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TPS92641: High power buck LED driver with high side sensing?

Morten Hjerde
Prodigy 200 points
Part Number: TPS92641
Other Parts Discussed in Thread: LM3409, LM3409HV,

Hello

We are using the LM3409HV with shunt FET in two commercial products. We now need higher power but are running into heat issues with the LM3409. The sense resistor seems to be the main cause of efficiency loss, but the diode and PMOS also contributes.

We are looking for a driver that can power a rather large bank of LEDs. Vin is 48 volt, Vf is 42 volt and the If is 3-5A. We are doing color mixing with 5 colors and the PWM duty cycle needs to be very precise. We are using 12 bit resolution. (I.e we are using 5 buck drivers to power the five banks of different color LEDs and controlling the duty cycle of each color to produce a final color or spectrum.)

It looks like TPS92641 with shunt FET might be a suitable part. Due to space restrictions on the emitter board we do not have room for separate return paths for the five led banks. High side sensing would allow for that.

1. Is there a way to adapt the TPS92641 for high side sensing?

2. Is there a different part better suited for this?

Thanks

/Morten

  • 0
    TI__Mastermind 25500 points

    Hello Morten,

    The TPS92641 cannot be adapted to high side current sense without adding a second control loop which would be difficult and add a lot of components. However, if you need high side sensing you should easily be able to do 5A thermally with the LM3409 with careful component selection. This is a high duty cycle application, nearing 90%, so going with a synchronous controller really will not buy you much in efficiency or thermally. It may even make the dissipation worse in the IC since it has to supply VCC current to two FETs instead of just one.

    The key will be the FET. If you can find a good combination of as low a gate charge as possible along with as low an Rds(on) as possible the LM3409 should be able to handle it. At such high power levels it may just require you to lower the switching frequency to reduce AC losses. The AC losses will be one of the most significant factors at 48V input since they are directly proportional to V^2.

    Regards,

    Clint