4576 MHz.
When the master clock for the device is a crystal/resonator, the crystal/resonator is connected between MCLK IN and
MCLK OUT. If an external clock is applied to MCLK IN, MCLK OUT provides an inverted clock signal. This clock can be
used to provide a clock source for external circuitry.
Chip Select. Active low logic input used to select the AD7715. With this input hardwired low, the AD7715 can operate
in its three-wire interface mode with SCLK, DIN, and DOUT used to interface to the device. CS can be used to select
the device in systems with more than one device on the serial bus or as a frame synchronization signal in
communicating with the AD7715.
Logic Input. Active low input which resets the control logic, interface logic, calibration coefficients, digital filter, and
analog modulator of the part to power-on status.
Analog Positive Supply Voltage, 3.3 V nominal (AD7715-3) or 5 V nominal (AD7715-5).
Analog Input. Positive input of the programmable gain differential analog input to the AD7715.
Analog Input. Negative input of the programmable gain differential analog input to the AD7715.
Reference Input. Positive input of the differential reference input to the AD7715. The reference input is differential
with the provision that REF IN(+) must be greater than REF IN(–). REF IN(+) can lie anywhere between AVDD and AGND.
Reference Input. Negative input of the differential reference input to the AD7715. The REF IN(−) can lie anywhere
between AVDD and AGND provided REF IN(+) is greater than REF IN(–).
Ground Reference Point for Analog Circuitry. For correct operation of the AD7715, no voltage on any of the other pins
should go more than 30 mV negative with respect to AGND.
Logic Output. A logic low on this output indicates that a new output word is available from the AD7715 data register.
The DRDY pin returns high upon completion of a read operation of a full output word. If no data read has taken place
between output updates, the DRDY line returns high for 500 × tCLK IN cycles prior to the next output update. While
DRDY is high, a read operation should not be attempted or in progress to avoid reading from the data register as it is
being updated. The DRDY line returns low again when the update has taken place. DRDY is also used to indicate when
the AD7715 has completed its on-chip calibration sequence.
Serial data output with serial data being read from the output shift register on the part. This output shift register can
contain information from the setup register, communications register or data register depending on the register
selection bits of the communications register.
Serial data input with serial data being written to the input shift register on the part. Data from this input shift register
is transferred to the setup register or communications register depending on the register selection bits of the
communications register.
Digital Supply Voltage, 3.3 V or 5 V nominal.
Ground reference point for digital circuitry.
Rev. D | Page 10 of 40
AD7715
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation of any code from a straight
line passing through the endpoints of the transfer function.
The endpoints of the transfer function are zero-scale (not to
be confused with bipolar zero), a point 0.5 LSB below the first
code transition (000 … 000 to 000 … 001) and Full-Scale, a
point 0.5 LSB above the last code transition (111 … 110 to 111
… 111). The error is expressed as a percentage of full scale.
Positive Full-Scale Error
Positive Full-Scale Error is the deviation of the last code
transition (111 . . . 110 to 111 . . . 111) from the ideal AIN(+)
voltage (AIN(−) + VREF/GAIN −3/2 LSBs). It applies to both
unipolar and bipolar analog input ranges.
Unipolar Offset Error
Unipolar Offset Error is the deviation of the first code transition
from the ideal AIN(+) voltage (AIN(−) + 0.5 LSB) when operating
in the unipolar mode.
Bipolar Zero Error
This is the deviation of the midscale transition (0111 . . . 111 to
1000 . . . 000) from the ideal AIN(+) voltage (AIN(−) − 0.5 LSB)
when operating in the bipolar mode.
Gain Error
This is a measure of the span error of the ADC. It includes fullscale errors but not zero-scale errors. For unipolar input ranges
it is defined as (full scale error—unipolar offset error) while for
bipolar input ranges it is defined as (full-scale error—bipolar
zero error).
Bipolar Negative Full-Scale Error
This is the deviation of the first code transition from the ideal
AIN(+) voltage (AIN(−) − VREF/GAIN + 0.5 LSB), when
operating in the bipolar mode.
Positive Full-Scale Overrange
Positive full-scale overrange is the amount of overhead available
to handle input voltages on AIN(+) input greater than AIN−) +
VREF/GAIN (for example, noise peaks or excess voltages due
to system gain errors in system calibration routines) without
introducing errors due to overloading the analog modulator
or overflowing the digital filter.
Negative Full-Scale Overrange
This is the amount of overhead available to handle voltages
on AIN(+) below AIN(−) −VREF/GAIN without overloading the
analog modulator or overflowing the digital filter. Note that the
analog input accepts negative voltage peaks even in the unipolar
mode provided that AIN(+) is greater than AIN(−) and greater
than AGND − 30 mV.
Offset Calibration Range
In the system calibration modes, the AD7715 calibrates its
offset with respect to the analog input. The offset calibration
range specification defines the range of voltages that the AD7715
can accept and still calibrate offset accurately.
Full-Scale Calibration Range
This is the range of voltages that the AD7715 can accept in the
system calibration mode and still calibrate full scale correctly.
Input Span
In system calibration schemes, two voltages applied in sequence
to the AD7715’s analog input define the analog input range. The
input span specification defines the minimum and maximum
input voltages from zero to full scale that the AD7715 can accept
and still calibrate gain accurately.
Rev. D | Page 11 of 40
AD7715
ON-CHIP REGISTERS
The AD7715 contains four on-chip registers, which can be
accessed by via the serial port on the part. The first of these
is a communications register that decides whether the next
operation is a read or write operation and also decides which
register the read or write operation accesses. 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 write or a read 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 register
on the part (including the communications register itself and
the output data register) starts with a write operation to the
communications register followed by a read operation from the
selected register. The communication register also controls the
standby mode and the operating gain of the part. The DRDY status
is also available by reading from the communications register. The
second register is a setup register that determines calibration
modes, filter selection and bipolar/unipolar operation. The
third register is the data register from which the output data
from the part is accessed. The final register is a test register
that is accessed when testing the device. It is advised that the
user does not attempt to access or change the contents of the
test register as it may lead to unspecified operation of the
device. The registers are discussed in more detail in the
following sections.
Rev. D | Page 12 of 40
AD7715
COMMUNICATIONS REGISTER (RS1, RS0 = 0, 0)
The communications register is an eight-bit register from which data can either be read or to which data can be written. 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. 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
register. This is the default state of the interface, and on power-up or after a reset, the AD7715 is in this default state waiting for a write
operation to the communications register. In situations where the interface sequence is lost, if a write operation to the device of sufficient
duration (containing at least 32 serial clock cycles) takes place with DIN high, the AD7715 returns to this default state. Table 7 outlines
the bit designations for the communications register.
Table 7. Communications Register
0/DRDY
ZERO
RS1
RS0
R/W
STBY
G1
G0
Table 8.
Bit Name
0/DRDY
ZERO
RS1, RS0
R/W
STBY
G1, G0
Description
For a write operation, a 0 must be written to this bit so that 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. Instead, it stays at this bit location
until a 0 is written to this bit. Once a 0 is written to this bit, the next 7 bits are loaded to the communications register. For a read
operation, this bit provides the status of the DRDY flag from the part. The status of this bit is the same as the DRDY output pin.
For a write operation, a 0 must be written to this bit for correct operation of the part. Failure to do this results in unspecified
operation of the device. For a read operation, a 0 is read back from this bit location.
Register Selection Bits. These bits select to which one of four on-chip registers the next read or write operation takes place as
shown in Table 9 along with the register size. When the read or write to the selected register is complete, the part returns to
where it is waiting for a write operation to the Communications Register. It does not remain in a state where it continues to
access the selected register.
Read/Write Select. This bit selects whether the next operation
is a read or write operation to the selected register. A 0 indicates a write cycle as the next operation to the appropriate register,
while a 1 indicates a read operation from the appropriate register.
Standby. Writing a 1 to this bit puts the part in its standby or power-down mode. In this mode, the part consumes only
10 μA of power supply current. The part retains its calibration and control word information when in STANDBY. Writing a 0 to
this bit places the part in its normal operating mode. The default value for this bit after power-on or RESET is 0.
Gain Select bits. See Table 10.
Table 9. Register Section
RS1
0
0
1
1
RS0
0
1
0
1
Register
Communications register
Setup register
Test register
Data register
Register Size
8 bits
8 bits
8 bits
16 bits
Table 10.
G2
0
0
1
1
G1
0
1
0
1
Gain Setting
1
2
32
128
Rev. D | Page 13 of 40
AD7715
SETUP REGISTER (RS1, RS0 = 0, 1); POWER ON/RESET STATUS: 28 HEX
The setup register is an eight-bit register from which data can either be read or to which data can be written. This register controls the
setup that the device is to operate in such as the calibration mode, and output rate, unipolar/bipolar operation etc. Table 11 outlines the
bit designations for the setup register.
Table 11. Setup Register
MD1
MD0
CLK
FS1
FS0
B/U
BUF
FSYNC
Table 12.
Bit Name
MD1, MD0
CLK
FS1, FS0
B/U
BUF
FSYNC
Description
Mode select bits. These bits select the operating mode of the AD7715 (see Table 13).
The clock bit (CLK) should be set in accordance with the operating frequency of the AD7715. If the device has a master clock
frequency of 2.4576 MHz, then this bit should be set to a 1. If the device has a master clock frequency of 1 MHz, then this bit
should be set to a 0. This bit sets up the correct scaling currents for a given master clock and also chooses (along with FS1 and
FS0) the output update rate for the device. If this bit is not set correctly for the master clock frequency of the device, then the
device may not operate to specification. The default value for this bit after power-on or reset is 1.
Along with the CLK bit, FS1 and FS0 determine the output update rate, filter first notch and −3 dB frequency as outlined in
Table 14. The on-chip digital filter provides a sinc3 (or (Sinx/x)3) filter response. In association with the gain selection, it also
determines the output noise (and therefore, the resolution) of the device. Changing the filter notch frequency, as well as the
selected gain, impacts resolution. Table 15 through Table 22 show the effect of the filter notch frequency and gain on the
output noise and effective resolution of the part. The output data rate (or effective conversion time) for the device is equal
to the frequency selected for the first notch of the filter. For example, if the first notch of the filter is selected at 50 Hz then a
new word is available at a 50 Hz rate or every 20 ms. If the first notch is at 500 Hz, a new word is available every 2 ms. The
default value for these bits is 1, 0.
The settling-time of the filter to a full-scale step input change is worst case 4 × 1/(output data rate). For example, with the first
filter notch at 50 Hz, the settling time of the filter to a full-scale step input change is 80 ms maximum. If the first notch is at
500 Hz, the settling time of the filter to a full-scale input step is 8 ms max. This settling-time can be reduced to 3 × 1/(output
data rate) by synchronizing the step input change to a reset of the digital filter. In other words, if the step input takes place
with the FSYNC bit high, the settling-time time is 3 × 1/(output data rate) from when FSYNC returns low.
