TPS54425 Open Loop

Simon Scurrell

Other Parts Discussed in Thread: TPS54425

Hello,

I'm currently testing a circuit which is using the TPS54425. The schematic is as-per the datasheet however L=3.3uH and the resistor values where chosen to give an output of 5V.

There is a 4A fuse in the output rail and the feedback VFB is fed from the other side of the fuse if that makes sense, however VO is fed from the non-fused side.

I was having some issues with the circuit powering up and so I removed the 4A fuse. Doing this however effectively disconnected the feedback to the convertor. My question is really could this open loop operation have damaged the device? Reason being that I have since replaced the fuse but now the TPS54425 does not produce a regulated output. EN is high and VREG5 is 5V, however Vout = 0V.

Any thoughts would be welcome. I've attached the circuit diagram.

Regards

Simon

over 11 years ago

0 Simon Scurrell over 11 years ago

Prodigy 30 points

I've managed to get some waveform data which may be of use. The device now seems to be starting up but then seems to switch off and the output starts discharging.

Attached is the waveform capture:

Yellow - 12V

Blue - EN

Pink - Vout

Green - PG

0 JohnTucker over 11 years ago in reply to Simon Scurrell

TI__Guru**** 191445 points

I would recommend connecting both the feedback and VO before the fuse. Also, can you include the SW node in your waveforms?

0 Simon Scurrell over 11 years ago in reply to JohnTucker

Prodigy 30 points

Hi John,

Thanks for your quick response. I will amend the circuit as you recommend.

I've attached some additional waveforms. This time the green waveform is showing the SW1 output. The 3 waveforms just show the same signals at various levels of zoom.

The waveforms were captured without the modifications you mentioned.

4162.TPS54425 Waveforms.zip

Regards,

Simon

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TPS54425 Open Loop