TPS62175 problem

Ronald Jansen

Other Parts Discussed in Thread: TPS62175

Hello,

I built a product using the TPS62175 step down regulator. The prototype is not working and I don't understand why. Can you help me find the problem?

Cin: 10uF/50V MLCC

Cout 47uF/16V MLCC

Lout: 10uH

Vout: set to 3.3V with 47K/150K resistors

Vin: 24V

Enable: connected to Vin

Sleep: connected to Vout

The output voltage is 0V. The switch gives pulses of 300ns at a frequency of 1000hz. There is no short circuit on the output.

FB = 0V

The chip seems to be in sleep mode. But for that it would have to assume that Vout is ok. But Vfb = 0V.

What am I missing?

Thanks in advance.

Ronald

over 8 years ago

0 Michael Helmlinger over 8 years ago

TI__Expert 5055 points

Hi Ronald,

So far its not clear what the issue is.
Could you post your schematic?

Regards,
Michael

0 Ronald Jansen over 8 years ago in reply to Michael Helmlinger

Intellectual 520 points

Hi Michael,

This is the schematic.

0 Michael Helmlinger over 8 years ago in reply to Ronald Jansen

TI__Expert 5055 points

Thanks for the schematic.

Is there a ground connection on the input caps on your board? There is no GND symbol in the schematic.

Regards,
Michael

0 Ronald Jansen over 8 years ago in reply to Michael Helmlinger

Intellectual 520 points

Thanks for the hint. Yes, they share the same 0V. I will correct this on the schematic.

0 Michael Helmlinger over 8 years ago in reply to Ronald Jansen

TI__Expert 5055 points

Ok.

Could you also share your layout of the TPS62175?

A scope plot of Vin, SW, Vout would be also good to have.

Thanks & Regards,
Michael

0 Ronald Jansen over 8 years ago in reply to Michael Helmlinger

Intellectual 520 points

This is the layout. Blue is copper bottom, red is copper top. The board is 1.55mm thick.

I was a bit surprised about the small trace to L5. It seems that I forgot to make this a copper area. But I guess the added inductance and resistance should not cause the problem I am having.

I will make the plots on monday when I am back at the office.

0 Ronald Jansen over 8 years ago in reply to Ronald Jansen

Intellectual 520 points

This morning I was making the plots. But my probe slipped and caused a short, which blew up the TPS62175.

So unfortunately I cannot do anything until it is replaced. I will have a new protoype board made. After which I can continue testing.

0 Ronald Jansen over 8 years ago in reply to Ronald Jansen

Intellectual 520 points

Unfortunately I didn't have time to test for a while. I now tested on the second prototype. Here the TPS62175 did not work at all.

As I already have it working fine in another design I think the schematic and layout should be ok. My guess is that there are floating pads due to soldering problems.

Do you have any specific recommendations on the past mask and solder mask for this design? We currently use a 100um stencil on a HAL PCB. Could it be that the solder paste would be applied too thin?

0 Michael Helmlinger over 8 years ago in reply to Ronald Jansen

TI__Expert 5055 points

I would recommend this application report:

www.ti.com/.../slua271a.pdf

There you will find the right information's for this package.

Regards,
Michael

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TPS62175 problem