The −3 dB frequency is determined by the programmed first notch frequency according to the relationship:
filter −3 dB frequency = 0.262 × filter first notch frequency
A 0 in this bipolar/unipolar operation bit selects bipolar operation. This is the default (power-on or reset) status of this bit. A 1
in this bit selects unipolar operation.
With this buffer control bit low, the on-chip buffer on the analog input is shorted out. With the buffer shorted out, the current
flowing in the AVDD line is reduced to 250 μA (all gains at fCLK IN = 1 MHz and gain of 1 or 2 at fCLK IN = 2.4576 MHz) or 500 μA
(gains of 32 and 128 @ fCLK IN = 2.4576 MHz) and the output noise from the part is at its lowest. When this bit is high, the onchip buffer is in series with the analog input allowing the input to handle higher source impedances.
When this filter synchronization bit is high, the nodes of the digital filter, the filter control logic and the this bit goes low, the
modulator and filter start to process data and a valid word is available in 3 × 1/(output update rate), that is, the settling-time of
the filter. This FSYNC bit does not affect the digital interface and does not reset the DRDY output if it is low.
Rev. D | Page 14 of 40
AD7715
Table 13.
MD1
0
MD0
0
0
1
1
0
1
1
Operating Mode
Normal mode. This operating mode is the default mode of operation of the device whereby the device is performing normal
conversions. The AD7705 is placed in this mode after power-on or reset.
Self-calibration. This is a one step calibration sequence and when complete the part returns to normal mode with MD1 and
MD0 returning to 0, 0. The DRDY output or DRDYbit goes high when calibration is initiated and returns low when this selfcalibration is complete and a new valid word is available in the data register. The zero-scale calibration is performed at the
selected gain on internally shorted (zeroed) inputs and the full-scale calibration is performed at the selected gain on an
internally generated VREF/selected gain.
Zero-scale system calibration. Zero-scale system calibration is performed at the selected gain on the input voltage provided
at the analog input during this calibration sequence. This input voltage should remain stable for the duration of the
calibration. The DRDY output or DRDY bit goes high when calibration is initiated and returns low when this zero-scale
calibration is complete and a new valid word is available in the data register. At the end of the calibration, the part returns to
normal mode with MD1 and MD0 returning to 0, 0.
Full-scale system calibration. Full-scale system calibration is performed at the selected gain on the input voltage provided at
the analog input during this calibration sequence. This input voltage should remain stable for the duration of the
calibration. The DRDY output or DRDY bit goes high when calibration is initiated and returns low when this full-scale
calibration is complete and a new valid word is available in the data register. At the end of the calibration, the part returns to
normal mode with MD1 and MD0 returning to 0, 0.
Table 14. Output Update Rates
CLK1
0
0
0
0
1
1
1
1
1
FS1
0
0
1
1
0
0
1
1
FS0
0
1
0
1
0
1
0
1
Output Update Rate
20 Hz
25 Hz
100 Hz
200 Hz
50 Hz
60 Hz
250 Hz
500 Hz
−3 dB Filter Cutoff
5.24 Hz
6.55 Hz
26.2 Hz
52.4 Hz
13.1 Hz
15.7 Hz (default status)
65.5 Hz
131 Hz
Assumes correct clock frequency at MCLK IN pin.
TEST REGISTER (RS1, RS0 = 1, 0)
DATA REGISTER (RS1, RS0 = 1, 1)
The part contains a test register, which is used in testing the
device. The user is advised not to change the status of any of the
bits in this register from the default (power-on or reset) status
of all 0s as the part will be placed in one of its test modes and
will not operate correctly. If the part enters one of its test modes,
exercising RESET will exit the part from the mode. An alternative scheme for getting the part out of one of its test modes, is to
reset the interface by writing 32 successive 1s to the part and
then load all 0s to the test register.
The data register on the part is a read-only 16-bit register
that contains the most up-to-date conversion result from the
AD7715. If the communications register data sets up the part
for a write operation to this register, a write operation must
actually take place to return the part to where it is expecting
a write operation to the communications register (the default
state of the interface). However, the 16 bits of data written to
the part will be ignored by the AD7715.
Rev. D | Page 15 of 40
AD7715
OUTPUT NOISE
AD7715-5
Table 15 shows the AD7715-5 output rms noise for the selectable notch and −3 dB frequencies for the part, as selected by FS1
and FS0 of the setup register. The numbers given are for the
bipolar input ranges with a VREF of 2.5 V. These numbers are
typical and are generated at a differential analog input voltage
of 0 V with the part used in unbuffered mode (BUF bit of the
setup register = 0). Table 16 meanwhile shows the output peakto-peak noise for the selectable notch and −3 dB frequencies
for the part. It is important to note that these numbers represent
the resolution for which there is no code flicker. They are not
calculated based on rms noise but on peak-to-peak noise. The
numbers given are for the bipolar input ranges with a VREF of
2.5 V and for the BUF bit of the setup register = 0. These numbers are typical, are generated at an analog input voltage of 0 V
and are rounded to the nearest LSB.
Meanwhile, Table 17 and Table 18 show rms noise and peakto-peak resolution respectively with the AD7715-5 operating
under the same conditions as above except that now the part is
operating in buffered mode (BUF bit of the setup register = 1).
Table 15. Output RMS Noise vs. Gain and Output Update Rate for AD7715-5 (Unbuffered Mode)
Filter First Notch and Output Data Rate
−3 dB Frequency
MCLK IN =
2.4576 MHz
50 Hz
60 Hz
250 Hz
500 Hz
MCLK IN =
2.4576 MHz
13.1 Hz
15.72 Hz
65.5 Hz
131 Hz
MCLK IN =
1 MHz
20 Hz
25 Hz
100 Hz
200 Hz
Typical Output RMS Noise (μV)
MCLK IN =
1 MHz
5.24 Hz
6.55 Hz
26.2 Hz
52.4 Hz
Gain = 1
3.8
4.8
103
530
Gain = 2
1.9
2.4
45
250
Gain = 32
0.6
0.6
3.0
18
Gain = 128
0.52
0.62
1.6
5.5
Table 16. Peak-to-Peak Resolution vs. Gain and Output Update Rate for AD7715-5 (Unbuffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Typical Peak-to-Peak Resolution in Bits
Gain = 1
16
16
13
10
Gain = 2
16
16
13
10
Gain = 32
16
16
13
10
Gain = 128
14
13
12
10
Table 17. Output RMS Noise vs. Gain and Output Update Rate for AD7715-5 (Buffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Typical Output RMS Noise (μV)
Gain = 1
4.3
5.1
103
550
Gain = 2
2.2
3.1
50
280
Gain = 32
0.9
1.0
3.9
18
Gain = 128
0.9
1.0
2.1
6
Table 18. Peak-to-Peak Resolution vs. Gain and Output Update Rate for AD7715-5 (Buffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Rev. D | Page 16 of 40
Typical Peak-to-Peak Resolution in Bits
Gain = 1
16
16
13
10
Gain = 2
16
16
13
10
Gain = 32
15
15
13
10
Gain = 128
13
13
12
10
AD7715
AD7715-3
Table 19 shows the AD7715-3 output rms noise for the selectable notch and −3 dB frequencies for the part, as selected by FS1
and FS0 of the setup register. The numbers given are for the
bipolar input ranges with a VREF of 1.25 V. These numbers are
typical and are generated at an analog input voltage of 0 V with
the part used in unbuffered mode (BUF bit of the setup register
= 0). Table 20 meanwhile shows the output peak-to-peak noise
for the selectable notch and −3 dB frequencies for the part. It is
important to note that these numbers represent the resolution
for which there is no code flicker. They are not calculated based
on rms noise but on peak-to-peak noise. The numbers given are
for the bipolar input ranges with a VREF of 1.25 V and for the
BUF bit of the setup register = 0. These numbers are typical,
are generated at an analog input voltage of 0 V and are rounded
to the nearest LSB.
Meanwhile, Table 21 and Table 22 show rms noise and peakto-peak resolution respectively with the AD7715-3 operating
under the same conditions as above except that now the part is
operating in buffered mode (BUF bit of the setup register = 1).
Table 19. Output RMS Noise vs. Gain and Output Update Rate for AD7715-3 (Unbuffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Typical Output RMS Noise (μV)
Gain = 1
3.0
3.4
45
270
Gain = 2
1.7
2.1
20
135
Gain = 32
0.7
0.7
2.2
9.7
Gain = 128
0.65
0.7
1.6
3.3
Table 20. Peak-to-Peak Resolution vs. Gain and Output Update Rate for AD7715-3 (Unbuffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Typical Peak-to-Peak Resolution in Bits
Gain = 1
16
16
13
11
Gain = 2
16
16
13
11
Gain = 32
14
14
13
10
Gain = 128
12
12
11
10
Table 21. Output RMS Noise vs. Gain and Output Update Rate for AD7715-3 (Buffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Typical Output RMS Noise (μV)
Gain = 1
4.5
5.1
50
270
Gain = 2
2.4
2.9
25
135
Gain = 32
0.9
0.9
2.6
9.7
Gain = 128
0.9
1.0
2
3.3
Table 22. Peak-to-Peak Resolution vs. Gain and Output Update Rate for AD7715-3 (Buffered Mode)
Filter First Notch and Output Data Rate
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
50 Hz
20 Hz
60 Hz
25 Hz
250 Hz
100 Hz
500 Hz
200 Hz
−3 dB Frequency
MCLK IN =
MCLK IN =
2.4576 MHz
1 MHz
13.1 Hz
5.24 Hz
15.72 Hz
6.55 Hz
65.5 Hz
26.2 Hz
131 Hz
52.4 Hz
Rev. D | Page 17 of 40
Typical Peak-to-Peak Resolution in Bits
Gain = 1
16
16
13
10
Gain = 2
16
16
13
11
Gain = 32
14
14
12
10
Gain = 128
12
12
11
10
AD7715
CALIBRATION SEQUENCES
The AD7715 contains a number of calibration options as
outlined in Table 13. Table 23 summarizes the calibration types,
the operations involved and the duration of the operations.
There are two methods of determining the end of calibration.
The first is to monitor when DRDY returns low at the end of
the sequence. DRDY not only indicates when the sequence is
complete but also that the part has a valid new sample in its
data register. This valid new sample is the result of a normal
conversion which follows the calibration sequence. The second
method of determining when calibration is complete is to
monitor the MD1 and MD0 bits of the setup register. When
these bits return to 0, 0 following a calibration command, it
indicates that the calibration sequence is complete. This method
does not give any indication of there being a valid new result in
the data register. However, it gives an earlier indication than
DRDY that calibration is complete. The duration to when the
mode bits (MD1 and MD0) return to 0, 0 represents the
duration of the calibration carried out. The sequence to when
DRDY goes low also includes a normal conversion and a
pipeline delay, tP, to correctly scale the results of this first
conversion. tP will never exceed 2000 × tCLK IN. The time for both
methods is given in Table 23.
