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PDF AD7708 Data sheet ( Hoja de datos )
| Número de pieza | AD7708 | |
| Descripción | ADCs | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
8-/10-Channel, Low Voltage,
Low Power, ⌺-⌬ ADCs
AD7708/AD7718
FEATURES
8-/10-Channel, High Resolution ⌺-⌬ ADCs
AD7708 Has 16-Bit Resolution
AD7718 Has 24-Bit Resolution
Factory-Calibrated
Single Conversion Cycle Setting
Programmable Gain Front End
Simultaneous 50 Hz and 60 Hz Rejection
VREF Select™ Allows Absolute and Ratiometric
Measurement Capability
Operation Can Be Optimized for
Analog Performance (CHOP = 0) or
Channel Throughput (CHOP = 1)
INTERFACE
3-Wire Serial
SPITM, QSPITM, MICROWIRETM, and DSP-Compatible
Schmitt Trigger on SCLK
POWER
Specified for Single 3 V and 5 V Operation
Normal: 1.28 mA Typ @ 3 V
Power-Down: 30 A (32 kHz Crystal Running)
On-Chip Functions
Rail-to-Rail Input Buffer and PGA
2-Bit Digital I/O Port
GENERAL DESCRIPTION
The AD7708/AD7718 are complete analog front-ends for low
frequency measurement applications. The AD7718 contains a
24-bit Σ-∆ ADC with PGA and can be configured as 4/5 fully-
differential input channels or 8/10 pseudo-differential input
channels. Two pins on the device are configurable as analog
inputs or reference inputs. The AD7708 is a 16-bit version of
the AD7718. Input signal ranges from 20 mV to 2.56 V can be
directly converted using these ADCs. Signals can be converted
directly from a transducer without the need for signal conditioning.
The device operates from a 32 kHz crystal with an on-board PLL
generating the required internal operating frequency. The output
data rate from the part is software programmable. The peak-to-
peak resolution from the part varies with the programmed gain
and output data rate.
The part operates from a single 3 V or 5 V supply. When operating
from 3 V supplies, the power dissipation for the part is 3.84 mW typ.
Both parts are pin-for-pin compatible allowing an upgradable
path from 16 to 24 bits without the need for hardware modifica-
tions. The AD7708/AD7718 are housed in 28-lead SOIC and
TSSOP packages.
APPLICATIONS
Industrial Process Control
Instrumentation
Pressure Transducers
Portable Instrumentation
Smart Transmitters
FUNCTIONAL BLOCK DIAGRAM
DVDD DGND
REFIN2(+)/AIN9 REFIN1(+) REFIN2(–)/AIN10 REFIN1(–) XTAL1 XTAL2
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
AINCOM
OSC
AND
PLL
POS BUF
MUX NEG BUF
PGA
REFIN(+)
REFIN(–)
⌺-⌬ ADC*
*AD7708 16-BIT ADC
*AD7718 24-BIT ADC
AVDD
SERIAL
INTERFACE
AND
CONTROL
LOGIC
AD7708 / AD7718
I/O PORT
DOUT
DIN
SCLK
CS
RDY
RESET
AVDD AGND
SPI and QSPI are trademarks of Motorola Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
VREF Select is a trademark of Analog Devices, Inc.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
P2 P1
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., 2001
1 page  
AD7708/AD7718
Parameter
B Grade
Unit
Test Conditions
LOGIC INPUTS (Continued)
SCLK Only (Schmitt-Triggered Input)2
VT(+)
VT(–)
VT(+) – VT(–)
VT(+)
VT(–)
VT(+)–VT(–)
XTAL1 Only2
VINL, Input Low Voltage
VINH, Input High Voltage
VINL, Input Low Voltage
VINH, Input High Voltage
Input Currents
Input Capacitance
1.4/2
0.8/1.4
0.3/0.85
0.95/2
0.4/1.1
0.3/0.85
0.8
3.5
0.4
2.5
± 10
–70
10
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
V max
V min
V max
V min
µA max
µA max
pF typ
DVDD = 5 V
DVDD = 5 V
DVDD = 5 V
DVDD = 3 V
DVDD = 3 V
DVDD = 3 V
DVDD = 5 V
DVDD = 5 V
DVDD = 3 V
DVDD = 3 V
Logic Input = DVDD
Logic Input = DGND, Typical –40 µA @ 5 V
and –20 µA at 3 V
All Digital Inputs
LOGIC OUTPUTS (Excluding XTAL2)5
VOH, Output High Voltage2
VOL, Output Low Voltage2
VOH, Output High Voltage2
VOL, Output Low Voltage2
Floating State Leakage Current
Floating State Output Capacitance
Data Output Coding
DVDD – 0.6
0.4
4
0.4
± 10
± 10
Binary
Offset Binary
V min
V max
V min
V max
µA max
pF typ
DVDD = 3 V, ISOURCE = 100 µA
DVDD = 3 V, ISINK = 100 µA
DVDD = 5 V, ISOURCE = 200 µA
DVDD = 5 V, ISINK = 1.6 mA
Unipolar Mode
Bipolar Mode
SYSTEM CALIBRATION2
Full-Scale Calibration Limit
Zero-Scale Calibration Limit
Input Span
1.05 × FS
–1.05 × FS
0.8 × FS
2.1 × FS
V max
V min
V min
V max
START-UP TIME
From Power-On
From Power-Down Mode
300 ms typ
1
ms typ
Oscillator Enabled
300
ms typ
Oscillator Powered Down
POWER REQUIREMENTS
Power Supply Voltages
AVDD–AGND
DVDD–DGND
DIDD (Normal Mode)
AIDD (Normal Mode)
DIDD (Power-Down Mode)
AIDD (Power-Down Mode)
Power Supply Rejection (PSR)
Chop Disabled
Chop Enabled
AVDD and DVDD can be operated independently of each other.
2.7/3.6
V min/max
AVDD = 3 V nom
4.75/5.25
V min/max
AVDD = 5 V nom
2.7/3.6
V min/max
DVDD = 3 V nom
4.75/5.25
V min
DVDD = 5 V nom
0.55
mA max
DVDD = 3 V, 0.43 mA typ
0.65
mA max
DVDD = 5 V, 0.5 mA typ
1.1
mA max
AVDD = 3 V or 5 V, 0.85 mA typ
10
µA max
DVDD = 3 V, 32.768 kHz Osc. Running
2
µA max
DVDD = 3 V, Oscillator Powered Down
30
µA max
DVDD = 5 V, 32.768 kHz Osc. Running
8
µA max
DVDD = 5 V, Oscillator Powered Down
1
µA max
AVDD = 3 V or 5 V
Input Range = ± 2.56 V, AIN = 1 V
70
dB min
95 dB typ
100 dB typ
NOTES
1Temperature range is –40°C to +85°C.
2Not production tested, guaranteed by design and/or characterization data at release.
3Following a self-calibration this error will be in the order of the noise for the programmed gain and update selected. A system calibration will completely remove this error.
4Recalibration at any temperature will remove these errors.
5I/O Port Logic Levels are with respect to AVDD and AGND.
Specifications are subject to change without notice.
REV. 0
–5–
5 Page 
CS
SCLK
DIN
RDY
CS
SCLK
DOUT
t11 t14
t12
t13
MSB
t15
Figure 2. Write Cycle Timing Diagram
t3
t4 t6
t5
t5A
MSB
t7
t6
Figure 3. Read Cycle Timing Diagram
AD7708/AD7718
t16
LSB
t10
t8
t9
LSB
REV. 0
–11–
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet AD7708.PDF ] | |
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