TPS54525: Intermittent starting

Chris Moon18

Part Number: TPS54525

Hey Everyone

I have a design for the TPS54525 based on a WebBench design with 11-13v input and 5v 4a output.
The issue is that sometimes it will work and output the correct voltage, other times it will fail and not output any voltage.
I have tried a different chip and replaced all the other components on the board multiple times just in-case its a failed component and nothing changed, It will still fail to work a majority of the time.
I have tried it under a 2amp load and with no load.
I have another design on the same board for 3.3v output that is copied and pasted from the 5v design and that works flawlessly, it only seems to be the 5v design that is affected.
I have attached pictures of the schematic and the board below.

If anyone can spot any potential issues in the schematic or the design, or suggest some tests i should perform, that would be fantastic.

Thank you for your time.
Chris

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over 7 years ago

0 Iven Su over 7 years ago

TI__Expert 8245 points

Hi,

Are 2amp load and no load good under 5V output? How do you connect SW to L3? Please give complete layout of all components.

0 Chris Moon18 over 7 years ago in reply to Iven Su

Prodigy 100 points

Hi Iven,
Thank you for your reply.
When the 5v out works, it works without issue whether its under load or not, the load doesn't appear to make a difference.
I have attached a new screen shot of the design with L3 marked.
I hope this makes things a bit clearer
Chris

0 Iven Su over 7 years ago in reply to Chris Moon18

TI__Expert 8245 points

Hi

The values and layout look fine. Do you capture some waveforms like SW and output when failure? They are now important to indentify the issue.

0 Jason Wang (BSR-MV) over 7 years ago in reply to Iven Su

TI__Genius 9550 points

Chris,
I noticed that EN connects to VCC via R11 in your schematic. Guess this is the root cause.
1. if VCC ramp up slow, the device will enter UVP and latch, so probe VCC waveform and check. (refer datasheet page 8: Over/Under Voltage Protection)
2. Remove R11, pull EN high after VCC ramp up to 12V. check if the issue can be resolved. if yes, suggest update your schematic: add resistor divider at EN pin: When VCC ramp up to about 9V, EN voltage is 1.6V accordingly.

0 Jason Wang (BSR-MV) over 7 years ago in reply to Jason Wang (BSR-MV)

TI__Genius 9550 points

Chris,
EN Pin has internal resistor to GND 440k(typical), so you can increase R11 to 1M ohm. Check if this changing can slove your issue.

0 Chris Moon18 over 7 years ago in reply to Jason Wang (BSR-MV)

Prodigy 100 points

Hi Jason,
Thank you for your help.
I will check this as soon as possible and update the results.
Chris

0 Chris Moon18 over 7 years ago in reply to Jason Wang (BSR-MV)

Prodigy 100 points

Hi Jason,
Thank you for that suggestion, It appears to have fixed the intermittent output issue,

However, I seem to have come across another issue, Im not sure if its ok to post in this thread or to make another.

The new issue is that the power supply now works so long as it is turned on before any current is drawn, However, if i draw current the moment the power supply is started, it fails to output any voltage at all.

I have had a look through the datasheet but cant seem to find any information about why this would happen.
Do you have any indea?

Chris

0 Jason Wang (BSR-MV) over 7 years ago in reply to Chris Moon18

TI__Genius 9550 points

Chris,
please open a new thread for this question. Post the VIN and Vout waveform for analysis. thanks!

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TPS54525: Intermittent starting