Table 23. Calibration Sequences
Calibration Type
Self Calibration
MD1, MD0
0, 1
ZS System Calibration
FS System Calibration
1, 0
1, 1
Calibration Sequence
Internal ZS Cal @ Selected Gain +
Internal FS Cal @ Selected Gain
ZS Cal on AIN @ Selected Gain
FS Cal on AIN @ Selected Gain
Rev. D | Page 18 of 40
Duration to Mode Bits
6 × 1/Output Rate
Duration to DRDY
3 × 1/Output Rate
3 × 1/Output Rate
4 × 1/Output Rate + tP
4 × 1/Output Rate + tP
9 ×1/Output Rate + tP
AD7715
CIRCUIT DESCRIPTION
The part contains a programmable-gain fully differential analog
input channel. The selectable gains on this input are 1, 2, 32,
and 128 allowing the part to accept unipolar signals of between
0 mV to 20 mV and 0 V to 2.5 V or bipolar signals in the range
from ±20 mV to ±2.5 V when the reference input voltage equals
2.5 V. With a reference voltage of 1.25 V, the input ranges are
from 0 mV to 10 mV to 0 V to +1.25 V in unipolar mode and
from ±10 mV to ±1.25 V in bipolar mode. Note that the bipolar
ranges are with respect to AIN(−) and not with respect to
AGND.
The input signal to the analog input is continuously sampled at
a rate determined by the frequency of the master clock, MCLK
IN, and the selected gain. A charge-balancing ADC (Σ-Δ modulator) converts the sampled signal into a digital pulse train whose
duty cycle contains the digital information. The programmable
gain function on the analog input is also incorporated in this Σ-Δ
modulator with the input sampling frequency being modified
to give the higher gains. A sinc3 digital low-pass filter processes
the output of the Σ-Δ modulator and updates the output register
at a rate determined by the first notch frequency of this filter.
The output data can be read from the serial port randomly or
periodically at any rate up to the output register update rate.
The first notch of this digital filter (and therefore its –3 dB
frequency) can be programmed via the setup register bits, FS0
and FS1. With a master clock frequency of 2.4576 MHz, the
programmable range for this first notch frequency is from 50 Hz
to 500 Hz giving a programmable range for the −3 dB frequency
of 13.1 Hz to 131 Hz. With a master clock frequency of 1 MHz,
the programmable range for this first notch frequency is from
20 Hz to 200 Hz giving a programmable range for the −3 dB
frequency of 5.24 Hz to 52.4 Hz.
The basic connection diagram for the AD7715-5 is shown in
Figure 4. This shows both the AVDD and DVDD pins of the AD7715
being driven from the analog 5 V supply. Some applications
have AVDD and DVDD driven from separate supplies. An AD780,
precision 2.5 V reference, provides the reference source for the
part. On the digital side, the part is configured for three-wire
operation with CS tied to DGND. A quartz crystal or ceramic
resonator provides the master clock source for the part. In most
cases, it is 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 vary
depending on the manufacturer’s specifications.
ANALOG
5V SUPPLY
10µF
0.1µF
0.1µF
AVDD DVDD
AD7715
DATA
READY
DRDY
AIN(+)
DIFFERENTIAL
ANALOG INPUT
CS
AIN(–)
RECEIVE
(READ)
DOUT
ANALOG
5V SUPPLY
ANALOG
GROUND
AGND
ANALOG
GROUND
DGND
VOUT
AD780
SCLK
RESET
VIN
SERIAL
DATA
SERIAL
CLOCK
DIN
5V
REF IN(+)
10µF
GND
0.1µF
MCLK IN
REF IN(–)
MCLK OUT
CRYSTAL OR
CERAMIC
RESONATOR
08519-004
The AD7715 is a Σ-Δ ADC with on-chip digital filtering,
intended for the measurement of wide dynamic range, low
frequency signals such as those in industrial control or process
control applications. It contains a Σ-Δ (or charge-balancing)
ADC, a calibration microcontroller with on-chip static RAM, a
clock oscillator, a digital filter, and a bidirectional serial communications port. The part consumes only 450 μA of power supply
current, making it ideal for battery-powered or loop-powered
instruments. The part comes in two versions, the AD7715-5
which is specified for operation from a nominal 5 V analog supply
(AVDD) and the AD7715-3 which is specified for operation from
a nominal 3.3 V analog supply. Both versions can be operated
with a digital supply (DVDD) voltage of 3.3 V or 5 V.
Figure 4. AD7715-5 Basic Connection Diagram
ANALOG INPUT
Analog Input Ranges
The AD7715 contains a differential analog input pair AIN(+)
and AIN(−). This input pair provides a programmable-gain,
differential input channel which can handle either unipolar or
bipolar input signals. It should be noted that the bipolar input
signals are referenced to the respective AIN(−) input of the
input pair.
In unbuffered mode, the common-mode range of the input is
from AGND to AVDD provided that the absolute value of the
analog input voltage lies between AGND − 30 mV and AVDD +
30 mV. This means that in unbuffered mode the part can handle
both unipolar and bipolar input ranges for all gains. In buffered
mode, the analog inputs can handle much larger source impedances but the absolute input voltage range is restricted to between
AGND + 50 mV to AVDD − 1.5 V, which also places restrictions
on the common-mode range. This means that in buffered mode
there are some restrictions on the allowable gains for bipolar
input ranges. Care must be taken in setting up the commonmode voltage and input voltage range so that the above limits
are not exceeded, otherwise there is a degradation in linearity
performance.
Rev. D | Page 19 of 40
AD7715
In unbuffered mode, the analog inputs look directly into the
input sampling capacitor, CSAMP. The dc input leakage current in
this unbuffered mode is 1 nA maximum. As a result, the analog
inputs see a dynamic load that is switched at the input sample
rate (see Figure 5). This sample rate depends on master clock
frequency and selected gain. CSAMP is charged to AIN(+) and
discharged to AIN(−) every input sample cycle. The effective
on-resistance of the switch, RSW, is typically 7 kΩ .
AIN(+)
RSW (7kΩ TYP)
AIN(–)
HIGH
IMPEDANCE
>1GΩ
CSAMP
(10pF)
VBIAS
Figure 5. Unbuffered Analog Input Structure
CSAMP must be charged through RSW and through any external
source impedances every input sample cycle. Therefore, in
unbuffered mode, source impedances mean a longer charge
time for CSAMP, and this may result in gain errors on the part.
Table 24 shows the allowable external resistance/capacitance
values, for unbuffered mode, such that no gain error to the
16-bit level is introduced on the part. Note that these capacitances
are total capacitances on the analog input, external capacitance
plus 10 pF capacitance from the pins and lead frame of the device.
Table 24. External R, C Combination for No 16-Bit Gain
Error (Unbuffered Mode Only)
Gain
1
2
32
128
External Capacitance (pF)
10
50
100
152 kΩ
53.9 kΩ
31.4 kΩ
75.1 kΩ
26.6 kΩ
15.4 kΩ
16.7 kΩ
5.95 kΩ
3.46 kΩ
16.7 kΩ
5.95 kΩ
3.46 kΩ
500
8.4 kΩ
4.14 kΩ
924 Ω
924 Ω
1000
4.76 kΩ
2.36 kΩ
526 Ω
526 Ω
The modulator sample frequency for the AD7715 remains at
fCLK IN/128 (19.2 kHz @ fCLK IN = 2.4576 MHz) regardless of the
selected gain. However, gains greater than 1 are achieved by a
combination of multiple input samples per modulator cycle and
a scaling of the ratio of reference capacitor to input capacitor. As
a result of the multiple sampling, the input sample rate of the device
varies with the selected gain (see Table 25). In buffered mode, the
input is buffered before the input sampling capacitor. In unbuffered
mode, where the analog input looks directly into the sampling
capacitor, the effective input impedance is 1/CSAMP × fS where
CSAMP is the input sampling capacitance and fS is the input
sample rate.
Table 25. Input Sampling Frequency vs. Gain
08519-005
SWITCHING FREQUENCY
DEPENDS ON fCLKIN AND
SELECTED GAIN
Input Sample Rate
5000
1.36 kΩ
670 Ω
150 Ω
150 Ω
In buffered mode, the analog inputs look into the high impedance
inputs stage of the on-chip buffer amplifier. CSAMP is charged via
this buffer amplifier such that source impedances do not affect
the charging of CSAMP. This buffer amplifier has an offset leakage
current of 1 nA. In this buffered mode, large source impedances
result in a small dc offset voltage developed across the source
impedance but not in a gain error.
Gain
1
2
32
128
Input Sampling Frequency (fS)
fCLK IN/64 (38.4 kHz @ fCLK IN = 2.4576 MHz)
2 × fCLK IN/64 (76.8 kHz @ fCLK IN = 2.4576 MHz)
8 × fCLK IN/64 (307.2 kHz @ fCLK IN = 2.4576 MHz)
8 × fCLK IN/64 (307.2 kHz @ fCLK IN = 2.4576 MHz)
Bipolar/Unipolar Inputs
The analog input on the AD7715 can accept either unipolar or
bipolar input voltage ranges. Bipolar input ranges do not imply
that the part can handle negative voltages on its analog input
since the analog input cannot go more negative than −30 mV to
ensure correct operation of the part. The input channel is fully
differential. As a result, the voltage to which the unipolar and
bipolar signals on the AIN(+) input are referenced is the voltage
on the respective AIN(−) input. For example, if AIN(−) is
2.5 V and the AD7715 is configured for unipolar operation with
a gain of 2 and a VREF of 2.5 V, the input voltage range on the
AIN(+) input is 2.5 V to 3.75 V. If AIN(−) is 2.5 V and the
AD7715 is configured for bipolar mode with a gain of 2 and a
VREF of 2.5 V, the analog input range on the AIN(+) input is
1.25 V to 3.75 V (that is, 2.5 V ± 1.25 V). If AIN(−) is at AGND,
the part cannot be configured for bipolar ranges in excess of
±30 mV.
Bipolar or unipolar options are chosen by programming the
B/U bit of the setup register. This programs the channel for
either unipolar or bipolar operation. Programming the channel
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.
Rev. D | Page 20 of 40
AD7715
REFERENCE INPUT
DIGITAL FILTERING
The reference inputs of the AD7715, REF IN(+) and REF IN(−),
provide a differential reference input capability. The commonmode range for these differential inputs is from AGND to AVDD.
The nominal reference voltage, VREF (REF IN(+) − REF IN(−)),
for specified operation is 2.5 V for the AD7715-5 and 1.25 V for
the AD7715-3. The part is functional with VREF voltages down
to 1 V but with degraded performance as the output noise will,
in terms of LSB size, be larger. REF IN(+) must always be
greater than REF IN(−) for correct operation of the AD7715.
The AD7715 contains an on-chip low-pass digital filter that
processes the output of the part’s Σ-Δ modulator. Therefore, the
part not only provides the analog-to-digital conversion function
but it also provides a level of filtering. Users should be aware
that there are a number of system differences when the filtering
function is provided in the digital domain rather than the
analog domain.
