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MOS Complete,
12-Bit, 100 kHz, Sampling ADCs
AD7870/AD7875/AD7876
FEATURES
Complete monolithic 12-bit ADCs with
2 μs track-and-hold amplifier
8 μs ADC
On-chip reference
Laser-trimmed clock
Parallel, byte, and serial digital interface
72 dB SNR at 10 kHz input frequency
(AD7870, AD7875)
57 ns data access time
Low power: −60 mW typical
Variety of input ranges
±3 V for AD7870
0 V to +5 V for AD7875
±10 V for AD7876
FUNCTIONAL BLOCK DIAGRAM
AGND
REF OUT
V
IN
V
DD
INPUT
SCALING
AD7870/AD7875/
AD7876
TRACK-AND-HOLD
COMP
3V
REFERENCE
12-BIT
DAC
CLK
CLOCK
SAR +
COUNTER
12/8/CLK
CONTROL LOGIC
CONVST
PARALLEL
AND SERIAL
INTERFACE
07730-001
CS
RD BUSY/INT
DB11
DB0
DGND
V
SS
Figure 1.
GENERAL DESCRIPTION
The AD7870/AD7875/AD7876 are fast, complete, 12-bit
analog-to-digital converters (ADCs). These converters consist
of a track-and-hold amplifier, an 8 μs successive approximation
ADC, a 3 V buried Zener reference, and versatile interface logic.
The ADCs feature a self-contained internal clock which is laser
trimmed to guarantee accurate control of conversion time. No
external clock timing components are required; the on-chip
clock may be overridden by an external clock if required.
The parts offer a choice of three data output formats: a single,
parallel, 12-bit word; two 8-bit bytes or serial data. Fast bus
access times and standard control inputs ensure easy interfacing
to modern microprocessors and digital signal processors.
All parts operate from ±5 V power supplies. The AD7870 and
AD7876 accept input signal ranges of ±3 V and ±10 V, respec-
tively, while the AD7875 accepts a unipolar 0 V to +5 V input
range. The parts can convert full power signals up to 50 kHz.
The AD7870/AD7875/AD7876 feature dc accuracy specifica-
tions, such as linearity, full-scale and offset error. In addition,
the AD7870 and AD7875 are fully specified for dynamic
performance parameters including distortion and signal-to-
noise ratio.
The parts are available in a 24-pin, 0.3 inch-wide, plastic or
hermetic dual-in-line package (DIP). The AD7870 and AD7875
are available in a 28-pin plastic leaded chip carrier (PLCC),
while the AD7876 is available and in a 24-pin small outline
(SOIC) package.
PRODUCT HIGHLIGHTS
1.
Complete 12-bit ADC on a chip.
The AD7870/AD7875/AD7876 provide all the functions
necessary for analog-to-digital conversion and combine a
12-bit ADC with internal clock, track-and-hold amplifier
and reference on a single chip.
Dynamic specifications for DSP users.
The AD7870 and AD7875 are fully specified and tested for
ac parameters, including signal-to-noise ratio, harmonic
distortion and intermodulation distortion.
Fast microprocessor interface.
Data access times of 57 ns make the parts compatible with
modern 8-bit and 16-bit microprocessors and digital signal
processors. Key digital timing parameters are tested and
guaranteed over the full operating temperature range.
2.
3.
Rev. C
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 ©1997–2009 Analog Devices, Inc. All rights reserved.
