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TPS54331: stop switching occasionally

Part Number: TPS54331

Hi,

my customer is using TPS54331 to generate 3.3V from 5V input, the schematic is as below:

The output 3.3V is to power C2000 MCU and pull up source of some comparator output. Most of the time the device can work normally. But sometimes the device will stop switching, the waveform is as below:

CH1(YELLOW) 5V input, CH2(BLUE) 3.3V output, CH3(purple) PH pin, CH4(green) BOOT pin.

By zoom out the waveform is:

By doing math BOOT-PH, we can see that the boot capacitor voltage gradually decrease to 2.4V and then the device stop switching.

It seems that the problem is caused by boot capacitor UVLO. But we've no idea why it will behave like this. We start the circuit 100 times, and could see it happen about 10 times.

  • Hi Howard,

    It should be caused by large duty cycle&low Vin.

    When high side is on, boot voltage will decrease. If the On time is too long, it will trigger Boot UVLO.

    You can increase input voltage to verify.

  • Hi, Howard 

    1. You did the (BOOT-PH)? why it is minus?  

    2. From you description, it sounds BOOT cap is discharged when switching, we should check the reason. 

     please check if there is leakage current on BOOT cap. 

    3. Does every board have this issue?