AD AD7441BRT Pseudo differential, 1msps, 12- & 10-bit adcs in 8-lead sot-23 Datasheet

PRELIMINARY TECHNICAL DATA
a
Pseudo Differential, 1MSPS,
12- & 10-Bit ADCs in 8-lead SOT-23
Preliminary Technical Data
FEATURES
Fast Throughput Rate: 1MSPS
Specified for VDD of 2.7 V to 5.25 V
Low Power at max Throughput Rate:
3.75 mW typ at 1MSPS with VDD = 3 V
9 mW typ at 1MSPS with VDD = 5 V
Pseudo Differential Analog Input
Wide Input Bandwidth:
70dB SINAD at 300kHz Input Frequency
Flexible Power/Serial Clock Speed Management
No Pipeline Delays
High Speed Serial Interface - SPI TM /QSPI TM /
MICROWIRE T M / DSP Compatible
Power-Down Mode: 1µA max
8 Pin SOT-23 and µSOIC Packages
APPLICATIONS
Transducer Interface
Battery Powered Systems
Data Acquisition Systems
Portable Instrumentation
Motor Control
Communications
GENERAL DESCRIPTION
The AD7451/AD7441 are respectively 12- and 10-bit,
high speed, low power, successive-approximation (SAR)
analog-to-digital converters that feature a pseudo differential analog input. These parts operate from a single 2.7 V
to 5.25 V power supply and feature throughput rates up to
1MSPS.
The parts contains a low-noise, wide bandwidth, differential track and hold amplifier (T/H) which can handle
input frequencies in excess of 1MHz with the -3dB point
being 20MHz typically. The reference voltage is 2.5 V
and is applied externally to the VREF pin.
The conversion process and data acquisition are controlled
using CS and the serial clock allowing the device to interface with Microprocessors or DSPs. The input signals are
sampled on the falling edge of CS and the conversion is
also initiated at this point.
AD7451/AD7441
FUNCTIONAL BLOCK DIAGRAM
VDD
VIN+
T/H
VIN-
12-BIT SUCCESSIVE
APPROXIMATION
ADC
VREF
SCLK
AD7451/
AD7441
CONTROL
LOGIC
SDATA
+5
GND
The AD7451/41 use advanced design techniques to achieve
very low power dissipation at high throughput rates.
PRODUCT HIGHLIGHTS
1.Operation with 2.7 V to 5.25 V power supplies.
2.High Throughput with Low Power Consumption.
With a 3V supply, the AD7451/41 offer 3.75mW typ
power consumption for 1MSPS throughput.
3.Pseudo Differential Analog Input.
The VIN- input can be used as an offset from ground
4.Flexible Power/Serial Clock Speed Management.
The conversion rate is determined by the serial clock,
allowing the power to be reduced as the conversion time
is reduced through the serial clock speed increase. These
parts also feature a shutdown mode to maximize power
efficiency at lower throughput rates.
5.No Pipeline Delay.
6.Accurate control of the sampling instant via a CS input
and once off conversion control.
The SAR architecture of these parts ensures that there are
no pipeline delays.
MICROWIRE is a trademark of National Semiconductor Corporation.
SPI and QSPI are trademarks of Motorola, Inc.
REV. PrC 24/05/02
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2002
PRELIMINARY TECHNICAL DATA
AD7451 - SPECIFICATIONS1
Parameter
DYNAMIC PERFORMANCE
Signal to (Noise + Distortion)
(SINAD) 2
Total Harmonic Distortion (THD) 2
Peak Harmonic or Spurious Noise2
Intermodulation Distortion (IMD) 2
Second Order Terms
Third Order Terms
Aperture Delay 2
Aperture Jitter 2
Full Power Bandwidth2
( VDD = 2.7V to 5.25V, fSCLK = 18MHz, fS = 1MHz, VREF = 2.5 V; FIN = 300kHz;
TA = TMIN to TMAX, unless otherwise noted.)
Test Conditions/Comments
B Version1
Unit
-80dB typ
-82dB typ
70
-75
-75
dB min
dB max
dB max
@ -3 dB
@ -0.1 dB
-85
-85
10
50
20
2.5
dB typ
dB typ
ns typ
ps typ
MHz typ
MHz typ
12
±1
Bits
LSB max
±1
±3
±3
LSB max
LSB max
LSB max
VIN+ - VIN-
V REF
V
When in Track
When in Hold
V REF
0.1 to 1
±1
20
6
V
V
µA max
pF typ
pF typ
DC Leakage Current
VREF Input Capacitance
2.5
±1
15
V
µA max
pF typ
LOGIC INPUTS
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
Input Capacitance, CIN4
2.4
0.8
±1
10
V min
V max
µA max
pF max
2.8
2.4
0.4
±1
10
Straight
(Natural)
Binary
V min
V min
V max
µA max
pF max
DC ACCURACY
Resolution
Integral Nonlinearity (INL) 2
Differential Nonlinearity (DNL) 2
Guaranteed No Missed Codes
to 12 Bits.
