TPS70933 failure

Hugo Ordonez

Other Parts Discussed in Thread: TPS709

TPS70933, failure

Does anybody know which are the failure modes for TPS70933?

I have a board with both TPS70933 and TPS70950, the TPS70933 is handling a load of a microcontroller and an AD7190 no more than 35 mA, but in both cases the regulator blew up (regulator output is only 0.7v) , there was smoke in one instance, after two failures, I decided to change the part for a MC33269DT-3.3 , this solved the issues. I really want to keep TPS70933 but I'm unable to explain the part failure, I though that in any cause the curren limiting would kick in.

over 12 years ago

0 Kartik Sinha over 12 years ago

TI__Expert 3300 points

Hi,

Thank you for your post. Can you please describe your circuit more:

Vin?
Peak Iload?
Operating temp?
Is your Vin controlled or are you exceeding the absolute maximum Vin at any time?

A schematic would also help.

Regards,

Kartik

0 Hugo Ordonez over 12 years ago in reply to Kartik Sinha

Prodigy 70 points

Vin: 12v

Peak Load : I assume it's no more than 35 mA

Operating Temp : 25 degrees Celsius

Vin comes from a regulated bench supply.

Are there any failure modes for this part?

0 Kartik Sinha over 12 years ago in reply to Hugo Ordonez

TI__Expert 3300 points

Hi,

Thanks for your reply. Do you have an inductor in the input to this LDO or a long PCB trace or wire that could be causing inductance?

What could be happening, is that when the LDO starts up, to charge the output cap, there is a sudden surge in the input current drawn from the power supply. Because of the inductance in the input line, this huge current surge leads to a large voltage spike which is possibly above the absolute maximum input and this damages your LDO. The max input for this device is 32V which is already pretty high. Can you measure the input pin with a scope and see what the conditions are at startup?

Also is there any other circuit blocks connected in parallel to the LDO input from the same power supply?

Regards,

Kartik

0 Hugo Ordonez over 12 years ago in reply to Kartik Sinha

Prodigy 70 points

No there is not any inductor, I have a PCB with only both regulators

0 Ryan Eslinger over 12 years ago in reply to Hugo Ordonez

TI__Guru 55940 points

Hi Hugo,

The absolute Max for the EN pin on both devices is +7V. By tying EN to IN with a Vin of 12V you are violating this spec.

Very Respectfully,

Ryan

0 Hugo Ordonez over 12 years ago in reply to Ryan Eslinger

Prodigy 70 points

0 Hugo Ordonez over 12 years ago in reply to Hugo Ordonez

Prodigy 70 points

Also could you please point me to a resource that cites the 7 volt figure? I can only see a minimum voltage, but not a maximium one.

0 Ryan Eslinger over 12 years ago in reply to Hugo Ordonez

TI__Guru 55940 points

Hi Hugo,

I found the Absolute Maximum on pg 2 of the datasheet:

Very Respectfully,

Ryan

0 rick rachford over 11 years ago in reply to Ryan Eslinger

Prodigy 20 points

That's too bad. I need a better performance alternative to the Micrel MIC5235 which at first glance the TPS709 series seemed ideal. based on the block diagram and the data sheet I'm assuming the EN input is pulled up to the bandgap reference? At this point a new board lay out isn't an option and my input voltage is a 9 volt battery. Does TI make a similar part with the same footprint/pinout with a sub 5uA Iq to replace the TPS709 that does not have the EN voltage limitation?

0 Ryan Eslinger over 11 years ago in reply to rick rachford

TI__Guru 55940 points

Hi Rick,

Unfortunately we do not have a pin to pin replacement at this time that fits your criteria.

Very Respectfully,

Ryan

0 rick rachford over 11 years ago in reply to Ryan Eslinger

Prodigy 20 points

That's too bad. Ti could have a drop in replacement for the Micrel part in applications that don't need or use the EN line by just not bonding it out. Something for marketing to think about.

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TPS70933 failure