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UCD3138: Why is the reference voltage vout_cmd 6144, not 12288?

Part Number: UCD3138

Hello, I was recently learning the UCD3138HSFBEVM_029 demo board . 

I met a serious problem. 

The reference value I calculated is 1.2V/0.09765625 mV=12288,that is  FeCtrl0Regs.RAMPDACEND.bit.RAMP_DAC_VALUE = 12288;

but the reference value in UCD3138HSFBEVM_029 is 6144.Why?

Please give an answer, thank you。

  • an expert will help you soon.
  • Hi, Here is the way how to get the 6144.

    pmbus_dcdc_config_translated[0].vout_cmd is used for programming the reference DAC. It is given below:

    FeCtrl0Regs.EADCDAC.bit.DAC_VALUE = pmbus_dcdc_config_translated[0].vout_cmd;

    pmbus_dcdc_config_translated[0].vout_cmd is calculated by the below formula:

    pmbus_dcdc_config_translated[0].vout_cmd = ((Uint32)pmbus_dcdc_config[0].vout_cmd * VOUT_DAC_SCALER) >> VOUT_MODE_EXP;

    VOUT_DAC_SCALER is 1034, and VOUT_MODE_EXP is 9.

    Take 6144 into the formula,

    DAC_VALUE = 6144 *1034/512 = 12408

    The DAC LSB = 0.097mV

    The reference voltage is 12408 * 0.097mV = 1.2V.

    Output voltage divider is 10, so it sets output voltage at 12.

    Regards,
    Sean