Offset Error 2
Gain Error 2
ANALOG INPUT
Full Scale Input Span
Absolute Input Voltage
V IN+
V IN- 3
DC Leakage Current
Input Capacitance
REFERENCE INPUT
V REF Input Voltage
LOGIC OUTPUTS
Output High Voltage, VOH
Output Low Voltage, VOL
Floating-State Leakage Current
Floating-State Output Capacitance 4
Output Coding
±1% tolerance for
specified performance
Typically 10nA, VIN = 0VorVDD
VDD = 5V; ISOURCE = 200µA
VDD = 3V; ISOURCE = 200µA
I SINK =200µA
–2–
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7451 - SPECIFICATIONS1
Parameter
CONVERSION RATE
Conversion Time
Track/Hold Acquisition Time 2
Step Input
Throughput Rate 6
POWER REQUIREMENTS
V DD
I DD5,7
Normal Mode(Static)
Normal Mode (Operational)
Full Power-Down Mode
Power Dissipation
Normal Mode (Operational)
Full Power-Down
AD7451/AD7441
Test Conditions/Comments
888ns with an 18MHz SCLK
Sine Wave Input
TBD
SCLK On or Off
VDD = 5 V.
VDD = 3 V.
SCLK On or Off
VDD
VDD
VDD
VDD
=5
=3
=5
=3
V.
V.
V. SCLK On or Off
V. SCLK On or Off
NOTES
1
Temperature ranges as follows: B Versions: –40°C to +85°C.
2
See ‘Terminology’ section.
3
A small DC input is applied to V IN- to provide a pseudo ground for V IN+
4
Sample tested @ +25°C to ensure compliance.
5
See POWER VERSUS THROUGHPUT RATE section.
6
See ‘Serial Interface Section’.
7
Measured with a midscale DC input.
Specifications subject to change without notice.
REV. PrC
–3–
B Version1
Units
16
200
TBD
1
SCLK cycles
ns max
ns max
MSPS max
2.7/5.25
Vmin/max
0.5
1.8
1.25
1
mA typ
mA max
mA max
µA max
9
3.75
5
3
mW max
mW max
µW max
µW max
PRELIMINARY TECHNICAL DATA
1
AD7441 - SPECIFICATIONS
Parameter
DYNAMIC PERFORMANCE
Signal to (Noise + Distortion)
(SINAD) 2
Total Harmonic Distortion (THD) 2
Peak Harmonic or Spurious Noise2
Intermodulation Distortion (IMD) 2
Second Order Terms
Third Order Terms
Aperture Delay 2
Aperture Jitter 2
Full Power Bandwidth2
( VDD = 2.7V to 5.25V, fSCLK = 18MHz, fS = 1MHz, VREF = 2.5 V; FIN = 300kHz;
TA = TMIN to TMAX, unless otherwise noted.)
Test Conditions/Comments
B Version1
Unit
-80dB typ
-82dB typ
61
-73
-73
dB min
dB max
dB max
@ -3 dB
@ -0.1 dB
-78
-78
10
50
20
2.5
dB typ
dB typ
ns typ
ps typ
MHz typ
MHz typ
10
±0.5
Bits
LSB max
±0.5
±3
±3
LSB max
LSB max
LSB max
VIN+ - VIN-
V REF
V
When in Track
When in Hold
V REF
0.1 to 1
±1
20
6
V
V
µA max
pF typ
pF typ
DC Leakage Current
VREF Input Capacitance
2.5
±1
15
V
µA max
pF typ
LOGIC INPUTS
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
Input Capacitance, CIN4
2.4
0.8
±1
10
V min
V max
µA max
pF max
2.8
2.4
0.4
±1
10
Straight
(Natural)
Binary
V min
V min
V max
µA max
pF max
DC ACCURACY
Resolution
Integral Nonlinearity (INL) 2
Differential Nonlinearity (DNL) 2
Guaranteed No Missed Codes
to 10 Bits.
