LM5175: LM5175 - Unstable operation, high current draw and excessive temperature

Fotis Panagiotopoulos

Part Number: LM5175

Hi,

We are using LM5175 in one of our new designs. During design we were advised the WEBENCH design and we studied carefully the datasheet.

A few days ago I received the first batch of prototypes for this board. However I face many issues with this regulator. Specifically:

The regulator gets very hot (70-80 °C under no load, Vin 12-24V).
The current draw gets excessive (sometimes more than 300mA @ 24V, with no load).
It exhibits unstable operation, i.e. it randomly cools-down or gets hot again, the current draw has great swings (from 30mA to more than 300mA). All these with no apparent reason.

The results can be reproduced with all 3 of our prototypes, in all working conditions (any Vin), regardless of the regulator's load (tested with no load, and up to 1.5A).

Any idea what may causes this instability?

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78190 points

Would you please show the SW1 and SW2 waveforms, and please specify the load conditions at the same time?

0 Fotis Panagiotopoulos over 7 years ago in reply to Youhao Xi

Prodigy 70 points

I was working on a specific prototype, which the problem was most severe. Unfortunately, the regulator on this prototype died, with no apparent reason.

Now I am working on another prototype, that exhibits a somewhat better behavior. It draws only 100mA. I attach the 'scope screenshot.

Blue is SW1, yellow is SW2, Vin 17V, Vout 12V, no load at output.

0 Fotis Panagiotopoulos over 7 years ago in reply to Fotis Panagiotopoulos

Prodigy 70 points

I changed the output capacitors. I used larger ones, of much lower ESR, and this seems to solved all my issues.

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LM5175: LM5175 - Unstable operation, high current draw and excessive temperature