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TPS92515HV: Charging C_BOOT at charged high capacity C_OUT condition

Karel Krajca
Prodigy 30 points
Part Number: TPS92515HV

In case of active BOOT UVLO, internal sink 5 mA is connected to discharge output capacitor. Then, C_BOOT is charged from VCC and the IC starts. However, in case of high capacity C_OUT (hundreds of uF), the discharge time is very long.

 

Is it possible to short SW node to GND for a very short time (approx 1 us; when IC is disabled by PWM low) to charge C_BOOT and then release PWM to start the IC operation? In this case, inductor current increases and after disconnection of SW, it will flow through the internal MOSFET to the input capacitor.

 

My question is:

Is internal MOSFET capable of conducting reverse current? It is a one pulse after switch on with C_OUT charged, IL,peak<100mA (Vout=40 V, L=470 uH). Per my opinion, it should not be a problem due to a body diode of the MOSFET.

Thank you

Karel

  • 0
    TI__Mastermind 25500 points

    Hello Karel,

    Yes, that is valid. The device will actually switch on an internal switch to do just that when boot uvlo is hit, but if you try to turn on at the wrong time it can have issues if you have very large output capacitance. So you can pull down SW at any time yourself to make sure that boot is charged for the next cycle.

    Regards,

    Clint