Document
04856-001
Data Sheet
3-Channel, Low Noise, Low Power, 16-/24-Bit, Σ-Δ ADC with On-Chip In-Amp
AD7798/AD7799
FEATURES
RMS noise: 27 nV at 4.17 Hz (AD7799) 65 nV at 16.7 Hz (AD7799) 40 nV at 4.17 Hz (AD7798) 85 nV at 16.7 Hz (AD7798)
Current: 380 µA typical Power-down: 1 µA maximum Low noise, programmable gain, instrumentation amp Update rate: 4.17 Hz to 470 Hz 3 differential inputs Internal clock oscillator Simultaneous 50 Hz/60 Hz rejection Reference detect Low-side power switch Programmable digital outputs Burnout currents Power supply: 2.7 V to 5.25 V –40°C to +105°C temperature range Independent interface power supply 16-lead TSSOP package
INTERFACE
3-wire serial SPI®, QSPI™, MICROWIRE™, and DSP compatible Schmitt trigger on SCLK
APPLICATIONS
Weigh scales Pressure measurement Strain gauge transducers Gas analysis Industrial process control Instrumentation Portable instrumentation Blood analysis Smart transmitters Liquid/gas chromotography 6-digit DVM
FUNCTIONAL BLOCK DIAGRAM
GND AVDD
REFIN(+) REFIN(–)
AD7798/AD7799
REFERENCE DETECT
AIN1(+) AIN1(–) AIN2(+) AIN2(–) AIN3(+)/P1 AIN3(–)/P2
PSW
AVDD
MUX
IN-AMP
Σ-Δ ADC
GND GND
INTERNAL CLOCK
Figure 1.
SERIAL INTERFACE
AND CONTROL
LOGIC
AD7798: 16-BIT AD7799: 24-BIT
DOUT/RDY DIN SCLK CS
DVDD
GENERAL DESCRIPTION
The AD7798/AD7799 are low power, low noise, complete analog front ends for high precision measurement applications. The AD7798/AD7799 contains a low noise, 16-/24-bit ∑-∆ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. With a gain setting of 64, the rms noise is 27 nV for the AD7799 and 40 nV for the AD7798 when the update rate equals 4.17 Hz.
On-chip features include a low-side power switch, reference detect, programmable digital output pins, burnout currents, and an internal clock oscillator. The output data rate from the part is software-programmable and can be varied from 4.17 Hz to 470 Hz.
The part operates with a power supply from 2.7 V to 5.25 V. The AD7798 consumes a current of 300 µA typical, whereas the AD7799 consumes 380 µA typical. Both devices are housed in a 16-lead TSSOP package.
Rev. B
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AD7798/AD7799
TABLE OF CONTENTS
Features .............................................................................................. 1 Interface ............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Characteristics..................................................................... 6 Absolute Maximum Ratings............................................................ 8
ESD Caution.................................................................................. 8 Pin Configuration and Function Descriptions............................. 9 Output Noise and Resolution Specifications .............................. 10
AD7798 ........................................................................................ 10 AD7799 ........................................................................................ 11 Typical Performance Characteristics ........................................... 12 On-Chip Registers .......................................................................... 13 Communication Register .......................................................... 13 Status Register............................................................................. 14 Mode Register ............................................................................. 14 Configuration Register .............................................................. 16 Data Register ............................................................................... 17 ID Register................................................................................... 17
REVISION .