Datasheet AD7794, AD7795 (Analog Devices)

6-Channel, Low Noise, Low Power, 24-/16-Bit ∑-Δ ADC with On-Chip In-Amp and Reference AD7794/AD7795 FEATURES Industrial process control Up to 23 effective bits Instrumentation RMS noise: 40 nV @ 4.17 Hz, 85 nV @ 16.7 Hz Blood analysis Current: 400 μA typical Smart transmitters Power-down: 1 μA maximum Liquid/gas chromatography Low noise, programmable gain, instrumentation amp 6-digit DVM Band gap reference with 4 ppm/°C drift typical GENERAL DESCRIPTION Update rate: 4.17 Hz to 470 Hz
The AD7794/AD7795 are low power, low noise, complete
Six differential analog inputs
analog front ends for high precision measurement applications.
Internal clock oscillator
They contain a low noise, 24-/16-bit ∑-Δ ADC with six
Simultaneous 50 Hz/60 Hz rejection
differential inputs. The on-chip low noise instrumentation
Reference detect
amplifier means that signals of small amplitude can be
Programmable current sources
interfaced directly to the ADC.
On-chip bias voltage generator Burnout currents
Each device contains a precision, low noise, low drift internal
Low-side power switch
band gap reference, and can also accept up to two external
Power supply: 2.7 V to 5.25 V
differential references. Other on-chip features include
Temperature range:
programmable excitation current sources, burnout currents,
B grade: –40°C to +105°C
and a bias voltage generator that is used to set the common-
C grade: –40°C to +125°C
mode voltage of a channel to AVDD/2. The low-side power
Independent interface power supply
switch can be used to power down bridge sensors between
24-lead TSSOP
conversions, minimizing the system’s power consumption. The
3-wire serial interface
AD7794/AD7795 can operate with either an internal clock or
SPI®, QSPI™, MICROWIRE™, and DSP compatible
an external clock. The output data rate from each part can vary
Schmitt trigger on SCLK
from 4.17 Hz to 470 Hz.
APPLICATIONS
Both parts operate with a power supply from 2.7 V to 5.25 V. The B-grade parts (AD7794 and AD7795) are specified for a
Temperature measurement
temperature range of −40°C to +105°C while the C-grade part
Pressure measurement
(AD7794) is specified for a temperature range of −40°C to
Weigh scales
+125°C. They consume a current of 400 μA typical and are
Strain gage transducers
housed in a 24-lead TSSOP.
Gas analysis FUNCTIONAL BLOCK DIAGRAM GND AVDD AIN4(+)/REFIN2(+) REFIN1(+) AIN4(–)/REFIN2(–) REFIN1(–) V REFERENCE BIAS BAND GAP DETECT REFERENCE VDD GND AIN1(+) DOUT/RDY AIN1(–) SERIAL INTERFACE DIN AIN2(+) Σ-Δ BUF IN-AMP AND ADC AIN2(–) SCLK LOGIC AIN3(+) CONTROL MUX CS AIN3(–) AIN5(+)/IOUT2 GND AIN5(–)/IOUT1 AIN6(+)/P1 TEMP INTERNAL DV SENSOR CLOCK DD AIN6(–)/P2 VDD AD7794/AD7795 PSW AD7794: 24-BIT ADC AD7795: 16-BIT ADC GND
001
CLK
04854- Figure 1.
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Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS TIMING DIAGRAMS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS RMS NOISE AND RESOLUTION SPECIFICATIONS CHOP ENABLED External Reference Internal Reference CHOP DISABLED TYPICAL PERFORMANCE CHARACTERISTICS ON-CHIP REGISTERS COMMUNICATIONS REGISTER RS2, RS1, RS0 = 0, 0, 0 STATUS REGISTER RS2, RS1, RS0 = 0, 0, 0; Power-On/Reset = 0x80 (AD7795)/0x88 (AD7794) MODE REGISTER RS2, RS1, RS0 = 0, 0, 1; Power-On/Reset = 0x000A CONFIGURATION REGISTER RS2, RS1, RS0 = 0, 1, 0; Power-On/Reset = 0x0710 DATA REGISTER RS2, RS1, RS0 = 0, 1, 1; Power-On/Reset = 0x0000(AD7795), 0x000000 (AD7794) ID REGISTER RS2, RS1, RS0 = 1, 0, 0; Power-On/Reset = 0xXF IO REGISTER RS2, RS1, RS0 = 1, 0, 1; Power-On/Reset = 0x00 OFFSET REGISTER RS2, RS1, RS0 = 1, 1, 0; Power-On/Reset = 0x8000 (AD7795), 0x800000 (AD7794)) FULL-SCALE REGISTER RS2, RS1, RS0 = 1, 1, 1; Power-On/Reset = 0x5XXX (AD7795), 0x5XXX00 (AD7794) ADC CIRCUIT INFORMATION OVERVIEW DIGITAL INTERFACE Single Conversion Mode Continuous Conversion Mode Continuous Read CIRCUIT DESCRIPTION ANALOG INPUT CHANNEL INSTRUMENTATION AMPLIFIER BIPOLAR/UNIPOLAR CONFIGURATION DATA OUTPUT CODING BURNOUT CURRENTS EXCITATION CURRENTS BIAS VOLTAGE GENERATOR REFERENCE REFERENCE DETECT RESET AVDD MONITOR CALIBRATION GROUNDING AND LAYOUT APPLICATIONS INFORMATION FLOWMETER OUTLINE DIMENSIONS ORDERING GUIDE