AD7870/AD7875/AD7876
TABLE OF CONTENTS
Features .............................................................................................. 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
AD7870 Specifications ................................................................. 3
AD7875/AD7876 Specifications................................................. 4
Timing Characteristics ................................................................ 6
Absolute Maximum Ratings............................................................ 7
ESD Caution .................................................................................. 7
Pin Configurations and Function Descriptions ........................... 8
Load Circuits ................................................................................... 10
Converter Details ............................................................................ 11
Internal Reference ...................................................................... 11
Track-and-Hold Amplifier ........................................................ 11
Analog Input ............................................................................... 11
Offset And Full-Scale Adjustment—AD7870 ........................ 12
Offset And Full-Scale Adjustment—AD7876 ........................ 13
Offset And Full-Scale Adjustment—AD7875 ........................ 13
Timing and Control ....................................................................... 14
Data Output Formats ................................................................. 14
Mode 1 Interface......................................................................... 14
Mode 2 Interface......................................................................... 15
Dynamic Specifications ............................................................. 16
Microprocessor Interface............................................................... 19
Parallel Read Interfacing ........................................................... 19
Two-Byte Read Interfacing ....................................................... 19
Serial Interfacing ........................................................................ 20
Standalone Operation ................................................................ 21
Applications Information .............................................................. 22
Layout Hints ................................................................................ 22
Noise ............................................................................................ 22
Outline Dimensions ....................................................................... 23
Ordering Guide .......................................................................... 25
REVISION HISTORY
2/09—Rev. B to Rev. C
Updated Format .................................................................. Universal
Reorganized Layout ............................................................ Universal
Deleted S Version ................................................................ Universal
Changes to Internal Clock Parameter, Table 1 and
Added Endnote to Table 1 ............................................................... 4
Changes to Internal Clock Parameter, Table 2.............................. 5
Changes to Mode 1 Interface Section .......................................... 14
Deleted Data Acquisition Board and Interface Connections
Sections and Figure 26 ................................................................... 15
Deleted Figure 27 and Power Supply Connections, Shorting
Plug Options and Components List Sections ............................. 16
Deleted Figure 28 and Figure 29 ................................................... 17
Deleted Figure 30 and Figure 31 ................................................... 18
Updated Outline Dimensions ....................................................... 23
Changes to Ordering Guide .......................................................... 25
Rev. C | Page 2 of 28
AD7870/AD7875/AD7876
SPECIFICATIONS
V
DD
= +5 V ± 5%, V
SS
= −5 V ± 5%, AGND = DGND = 0 V, f
CLK
= 2.5 MHz external, unless otherwise stated. All Specifications T
min
to
T
max
, unless otherwise noted.
AD7870 SPECIFICATIONS
Table 1.
Parameter
DYNAMIC PERFORMANCE
2
Signal-to-Noise Ratio
3
(SNR)
@ +25°C
T
MIN
to T
MAX
Total Harmonic Distortion (THD)
Peak Harmonic or Spurious Noise
Intermodulation Distortion (IMD)
Second Order Terms
Third Order Terms
Track-and-Hold Acquisition Time
DC ACCURACY
Resolution
Minimum Resolution for which No Missing Codes
are Guaranteed
Integral Nonlinearity
Integral Nonlinearity
Differential Nonlinearity
Bipolar Zero Error
Positive Full-Scale Error
4
Negative Full-Scale Error
4
ANALOG INPUT
Input Voltage Range
Input Current
REFERENCE OUTPUT
REF OUT @ +25°C
REF OUT Tempco
Reference Load Sensitivity
(ΔREF OUT/ΔI)
LOGIC INPUTS
Input High Voltage, V
INH
Input Low Voltage, V
INL
Input Current, I
IN
Input Current (12/8/CLK Input Only)
Input Capacitance, C
IN 5
LOGIC OUTPUTS
Output High Voltage, V
OH
Output Low Voltage, V
OL
DB11 to DB0
Floating-State Leakage Current
Floating-State Output Capacitance
5
J, A
ADN7870
1
K, B
L, C
T
Units
Test Conditions/Comments
70
70
−80
−80
70
70
−80
−80
72
71
−80
−80
69
69
−78
−78
dB min
dB min
dB max
dB max
V
IN
= 10 kHz sine wave, f
SAMPLE
= 100 kHz
Typically 71.5 dB for 0 < V
IN
< 50 kHz
V
IN
= 10 kHz sine wave, f
SAMPLE
= 100 kHz
Typically −86 dB for 0 < V
IN
< 50 kHz
V
IN
= 10 kHz, f
SAMPLE
= 100 kHz
Typically −86 dB for 0 < V
IN
< 50 kHz
fa = 9 kHz, fb = 9.5 kHz, f
SAMPLE
= 50 kHz
fa = 9 kHz, fb = 9.5 kHz, f
SAMPLE
= 50 kHz
−80
−80
2
12
12
±1/2
−80
−80
2
12
12
±1/2
±1
±1
±5
±5
±5
±3
±500
2.99
3.01
±60
±1
−80
−80
2
12
12
±1/4
±1/2
±1
±5
±5
±5
±3
±500
2.99
3.01
±35
±1
−78
−78
2
12
12
±1/2
±1
±1
±5
±5
±5
±3
±500
2.99
3.01
±35
±1
dB max
dB max
μs max
Bits
Bits
LSB typ
LSB max
LSB max
LSB max
LSB max
LSB max
V
μA max
V min
V max
ppm/°C
max
mV max
±5
±5
±5
±3
±500
2.99
3.01
±60
±1
Reference load current change (0 μA to
500 μA). Reference load should not be
changed during conversion.