Both reference inputs provide a high impedance, dynamic load
similar to the analog inputs in unbuffered mode. The maximum
dc input leakage current is ±1 nA over temperature and source
resistance may result in gain errors on the part. In this case,
the sampling switch resistance is 5 kΩ typical and the reference
capacitor (CREF) varies with gain. The sample rate on the reference inputs is fCLK IN/64 and does not vary with gain. For gains
of 1 and 2, CREF is 8 pF; for a gain of 32, it is 4.25 pF, and for a
gain of 128, it is 3.3125 pF.
The output noise performance outlined in Table 15 through
Table 22 is for an analog input of 0 V which effectively removes
the effect of noise on the reference. To obtain the same noise
performance as shown in the noise tables over the full input
range requires a low noise reference source for the AD7715. If
the reference noise in the bandwidth of interest is excessive, it
will degrade the performance of the AD7715. In applications
where the excitation voltage for the bridge transducer on the
analog input also derives the reference voltage for the part,
the effect of the noise in the excitation voltage will be removed
as the application is ratiometric. Recommended reference
voltage sources for the AD7715-5 include the AD780, REF43
and REF192, while the recommended reference sources for
the AD7715-3 include the AD589 and AD1580. It is generally
recommended to decouple the output of these references to
further reduce the noise level.
First, since digital filtering occurs after the A-to-D conversion
process, it can remove noise injected during the conversion
process. Analog filtering cannot do this. Also, the digital filter
can be made programmable far more readily than an analog
filter. Depending on the digital filter design, this gives the user
the capability of programming cutoff frequency and output
update rate.
On the other hand, analog filtering can remove noise superimposed on the analog signal before it reaches the ADC. Digital
filtering cannot do this and noise peaks riding on signals near
full scale have the potential to saturate the analog modulator
and digital filter, even though the average value of the signal is
within limits. To alleviate this problem, the AD7715 has overrange
headroom built into the Σ-Δ modulator and digital filter which
allows overrange excursions of 5% above the analog input range. If
noise signals are larger than this, consideration should be given
to analog input filtering, or to reducing the input channel voltage
so that its full scale is half that of the analog input channel full
scale. This provides an overrange capability greater than 100%
at the expense of reducing the dynamic range by 1 bit (50%).
In addition, the digital filter does not provide any rejection at
integer multiples of the digital filter’s sample frequency. However,
the input sampling on the part provides attenuation at multiples
of the digital filter’s sampling frequency so that the unattenuated
bands actually occur around multiples of the sampling frequency
fS (as defined in Table 25). Thus the unattenuated bands occur
at n × fS (where n = 1, 2, 3 … ). At these frequencies, there are
frequency bands, ±f3 dB wide (f3 dB is the cutoff frequency of the
digital filter) at either side where noise passes unattenuated to
the output.
Rev. D | Page 21 of 40
AD7715
Filter Characteristics
3
The AD7715’s digital filter is a low-pass filter with a (sinx/x)
response (also called sinc3). The transfer function for this filter
is described in the z-domain by
⎡ 1 1 − z −N ⎤
H (z ) = ⎢ ×
−1 ⎥
⎣⎢ N 1 − z ⎥⎦
3
and in the frequency domain by
⎛
f
Sin⎜⎜ N × π ×
f
1
S
⎝
×
H( f ) =
N
⎛
f ⎞
⎟
Sin⎜⎜ π ×
f S ⎟⎠
⎝
Post-Filtering
⎞
⎟
⎟
⎠
3
where N is the ratio of the modulator rate to the output rate and
fMOD is the modulator rate.
Figure 6 shows the filter frequency response for a cutoff frequency
of 15.72 Hz which corresponds to a first filter notch frequency
of 60 Hz. The plot is shown from dc to 390 Hz. This response is
repeated at either side of the digital filter’s sample frequency
and at either side of multiples of the filter’s sample frequency.
0
–20
–40
–60
GAIN (dB)
–80
–100
–120
–140
–160
–180
–200
–240
60
120
180
240
FREQUENCY (Hz)
300
360
08519-006
–220
0
Because the AD7715 contains this on-chip, low-pass filtering,
there is a settling time associated with step function inputs and
data on the output is invalid after a step change until the settling
time has elapsed. The settling time depends upon the output
rate chosen for the filter. The settling time of the filter to a fullscale step input can be up 4 times the output data period. For a
synchronized step input (using the FSYNC function), the
settling time is 3 times the output data period.
The on-chip modulator provides samples at a 19.2 kHz output
rate with fCLK IN at 2.4576 MHz. The on-chip digital filter decimates
these samples to provide data at an output rate that corresponds
to the programmed output rate of the filter. Because the output
data rate is higher than the Nyquist criterion, the output rate
for a given bandwidth satisfys most application requirements.
However, there may be some applications that require a higher
data rate for a given bandwidth and noise performance.
Applications that need this higher data rate do require some
post-filtering following the digital filter of the AD7715.
For example, if the required bandwidth is 7.86 Hz but the
required update rate is 100 Hz, the data can be taken from the
AD7715 at the 100 Hz rate giving a −3 dB bandwidth of 26.2 Hz.
Post-filtering can be applied to this to reduce the bandwidth
and output noise, to the 7.86 Hz bandwidth level, while
maintaining an output rate of 100 Hz.
Post-filtering can also be used to reduce the output noise from
the device for bandwidths below 13.1 Hz. At a gain of 128 and
a bandwidth of 13.1 Hz, the output rms noise is 520 nV. This is
essentially device noise or white noise and because the input is
chopped, the noise has a primarily flat frequency response. By
reducing the bandwidth below 13.1 Hz, the noise in the resultant
pass-band can be reduced. A reduction in bandwidth by a factor
of 2 results in a reduction of approximately 1.25 in the output
rms noise. This additional filtering results in a longer settling time.
Figure 6. Frequency Response of AD7715 Filter
The response of the filter is similar to that of an averaging filter
but with a sharper roll-off. The output rate for the digital filter
corresponds with the positioning of the first notch of the filter’s
frequency response. Thus, for the plot of Figure 6 where the
output rate is 60 Hz, the first notch of the filter is at 60 Hz. The
notches of this (sinx/x)3 filter are repeated at multiples of the
first notch. The filter provides attenuation of better than 100 dB
at these notches.
The cutoff frequency of the digital filter is determined by the
value loaded to the FS0 to FS1 bits in the setup register. programming a different cutoff frequency via FS0 and FS1 does not alter
the profile of the filter response; it changes the frequency of the
notches. The output update of the part and the frequency of the
first notch correspond.
Rev. D | Page 22 of 40
AD7715
ANALOG FILTERING
The digital filter does not provide any rejection at integer multiples of the modulator sample frequency, as outlined earlier.
However, due to the high oversampling ratio of AD7715, these
bands occupy only a small fraction of the spectrum and most
broadband noise is filtered. This means that the analog filtering
requirements in front of the AD7715 are considerably reduced
vs. a conventional converter with no on-chip filtering. In addition,
because the part’s common-mode rejection performance of 95 dB
extends out to several kilohertz, common-mode noise in this
frequency range is substantially reduced.
Depending on the application, however, it may be necessary to
provide attenuation in front of the AD7715 to eliminate
unwanted frequencies from these bands which the digital filter
will pass. It may also be necessary in some applications to
provide analog filtering in front of the AD7715 to ensure that
differential noise signals outside the band of interest do not
saturate the analog modulator.
If passive components are placed in front of the AD7715, in
unbuffered mode, take care to ensure that the source impedance
is low enough so as not to introduce gain errors in the system.
This significantly limits the amount of passive antialiasing
filtering which can be provided in front of the AD7715 when it
is used in unbuffered mode. However, when the part is used
in buffered mode, large source impedances simply result in a
small dc offset error (a 10 kΩ source resistance causes an offset
error of less than 10 μV). Therefore, if the system requires any
significant source impedances to provide passive analog
filtering in front of the AD7715, it is recommended that the
part be operated in buffered mode.
CALIBRATION
The AD7715 provides a number of calibration options that
can be programmed via the MD1 and MD0 bits of the setup
register. The different calibration options are outlined in the
setup register and calibration sequences sections. A calibration
cycle may be initiated at any time by writing to the MD1 and
MD0 bits of the setup register. Calibration on the AD7715
removes offset and gain errors from the device. A calibration
routine should be initiated on the device whenever there is a
change in the ambient operating temperature or supply voltage.
It should also be initiated if there is a change in the selected
gain, filter notch or bipolar/unipolar input range.
The AD7715 offers self-calibration and system-calibration
facilities. For full calibration to occur on the selected channel,
the on-chip microcontroller must record the modulator output
for two different input conditions. These are zero-scale and
full-scale points. These points are derived by performing a
conversion on the different input voltages provided to the input
of the modulator during calibration. As a result, the accuracy
of the calibration can only be as good as the noise level that it
provides in normal mode. The result of the zero-scale calibration
conversion is stored in the zero-scale calibration register while
the result of the full-scale calibration conversion is stored in the
full-scale calibration register. With these readings, the on-chip
microcontroller can calculate the offset and the gain slope for
the input to output transfer function of the converter. Internally, the
part works with a resolution of 33 bits to determine its conversion
result of 16 bits.
Self-Calibration
A self-calibration is initiated on the AD7715 by writing the
appropriate values (0, 1) to the MD1 and MD0 bits of the setup
register. In the self-calibration mode with a unipolar input
range, the zero-scale point used in determining the calibration
coefficients is with the inputs of the differential pair internally
shorted on the part (that is, AIN(+) = AIN(−) = internal bias
voltage). The PGA is set for the selected gain (as per G1 and
G0 bits in the communications register) for this zero-scale
calibration conversion. The full-scale calibration conversion
is performed at the selected gain on an internally generated
voltage of VREF/selected gain.
The duration time for the calibration is 6 × 1/output rate. This
is made up of 3 × 1/output rate for the zero-scale calibration
and 3 × 1/output rate for the full-scale calibration. At this time,
the MD1 and MD0 bits in the setup register return to 0, 0.
This gives the earliest indication that the calibration sequence
is complete. The DRDY line goes high when calibration is
initiated and does not return low until there is a valid new word
in the data register. The duration time from the calibration
command being issued to DRDY going low is 9 × 1/output rate.
This is made up of 3 × 1/output rate for the zero-scale calibration,
3 × 1/output rate for the full-scale calibration, 3 × 1/output rate
for a conversion on the analog input and some overhead to set
up the coefficients correctly. If DRDY is low before (or goes low
during) the calibration command write to the setup register,
it may take up to one modulator cycle (MCLK IN/128) before
DRDY goes high to indicate that calibration is in progress.
Therefore, DRDY should be ignored for up to one modulator
cycle after the last bit is written to the setup register in the
calibration command.