Offset Error2
Gain Error 2
ANALOG INPUT
Full Scale Input Span
Absolute Input Voltage
V IN+
V IN- 3
DC Leakage Current
Input Capacitance
REFERENCE INPUT
VREF Input Voltage
LOGIC OUTPUTS
Output High Voltage, VOH
Output Low Voltage, VOL
Floating-State Leakage Current
Floating-State Output Capacitance 4
Output Coding
±1% tolerance
for specified performance
Typically 10nA, VIN = 0VorVDD
VDD = 5V; ISOURCE = 200µA
VDD = 3V; ISOURCE = 200µA
I SINK =200µA
–4–
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7441 - SPECIFICATIONS1
Parameter
CONVERSION RATE
Conversion Time
Track/Hold Acquisition Time 2
AD7451/AD7441
Test Conditions/Comments
888ns with an 18MHz SCLK
Sine Wave Input
Step Input
Throughput Rate 6
POWER REQUIREMENTS
V DD
I DD6,7
Normal Mode(Static)
Normal Mode (Operational)
Full Power-Down Mode
Power Dissipation
Normal Mode (Operational)
Full Power-Down
SCLK On or Off
VDD = 5 V.
VDD = 3 V.
SCLK On or Off
VDD
VDD
VDD
VDD
=5
=3
=5
=3
V.
V.
V. SCLK On or Off
V. SCLK On or Off
NOTES
1
Temperature ranges as follows: B Versions: –40°C to +85°C.
2
See ‘Terminology’ section.
3
A small DC input is applied to VIN- to provide a pseudo ground for VIN+
4
Sample tested @ +25°C to ensure compliance.
5
See POWER VERSUS THROUGHPUT RATE section.
6
See ‘Serial Interface Section’.
7
Measured with a midscale DC input.
Specifications subject to change without notice.
REV. PrC
–5–
B Version1
Units
16
200
TBD
1
SCLK cycles
ns max
ns max
MSPS max
2.7/5.25
Vmin/max
0.5
1.8
1.25
1
mA typ
mA max
mA max
µA max
9
3.75
5
3
mW max
mW max
µW max
µW max
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
TIMING SPECIFICATIONS 1,2
Parameter
4
fSCLK
t CONVERT
t QUIET
t1
t2
t 35
t 45
t5
t6
t7
t 86
t POWER-UP 7
Limit at
T MIN, TMAX
Units
( VDD = 2.7V to 5.25V, fSCLK = 18MHz, fS = 1MHz, VREF = 2.5 V; FIN = 300kHz;
TA = TMIN to TMAX, unless otherwise noted.)
Description
10
18
16 x tSCLK
888
25
kHz min
MHz max
ns max
ns min
10
10
20
40
0.4 t SCLK
0.4 t SCLK
10
10
35
1
ns
ns
ns
ns
ns
ns
ns
ns
ns
µs
tSCLK = 1/fSCLK
Minimum Quiet Time between the End of a Serial Read and the
Next Falling Edge of CS
Minimum CS Pulsewidth
CS falling Edge to SCLK Falling Edge Setup Time
Delay from CS Falling Edge Until SDATA 3-State Disabled
Data Access Time After SCLK Falling Edge
SCLK High Pulse Width
SCLK Low Pulse Width
SCLK Edge to Data Valid Hold Time
SCLK Falling Edge to SDATA 3-State Enabled
SCLK Falling Edge to SDATA 3-State Enabled
Power-Up Time from Full Power-Down
min
min
max
max
min
min
min
min
max
max
NOTES
1
Sample tested at +25°C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 Volts.
2
See Figure 1, Figure 2 and the ‘Serial Interface’ section.
3
Common Mode Voltage.
4
Mark/Space ratio for the SCLK input is 40/60 to 60/40.
5
Measured with the load circuit of Figure 3 and defined as the time required for the output to cross 0.8 V or 2.4 V with V DD = 5 V and time for
an output to cross 0.4 V or 2.0 V for VDD = 3 V.
6
t 8 is derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 2. The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t 8, quoted in the
timing characteristics is the true bus relinquish time of the part and is independent of the bus loading.
7
See ‘Power-up Time’ Section.
Specifications subject to change without notice.
t1
+5
t CONVERT
t2
SCLK
2
1
3
4
0
13
5
0
0
DB11
0
14
15
t6
t7
t4
t3
SDATA
B
t5
DB10
DB2
16
t8
DB1
t QUIET
DB0
3-STATE
4 LEADING ZERO’S
Figure 1. AD7451 Serial Interface Timing Diagram
t1
+5
t CONVERT
t2
SCLK
1
2
3
4
0
5
t4
t3
SDATA
B
t5
0
0
0
4 LEADING ZERO’S
DB9
13
14
t6
t7
DB8
15
DB0
16
t8
0
0
2 TRAILING ZEROS
Figure 2. AD7441 Serial Interface Timing Diagram
–6–
t QUIET
3-STATE
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
ABSOLUTE MAXIMUM RATINGS1
(TA = +25°C unless otherwise noted)
IOL
1.6mA
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V
VIN+ to GND . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V
–0.3 V to VDD + 0.3 V
VIN- to GND . . . . . . . . . . . . . . .
