Unable to get desired resistance in AD5122A

Hello all,

I'm working AD5122a and set the wiper to maximum (0x7f) and tested resistance between w1 and b1 terminals of AD5122A then i got 0.9 Kilo ohm instead of 100 kilo ohm.

My code: 

i2c_write(0xd0, 0x09);                          // set control register of potentiometer mode, i2c burst mode

i2c_write(0x90, 0x80);                         // set to normal mode

i2c_write(0xc0, 0x00);                        // set to normal mode

i2c_write(0x10, 0x7f);                       // set rdac register with highest value.

AD5122A  -- AD5122ABCPZ100-RL7 

R A,B  ---100 Kilo ohm
Resolution --- 128
Interface --- I2C

Please guide me where I'm doing mistake.

Thanks,

Ashok.

  • Hi

    Did you read back the RDAC1 register to confirm whether the RDAC1 register is updated with 0x7F.?

    Are the resistor terminals connected to any signals ? 

  • Hello vsethia,

    Thank you for quick reply. 

    Did you read back the RDAC1 register to confirm whether the RDAC1 register is updated with 0x7F.?

    Yes, I read rdac1 register by sending command

    i2c_write(0x30, 0x03);                                // set to address of rdac1 with read command

    but i got 0x7e instead of 0x7f. I verified this in debug mode.

    And also changed rdac1 register 0x40 and read the contents of rdac is 64. So, i can able write and read RDAC1 register. 

    Are the resistor terminals connected to any signals ? 

    Terminals of w1 and b1 is connected to OP-Amp of "OPA2320AID" pin numbers between 1 and  2. as feedback resistance of op-amp.

    I tested the resistance between those pins (pin 1 and 2) of OPA2320AID but i got 0.9 kilo ohm.

    Please guide me,

    Thanks,

    Ashok.