For bipolar input ranges in the self-calibrating mode, the
sequence is very similar to that just outlined. In this case, the
two points are exactly the same as above, but because the part
is configured for bipolar operation, the shorted inputs point is
actually midscale of the transfer function.
Rev. D | Page 23 of 40
AD7715
System Calibration
System calibration allows the AD7715 to compensate for system
gain and offset errors as well as its own internal errors. System
calibration performs the same slope factor calculations as self
calibration but uses voltage values presented by the system to
the AIN inputs for the zero- and full-scale points. full system
calibration requires a two step process, a zero-scale system
calibration followed by a full-scale system calibration.
For a full system calibration, the zero-scale point must be
presented to the converter first. It must be applied to the
converter before the calibration step is initiated and remain
stable until the step is complete. Once the system zero scale
voltage has been set up, a zero-scale system calibration is then
initiated by writing the appropriate values (1, 0) to the MD1
and MD0 bits of the setup register. The zero-scale system
calibration is performed at the selected gain. The duration of
the calibration is 3 × 1/output rate. At this time, the MD1 and
MD0 bits in the setup register return to 0, 0. This gives the
earliest indication that the calibration sequence is complete. The
DRDY line goes high when calibration is initiated and does not
return low until there is a valid new word in the data register.
The duration time from the calibration command being issued
to DRDY going low is 4 × 1/output rate as the part performs a
normal conversion on the AIN voltage before DRDY goes low.
If DRDY is low before (or goes low during) the calibration
command write to the setup register, it may take up to one
modulator cycle (MCLK IN/128) before DRDY goes high to
indicate that calibration is in progress. Therefore, DRDY should
be ignored for up to one modulator cycle after the last bit is
written to the setup register in the calibration command.
After the zero-scale point is calibrated, the full-scale point is
applied to AIN and the second step of the calibration process is
initiated by again writing the appropriate values (1, 1) to MD1
and MD0. Again, the full-scale voltage must be set up before the
calibration is initiated and it must remain stable throughout the
calibration step. The full-scale system calibration is performed
at the selected gain. The duration of the calibration is 3 × 1/output
rate. At this time, the MD1 and MD0 bits in the setup register
return to 0, 0. This gives the earliest indication that the calibration
sequence is complete. The DRDY line goes high when calibration is
initiated and does not return low until there is a valid new word
in the data register. The duration time from the calibration
command being issued to DRDY going low is 4 × 1/output rate
as the part performs a normal conversion on the AIN voltage
before DRDY goes low. If DRDY is low before (or goes low
during) the calibration command, write to the setup register, it
may take up to one modulator cycle (MCLK IN/128) before
DRDY goes high to indicate that calibration is in progress.
Therefore, DRDY should be ignored for up to one modulator
cycle after the last bit is written to the setup register in the
calibration command.
In the unipolar mode, the system calibration is performed
between the two endpoints of the transfer function. In the
bipolar mode, it is performed between midscale (zero differential
voltage) and positive full scale.
The fact that the system calibration is a two-step calibration
offers another feature. After the sequence of a full system calibration has been completed, additional offset or gain calibrations
can be performed by themselves to adjust the system zero
reference point or the system gain. Calibrating one of the
parameters, either system offset or system gain, does not
affect the other parameter.
System calibration can also be used to remove any errors from
source impedances on the analog input when the part is used in
unbuffered mode. A simple R, C antialiasing filter on the front
end may introduce a gain error on the analog input voltage but
the system calibration can be used to remove this error.
Span and Offset Limits
Whenever a system calibration mode is used, there are limits
on the amount of offset and span which can be accommodated.
The overriding requirement in determining the amount of
offset and gain that can be accommodated by the part is the
requirement that the positive full-scale calibration limit is
≤ 1.05 × VREF/GAIN. This allows the input range to go 5%
above the nominal range. The in-built headroom in the
analog modulator of the AD7715 ensures that the part still
operates correctly with a positive full-scale voltage which is
5% beyond the nominal.
The range of input span in both the unipolar and bipolar modes
has a minimum value of 0.8 × VREF/GAIN and a maximum value
of 2.1 × VREF/GAIN. However, the span (which is the difference
between the bottom of the AD7715’s input range and the top
of its input range) must take into account the limitation on the
positive full-scale voltage. The amount of offset that can be
accommodated depends on whether the unipolar or bipolar
mode is being used. Once again, the offset must take into account
the limitation on the positive full-scale voltage. In unipolar
mode, there is considerable flexibility in handling negative
(with respect to AIN(−)) offsets. In both unipolar and bipolar
modes, the range of positive offsets which can be handled by the
part depends on the selected span. Therefore, in determining the
limits for system zero-scale and full-scale calibrations, the user
has to ensure that the offset range plus the span range does exceed
1.05 × VREF/GAIN. This is best illustrated by looking at the
following examples.
Rev. D | Page 24 of 40
AD7715
If the part is used in unipolar mode with a required span of
0.8 × VREF/GAIN, then the offset range which the system
calibration can handle is from −1.05 × VREF/GAIN to +0.25 ×
VREF/GAIN. If the part is used in unipolar mode with a required
span of VREF/GAIN, then the offset range which the system
calibration can handle is from −1.05 × VREF/GAIN to +0.05 ×
VREF/GAIN. Similarly, if the part is used in unipolar mode and
required to remove an offset of 0.2 × VREF/GAIN, then the span
range which the system calibration can handle is 0.85 ×
VREF/GAIN.
If the part is used in bipolar mode with a required span of ±0.4 ×
VREF/GAIN, then the offset range which the system calibration
can handle is from −0.65 × VREF/GAIN to +0.65 × VREF/GAIN. If
the part is used in bipolar mode with a required span of ±VREF/
GAIN, then the offset range which the system calibration can
handle is from −0.05 × VREF/GAIN to +0.05 × VREF/GAIN.
Similarly, if the part is used in bipolar mode and required to
remove an offset of ±0.2 × VREF/GAIN, then the span range
which the system calibration can handle is ±0.85 × VREF/GAIN.
Power-Up and Calibration
On power-up, the AD7715 performs an internal reset that sets
the contents of the internal registers to a known state. There are
default values loaded to all registers after a power-on or reset.
The default values contain nominal calibration coefficients for
the calibration registers. However, to ensure correct calibration
for the device a calibration routine should be performed after
power-up.
The power dissipation and temperature drift of the AD7715
are low, and no warm-up time is required before the initial
calibration is performed. However, if an external reference is
being used, this reference must have stabilized before calibration is
initiated. Similarly, if the clock source for the part is generated
from a crystal or resonator across the MCLK pins, the start-up
time for the oscillator circuit should elapse before a calibration
is initiated on the part (see the Clocking and Oscillator Circuit
section).
Rev. D | Page 25 of 40
AD7715
USING THE AD7715
CLOCKING AND OSCILLATOR CIRCUIT
The AD7715 requires a master clock input, which may be an
external CMOS compatible clock signal applied to the MCLK
IN pin with the MCLK OUT pin left unconnected. Alternatively,
a crystal or ceramic resonator of the correct frequency can be
connected between MCLK IN and MCLK OUT in which case
the clock circuit functions as an oscillator, providing the clock
source for the part. The input sampling frequency, the modulator sampling frequency, the −3 dB frequency, output update
rate and calibration time are all directly related to the master
clock frequency, fCLK IN. Reducing the master clock frequency by
a factor of 2 will halve the above frequencies and update rate,
and double the calibration time. The current drawn from the
DVDD power supply is also directly related to fCLK IN. Reducing
fCLK IN by a factor of 2 will halve the DVDD current but does not
affect the current drawn from the AVDD power supply.
When operating with a clock frequency of 1 MHz, the ESR
value for different crystal types varies significantly. As a result,
the DVDD current drain varies across crystal types. When using
a crystal with an ESR of 700 Ω or when using a ceramic resonator,
the increase in the typical DVDD current over an externallyapplied clock is 50 μA with DVDD = 3 V and 175 μA with DVDD
= 5 V. When using a crystal with an ESR of 3 kΩ, the increase in
the typical DVDD current over an externally applied clock is 100 μA
with DVDD = 3 V and 400 μA with DVDD = 5 V.
The on-chip oscillator circuit also has a start-up time associated
with it before it is oscillating at its correct frequency and correct
voltage levels. The typical start-up time for the circuit is 10 ms
with a DVDD of 5 V and 15 ms with a DVDD of 3 V. At 3 V supplies,
depending on the loading capacitances on the MCLK pins, a
1 MΩ feedback resistor may be required across the crystal or
resonator to keep the start up times around the 15 ms duration.
Using the part with a crystal or ceramic resonator between the
MCLK IN and MCLK OUT pins generally causes more current
to be drawn from DVDD than when the part is clocked from a
driven clock signal at the MCLK IN pin. This is because the onchip oscillator circuit is active in the case of the crystal or ceramic
resonator. Therefore, the lowest possible current on the AD7715
is achieved with an externally applied clock at the MCLK IN pin
with MCLK OUT unconnected and unloaded.
The master clock of AD7715 appears on the MCLK OUT pin
of the device. The maximum recommended load on this pin is
one CMOS load. When using a crystal or ceramic resonator to
generate the clock of the AD7715, it may be desirable to then
use this clock as the clock source for the system. In this case, it
is recommended that the MCLK OUT signal is buffered with a
CMOS buffer before being applied to the rest of the circuit.
The amount of additional current taken by the oscillator depends
on a number of factors—first, the larger the value of capacitor
placed on the MCLK IN and MCLK OUT pins, then the larger
the DVDD current consumption on the AD7715. Take care not
to exceed the capacitor values recommended by the crystal and
ceramic resonator manufacturers to avoid consuming unnecessary
DVDD current. Typical values recommended by crystal or
ceramic resonator manufacturers are in the range of 30 pF to
50 pF, and if the capacitor values on MCLK IN and MCLK OUT
are kept in this range, they will not result in any excessive DVDD
current. Another factor that influences the DVDD current is the
effective series resistance (ESR) of the crystal which appears
between the MCLK IN and MCLK OUT pins of the AD7715.
As a general rule, the lower the ESR value then the lower the
current taken by the oscillator circuit.
The FSYNC bit of the setup register allows the user to reset the
modulator and digital filter without affecting any of the setup
conditions on the part. This allows the user to start gathering
samples of the analog input from a known point in time, that is,
when the FSYNC is changed from 1 to 0.
When operating with a clock frequency of 2.4576 MHz, there
is 50 μA difference in the DVDD current between an externally
applied clock and a crystal resonator when operating with a
DVDD of 3 V. With DVDD = 5 V and fCLK IN = 2.4576 MHz, the
typical DVDD current increases by 200 μA for a crystal/resonat
or supplied clock vs. an externally applied clock. The ESR values
for crystals and resonators at this frequency tend to be low and
as a result there tends to be little difference between different
crystal and resonator types.
