AD7731 Analog Devices, AD7731 Datasheet - Page 36

• Manufacturer Part Number: AD7731
• Description: Low Noise, High Throughput 24-Bit Sigma-Delta ADC
• Manufacturer: Analog Devices

Specifications of AD7731

• Resolution (bits): 24bit
• # Chan: 3
• Sample Rate: 5MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni
• Ain Range: (2Vref/PGA Gain) p-p,(Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: DIP,SOIC,SOP

AD7731
CONFIGURING THE AD7731
The AD7731 contains twelve on-chip registers which can be accessed via the serial interface. Figure 5 and Figure 6 have outlined a
flowchart for the reading and writing of these registers. Table XIX and Table XX outline sample pseudo-code for some commonly
used routines. The required operating conditions will dictate the values loaded to the Mode and Filter Registers. The values given
here are for example purposes only.
Write 03 Hex to Serial Port
Write 1332 Hex to Serial Port
Write 02 Hex to Serial Port
Write B174 Hex to Serial Port
Wait for RDY Low
Write 02 Hex to Serial Port
Write 9174 Hex to Serial Port
Wait for RDY Low
1
CHANNEL = 4 Hex
CH_LOOP: MODE = 2177 Hex
MODE = MODE AND CHANNEL
Write 02 Hex to Serial Port
Write MODE to Serial Port
Wait for RDY Low
Write 11 Hex to Serial Port
Read 24-Bit Data From Serial Port
Increment CHANNEL
If CHANNEL = 7Hex Then Set CHANNEL = 4 Hex
Loop to CH_LOOP
This operation is not necessary if the default values of the Filter Register are the values used in the application.
Table XX. Pseudo-Code for Looping AD7731 Through Three Fully-Differential Channels
Table XIX. Pseudo-Code for Initiating a Self-Calibration after Power-On/Reset
1
1
/* Writes to Communications Register Setting Next Operation as Write to
Filter Register*/
/* Writes to Filter Register Setting a 1 kHz Output Rate in nonCHOP
Mode*/
/* Writes to Communications Register Setting Next Operation as Write to
Mode Register*/
/* Writes to Mode Register Initiating Internal Full-Scale Calibration for
0 V to +1.28 V Input Range on Channel Pair AIN1/AIN2*/
/* Wait for RDY pin to go low to indicate end of calibration cycle*/
/* Writes to Communications Register Setting Next Operation as Write to
Mode Register*/
/* Writes to Mode Register Initiating Internal Zero-Scale Calibration for
0 V to +1.28 V Input Range*/
/* Wait for RDY pin to go low to indicate end of calibration cycle*/
/* The part has now completed self-calibration and is in idle mode*/
/* Sets a Variable Called CHANNEL*/
/* Sets a Variable Called MODE */
/* Logical AND of Both Variables */
/* Writes to Communications Register Setting Next Operation as Write to
Mode Register*/
/* Writes to Mode Register Setting Continuous Conversion Mode for 0 V
to +1.28 V Input Range on Channel Determined by CHANNEL Variable*/
/* Wait for RDY pin to go low to Indicate Output Update*/
/* Writes to Communications Register Setting Next Operation as Read
From Data Register*/
/* Read Conversion Result from AD7731’s Data Register*/
/* Increments Channel Address*/
/* Resets Channel Address*/
–36–
REV. A
REV. 0