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AMC60804: IDAC no load voltage test

Part Number: AMC60804

Hi team!

If AMC60804 IDAC is no load and power supply works, IDAC output voltage is 0 or 1.8V. Is this phenomenon normal?

  • Supplement:

    AMC60804 with no load on IDAC

    1.IDAC output voltage is automatically adjusted to PVDD due to unstable high accuracy recovery of ADC monitor even when DACIN setting= 0?That is, even without a load at DACIN 0, the output voltage per IDAC could be 0V or PVDD?
    2.In addition to detecting that the Alarm signal enters Protection protection, If IDAC external load short without detecting alarm signal at full load 150mA, will it automatically enter protection and power down?

  • Hi Hale,

    Can you elaborate on your initial question? Are you seeing the IDAC output voltage go to both 0 or 1.8V depending on certain conditions? If so, what conditions cause the output to be at 0V and what conditions cause the output to be at 1.8V? You can set unused/unloaded IDACs in power down mode so that the outputs are forced to 0V. 

    Just to confirm, is your PVDD 1.8V? 

    The IDACs will not enter power down mode if there is a load short unless the alarm function is used. If the output is shorted to PVDD then the output will go to 0mA because the compliance voltage is not being met:

    Best,

    Katlynne Jones

  • Hi Katlynne!

    The supply power is VDD1,2=3.3V,  VIO=3.3V, PVDD=1.8V, VCC1,2=3.3V. As the customer set IDAC=0, no load, some IDAC output voltage go to 0 and some IDAC output voltage go to 1.8V on one device. The customer need to use the VDAC, IDAC and they test the device. And they found that IDAC without load would be 0 or about PVDD. So is this phenomenon normal?

    As figure 6-44 shown, DAC output from PVDD shouldn't be PVDD when output current is 0(open load). You mean that the only chance is that the output is shorted to PVDD. Am I understanding this correctly?

  • Hi Hale,

    I will check the first question with the designer. Do they see this behavior when the IDACs are set in power down mode?

    The figure represents the output current vs headroom. In this figure the output is set to full scale (150mA) and the plot shows how the current regulation ability decreases as the headroom decreases. I don't think this is relevant to your first question. There is no built in short circuit power down unless you are using the alarm feature. The IDAC output will inherently go to 0 when shorted to PVDD because the compliance voltage is not being met as shown in figure 6-44.

    I will let you know when I hear back.  

    Best,

    Katlynne Jones 

  • Hi Hale,

    Here is the explanation:

    This is a unipolar current DAC. It sources current from PVDD to the load.

    This current DAC has offset in the range of ±500uA typical. When the offset is negative, it will turn itself off for code=0.  This is because the IDAC is unipolar. It cannot output a negative current. When the output is off, it is tri-state and any load will pull it to ground.

    When the offset is positive (i.e. 500uA), for code=0, the current source will source 500uA into no load and will pull itself to the supply.

    Best,

    Katlynne Jones