TPS62177 burning at start-up

Serdar Köse

I followed a design on Webench to convert 24 Vdc to 3.3 Vdc.

Schematics is the same but changed the layout a little bit

I am having a serious problem on the highlighted part (24V in), my modules are fried up, I often see a flame. I tested 20 modules, 10 of them are burnt with a flame.

Here are some examples of the modules. Either the highlighted line burns or the IC explodes.

I check by a DMM that there is no short circuit between Vin-Vout-GNDs. I inspected the connections with a microscope that looked fine.

Here is how I test the DC-DC converters. I supply 24V from a PSU, and place 1.8 M ohm resistor between Vout and ground to measure the voltage by an oscilloscope. (I know red should be used for V, not for Ground, it was just closest wire to me)

I suspected flux to reduce the resistance between the Vin - Ground, so I cleaned the boards, but the problem remains.

It seems like the board drawns too much current somehow, does anyone have a guess/idea what could be the problem?

over 9 years ago

0 Peter Meaney over 9 years ago

TI__Mastermind 31580 points

Hi Serdar, this post belongs in the non isolated dc/dc forum, I will move it and one of my colleagues will pick it up there.

Regards

Peter

0 Serdar Köse over 9 years ago in reply to Peter Meaney

Genius 3360 points

Thank you Peter, I am looking forward to hearing from TI's experts.

0 Chris Glaser over 9 years ago in reply to Serdar Köse

TI__Guru*** 148130 points

Thanks for posting your schematic and layout.

With the long wires from your input supply, I think you need more Cin. You can measure the Vin voltage at the IC to see it going above 30V. Here is a blog I wrote about this: e2e.ti.com/.../what-is-that-giant-tantalum-cap-on-the-input-of-the-evm

0 Serdar Köse over 9 years ago in reply to Chris Glaser

Genius 3360 points

Hi Chris,

Thank you for the answer and the link. It is informative.

On my application, 24V source will be wired up to DC2DC module by a 3.5 meter cable (22 or 24 awg) - load consumes about 30 mA.

In this case, is it better to place a diode or something like this to not to have any overshot problem?

I read that the capacitor selection depends on the application, but I would appreciate to know that what would be your best guess about the capacitor value? Would 22 uF sounds fine or 100 uF? (It is my responsibility if anything goes wrong).

Do you recommend to use MLCC to have a longer life time of the DC2DC?

0 Chris Glaser over 9 years ago in reply to Serdar Köse

TI__Guru*** 148130 points

The best solution is to have the input supply soft start instead of hot plug. If this is not possible, then you need to somehow protect the IC from an OV. A cap with ESR is one way to snub the hot plug event, while a TVS is another possibility. Finally, with such a low current, you might add a resistor in series with Vin to damp things.

There is a transient model on the product page, so you could simulate the cable and added capacitance with this.

0 Serdar Köse over 9 years ago in reply to Chris Glaser

Genius 3360 points

Thank you Chris. I appreciate for the high quality answer.

I will test your suggestions.

The webench design I refer is on http://webench.ti.com/webench5/power/webench5.cgi?DesignId=79&base_pn=TPS62177&app=

I couldn't find where to select the cable length (and type?). Could you please tell me where do I define it?

0 Chris Glaser over 9 years ago in reply to Serdar Köse

TI__Guru*** 148130 points

There are transient models here: www.ti.com/.../toolssoftware The forum for software tools is here: e2e.ti.com/.../

Power management

Power management forum

TPS62177 burning at start-up