Digital Input Voltage to GND . . . . . . . . -0.3 V to +7 V
Digital Output Voltage to GND . -0.3 V to VDD + 0.3 V
VREF to GND . . . . . . . . . . . . . . . . . -0.3 V to VDD +0.3 V
Input Current to Any Pin Except Supplies2 . . . . ±10mA
Operating Temperature Range
Commercial (A, B Version) . . . . . . . . . -40oC to +85oC
Storage Temperature Range . . . . . . . . . -65oC to +150oC
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . +150 o C
␪JA Thermal Impedance . . . . . . . . . . 205.9°C/W (µSOIC)
211.5°C/W (SOT-23)
␪JC Thermal Impedance . . . . . . . . . 43.74°C/W (µSOIC)
91.99°C/W (SOT-23)
Lead Temperature, Soldering
Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . +215 o C
Infared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . +220 o C
E S D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5kV
TO
OUT PUT
PIN
+1.6V
CL
50pF
IOH
200µA
Figure 3. Load Circuit for Digital Output Timing
Specifications
NOTES
1
Stresses above those listed under “Absolute Maximum Ratings” may cause permanent
damage to the device. This is a stress rating only and functional operation of the device
at these or any other conditions above those listed in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
2
Transient currents of up to 100 mA will not cause SCR latch up.
ORDERING GUIDE
Model
Range
AD7451BRT
AD7451BRM
AD7441BRT
AD7441BRM
TBD
EVAL-CONTROL BRD2 3
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
Evaluation Board
Controller Board
Linearity
Error (LSB)1
Package
Option 4
Branding Information
±1 LSB
±1 LSB
±0.5 LSB
±0.5 LSB
RT-8
RM-8
RT-8
RM-8
TBD
TBD
TBD
TBD
NOTES
1
Linearity error here refers to Integral Non-linearity Error.
2
This can be used as a stand-alone evaluation board or in conjunction with the EVALUATION BOARD CONTROLLER for evaluation/demonstration purposes.
3
EVALUATION BOARD CONTROLLER. This board is a complete unit allowing a PC to control and communicate with all Analog Devices
evaluation boards ending in the CB designators. To order a complete Evaluation Kit, you will need to order the ADC evaluation board i.e.
TBD, the EVAL-CONTROL BRD2 and a 12V AC transformer. See the TBD technote for more information.
4
RT = SOT-23; RM = µSOIC
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V
readily accumulate on the human body and test equipment and can discharge without
detection. Although the AD7451/AD7441 features proprietary ESD protection circuitry,
permanent damage may occur on devices subjected to high-energy electrostatic
discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
REV. PrC
–7–
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
PIN FUNCTION DESCRIPTION
Pin Mnemonic
V REF
V IN+
V INGND
CS
SDATA
SCLK
VDD
Function
Reference Input for the AD7451/41. An external 2.5 V reference must be applied to this input.This pin
should be decoupled to GND with a capacitor of at least 0.1µF.
Non-Inverting Input.
Inverting Input. This pin sets the ground reference point for the VIN+ input. Connect to Ground or to
a small DC offset to provide a pseudo ground.
Analog Ground. Ground reference point for all circuitry on the AD7451/41. All analog input
signals and any external reference signal should be referred to this GND voltage.
Chip Select. Active low logic input. This input provides the dual function of initiating a conversion on
the AD7451/41 and framing the serial data transfer.
Serial Data. Logic Output. The conversion result from the AD7451/41 is provided on this out
put as a serial data stream. The bits are clocked out on the falling edge of the SCLK input. The data
stream of the AD7451 consists of four leading zeros followed by the 12 bits of conversion data which
are provided MSB first; the data stream of the AD7441 consists of four leading zeros, followed by the
10-bits of conversion data, followed by two trailing zeros. In both cases, the output coding is Straight
(Natural) Binary.
Serial Clock. Logic input. SCLK provides the serial clock for accessing data from the part. This clock
input is also used as the clock source for the conversion process.
Power Supply Input. VDD is 2.7 V to 5.25 V. This supply should be decoupled to GND with a 0.1µF
Capacitor and a 10µF Tantalum Capacitor.
PIN CONFIGURATION 8-LEAD SOT-23
VDD
1
SCLK
2
SDATA
3
AD7451/AD7441
SOT-23
TOP VIEW
8
VREF
7
VIN +
6
VIN -
5
GND
(Not to Scale)
+5
4
PIN CONFIGURATION µSOIC
VREF
1
VIN +
2
VIN -
3
AD7451/AD7441
µSOIC
TOP VIEW
8
VDD
7
SCLK
6
SDATA
5
+5
(Not to Scale)
GND
4
–8–
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
TERMINOLOGY
tortion products to the rms amplitude of the sum of the
fundamentals expressed in dBs.
