TPS82140: Entery capacitor becomes in short-circuit

Hi Romuald,

Is the input 12V? You may want to probe the input voltage and check if there are any repetitive spikes on the input line above the 16V rating of the capacitor during power up, or during any other transient events.

Kris

Thank you Kris for your answer.

The input voltage is 7,2V (2 Li-SOCL2 batteries) and 3,6V for the output.

i will check tomorrow and come back.

Thank's again !

Romuald

Hi Romuald, did you get a chance to check for high transients on your input?

Hi Kris,

i made measurement on my card. The start up is quiet, tensions grow up slowly. But after few seconds, the TPS82140 goes into an unstable state. i can see oscillations with a big amplitude (13,5V max) ! i think this is caused by the consumption which passes from few mA to about 1A by spikes, during a short time.

Oscillations can be seen on the input and sometimes on the output.

On the card powered by the TPS82140, we have 2 470uF electrochimical capacitors and several other ceramics.

How can i avoid this phenomen ? 

Thank's

Romuald

Correction :

Perhaps the oscillations observed aren't true... i think it's a bad use of oscilloscope. i'm not sure i will verify... and i'll come back to you.

Regards

Romuald

Hello,

OK, the oscillations i see are due to our GPRS communication. It's "normal" to see this fog during transmission with 1GHz BP oscillo.

i did several measures in different conditions (standby of our product, normal consumtion with spikes...) and it's OK for the tension measured on the first capacitor.

When we look for this problem on Internet about X5R capacitor, we can find some issues due to MLCC cracks, because of mecanical stress. Perhaps it's our problem... We will see with our manufacturer.

Thank you if anyone has an idea ?

Best reards

Romuald