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TPS5450 TPS5430

Bruno Hadjelis
Prodigy 40 points
Other Parts Discussed in Thread: TPS5450, TPS5430-Q1

Hello,

I successfully used TPS5450-Q1 and  TPS5430-Q1 circuits to provide +5V from a 14V battery voltage.

However, I need to understand and deepen the behavior of the chopper in a mode of failure of the bootstrap capacitor ( pin N°1 BOOT).
What is the behavior of the TPS5450 in case of low voltage at the terminals of  this capacitor (BOOT / PH), with a stable 12V at VIN pin ?

The high-side mosfet could have a thermal runaway before the thermal protection could be active ?

Is there any under-voltage protection on BOOT pin ( Vin = 12v) ?

Thanks in advance for your answering.

  • 0
    TI__Guru**** 191445 points

    The BOOT function is to provide drive voltage for the high side FET.  When the FET is off, the PH node is usually clamped to ground by the catch diode.  Then the BOOT cap is charged by the internal BOOT regulator.  When the high side FET is on the BOOT cap allows the BOOT voltage to be above VIN to keep the high side FET turned on.  There is no BOOT UVLO function on this device.  It can provide sufficient charge for the high side driver with input voltage as low as 5.5 V.  At 12 V input, the BOOT cap is fully charged to the regulated BOOT voltage.

  • 0 in reply to JohnTucker
    Prodigy 40 points

    The questions is about the voltage across this BOOT pin / PH during the FET is ON.

    In case of undervoltage at BOOT Cap what is the behavior of the FET ?

    Thanks

  • 0 in reply to Bruno Hadjelis
    TI__Guru**** 191445 points

    If for some reason the BOOT cap charge is depleted, then the high side FET will turn off as there will be no gate drive.

  • 0 in reply to JohnTucker
    Prodigy 40 points

    Thanks John.

    During a voltage drop across this boot cap, the Rdson is increasing. The voltage across the FET ( Rdson . Current ) is increasing also, and the current limiting circuit switched off the FET. This cycle by cycle current limiting is also a voltage monitoring for the bootstrap cap.

    Bests regards.