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LM25118-Q1: LM25118-Q1

Malek Hattab
Prodigy 10 points
Part Number: LM25118-Q1

Hello,

LM25118-Q1 is used in our design to provide 12V/5A at the output from input 8V~33V. The design is tested many times, the response is good when no load and full load conditions are applied over the entire input range.

UVLU is connected to two resistors to achieve 5V voltage divider network and enable signal is powered from the same input using two diodes oring inputs: 1. manual switch 2. PMOS controlled by MCU signal.

The problem is when input voltage is high (lets say > 26V), the system is working fine with no load and full load conditions. after that, when trying to toggle an external switch to enable the power supply (testing), IC will be damaged, and output voltage drops to 3.7V even at no load condition (the same behavior has been observed for many boards). Also the internal bootstrap diode is shorted. 

What is exactly the reason behind this problem and how we can solve it? The problem at the start-up with high input voltage after toggling on the switch. The following image shows the power supply circuit, some components are not populated (DNI) and the input is protected against reverse polarity and overvoltage transients, etc.

 

  • 0
    TI__Guru 59415 points

    Hello Malek,

    Do you mean, there is a switch on the DC_BAT voltage? Can you observe DC_BAT and DC_12V when you toggle the switch?

    In generall toggling switches causes normally bouncing, so might this be the issue as parasitic inductances can cause really high voltages when switches are toggled.

    Best regards,
    Brigitte

  • 0
    Prodigy 10 points

    Hi Brigitte,

    No, the toggle switch is connected between ignition_in signal and main input voltage (before the protection circuit). So VIN and UVLO pins always powered and enable pin is controlled.

    Anyway, I replaced the capacitor at SS pin with higher one to increase the soft start time up to 120ms. It works fine at startup with the desired maximum input voltage, I will continue testing on many boards.

    Do you have any recommendations?

    All the best,

  • 0 in reply to Malek Hattab
    TI__Guru 59415 points

    Hello Malek,

    The SS capacitor limits the current in the power stage during startup. Damage could for example happen if the inductor current is going high enough to force the inductor into saturation. Especially at startup, the inductor current will increase fast as the output capacitors are empty, if the softstart is too short.

    Best regards,
    Brigitte