TPS54308: Buck regulator over-current problem

Roman Chak10

Part Number: TPS54308

Hi, I designed a buck regulator shown below. I have received my prototypes. When I test them I can't increase input voltage above 4.6V. If I set voltage higher than 4.6V I get an overcurrent condition on my power supply and a couple of seconds later TPS54308 gets damaged. I do not have any load applied. Can anyone help me to figure out the issue? My circuit is shown below.

Thank you,

over 6 years ago

0 Sam(MPAA) Zhang over 6 years ago

TI__Mastermind 19080 points

Hi Roman,

Theoretically, TPS54308 has over current protection itself. If there is a short on the output, the part should enter hiccup mode. I've two questions,

Q1: You mentioned the part is damaged, could you help to confirm if there is a short between SW and GND? Or between SW and VIN?

Q2: Does the part work well in some VIN range below 4.6V?

Thanks a lot!

Best Regards,
Sam Zhang

0 Roman Chak10 over 6 years ago in reply to Sam(MPAA) Zhang

Intellectual 450 points

Hi Sam, the following pins are shorted to ground:
SW
BOOT
VIN
The 3.3V supply works below 4.6V and also I removed the 5V TPS54308 and 3.3V line worked fine up to 20V input. Something is wrong with my 5V buck regulator.

Thank you

0 Roman Chak10 over 6 years ago in reply to Roman Chak10

Intellectual 450 points

Hi Sam, for some reason on the 5V line pin 3 and pin 6 get shorted. Can you help me with that?
Thank you.

0 Roman Chak10 over 6 years ago in reply to Roman Chak10

Intellectual 450 points

It looks like the high side power switch gets shorted.

0 Sam(MPAA) Zhang over 6 years ago in reply to Roman Chak10

TI__Mastermind 19080 points

Hi,

Are SW, Boot, VIN all short to ground? Or just VIN shorts to Boot? If the high side MOSFET is shorted, there should be a short between VIN and SW pin.
When you are measuring the short, please take the bode diode and ESD protection diode into consideration, you can swap the probe to confirm if it is a short or a diode in forward direction.

By the way, did you try to do an A-B-A test with the normal part on 3.3V power rail?

Best Regards,
Sam Zhang

0 Roman Chak10 over 6 years ago in reply to Sam(MPAA) Zhang

Intellectual 450 points

Hi Sam, right now I have pins 3,6,2 shorted together. It fails different each time. Sometimes SW pin gets shorted to the GND. Sometimes 3 and 6 get shorted together, and it happens only on 5V line.
What would happen if the boot capacitor is 1uF instead of 0.1uF?
What is A-B-A test?

Thank you

0 Sam(MPAA) Zhang over 6 years ago in reply to Roman Chak10

TI__Mastermind 19080 points

Hi Roman,

With 1uF boot cap, it will take longer time to charge the cap to the boot threshold voltage at power-up. You can try but I don't think that's the cause for this issue.

For A-B-A test, I mean you may try to put the good part from 3.3V rail on 5V rail.

0 Roman Chak10 over 6 years ago in reply to Sam(MPAA) Zhang

Intellectual 450 points

Hi Sam, I replaced bad component several times.

Thank you

0 Roman Chak10 over 6 years ago in reply to Roman Chak10

Intellectual 450 points

Hi Sam, I need to resolve this issue. It stops my production line. Can you recommend what I need to check?
Thank you

0 Sam(MPAA) Zhang over 6 years ago in reply to Roman Chak10

TI__Mastermind 19080 points

Hi Roman,

The typical rising VIN UVLO value is 4.1V. Is there any output on the 5V power rail when VIN is 4.1~4.6V? Could you post things below or send them to me by email?

1. Waveform of VIN, SW, VOUT as VIN increase TO 4.6V?
2. Layout for the 5V power rail?

My email is sam.zhang@ti.com. Thanks!

Best Regards,
Sam Zhang

0 Sam(MPAA) Zhang over 6 years ago in reply to Roman Chak10

TI__Mastermind 19080 points

Hi Roman,

Also, when and how was the part enabled during the start up?

0 Roman Chak10 over 6 years ago in reply to Sam(MPAA) Zhang

Intellectual 450 points

Hi Sam, I left the EN pin floating. So it gets enabled as soon as power is applied.

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TPS54308: Buck regulator over-current problem