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Adjustable output DCDC

HUGUES MARCEAU
Prodigy 170 points
Other Parts Discussed in Thread: TPS61088, PMP9774, OPA4377

Hi,

I would like to control the voltage output of boost DCDC iC (i.e. TPS61088) with a microcontroller and would like to avoid using an expensive digital trim pot.

Is there common practices that could be recommended?

Kind regards.

  • 0
    TI__Mastermind 40080 points

    Hi,

    Yes, you can aviod to use a digital trim pot.

    1. Please refer to PMP9774, this document illustrates the way to implement the output volatge adjustment;

    2. Since you alreay has a microcontroller, could it output a DC voltage that can adjust the output voltage directly, like the following picture:

    1) Use a DAC voltage from the MCU inseries with a resistor to connected to FB pin;

    2) If the output voltage is only 2-3 points, then use two signal MOSFET, two resisotrs to realize this.

  • 0 in reply to Helen chen
    Prodigy 120 points

    Wow, what a find, I need to do this also.

    If using an MCU DAC output to control the output voltage of the TPS61088 between 6.5-12.5V, what values of R11, R13 and R55 would be required?

    Do I need to buffer the MCU from the feedback pin to protect the MCU? It seems a tad risky to connect a voltage divider which has it's own voltage to an MCU DAC which will attempt to drive a particular voltage.

    Cheers,

    Franc

  • 0 in reply to FnGas
    TI__Mastermind 40080 points

    Hi,

    It depends on the voltage level of the DAC output. Suggest the voltage level should be within 1V, at least 0.1V below the TPS61088's 1.2V reference. So if the DAC range is 0-0.8V, when VDAC=0V, Vo=6.5V, When VDAC=0.8V, Vo=12.4V, then you can choose the resistor value according to the following picture.
    Suggest you use a single amplifier and signal MOSFET as the buffer. Please read PMP9774 in detail, it tells you the calculation step. The difference with the PMP9774 is   that you can delete U3A, U3, U3D in your applicaiton.

    By the way, Could you please share the detailed application information for us? Like in what kind of equipment? Volume? We need to collect these application information at the customer side to better unstanding the marketing needs. You can send the information to me by email, my email address is helen-chen@ti.com

  • 0 in reply to Helen chen
    Prodigy 120 points

    Thanks Helen.

    I'd like to minimize complexity and keep BOM cost as low as possible (the OPA4377 are $3.98ea in Aus). Is it possible to remove the amplifier and connect the output of the MCU DAC directly to the gate of Q1? What are the risks of a direct DAC to Q1 configuration?

    Just in case I don't implement the DAC control, is it possible to replace R0 and R1 with a mechanical potentiometer? If so what specs should I keep in mind when selecting the potentiometer?


    Cheers,
    Franc