Signal to (Noise + Distortion) Ratio
This is the measured ratio of signal to (noise + distortion)
at the output of the ADC. The signal is the rms amplitude
of the fundamental. Noise is the sum of all
nonfundamental signals up to half the sampling frequency
(fS/2), excluding dc. The ratio is dependent on the number
of quantization levels in the digitization process; the more
levels, the smaller the quantization noise. The theoretical
signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by:
Aperture Delay
This is the amount of time from the leading edge of the
sampling clock until the ADC actually takes the sample.
Aperture Jitter
This is the sample to sample variation in the effective
point in time at which the actual sample is taken.
Full Power Bandwidth
Thus for a 12-bit converter, this is 74 dB and for a 10-bit
converter this is 62dB.
The full power bandwidth of an ADC is that input frequency at which the amplitude of the reconstructed
fundamental is reduced by 0.1dB or 3dB for a full scale
input.
Total Harmonic Distortion
Integral Nonlinearity (INL)
Total harmonic distortion (THD) is the ratio of the rms
sum of harmonics to the fundamental. For the AD7450, it
is defined as:
This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function.
Signal to (Noise + Distortion) = (6.02 N + 1.76) dB
Differential Nonlinearity (DNL)
THD (dB ) = 20 log
V2
2
2
2
+V3 +V 4
2
2
+V5 +V 6
This is the difference between the measured and the ideal 1
LSB change between any two adjacent codes in the ADC.
V1
Offset Error
where V1 is the rms amplitude of the fundamental and V2,
V3, V4, V5 and V6 are the rms amplitudes of the second to
the sixth harmonics.
This is the deviation of the first code transition (000...000 to
000...001) from the ideal (i.e. AGND + 1LSB)
Gain Error
Peak Harmonic or Spurious Noise
Peak harmonic or spurious noise is defined as the ratio of
the rms value of the next largest component in the ADC
output spectrum (up to fS/2 and excluding dc) to the rms
value of the fundamental. Normally, the value of this
specification is determined by the largest harmonic in the
spectrum, but for ADCs where the harmonics are buried
in the noise floor, it will be a noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa
and fb, any active device with nonlinearities will create
distortion products at sum and difference frequencies of
mfa ± nfb where m, n = 0, 1, 2, 3, etc. Intermodulation
distortion terms are those for which neither m nor n are
equal to zero. For example, the second order terms include (fa + fb) and (fa – fb), while the third order terms
include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).
The AD7451/41 is tested using the CCIF standard where
two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are
usually distanced in frequency from the original sine waves
while the third order terms are usually at a frequency close
to the input frequencies. As a result, the second and third
order terms are specified separately. The calculation of the
intermodulation distortion is as per the THD specification
where it is the ratio of the rms sum of the individual dis-
REV. PrC
This is the deviation of the last code transition (111...110 to
111...111) from the ideal (i.e., VREF - 1LSB), after the Offset
Error has been adjusted out.
Track/Hold Acquisition Time
The track/hold amplifier returns into track mode on the
13th SCLK rising edge (see the “Serial Interface Section”). The track/hold acquisition time is the minimum
time required for the track and hold amplifier to remain in
track mode for its output to reach and settle to within 0.5
LSB of the applied input signal.
Power Supply Rejection
Ratio (PSRR)
The power supply rejection ratio is defined as the ratio of
the power in the ADC output at full-scale frequency, f, to
the power of a 200mV p-p sine wave applied to the ADC
VDD supply of frequency fs. The frequency of this input
varies from 1kHz to 1MHz.
PSRR (dB) = 10 log (Pf/Pfs)
Pf is the power at frequency f in the ADC output; Pfs is
the power at frequency fs in the ADC output.
–9–
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
PERFORMANCE CURVES
(Default Conditions: TA = 25°C, Fs = 1MSPS, FSCLK = 18MHz, VDD = 2.7 V to 5.25 V, VREF = 2.5 V)
0
TITLE
TITLE
0
6*,
0
0
0
0
0
0
0
TITLE
0
6*,
0
0
0
0
0
0
0
TITLE
0
0
0
TPC 3. PSRR vs. Supply Ripple Frequency with Supply
Decoupling of TBD
TPC 1. SINAD vs Analog Input Frequency for Various
Supply Voltages
0
TITLE
TPC 2 and TPC 3 shows the Power Supply Rejection
Ratio (see Terminology) versus VDD supply ripple frequency for the AD7451/41 with and without power supply
decoupling respectively.
