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DAC081C081: Current Source for Boost control

Ambroise Suter
Expert 3860 points
Part Number: DAC081C081
Other Parts Discussed in Thread: DAC53701, DAC53204, DAC53202

Hello,

We are planning to use the DAC081C081 to adjust the output voltage of the LM51571 via the FB pin.

Similar to this application note: How to Dynamically Adjust Power Module Output Voltage (ti.com)

Can you share details on the output stage of the DAC? does it have any resistors to GND always on?

Can it be damaged with reverse current?

Thank you and best regards,

Ambroise

  • 0
    TI__Mastermind 29698 points

    Hi Ambroise,

    The DAC output is only grounded when in power down mode. On powerup, the DAC output is 0V (not grounded) which will still cause an un-intended output on the LM51571 until you are able to update the DAC output. For this reason, we recommend the DAC53701 or DAC53204 for these applications. Both are Hi-Z output when the device powers on which sets the LM51571 to the nominal output until the DAC output is powered on. The DAC53204 also has a Hi-Z output even when VDD is powered off. 

    The FB pin of boost converters typically only have a small leakage current and the current required to boas the FB resistor network is very small. What type of reverse current are you expecting? The DAC081C081 can source/sink current depending on what load is connected, but will lose it's ability to regulate the output voltage beyond a certain load. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    TI__Expert 3860 points

    Hi Katlynn,

    Thank you for your detailed response, we will opt for the DAC53202 in that case. 
    We expect max 400uA on the FB pin. The reverse current would be quite small. Should we add a resisitor on the output? Any minimum size we recommend?

    Best regards,
    Ambroise

  • 0 in reply to Ambroise Suter
    TI__Mastermind 29698 points

    Hi  Ambroise,

    Yes, you will need a series resistor. 

    This app note describes how to calculate the three resistors:

    Voltage Margining and Scaling Circuit with Voltage Output Smart DAC

    You already have Rtop and Rbot chosen so you can skip to choosing the series resistance and the output range of the DAC to acheive the LM51571 output range you want. 

    We are working on releasing a calculator tool to help with that calculation, but it's not quite ready yet. If you have any trouble please let me know and I can help you out. 

    Best,

    Katlynne Jones