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AD5758 reprogramming between current to voltage modes

Hello,

I would like to know how reprogramming between current mode (DPC current mode) to voltage mode (DPC voltage mode)  should be properly performed.I thinks that procedure described in data-sheet is not sufficient enough, because it does not take changing DCDC_CONFIG1 register into account. This register must be  changed in order to change DCDC_MODE from DPC current to DPC voltage mode.

  • Hi Dawid,

    The section of the datasheet you referred to is describing the process of changing the current output range, not changing between voltage and current mode.

    To change from current to voltage mode (the same flow should be taken to change from voltage to current):

    1. Write to the DAC_INPUT register. Set the output to 0 mA.
    2. Write the the DAC_CONFIG register. Disable the output (OUT_EN = 0).
    3. Write to the DCDC_CONFIG1. Set up the dcdc converter mode. Wait 300 us for the 3 wire communications to complete.
    4. Write the the DAC_CONFIG register. Configure the output range, slew rate and internal/external RSET (RSET is used for current output mode) keeping OUT_EN = 0. 
    5. Write to the DAC_INPUT register. Set the DAC to 0 V (0x0000 in unipolar range, 0x8000 in bipolar range).
    6. Rewrite the same word to the DAC_CONFIG register as in Step 4 except, this time, with the OUT_EN bit enabled. Allow 1.25 ms minimum between Step 3 and Step 6; this is the time from when the dc-to-dc is enabled to when the VIOUT output is enabled.
    7. Write the required DAC code to the DAC_INPUT register.

    Regards,

    Valerie

  • Hi Valerie,

    thanks for quick answer, I would try to implement as you've advised. A few more follow-up questions

    1. Regarding step 1. What should I write to DAC_INPUT in case of unipolar mode or 4-20mA mode ? Is it 0x8000 and 0x0000 ( in the end 4mA) consecutively ?

    2. Regarding steps 2,4,6 , should I wait 500us or poll CAL_MEM_UNREFRESHED flag ?

    Regards,

    Dawid

  • Hi Dawid,

    1.For unipolar mode write 0x0000, you will either get 0 mA or 4 mA (4-20mA range) as you said.

    2. After step 4 wait 500us or poll the CAL_MEM_UNREFRESHED flag. This wait is required for the internal calibrations to complete when change the output range or output mode. The 1.25ms wait mentioned  in step 6 is to ensure the DCDC voltage has fully configured and settled before enabling the output. 

    Regards,

    Valerie