TITLE
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TPC 4. THD vs. Analog Input Frequency for Various
Source Impedances
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TPC 2. PSRR vs. Supply Ripple Frequency without Supply
Decoupling
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TPC 5. THD vs. Analog Input Frequency for Various
Supply Voltages
–10–
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
AD7451 PERFORMANCE CURVES
(Default Conditions: TA = 25°C, Fs = 1MSPS, FSCLK
= 18MHz, VDD = 2.7 V to 5.25 V, VREF = 2.5 V)
0
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TITLE
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0
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TPC 6. AD7451 Dynamic Performance
TPC 9. Histogram of 10000 conversions of a DC Input for
the AD7451
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TPC 7. Typical DNL For the AD7451
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TPC 8. Typical INL For the AD7451
REV. PrC
–11–
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
AD7441 PERFORMANCE CURVES
(Default Conditions: TA = 25°C, Fs = 1MSPS, FSCLK
= 18MHz, VDD = 2.7 V to 5.25 V, VREF = 2.5 V)
0
6*,
0
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TITLE
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0
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TPC 13. Histogram of 10000 conversions of a DC Input for
the AD7441
TPC 10. AD7441 Dynamic Performance
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TPC 11. Typical DNL For the AD7441
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TPC 12. Typical INL For the AD7441
0
–12–
REV. PrC
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
SERIAL INTERFACE
Figures 1 and 2 show detailed timing diagrams for the
serial interface of the AD7451 and the AD7441 respectively. The serial clock provides the conversion clock and
also controls the transfer of data from the device during
conversion. CS initiates the conversion process and frames
the data transfer. The falling edge of CS puts the track
and hold into hold mode and takes the bus out of threestate. The analog input is sampled and the conversion
initiated at this point. The conversion will require 16
SCLK cycles to complete.
Once 13 SCLK falling
hold will go back into
as shown at point B in
SCLK falling edge the
three-state.
edges have occurred, the track and
track on the next SCLK rising edge
Figures 1 and 2. On the 16th
SDATA line will go back into
If the rising edge of CS occurs before 16 SCLKs have
elapsed, the conversion will be terminated and the SDATA
line will go back into three-state on the 16th SCLK falling
edge.
The conversion result from the AD7451/41 is provided on
the SDATA output as a serial data streatm. The bits are
clocked out on the falling edge of the SCLK input. The data
streatm of the AD7451 consists of four leading zeros,
followed by 12 bits of conversion data which is provided MSB
first; the data stream of the AD7441 consists of four leading
zeros, followed by the 10 bits of conversion data, followed by
two trailing zeros, which is also provided MSB first. In both
cases, the output coding is straight (natural) binary.
16 serial clock cycles are required to perform a conversion
and to access data from the AD7451/41. CS going low
provides the first leading zero to be read in by the microcontroller or DSP. The remaining data is then clocked out
on the subsequent SCLK falling edges beginning with the
second leading zero. Thus the first falling clock edge on the
serial clock provides the second leading zero. The final bit
in the data transfer is valid on the 16th falling edge, having
been clocked out on the previous (15th) falling edge. Once
the conversion is complete and the data has been accessed
after the 16 clock cycles, it is important to ensure that, before
the next conversion is initiated, enough time is left to meet
the acquisition and quiet time specifications - see the Timing
Examples. To achieve 1MSPS with an 18MHz clock for
VDD = 3 V and 5 V, an 18 clock burst will perform the
conversion and leave enough time before the next conversion
for the acquisition and quiet time.
In applications with a slower SCLK, it may be possible to
read in data on each SCLK rising edge i.e. the first rising
edge of SCLK after the CS falling edge would have the
leading zero provided and the 15th SCLK edge would have
DB0 provided.
Timing Example 1
Having FSCLK = 18MHz and a throughput rate of
1MSPS gives a cycle time of:
1/Throughput = 1/1000000 = 1µs
A cycle consists of:
t2 + 12.5 (1/FSCLK) + tACQ = 1µs.
Therefore if t2 = 10ns then:
10ns + 12.5(1/18MHz) + tACQ = 1µs
tACQ = 296ns
This 296ns satisfies the requirement of 200ns for tACQ.
From Figure 4, tACQ comprises of:
2.5(1/FSCLK) + t8 + tQUIET
where t8 = 35ns. This allows a value of 122ns for tQUIET
satisfying the minimum requirement of 25ns.
Timing Example 2
Having FSCLK = 5MHz and a throughput rate of
315kSPS gives a cycle time of :
1/Throughput = 1/315000 = 3.174µs
A cycle consists of:
t2 + 12.5 (1/FSCLK) + tACQ = 3.174µs.