V
DD
= 5 V ± 5%
V
DD
= 5 V ± 5%
V
IN
= 0 V to V
DD
V
IN
= V
SS
to V
DD
2.4
0.8
±10
±10
10
4.0
0.4
±10
15
2.4
0.8
±10
±10
10
4.0
0.4
±10
15
2.4
0.8
±10
±10
10
4.0
0.4
±10
15
2.4
0.8
±10
±10
10
4.0
0.4
±10
15
V min
V max
μA max
μA max
pF max
V min
V max
μA max
pF max
I
SOURCE
= 40 μA
I
SINK
= 1.6 mA
Rev. C | Page 3 of
28
AD7870/AD7875/AD7876
Parameter
CONVERSION TIME
External Clock (f
CLK
= 2.5 MHz)
Internal Clock
6
POWER REQUIREMENTS
V
DD
V
SS
I
DD
I
SS
Power Dissipation
J, A
8
6.5/9
ADN7870
1
K, B
L, C
8
6.5/9
8
6.5/9
T
8
6.5/9
Units
μs max
μs min/
μs max
V nom
V nom
mA max
mA max
mW max
±5% for specified performance
±5% for specified performance
Typically 8 mA
Typically 4 mA
Typically 60 mW
Test Conditions/Comments
+5
−5
13
6
95
+5
−5
13
6
95
+5
−5
13
6
95
+5
−5
13
6
95
1
2
The temperature range for the J, K, and L versions is from 0°C to +70°C; for the A, B, and C versions is−40°C to +85°C; and for the T version is −55°C to +125°C.
V
IN
(p-p) = ±3 V.
3
SNR calculation includes distortion and noise components.
4
Measured with respect to internal reference and includes bipolar offset error.
5
Sample tested @ +25°C to ensure compliance.
6
Conversion time specification for the AD7870A device with internal clock used is 8 μs/10 μs minimum/maximum.
AD7875/AD7876 SPECIFICATIONS
Table 2.
Parameter
DC ACCURACY
Resolution
Min Resolution for which No Missing
Codes Are Guaranteed
Integral Nonlinearity @ +25°C
T
MIN
to T
MAX
(AD7875 Only)
T
MIN
to T
MAX
(AD7876 Only)
Differential Nonlinearity
Unipolar Offset Error (AD7875 Only)
Bipolar Zero Error (AD7876 Only)
Full-Scale Error at +25°C
2
Full-Scale TC
2
Track-and-Hold Acquisition Time
DYNAMIC PERFORMANCE
3
(AD7875
ONLY)
Signal-to-Noise Ratio
4
(SNR)
@ +25°C
T
MIN
to T
MAX
Total Harmonic Distortion (THD)
Peak Harmonic or Spurious Noise
Intermodulation Distortion (IMD)
Second Order Terms
Third Order Terms
AD7875/AD7876
1
K, B
L, C
T
12
12
±1
±1
±1
±1
±5
±6
±8
±60
2
12
12
±1/2
±1
±1/2
±1
±5
±2
±8
±35
2
12
12
±1
±1
±1
±1.5/−1.0
±5
±6
±8
±60
2
Units
Bits
Bits
LSB max
LSB max
LSB max
LSB max
LSB max
LSB max
LSB max
ppm/°C max
μs max
Test Conditions/Comments
Typical full-scale error is ±1 LSB
Typical TC is ±20 ppm/°C
70
70
−80
−80
72
71
−80
−80
69
69
−78
−78
dB min
dB min
dB max
dB max
V
IN
= 10 kHz sine wave, f
SAMPLE
= 100 kHz
Typically 71.5 dB for 0 < V
IN
< 50 kHz
V
IN
= 10 kHz sine wave, f
SAMPLE
= 100 kHz
Typically −86 dB for 0 < V
IN
< 50 kHz
V
IN
= 10 kHz, f
SAMPLE
= 100 kHz
Typically −86 dB for 0 < V
IN
< 50 kHz
fa = 9 kHz, fb = 9.5 kHz, f
SAMPLE
= 50 kHz
fa = 9 kHz, fb = 9.5 kHz, f
SAMPLE
= 50 kHz
−80
−80
−80
−80
−78
−78
dB max
dB max
Rev. C | Page 4 of
28
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