SYSTEM SYNCHRONIZATION
With a 1 in the FSYNC bit of the setup register, the digital filter
and analog modulator are held in a known reset state and the
part is not processing any input samples. When a 0 is then
written to the FSYNC bit, the modulator and filter are taken
out of this reset state and on the next master clock edge the
part starts to gather samples again.
The FSYNC input can also be used as a software start convert
command allowing the AD7715 to be operated in a conventional converter fashion. In this mode, writing to the FSYNC bit
starts a conversion and the falling edge of DRDY indicates when
the conversion is complete. The disadvantage of this scheme is
that the settling time of the filter has to be taken into account
for every data register update. This means that the rate at which
the data register is updated is three times slower in this mode.
Rev. D | Page 26 of 40
AD7715
Because the FSYNC bit resets the digital filter, the full settling
time of 3 × 1/output rate must elapse before there is a new word
loaded to the output register on the part. If the DRDY signal is
low when FSYNC goes to a 0, the DRDY signal will not be reset
high by the FSYNC command. This is because the AD7715
recognizes that there is a word in the data register that has not
been read. The DRDY line stays low until an update of the data
register takes place at which time it goes high for 500 × tCLK IN
before returning low again. A read from the data register resets
the DRDY signal high, and it does not return low until the
settling time of the filter has elapsed (from the FSYNC command)
and there is a valid new word in the data register. If the DRDY
line is high when the FSYNC command is issued, the DRDY
line will not return low until the settling time of the filter has
elapsed.
RESET INPUT
The RESET input on the AD7715 resets all the logic, the digital
filter, and the analog modulator while all on-chip registers are
reset to their default state. DRDY is driven high and the AD7715
ignores all communications to any of its registers while the
RESET input is low. When the RESET input returns high, the
AD7715 starts to process data, and DRDY returns low in 3 ×
1/output rate indicating a valid new word in the data register.
However, the AD7715 operates with its default setup conditions
after a reset and it is generally necessary to set up all registers
and carry out a calibration after a reset command.
The on-chip oscillator circuit of the AD7715 continues to function even when the RESET input is low. The master clock signal
continues to be available on the MCLK OUT pin. Therefore, in
applications where the system clock is provided by the clock of the
AD7715, the AD7715 produces an uninterrupted master clock
during RESET commands.
STANDBY MODE
The STBY bit in the communications register of the AD7715
allows the user to place the part in a power-down mode when it
is not required to provide conversion results. The AD7715 retains
the contents of all its on-chip registers (including the data register)
while in standby mode. When released from standby mode, the
part starts to process data and a new word is available in the
data register in 3 × 1/output rate from when a 0 is written to
the STBY bit.
The STBY bit does not affect the digital interface, and it does
not affect the status of the DRDY line. If DRDY is high when the
STBY bit is brought low, it will remain high until there is a valid
new word in the data register. If DRDY is low when the STBY
bit is brought low, it will remain low until the data register is
updated at which time the DRDY line returns high for 500 ×
tCLK IN before returning low again. If DRDY is low when the part
enters its standby mode (indicating a valid unread word in the
data register), the data register can be read while the part is in
standby. At the end of this read operation, the DRDY line will
be reset high as normal.
Placing the part in standby mode reduces the total current to
5 μA typical when the part is operated from an external master
clock provided this master clock is stopped. If the external clock
continues to run in standby mode, the standby current increases to
150 μA typical with 5 V supplies and 75 μA typical with 3.3 V
supplies. If a crystal or ceramic resonator is used as the clock
source, then the total current in standby mode is 400 μA typical
with 5 V supplies and 90 μA with 3.3 V supplies. This is because
the on-chip oscillator circuit continues to run when the part is
in its standby mode. This is important in applications where the
system clock is provided by the clock of the AD7715, so that the
AD7715 produces an uninterrupted master clock even when it
is in its standby mode.
ACCURACY
Σ-Δ ADCs, like VFCs and other integrating ADCs, do not
contain any source of nonmonotonicity and inherently offer
no missing codes performance. The AD7715 achieves excellent
linearity by the use of high quality, on-chip capacitors, which
have a very low capacitance/voltage coefficient. The device also
achieves low input drift through the use of chopper-stabilized
techniques in its input stage. To ensure excellent performance
over time and temperature, the AD7715 uses digital calibration
techniques which minimize offset and gain error.
DRIFT CONSIDERATIONS
The AD7715 uses chopper stabilization techniques to minimize
input offset drift. Charge injection in the analog switches and dc
leakage currents at the sampling node are the primary sources
of offset voltage drift in the converter. The dc input leakage
current is essentially independent of the selected gain. Gain
drift within the converter depends primarily upon the temperature
tracking of the internal capacitors. It is not affected by leakage
currents.
Measurement errors due to offset drift or gain drift can be
eliminated at any time by recalibrating the converter. Using
the system calibration mode can also minimize offset and
gain errors in the signal conditioning circuitry. Integral and
differential linearity errors are not significantly affected by
temperature changes.
Rev. D | Page 27 of 40
AD7715
POWER SUPPLIES
There is no specific power sequence required for the AD7715;
either the AVDD or the DVDD supply can come up first. While
the latch-up performance of the AD7715 is good, it is important
that power is applied to the AD7715 before signals at REF IN,
AIN, or the logic input pins to avoid excessive currents. If this
is not possible, then the current that flows in any of these pins
should be limited. If separate supplies are used for the AD7715
and the system digital circuitry, then the AD7715 should be
powered up first. If it is not possible to guarantee this, then
current limiting resistors should be placed in series with the
logic inputs to again limit the current.
During normal operation the AD7715 analog supply (AVDD)
should always be greater than or equal to its digital supply (DVDD).
Supply Current
The current consumption on the AD7715 is specified for supplies
in the range 3 V to 3.6 V and in the range 4.75 V to 5.25 V. The
part operates over a 2.85 V to 5.25 V supply range and the IDD
for the part varies as the supply voltage varies over this range.
Figure 7 shows the variation of the typical IDD with VDD voltage
for both a 1 MHz external clock and a 2.4576 MHz external
clock at 25°C. The AD7715 is operated in unbuffered mode.
The relationship shows that the IDD is minimized by operating
the part with lower VDD voltages. IDD on the AD7715 is also
minimized by using an external master clock or by optimizing
external components when using the on-chip oscillator circuit.
0.9
0.8
0.7
MCLK IN = 2.4576MHz
0.6
The printed circuit board that houses the AD7715 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 which can be separated easily. A minimum
etch technique is generally best for ground planes as it gives the
best shielding. Digital and analog ground planes should only be
joined in one place. If the AD7715 is the only device requiring
an AGND to DGND connection, then the ground planes
should be connected at the AGND and DGND pins of the
AD7715. If the AD7715 is in a system where multiple devices
require AGND to DGND connections, the connection should
still be made at one point only, a star ground point which
should be established as close as possible to the AD7715.
Avoid running digital lines under the device as these couples
noise onto the die. The analog ground plane should be allowed
to run under the AD7715 to avoid noise coupling. The power
supply lines to the AD7715 should use as large 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 reduces 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.
0.5
MCLK IN = 1MHz
0.4
0.3
0.2
0.1
0
2.85
3.15
4.05
4.35
4.65
3.45
3.75
SUPPLY VOLTAGE, AVDD AND DVDD (V)
4.95
5.25
08519-007
SUPPLY CURRENT, AV DD AND DVDD (mA)
1.0
saturate the analog modulator. As a result, the AD7715 is more
immune to noise interference than a conventional high
resolution converter. However, because the resolution of the
AD7715 is so high and the noise levels from the AD7715 so low,
care must be taken with regard to grounding and layout.
Figure 7. IDD vs. Supply Voltage
Grounding and Layout
Because the analog inputs and reference input are differential,
most of the voltages in the analog modulator are commonmode voltages. The excellent common-mode rejection of
the part removes common-mode noise on these inputs. The
analog and digital supplies to the AD7715 are independent
and separately pinned out to minimize coupling between the
analog and digital sections of the device. The digital filter
provides 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 those noise sources do not
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 must 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 disc ceramic capacitors
to DGND. In systems where a common supply voltage is used to
drive both the AVDD and DVDD of the AD7715, it is recommended
that the AVDD supply of the system is used. This supply should
have the recommended analog supply decoupling capacitors
between the AVDD pin of the AD7715 and AGND and the
recommended digital supply decoupling capacitor between
the DVDD pin of the AD7715 and DGND.
Rev. D | Page 28 of 40
AD7715
Evaluating the AD7715 Performance
DIGITAL INTERFACE
The recommended layout for the AD7715 is outlined in the
evaluation board for the AD7715. The evaluation board
package includes a fully assembled and tested evaluation board,
documentation, software for controlling the board over the USB
port of a PC and software for analyzing the performance of the
AD7715 on the PC. The evaluation board model number is
EVAL-AD7715-3EBZ .
The programmable functions of the AD7715 are controlled
using a set of on-chip registers as outlined previously. Data is
written to these registers via the serial interface of the part and
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.
Noise levels in the signals applied to the AD7715 may also affect
performance of the part. The AD7715 software evaluation
package allows the user to evaluate the true performance of the
part, independent of the analog input signal. The scheme
involves using a test mode on the part where the differential
inputs to the AD7715 are internally shorted together to provide
a zero differential voltage for the analog modulator. External to
the device, connect the AIN(−) input to a voltage which is
within the allowable common-mode range of the part. This
scheme should be used after a calibration has been performed
on the part.
The serial interface of the AD7715 consists of five signals, CS,
SCLK, DIN, DOUT, and DRDY. 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 DRDY line is used as a status signal to indicate when
data is ready to be read from the data register of the AD7715.
DRDY goes low when a new data word is available in the output
register. It is reset high when a read operation from the data
register is complete. It also goes high prior to the updating 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 AD7715 in systems where a number of parts are
connected to the serial bus.
Rev. D | Page 29 of 40
AD7715
Figure 8 and Figure 9 show timing diagrams for interfacing to
the AD7715 with CS used to decode the part. Figure 8 is for a
read operation from the AD7715’s output shift register, while
Figure 9 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 DRDY line returns high after the first read
operation. Take care, however, to ensure that the read operations
have been completed before the next output update is about to
take place.
The AD7715 serial interface can operate in three-wire mode by
tying the CS input low. In this case, the SCLK, DIN and DOUT
lines are used to communicate with the AD7715 and the status
of DRDY can be obtained by interrogating the MSB of the communications 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 AD7715 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 because 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.
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 AD7715 DIN line for
at least 32 serial clock cycles, the serial interface is reset. This
ensures that in three-wire systems that if the interface gets lost
either via a software error or by some glitch in the system, it can
be reset back into a known state. This state returns the interface
to where the AD7715 is expecting a write operation to its communications register. This operation in itself does not reset the
contents of any registers, but because the interface was lost, the
information that was written to any of the registers is unknown
and it is advisable to set up all registers again.