Therefore if t2 is 10ns then:
10ns + 12.5(1/5MHz) + tACQ = 3.174µs
tACQ = 664ns
This 664ns satisfies the requirement of 200ns for tACQ.
From Figure 4, tACQ comprises of:
2.5(1/FSCLK) + t8 + tQUIET
where t8 = 35ns. This allows a value of 129ns for tQUIET
satisfying the minimum requirement of 25ns.
As in this example and with other slower clock values, the
signal may already be acquired before the conversion is
complete but it is still necessary to leave 25ns minimum
tQUIET between conversions. In example 2 the signal should
be fully acquired at approximately point C in Figure 4.
+5
t CONVERT
SCLK
t
10ns 2
1
2
3
4
C
B
t5
5
13
14
t6
16
t8
tQUIET
t ACQUISITION
12.5(1/fSCLK )
1/Throughput
REV. PrC
15
Figure 4. Serial Interface Timing Example
–13–
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
MODES OF OPERATION
The mode of operation of the AD7451 and the AD7441 is
selected by controlling the logic state of the CS signal during
a conversion. There are two possible modes of operation,
Normal Mode and Power-Down Mode. The point at which
CS is pulled high after the conversion has been initiated will
determine whether or not the AD7451/41 will enter the
power-down mode. Similarly, if already in power-down, CS
controls whether the devices will return to normal operation
or remain in power-down. These modes of operation are
designed to provide flexible power management options.
These options can be chosen to optimize the power dissipation/throughput rate ratio for differing application
requirements.
Normal Mode
This mode is intended for fastest throughput rate performance. The user does not have to worry about any
power-up times with the AD7451/41 remaining fully
powered up all the time. Figure 5 shows the general diagram of the operation of the AD7451/41 in this mode.
The conversion is initiated on the falling edge of CS as
described in the ‘Serial Interface Section’. To ensure the
part remains fully powered up, CS must remain low until
at least 10 SCLK falling edges have elapsed after the falling edge of CS.
If CS is brought high any time after the 10th SCLK falling edge, but before the 16th SCLK falling edge, the part
will remain powered up but the conversion will be terminated and SDATA will go back into three-state. Sixteen
serial clock cycles are required to complete the conversion
and access the complete conversion result. CS may idle
high until the next conversion or may idle low until sometime prior to the next conversion. Once a data transfer is
complete, i.e. when SDATA has returned to three-state,
another conversion can be initiated after the quiet time,
tQUIET has elapsed by again bringing CS low.
+5
Once CS has been brought high in this window of
SCLKs, the part will enter power down and the conversion that was initiated by the falling edge of CS will be
terminated and SDATA will go back into three-state.
The time from the rising edge of CS to SDATA threestate enabled will never be greater than t8 (see the
‘Timing Specifications’). If CS is brought high before
the second SCLK falling edge, the part will remain in
normal mode and will not power-down. This will avoid
accidental power-down due to glitches on the CS line.
In order to exit this mode of operation and power the
AD7451/41 up again, a dummy conversion is performed.
On the falling edge of CS the device will begin to power
up, and will continue to power up as long as CS is held
low until after the falling edge of the 10th SCLK. The
device will be fully powered up after 1µsec has elapsed
and, as shown in Figure 7, valid data will result from the
next conversion.
If CS is brought high before the 10th falling edge of
SCLK, the AD7451/41 will again go back into powerdown. This avoids accidental power-up due to glitches on
the CS line or an inadvertent burst of eight SCLK cycles
while CS is low. So although the device may begin to
power up on the falling edge of CS, it will again powerdown on the rising edge of CS as long as it occurs before
the 10th SCLK falling edge.
+5
1
2
10
SCLK
THREE STATE
SDATA
Figure 6. Entering Power Down Mode
Power up Time
SCLK
SDATA
1
10
4 LEADING ZEROS + CONVERSION RESULT
Figure 5. Normal Mode Operation
Power Down Mode
16
The power up time of the AD7451/41 is typically 1µsec,
which means that with any frequency of SCLK up to
18MHz, one dummy cycle will always be sufficient to
allow the device to power-up. Once the dummy cycle is
complete, the ADC will be fully powered up and the input
signal will be acquired properly. The quiet time tQUIET
must still be allowed from the point at which the bus goes
back into three-state after the dummy conversion, to the
next falling edge of CS.
