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TPS92520-Q1: Can I use the two outputs differentially to drive a TEC?

John Peck66
Prodigy 100 points
Part Number: TPS92520-Q1
Other Parts Discussed in Thread: LM3409

We currently use an FPGA to generate complementary PWM signals for a TEC at 300kHz.  We use these to cool detector diodes, and would like to go to higher frequencies to reduce detector noise.  We've tried using dual synchronous buck controllers for this, but we've had problems with controller outputs being able to sink as well as source current.  If we used the outputs differentially, could we use this controller to both heat and cool using a TEC?

  • 0
    TI__Mastermind 28655 points

    Hello,

    Is the TEC an inductive load?

    Or are you looking at just applying a voltage either direction and limit power by PWMing or is this a current drive?  If so an H-bridge driver might be a better way to go.

    It would be good to know the load characteristics and what you are looking at trying to accomplish.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 100 points

    > Is the TEC an inductive load?

    No, this TEC acts like a resistor.

    > Or are you looking at just applying a voltage either direction and
    > limit power by PWMing or is this a current drive?

    I really want to apply variable, bidirectional current through this
    load. The current through the load means more to me than the voltage.
    We're using an H-bridge now -- using an FPGA to generate the gate
    drive waveforms. There are some designs where this is inconvenient,
    and it would be nice to have a standalone PWM current driver.

  • 0 in reply to John Peck66
    TI__Mastermind 28655 points

    Hello,

    I would still recommend an H-bridge and place an inductor in series with the TEC so it can be designed to regulate current, that is if there is enough voltage headroom to do this.  Our parts for driving LEDs aren't meant to regulate current that way.  An H-bridge with current sense in the bottom to regulate current with a control loop or even hysteretic control should work. 

    You might be able to take one of our controllers and figure out how to drive an H-bridge but that might be more complicated than just using a DC brush type H-bridge driver (single four switch H-bridge set up for regulating current).  Using the LM3409 with current sense at the top but you would have to figure out how to switch between the upper P-channel MOSFETs and turn on one of two lower MOSFETs to complete the switching path.  You may also need two schottky diodes across the lower MOSFETs if the body diode isn't ideal for switching at 300 KHz.

    You do need an inductor to regulate current either way.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 100 points

    Thanks for the recommendation.  And thanks for thinking about this.

  • 0 in reply to John Peck66
    TI__Mastermind 28655 points

    Hello John,

    If you have the gate drivers for the high side of the bridge you could use something like the LM3409 to supply the top side of the H-bridge through an inductor, just turn on which ever two MOSFETs for the current direction before (not switching just on).  I would also place a small capacitor across the TEC.  Current sense is on the top side of the LM3409.  There would have to be enough voltage headroom for this.  I still think the correct current regulating H-bridge makes more sense though.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 100 points

    Thanks again.  I'll start looking at Brushed DC motor drivers and post some questions in a different forum.