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TPS92641: Lowering internal power dissipation

Eric De Vleeschauwer
Prodigy 40 points
Part Number: TPS92641

Application:

Universal high power, high voltage Led-driver to be used in combination with several Ledstrips. Input voltage of the power rail: 65V. Maximum Ledstring-voltage: 40V, Maximum Led-current:2A. Maximum Ledpower:25W

Maximum ambient temperature: 80°C. The complete Led-driver is potted. Maximum measured temperature of the TPS92641: 115°C

Auxiliary 10V power rail available on the board. Switching Mosfets selected for low gate charge.

We want to reduce the temperature of the TPS92641 by reducing the internal power dissipation. As this is an existing design, we want to stay as close as posible to the original design.

Question: can we connect the auxiliary 10V (thru a diode) to the Vcc-pin? Any risk of damaging the controller (for instance because the Vin-pin drops to zero with the Vcc-pin still at 10V)?

Question: can we connect the auxiliary 10V to the Vin-pin with the top-Mosfet, Ron and RUDIM1 connected to 65V power rail? Looks (from the functional block diagram) like the Vin-pin is only used to power the internal LDO and the functional block generating some references.

Eric

  • 0
    TI__Mastermind 25500 points

    Hello Eric,

    This device is designed so that you can drive VCC externally for this reason. So yes, this is the preferred method as long as you stay under the abs max which you are. But your concerns are good too, you want to shut the VCC supply down with VIN because there will be a body diode between the two since it is a linear regulator. But driving VCC externally will for sure reduce dissipation in the 641 IC.

    For the second one, no, it cannot be driven that way. The block diagram isn't clear about this, but you can find it in the text. The current limit protection measures the voltage between the VIN pin and the SW pin as described in the datasheet. So the VIN pin needs to be at the same potential as the drain of the high side FET. If VIN is at a lower potential than SW you can get erratic operation due to current limit and bias currents through other body diodes between SW and VIN.

    Regards,

    Clint