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DAC8775: VOUT_x, IOUT_x status on some POWER OFF condition

Motoyasu Hattori
Genius 10965 points
Part Number: DAC8775

Hi,

Could you please let us know the VOUT_x, IOUT_x pin status on the following conditions?

 

CASE1:

  • DVDD : Power_OFF
  • AVDD : Powered
  • VPOS_IN_x : Powered
  • VNEV_IN_x : Powered

 

CASE2:

  • DVDD : Powered
  • AVDD : Powered
  • VPOS_IN_x : Powered
  • VNEG_IN_x : Power_OFF

 

On both cases, internal buck boost circuit on DAC8775 is NOT used.   Please advise us.

Thanks and best regards,
M.HATTORI.

  • 0
    TI__Guru 53773 points

    Lucas will provide an answer today.

    Thanks,

    Paul

  • 0
    TI__Expert 4590 points

    Hi,

    Are you asking about the status of the VOUT and IOUT pins when the output is disabled or enabled?

    Thanks,
    Lucas

  • 0 in reply to Lucas Burnette
    TI__Genius 10965 points

    Lucas-san,

    Output is enable.   I am waiting your comments.

    Thanks and best regards,
    M.HATTORI.

  • 0 in reply to Motoyasu Hattori
    TI__Guru* 97595 points

    Hattori-san,


    I haven't had a chance to test this with DVDD off settings, but I don't think that DVDD will affect the DAC for either of the voltage or current outputs. In this test, the internal DVDD is enabled.

    Also, I'm not sure what setting you have for the VNEG_IN_x. When connected, assume that this is connected to GND.

    When in Case 1 (AVDD=VPOS_IN_x=12V, VNEG_IN_x=GND, except with DVDD LDO ON),

    VOUT (0 to 5V range) = +40mV
    IOUT (0 to 20mA range) = 0 mV

    This is not unexpected. The output of VOUT is driven with the VOUT buffer, and it will be a limited to this 40mV similar to an op-amp output driving into the negative rail. If VNEG_IN is lower than ground, I would expect that the VOUT would be able to drive to 0V.

    The IOUT appears to drive the current correctly. I did test the output with the current load of 249Ω and didn't see any incorrect values.

    When in Case 2 (AVDD=VPOS_IN_x=12V, VNEG_IN_x=Floating, DVDD LDO ON),

    VOUT = +280mV
    IOUT = +0.05mV (unloaded)

    With VNEG_IN_x is floating, the VOUT buffer doesn't have its negative supply connected correctly. In this case, the buffer appears to have some pull to the VNEG_IN_x to ground internally so it doesn't just float off. It does seem to have some operation, and it does look like it starts to operate with the code greater than 3000h.

    For IOUT, there does appear to be some amount of offset at the zero code. However it is very small, and it does not appear to affect other output values. Again, I would consider a floating VNEG_IN_x an invalid condition.

    I'm not sure if this is what you are looking for. If you need a different configuration, can you be more specific with the settings being used for the device?


    Joseph Wu