This mode is intended for use in applications where
slower throughput rates are required; either the ADC is
When running at the maximum throughput rate of
powered down between each conversion, or a series of
1MSPS, the AD7451/41 will power up and acquire a sigconversions may be performed at a high throughput rate
nal within ±0.5LSB in one dummy cycle, i.e. 1µs. When
and the ADC is then powered down for a relatively long
powering up from the power-down mode with a dummy
duration between these bursts of several conversions.
cycle, as in Figure 7, the track and hold, which was in
When the AD7451/AD7441 is in the power down mode,
hold mode while the part was powered down, returns to
all analog circuitry is powered down. To enter power
track mode after the first SCLK edge the part receives
down mode, the conversion process must be interrupted
after the falling edge of CS. This is shown as point A in
by bringing CS high anywhere after the second falling
Figure 7.
edge of SCLK and before the tenth falling edge of SCLK
as shown in Figure 6.
REV. PrC
–14–
PRELIMINARY TECHNICAL DATA
AD7451/AD7441
tPOWERUP
THE PART BEGINS
TO POWER UP
+5
SCLK
SDATA
A
1
THE PART IS FULLY POWERED
UP WITH VIN FULLY ACQUIRED
10
16
1
INVALID DATA
10
16
VALID DATA
Figure 7. Exiting Power Down Mode
Although at any SCLK frequency one dummy cycle is
POWER VERSUS THROUGHPUT RATE
sufficient to power the device up and acquire VIN, it does
By using the power-down mode on the AD7451/41 when
not necessarily mean that a full dummy cycle of 16
not converting, the average power consumption of the
SCLKs must always elapse to power up the device and
ADC decreases at lower throughput rates. Figure 8 shows
acquire VIN fully; 1µs will be sufficient to power the dehow, as the throughput rate is reduced, the device remains
vice up and acquire the input signal.
in its power-down state longer and the average power consumption reduces accordingly. It shows this for both 5V
and 3V power supplies.
For example, if a 5MHz SCLK frequency was applied to
the ADC, the cycle time would be 3.2µs (i.e. 1/(5MHz) x
For example, if the AD7451/41 is operated in continous
16). In one dummy cycle, 3.2µs, the part would be powsampling mode with a throughput rate of 100kSPS and an
ered up and VIN acquired fully. However after 1µs with a
SCLK of 18MHz and the device is placed in the power
5MHz SCLK only 5 SCLK cycles would have elapsed. At
down mode between conversions, then the power conthis stage, the ADC would be fully powered up and the
sumption is calculated as follows:
signal acquired. So, in this case the CS can be brought
high after the 10th SCLK falling edge and brought low
again after a time tQUIET to initiate the conversion.
Power dissipation during normal operation = 9mW max
(for VDD = 5V).
When power supplies are first applied to the AD7451/41,
the ADC may either power up in the power-down mode or
If the power up time is 1 dummy cycle i.e. 1µsec, and the
normal mode. Because of this, it is best to allow a dummy
remaining conversion time is another cycle i.e. 1µsec, then
cycle to elapse to ensure the part is fully powered up bethe AD7451/41 can be said to dissipate 9mW for 2µsec
fore attempting a valid conversion. Likewise, if the user
during each conversion cycle.
wishes the part to power up in power-down mode, then the
dummy cycle may be used to ensure the device is in
If the throughput rate = 100kSPS then the cycle time =
power-down by executing a cycle such as that shown in
10µsec and the average power dissipated during each cycle
Figure 6.
is:
(2/10) x 9mW = 1.8mW
Once supplies are applied to the AD7451/41, the power
For the same scenario, if VDD = 3V, the power dissipation
up time is the same as that when powering up from the
during normal operation is 3.75mW max.
power-down mode. It takes approximately 1µs to power
The AD7450 can now be said to dissipate 3.75mW for
up fully if the part powers up in normal mode. It is not
2µsec* during each conversion cycle.
necessary to wait 1µs before executing a dummy cycle to
The average power dissipated during each cycle with a
ensure the desired mode of operation. Instead, the dummy
throughput rate of 100kSPS is therefore:
cycle can occur directly after power is supplied to the
(2/10) x 3.75mW = 0.75mW
ADC. If the first valid conversion is then performed diThis is how the power numbers in Figure 8 are calculated.
rectly after the dummy conversion, care must be taken to
ensure that adequate acquisition time has been allowed.
As mentioned earlier, when powering up from the powerdown mode, the part will return to track upon the first
SCLK edge applied after the falling edge of CS. However, when the ADC powers up initially after supplies are
applied, the track and hold will already be in track. This
means if (assuming one has the facility to monitor the
ADC supply current) the ADC powers up in the desired
mode of operation and thus a dummy cycle is not required
to change mode, then neither is a dummy cycle required
to place the track and hold into track.
TBD
Figure 8. Power vs. Throughput rate for the
Power Down Mode
For throughput rates above 320kSPS, it is recommended
that for optimum power performance, the serial clock
frequency is reduced.
REV. PrC
–15–