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Original question:

Amc7904 negative dac o/p voltage

AMC7904

Naruto uzumaki
Prodigy 30 points

Hi,

We followed the procedure to update the voltage to the particular as mentioned in the data sheet.

once we update the dac registers it is updating after we changed the page from page_2 to page_1 only.

please let me know the procedure to update the dac registers.

regrds,

naruto

  • 0
    TI__Guru 54163 points

    Hi,

    The simplest way to update the DAC registers is to use the DAC overwrite mode.  Here are the steps:

    Device Configuration|LUT Configuration Register    13 // this stops the device from being in LUT mode.
    Device Configuration|DAC Overwrite Enable Register    0F // this enables overwrite mode
    Device Configuration|Drive Enable Register    33 // this disables the DRVENx pins from being in control
    Device Configuration|Drive Enable Select Register    33 // this enables the SW drive enable bits
    DACs|DAC0 Overwrite    0800 // these write to the DACs.
    DACs|DAC1 Overwrite    0800
    DACs|DAC2 Overwrite    0800
    DACs|DAC3 Overwrite    0800
    DACs|CLAMP1 Overwrite    0400
    DACs|CLAMP2 Overwrite    0400

    THanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 30 points

    Hi Paul,

    Thanks for the response.

    The above mentioned is for SW drive, but we are using the pins to drive the o/p voltage.

    We re following the below steps to update  the DAC.

    1. Writing to page register(0x7e) = 1 //sets the page to 1

    2. LUT Configuration Register 0x10 //disables the LUT mode.

    3. Configuration 1 Register 0x40 //shutdown the temperature sensors

    4. Interrupt Mode Register 0xC0 //Release DACs from start-up current mode.

    5. Setting the bit of DAC Overwrite Enable Register according to our need.

    6. Change the page to 2.(0x7e =2)

    7. Write to the corresponding DAC overwrite register.

    8. Enable the DRVEN pin.

    After the step 7 the DAC overwrite register is not updating, but the DAC overwrite registers gets updated value only when we change the page from 2 to 1.

    Please let me know why the page register is affecting the updation of the value to DAC overwrite registers.

    Regards,

  • 0 in reply to Naruto uzumaki
    TI__Guru 54163 points

    I have never seen that behavior before.  Are you using I2C or SPI?

  • 0 in reply to Paul_Frost
    Prodigy 30 points

    Hi,

    We are using i2c interface. Please confirm us the above the steps are correct or not?.

  • 0 in reply to Naruto uzumaki
    TI__Guru 54163 points

    My concern is that your I2C is mis-formated.  Perhaps you are missing a STOP or a NACK that would result in the device not latching the value.  Can you take an oscilloscope image where you trigger off of the page change command (step 6 or step 9?) to confirm where the DAC outputs start to slew? It would be interesting to capture the command writing to the overwrite register (step 7) while monitoring the DAC output as well.

  • 0 in reply to Paul_Frost
    Prodigy 30 points

    Hi,

    Sure will do this exercise. This issue is happening in the multiple boards. Only one of the board is working fine without the above issue. One more observation is that after i2cset to page 1 and i2cdump of the reg, DAC registers are updating.Not just with the i2cset.

    Regards