AD5252 no output reflected on wiper terminal

Hi,

                 I'm trying to interface AD5252 B1(1 K) variant chip to replace a mechanical potentio-meter. I'm Using I2C to interface AD5252 with a controller. I can able to read & write using I2C on the AD5252 chip. The issue is that i cannot see any change on the wiper terminal of the chip after writing the 0x01 (RDAC1) & 0x03 (RDAC3) registers with a data bit data between 0 to 255.

whenever i read the 0x01 register i see only 128 always.

connections :

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Grounded AD0 & AD1 pins to use i2c slave address as 0x58 for write & 0x59 for read.

A1 is pulled to high & B1 is connected to gnd.

Please anyone help me on this issue.

  • 0
    •  Analog Employees 
    on May 31, 2017 6:34 AM

    Hi lingaraj,

    It seems that you are not able to write to the RDAC registers since you are always getting 128 during readback. What is the status of the WP (write protect) pin? The WP pin should be at logic 1 for you to update the RDAC registers or the EEMEM.

    (see EEMEM Write Protection section of the data sheet. page 18).

    Best regards,

    Rainier

  • Hi Rainier,

                    Yes you are right. WP is initially grounded & checked it by connecting it to high, I can able to see what i write in RDAC. Thank you. But if i write 0x00, across wiper still i can read 86 Ohms. Is it possible to make it to zero Ohms. I've read about the tolerance stuff in the datasheet, can't able to understand it properly. What i understand was Wiper will always have a ideal resistance of 75 Ohms?

  • 0
    •  Analog Employees 
    on May 31, 2017 10:21 AM

    Hi Lingaraj,

    The wiper resistance can't be zeroed out as this is the on-resistance of the switch connected between the W pin and the tap point on the resistor string. The 75 ohms wiper resistance is only a typical value and may vary depending on your circuit conditions. See Figure 9 on the data sheet which describes how the wiper resistance typically changes with VDD and VBIAS (Vab).

    Regarding the tolerance specification, for a 1kohm AD5252, the initial tolerance at ambient temperature should be within +/-30%. So upon power-up, the resistance across A & B terminal should be within 700-1300 ohms.

    Best regards,

    Rainier 

  • Hi rosario,

                         Will the tolerance change with respect to Vdd & Vbias, temperature or is it constant?.Thank you in advance.

  • 0
    •  Analog Employees 
    on Jun 6, 2017 12:08 PM

    Hi Lingaraj,

    The initial tolerance may vary with different VDD & VBIAS but it should still be within +/-30%.

    The resistance will vary if the temperature changes. See the Resistance Temperature Coefficient specification and typical performance curve (Figure 12) to assess how much the resistance would change with the change in temperature.

    Best regards,

    Rainier