Some microprocessor or microcontroller serial interfaces have
a single serial data line. In this case, it is possible to connect
the DOUT and DIN lines of the AD7715 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 back to a known
state is somewhat different than described previously. 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 into a known state.
DRDY
t10
t3
CS
t4
t8
t6
SCLK
t7
MSB
DOUT
t9
08519-008
t5
LSB
Figure 8. Read Cycle Timing Diagram
CS
t11
t16
t14
SCLK
t13
DIN
LSB
MSB
Figure 9. Write Cycle Timing Diagram
Rev. D | Page 30 of 40
08519-009
t15
t12
AD7715
CONFIGURING THE AD7715
The AD7715 contains three on-chip registers which the user
accesses via the serial interface. Communication with any of
these registers is initiated by writing to the communications
register first. Figure 10 outlines a flow chart of the sequence
which is used to configure all registers after a power-up or reset.
The flowchart also shows two different read options—the first
where the DRDY pin is polled to determine when an update of
the data register has taken place, the second where the DRDY
bit of the communications register is interrogated to see if a
data register update has taken place. Also included in the
flowing diagram is a series of words which should be written
to the registers for a particular set of operating conditions.
These conditions are gain of 1, no filter sync, bipolar mode,
buffer off, clock of 2.4576 MHz, and an output rate of 60 Hz.
START
POWER-ON/RESET FOR AD7715
CONFIGURE AND INITIALIZE
MICROCONTROLLER/MICROPROCESSOR SERIAL PORT
WRITE TO COMMUNICATIONS REGISTER SETTING UP
GAIN AND SETTING UP NEXT OPERATION TO BE A
WRITE TO THE SETUP REGISTER (10 HEX)
WRITE TO SETUP REGISTER SETTING UP REQUIRED
VALUES AND INITIATING A SELF CALIBRATION (68 HEX)
POLL DRDY PIN
NO
WRITE TO COMMUNICATIONS REGISTER SETTING UP SAME
GAIN AND SETTING UP NEXT OPERATION TO BE A READ FROM
THE COMMUNICATIONS REGISTER (08 HEX)
DRDY
LOW?
READ FROM COMMUNICATIONS REGISTER
YES
WRITE TO COMMUNICATIONS REGISTER SETTING UP
SAME GAIN AND SETTING UP NEXT OPERATION TO
BE A READ FROM THE DATA REGISTER (38 HEX)
POLL DRDY BIT OF COMMUNICATIONS REGISTER
NO
READ FROM DATA REGISTER
DRDY
LOW?
YES
READ FROM DATA REGISTER
Figure 10. Flow Chart for Setting Up and Reading from the AD7715
Rev. D | Page 31 of 40
08519-010
WRITE TO COMMUNICATIONS REGISTER SETTING UP
SAME GAIN AND SETTING UP NEXT OPERATION TO BE
A READ FROM THE DATA REGISTER (38 HEX)
AD7715
MICROCONTROLLER/MICROPROCESSOR INTERFACING
The serial interface on the AD7715 has the capability of operating
from just three wires and is compatible with SPI interface
protocols. The three-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 rise and fall times of the digital inputs to the AD7715
(especially the SCLK input) should be no longer than 1 μs.
Most of the registers on the AD7715 are 8-bit registers. This
facilitates easy interfacing to the 8-bit serial ports of microcontrollers. Some of the registers on the part are up to 16 bits,
but data transfers to these 16-bit registers can consist of a full
16-bit transfer or two 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 AD7715.
Even though some of the registers on the AD7715 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 setup register is to
be updated, the processor must first write to the communications
register (saying that the next operation is a write to the setup
register) and then write eight bits to the setup register. This
can all be done in a single 16-bit transfer if required 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.
AD7715 TO 68HC11 INTERFACE
Figure 11 shows an interface between the AD7715 and the
68HC11 microcontroller. The diagram shows the minimum
(three-wire) interface with CS on the AD7715 hardwired low. In
this scheme, the DRDY bit of the communications register is
monitored to determine when the data register is updated. An
alternative scheme, which increases the number of interface
lines to four, is to monitor the DRDY output line from the
AD7715. The monitoring of the DRDY line can be done in
two ways. First, DRDY 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 DRDY. The
second scheme is to use an interrupt driven system, in which
case the DRDY output is connected to the IRQ input of the
68HC11. For interfaces that require control of the CS input on
the AD7715, one of the port bits of the 68HC11 (such as PC1),
which is configured as an output, can be used to drive the CS input.
DVDD
SS
SCK
DVDD
RESET
SCLK
AD7715
68HC11
MISO
DOUT
MOSI
DIN
CS
08519-011
The flexible serial interface of the AD7715 allows for easy
interface to most microcontrollers and microprocessors. The
flow chart of Figure 10 outlines the sequence which should be
followed when interfacing a microcontroller or microprocessor
to the AD7715. Figure 11, Figure 12, and Figure 13 show some
typical interface circuits.
Figure 11. AD7715 to 68HC11 Interface
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 AD7715 is not capable of full duplex
operation. If the AD7715 is configured for a write operation, no
data appears on the DOUT lines even when the SCLK input is
active. Similarly, if the AD7715 is configured for a read
operation, data presented to the part on the DIN line is ignored
even when SCLK is active.
Coding for an interface between the 68HC11 and the AD7715 is
given in the C Code for Interfacing AD7715 to 68HC11 section.
In this example, the DRDY output line of the AD7715 is connected to the PC0 port bit of the 68HC11 and is polled to
determine its status.
Rev. D | Page 32 of 40
AD7715
AD7715 TO 8XC51 INTERFACE
AD7715 TO ADSP-2103/ADSP-2105 INTERFACE
An interface circuit between the AD7715 and the 8XC51
microcontroller is shown in Figure 12. The diagram shows the
minimum number of interface connections with CS on the
AD7715 hardwired low. In the case of the 8XC51 interface, the
minimum number of interconnects is just two. In this scheme,
the DRDY bit of the communications register is 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 DRDY output line from the AD7715. The
monitoring of the DRDY line can be done in two ways. First,
DRDY can be connected to one of the 8XC51’s port bits (such
as P1.0) which is configured as an input. This port bit is then
polled to determine the status of DRDY. The second scheme
is to use an interrupt driven system in which case, the DRDY
output is connected to the INT1 input of the 8XC51. For
interfaces that require control of the CS input on the AD7715,
one of the port bits of the 8XC51 (such as P1.1), which is
configured as an output, can be used to drive the CS input.
Figure 13 shows an interface between the AD7715 and the
ADSP-2103/ADSP-2105 DSP processor. In the interface shown,
the DRDY bit of the communications register is monitored to
determine when the data register is updated. The alternative
scheme is to use an interrupt driven system, in which case the
DRDY 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 AD7715
is active when either the RFS or TFS outputs from the ADSP2103/ADSP-2105 are active. The serial clock rate on the ADSP2103/ADSP-2105 should be limited to 3 MHz to ensure correct
operation with the AD7715.
DVDD
RESET
DVDD
8XC51
AD7715
10kΩ
P3.0
DOUT
DIN
SCLK
CS
08519-012
P3.1
Figure 12. AD7715 to 8XC51 Interface
Rev. D | Page 33 of 40
RESET
RFS
TFS
ADSP-2103/
ADSP-2105
CS
AD7715
DR
DOUT
DT
DIN
SCLK
SCLK
Figure 13. AD7715 to ADSP-2103/ADSP-2105 Interface
08519-013
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 AD7715 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 AD7715 rearranged
before being written to the output serial register. Similarly, the
AD7715 outputs the MSB first during a read operation while
the 8XC51 expects the LSB first. Therefore, the data which is
read into the serial buffer needs to be rearranged before the
correct data word from the AD7715 is available in the
accumulator.
DVDD
AD7715
CODE FOR SETTING UP THE AD7715
The C Code for Interfacing AD7715 to 68HC11 section gives
a set of read and write routines in C code for interfacing the
68HC11 microcontroller to the AD7715. The sample program
sets up the various registers on the AD7715 and reads 1000
samples from the part into the 68HC11. The setup conditions
on the part are exactly the same as those outlined for the
flowchart of Figure 10. In the example code given here, the
DRDY output is polled to determine if a new valid word is
available in the data register.
The sequence of the events in this program are as follows:
1.
2.
3.
4.
5.
Write to the communications register, setting the gain to 1
with standby inactive.
Write to the setup register, setting bipolar mode, buffer
off, no filter synchronization, confirming a clock frequency
of 2.4576 MHz, setting the output rate for 60 Hz and
initiating a self-calibration.
Poll the DRDY output.
Read the data from the data register.
Loop around doing Step 3 and Step 4 until the specified
number of samples have been taken.
C CODE FOR INTERFACING AD7715 TO 68HC11
/* This program has read and write routines for the 68HC11 to interface to the AD7715 and the sample
program sets the various registers and then reads 1000 samples from the part. */
#include <math.h>
#include <io6811.h>
#define NUM_SAMPLES 1000 /* change the number of data samples */
#define MAX_REG_LENGTH 2 /* this says that the max length of a register is 2 bytes */
Writetoreg (int);
Read (int,char);
char *datapointer = store;
char store[NUM_SAMPLES*MAX_REG_LENGTH + 30];
void main()
{
/* the only pin that is programmed here from the 68HC11 is the /CS and this is why the PC2 bit
of PORTC is made as an output */
char a;
DDRC = 0x04; /* PC2 is an output the rest of the port bits are inputs */
PORTC | = 0x04; /* make the /CS line high */
Writetoreg(0x10); /* set the gain to 1, standby off and set the next operation as write to the setup
register */
Writetoreg(0x68); /* set bipolar mode, buffer off, no filter sync, confirm clock as 2.4576MHz, set
output rate to 60Hz and do a self calibration */
while(PORTC & 0x10); /* wait for /DRDY to go low */
for(a=0;a<NUM_SAMPLES;a++);
{
Writetoreg(0x38); /*set the next operation for 16 bit read from the data register */
Read(NUM_SAMPLES,2);
}
}
Writetoreg(int byteword);
{
int q;
SPCR = 0x3f;
SPCR = 0X7f; /* this sets the WiredOR mode(DWOM=1), Master mode(MSTR=1), SCK idles high(CPOL=1), /SS
can be low always (CPHA=1), lowest clock speed(slowest speed which is master clock /32 */
DDRD = 0x18; /* SCK, MOSI outputs */
q = SPSR;
q = SPDR; /* the read of the staus register and of the data register is needed to clear the interrupt
which tells the user that the data transfer is complete */
Rev. D | Page 34 of 40
AD7715
PORTC &= 0xfb; /* /CS is low */
SPDR = byteword; /* put the byte into data register */
while(!(SPSR & 0x80)); /* wait for /DRDY to go low */
PORTC |= 0x4; /* /CS high */
}
Read(int amount, int reglength)
{
int q;
SPCR = 0x3f;
SPCR = 0x7f; /* clear the interrupt */
DDRD = 0x10; /* MOSI output, MISO input, SCK output */
while(PORTC & 0x10); /* wait for /DRDY to go low */
PORTC & 0xfb ; /* /CS is low */
for(b=0;b<reglength;b++)
{
SPDR = 0;
while(!(SPSR & 0x80)); /* wait until port ready before reading */
*datapointer++=SPDR; /* read SPDR into store array via datapointer */
}
PORTC|=4; /* /CS is high */
}
Rev. D | Page 35 of 40
AD7715
APPLICATIONS INFORMATION
The AD7715 provides a low cost, high resolution analog-todigital function. Because the analog-to-digital function is
provided by a Σ-Δ architecture, it makes the part more immune
to noisy environments thus making the part ideal for use in
industrial and process control applications. It also provides a
programmable gain amplifier, a digital filter and 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 AD7715 in a system allows the system
designer to achieve a much higher level of resolution because
noise performance of the AD7715 is significantly better than
that of the integrating ADCs.
