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Original question:

DAC53004: OUT voltage saturates at 1.8V even though 0V is asked (force-sense configuration with MOSFET)

DAC53004: Unexpected ramp down of the OUT signal

Aurelie Duval
Prodigy 150 points
Part Number: DAC53004

Hello,

I am using the DAC53004 to control the current in a load with a force-sense configuration with a MOSFET:

We are doing pulses of 50us/250us, with about 20ms rest in-between. Once the pulse is done, we set the DAC-X-DATA registers to 0 and we cut the 9V (so Vd = 0V).

It means that when we cut the 9V, the FB0 sees 0V. At this moment, I can observe a ramp down on the OUT signal. I couldn't find in the datasheet any explanation for this behaviour. I was expecting it to go down to 0V faster. This is what I am seeing: Blue is FB0 and Green is OUT0.

Do you have an explanation for that? is there a way to make the OUT0 go to 0V quicker?

Best Regards,

Aurélie

  • 0
    TI__Mastermind 30728 points

    Hi Aurélie,

    Again, please share a full schematic. OUT0 in the DAC is the output of the amplifier. It adjusts itself so that the voltage at FB0 is equal to the value you configure in the data register. Please also measure Vd or the 9-V supply voltage on the scope. they likely have the same slope as OUT0 as the 9V supply ramps down. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 150 points

    Hi Katlynne,

    Here is the schematic:

    The supply of the DAC and the 9V supply are separated on my test board.

    There is no ramp on the 1V8 nor the 9V, we actually use the signals PMOS_G_A and PMOS_G_B to make our pulses.

    The ramp on OUT0 starts when the PMOS are disabled/opened.

    Best Regards,

    Aurelie

  • 0 in reply to Aurelie Duval
    TI__Mastermind 30728 points

    Hi Aurelie,

    Thanks for the schematic. I understand that the PMOS is turning the 9-V supply to the NMOS on/off. So you are doing this as well as changing the DAC-X-DATA value to 0? Is it possible to measure the drain of the NMOS? It seems like the FB is responding when the new value is written to DAC-X-DATA, so the OUT pin must be responding to something else as it goes to 0 when you remove the 9-V supply. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 150 points

    Hi Kaltynne,

    I will do the measurement again alter once we get the final PCB. I will also try to play with the VOUT-PDN register instead of asking for 0V.

    If the issue is still there, I ll come back to you in few weeks.

    Thanks for your help.

    Best,

    Aurelie