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TPS92641: Reducing internal power dissipation.

James Powell
Prodigy 70 points
Part Number: TPS92641
Other Parts Discussed in Thread: LM5122,

I am using the above part in several applications, one of which the supply voltage for the LED string requires circa 60V+.

With my current choice of mosfets and switching frequency, the power dissipation in the device is too high and I have no margin for higher ambient temperatures that I require.

I know I can look at changing the mosfets and lowering the switching frequency but this is not ideal.

a) Can you feed VCC to the device from an external supply with a diode so the internal regulator is not used.  I have used this technique with the LM5122 (page 15 of 5122 data) but not sure if this method can be used for the TPS part.

b) Could I feed Vin to the TPS form a lover voltage, say 12V but still have the have the LED string at 60V.  From the chip block diagram this looks potentially possible.

Many thanks

James

  • 0
    TI__Mastermind 25500 points

    Hello James,

    Yes, you can drive the VCC pin with an external supply. Just be sure that you do not violate the abs max rating of the VCC pin. This is the usual method when power dissipation becomes a concern at high input voltages. Also make sure the supply is capable of sourcing enough current. Each FET will draw Qg*Fsw.

    The second option will not work. The TPS92641 senses from VIN to SW (across the high side FET) for current limit. So VIN has to be at the same potential as the drain of the high side FET. If VIN goes lower than SW you will reverse bias the internal circuitry and the device will misbehave.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 70 points

    Hi Clint

    Many thanks for the very prompt reply and guidance!

    Best regards

    James