TPS54325 output 0V

kerb huang

Intellectual 690 points

Other Parts Discussed in Thread: TPS54325

Hello,

We use TPS54325 to generate DC 3.3V, but TPS54325 output only 0V.

PG pin is low, VBST pin is 5.2V, VCC VIN EN pins are connected to DC 12V, SS pin is 5.5V, VREG5 pin is 5.5V.

why did this happen?

Thank you!

Kerb

over 7 years ago

0 Anthony Lang over 7 years ago

TI__Expert 4875 points

Hi Kerb,

From the voltage level on the pins, the IC is not damaged. Could you help me to check the waveform of SW pin and the voltage level on FB? Also keep in mind to check the solder connection. I need to collect more info to give you an analysis of this issue.

Best
Anthony

0 kerb huang over 7 years ago in reply to Anthony Lang

Intellectual 690 points

Hi Anthony,

FB and SW pins are almost DC 0V.(oscilloscope )

Thank you,
Kerb

0 Anthony Lang over 7 years ago in reply to kerb huang

TI__Expert 4875 points

HI Kerb,

Is it possible that you shown me the schematic? What is the value of the output cap?

Best
Anthony

0 kerb huang over 7 years ago in reply to Anthony Lang

Intellectual 690 points

Hi Anthony,

the following is the schematic.

Thank you,

Kerb

0 JohnTucker over 7 years ago in reply to kerb huang

TI__Guru**** 191445 points

You have probably latched off the switching FETs due to one of the protection circuits. Can we see your start up waveforms? Vin, Vout, SS and SW?

0 kerb huang over 7 years ago in reply to JohnTucker

Intellectual 690 points

Hi John,

why did this happen?

Thank you,
Kerb

0 JohnTucker over 7 years ago in reply to kerb huang

TI__Guru**** 191445 points

I can't be sure without seeing waveforms. But I have seen cases where if VIN ramps up slowly, the output may not be in regulation at the end of 1.7 x SS time. In that case UVP can latch off the output. It is just a suggestion for you to look at.

0 kerb huang over 7 years ago in reply to JohnTucker

Intellectual 690 points

Hi John，

the following are waveform:

channel 1 is VIN, channel 2 is VO,

channel 1 is VIN, channel 2 is SW pins,

channel 1 is VIN, channel 2 is SS pin,

Thank you,

Kerb

0 JohnTucker over 7 years ago in reply to kerb huang

TI__Guru**** 191445 points

Yes UVP protection definitely the problem. You have only 1.8 V or so on the output at the end of 1.7 x SS time. So both high side and low side FET are latched off. You will need to figure out what is clamping the output to 1.8 V rather than regulating to the proper 3.3 V. Possibly some other circuit on you board.

0 Anthony Lang over 7 years ago in reply to kerb huang

TI__Expert 4875 points

Hi Kerb,

Could you also try to take out one 100UF output cap and power on the converter again. Your output cap is too big.

Best

Anthony

0 JohnTucker over 7 years ago in reply to Anthony Lang

TI__Guru**** 191445 points

The output capacitance is much larger than the recommended value. I have tested TPS54325 with output capacitance that large without issue however. It may possibly depend on the ESR. It is wort a try to remove it, but I think your problem lies elsewhere as your output voltage looks like it is clamped to 1.8 V. Do you have a 1.8 V rail in your system? The best thing to try is to completely disconnect the TPS54325 3.3 V output from any load or connection in your system and see if it comes up properly by itself. I have seen issues where there are leakage paths in external circuits which prevent converters from powering up properly.

0 kerb huang over 7 years ago in reply to JohnTucker

Intellectual 690 points

Hi John,

we have solved the problem. solder GND pin of MEMS Oscillator to 3.3V, VDD of MEMS Oscillator to PCB GND.

Thank you,

kerb

Power management

Power management forum

TPS54325 output 0V