PRESSURE MEASUREMENT
One typical application of the AD7715 is pressure measurement.
Figure 14 shows the AD7715 used with a pressure transducer,
the BP01 from Sensym. 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 (that is, the
voltage between its IN(+) and IN(−) terminals).
Assuming a 5 V excitation voltage, the full-scale output range
from the transducer is 15 mV. The excitation voltage for the
bridge is also used to generate the reference voltage for the
AD7715. Therefore, variations in the excitation voltage do not
introduce errors in the system. Choosing resistor values of 24 kΩ
and 15 kΩ as per the diagram give a 1.92 V reference voltage for
the AD7715 when the excitation voltage is 5 V.
The on-chip PGA allows the AD7715 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 and AVDD
when the part is operated in unbuffered mode. It allows the user
to connect the transducer directly to the input of the AD7715.
The programmable gain front end on the AD7715 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.
Using the part with a programmed gain of 128 results in the
full-scale input span of the AD7715 being 15 mV which
corresponds with the output span from the transducer.
+5V
EXCITATION VOLTAGE = +5V
AVDD
DVDD
AD7715
IN(+)
OUT(+)
CHARGE BALANCING ADC
AIN(+)
AIN(–)
BUFFER
IN(–)
PGA
A = 1 TO 128
AUTO-ZEROED
Σ-∆
MODULATOR
DIGITAL
FILTER
MCLK IN
24kΩ
CLOCK
GENERATION
MCLK OUT
SERIAL INTERFACE
REF IN(+)
REGISTER BANK
RESET
REF IN(–)
15kΩ
DRDY
AGND
DGND
DOUT
DIN
CS
Figure 14. Pressure Measurement Using the AD7715
Rev. D | Page 36 of 40
SCLK
08519-014
OUT(–)
AD7715
resistances RL1 and RL4, but these simply shift the commonmode voltage. There is no voltage drop across lead resistances
RL2 and RL3 as the input current to the AD7715 is very low. The
lead resistances present a small source impedance so it would
not generally be necessary to turn on the buffer on the AD7715.
If the buffer is required, the common-mode voltage should be
set accordingly by inserting a small resistance between the bottom
end of the RTD and AGND of the AD7715. In the application
shown in Figure 16, an external 400 μA current source provides
the excitation current for the PT100 and it also generates the
reference voltage for the AD7715 via the 6.25 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 6.25 kΩ resistor must have
a low temperature coefficient to avoid errors in the reference
voltage over temperature.
TEMPERATURE MEASUREMENT
Another application area for the AD7715 is in temperature
measurement. Figure 15 outlines a connection from a thermocouple to the AD7715. In this application, the AD7715 is operated
in its buffered mode to allow large decoupling capacitors on the
front end to eliminate any noise pickup that there may have
been in the thermocouple leads. When the AD7715 is operated
in buffered mode, it has a reduced common-mode range. To place
the differential voltage from the thermocouple on a suitable
common-mode voltage, the AIN(−) input of the AD7715 is
biased up at the reference voltage, 2.5 V.
Figure 16 shows another temperature measurement application
for the AD7715. In this case, the transducer is an resistive temperature device (RTD), a PT100. The arrangement is a 4-lead
RTD configuration. There are voltage drops across the lead
5V
AVDD
DVDD
AD7715
THERMOCOUPLE
JUNCTION
R
AIN(+)
R
AIN(–)
C
CHARGE BALANCING ADC
PGA
BUFFER
AUTO-ZEROED
Σ-∆
MODULATOR
A = 1 TO 128
C
DIGITAL
FILTER
MCLK IN
+5V
CLOCK
GENERATION
+VIN
MCLK OUT
SERIAL INTERFACE
REF192 VOUT
REF IN(+)
REGISTER BANK
RESET
REF IN(–)
DRDY
GND
DGND
DOUT
DIN
08519-015
AGND
SCLK
CS
Figure 15. Thermocouple Measurement Using the AD7715
+5V
400µA
REF IN(+)
RL1
RL2
6.25kΩ
AVDD
DVDD
AD7715
REF IN(–)
AIN(+)
CHARGE BALANCING ADC
BUFFER
RTD
PGA
AIN(–)
A = 1 TO 128
AUTO-ZEROED
Σ-∆
MODULATOR
DIGITAL
FILTER
RL4
MCLK IN
CLOCK
GENERATION
AGND
MCLK OUT
SERIAL INTERFACE
REGISTER BANK
RESET
DGND
DRDY
DOUT
DIN
CS
Figure 16. RTD Measurement Using the AD7715
Rev. D | Page 37 of 40
SCLK
08519-016
RL3
AD7715
The AD7715 consumes only 450 μA, leaving 3 mA available for
the rest of the transmitter. Figure 17 shows a block diagram of a
smart transmitter which includes the AD7715. Not shown in
Figure 17 is the isolated power source required to power the
front end.
SMART TRANSMITTERS
Another area where the low power, single supply, three-wire
interface capabilities is of benefit is in smart transmitters. Here,
the entire smart transmitter must operate from the 4 mA 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.
ISOLATION
BARRIER
MAIN TRANSMITTER ASSEMBLY
3V
ISOLATED SUPPLY
REF IN
VOLTAGE
REFERENCE
VCC
DAC
MICROCONTROLLER UNIT
SENSORS
RTD
mV
ohm
TC
AD7715
MCLK
IN
MCLK
OUT
DGND
AGND
*PID
*RANGE SETTING
*CALIBRATION
*LINEARIZATION
*OUTPUT CONTROL
*SERIAL COMMUNICATION
*HART PROTOCOL
4mA
TO
20mA
LOOP
RTN
COM
3V
HART
MODEM
BELL 202
COM
ISOLATED GROUND
Figure 17. Smart Transmitter Using the AD7715
Rev. D | Page 38 of 40
INPUT/OUTPUT
STAGE
SIGNAL
CONDITIONER
WAVEFORM
SHAPER
BANDPASS
FILTER
08519-017
VOLTAGE
REFERENCE
DVDD AVDD
VOLTAGE
REGULATOR
AD7715
OUTLINE DIMENSIONS
0.800 (20.32)
0.790 (20.07)
0.780 (19.81)
16
9
1
0.280 (7.11)
0.250 (6.35)
0.240 (6.10)
8
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
0.100 (2.54)
BSC
0.060 (1.52)
MAX
0.210 (5.33)
MAX
0.195 (4.95)
0.130 (3.30)
0.115 (2.92)
0.015
(0.38)
MIN
0.150 (3.81)
0.130 (3.30)
0.115 (2.92)
0.015 (0.38)
GAUGE
PLANE
SEATING
PLANE
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
0.014 (0.36)
0.010 (0.25)
0.008 (0.20)
0.430 (10.92)
MAX
0.005 (0.13)
MIN
0.070 (1.78)
0.060 (1.52)
0.045 (1.14)
073106-B
COMPLIANT TO JEDEC STANDARDS MS-001-AB
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS.
Figure 18. 16-Lead Plastic Dual In-Line Package [PDIP]
Narrow Body
(N-16)
Dimensions shown in inches and (millimeters)
10.50 (0.4134)
10.10 (0.3976)
9
16
7.60 (0.2992)
7.40 (0.2913)
8
1.27 (0.0500)
BSC
0.30 (0.0118)
0.10 (0.0039)
COPLANARITY
0.10
0.51 (0.0201)
0.31 (0.0122)
10.65 (0.4193)
10.00 (0.3937)
0.75 (0.0295)
0.25 (0.0098)
2.65 (0.1043)
2.35 (0.0925)
SEATING
PLANE
45°
8°
0°
0.33 (0.0130)
0.20 (0.0079)
COMPLIANT TO JEDEC STANDARDS MS-013- AA
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.
Figure 19. 16-Lead Standard Small Outline Package [SOIC_W]
Wide Body
(RW-16)
Dimensions shown in millimeters and (inches)
Rev. D | Page 39 of 40
1.27 (0.0500)
0.40 (0.0157)
032707-B
1
AD7715
5.10
5.00
4.90
16
9
4.50
4.40
4.30
6.40
BSC
1
8
PIN 1
1.20
MAX
0.15
0.05
0.20
0.09
0.30
0.19
0.65
BSC
COPLANARITY
0.10
SEATING
PLANE
8°
0°
0.75
0.60
0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AB
Figure 20. 16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
ORDERING GUIDE
Model
AD7715AN-5
AD7715ANZ-5 1
AD7715AR-5
AD7715AR-5REEL
AD7715ARZ-51
AD7715ARZ-5REEL1
AD7715ARU-5
AD7715ARU-5REEL
AD7715ARU-5REEL7
AD7715ARUZ-51
AD7715ARUZ-5REEL71
AD7715ACHIPS-5
AD7715AN-3
AD7715ANZ-31
AD7715AR-3
AD7715AR-3REEL
AD7715ARZ-31
AD7715ARZ-3REEL1
AD7715ARU-3
AD7715ARU-3REEL
AD7715ARU-3REEL7
AD7715ARUZ-31
AD7715ARUZ-3REEL71
AD7715ACHIPS-3
EVAL-AD7715-3EBZ1
1
AVDD Supply
5V
5V
5V
5V
5V
5V
5V
5V
5V
5V
5V
5V
3V
3V
3V
3V
3V
3V
3V
3V
3V
3V
3V
3V
3V
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
16-Lead Plastic Dual In-Line Package [PDIP]
16-Lead Plastic Dual In-Line Package [PDIP]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Plastic Dual In-Line Package [PDIP]
16-Lead Plastic Dual In-Line Package [PDIP]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Standard Small Outline Package [SOIC_W]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
Evaluation Board
Z = RoHS Compliant Part.
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08519-0-12/09(D)
Rev. D | Page 40 of 40
Package Option
N-16
N-16
RW-16
RW-16
RW-16
RW-16
RU-16
RU-16
RU-16
RU-16
RU-16
Die
N-16
N-16
RW-16
RW-16
RW-16
RW-16
RU-16
RU-16
RU-16
RU-16
RU-16
Die