TPS53355 problems

Denny Ambrosini

HI all.

My design requires an 30A @ 0.65V output.

I follow the istructions in webench and the instructions for layout in datasheet.

The components are the same that webench software advice.

When i light up the circuit there is no output voltage, in the LL pin i can see the controller switching but at the output of the inductor i have 0V.

PGOOD 0V, VBST 5V, EN 4.2V, VREG 5V.

Maybe the iductor is too far from IC?there are 25cm of distance.

I know thats difficult to reply this demand but, anyone can tall me what are tipical errors using this chip?

The schematic is ok, I m sure! connections in layout are ok.

I think the problem is at start, circuit cannot reach the 0.65 V , VFB 0V consequently PGOOD 0V.

Farther after 15 seconds everything shut down(I can no longer see the ic switching in LL node).

I wish anyone can help me.

Thanks

over 11 years ago

0 JohnTucker over 11 years ago

TI__Guru**** 191445 points

25 cm is way to far for the inductor. The circulating loop from LL to the inductor, output capacitors and back to ground should be made a small as possible. Usually the trace from LL to the output inductor is less than 1 cm. Can you post your schematic and layout?

0 Denny Ambrosini over 11 years ago in reply to JohnTucker

Prodigy 60 points

0 Denny Ambrosini over 11 years ago in reply to Denny Ambrosini

Prodigy 60 points

The LL and VOUT trace are too small for 30A, this is a problem I know. The circuit can also work with a 15 A load.

I post Waveforms.

Thanks

0 Denny Ambrosini over 11 years ago in reply to Denny Ambrosini

Prodigy 60 points

VFB vs. LL

EN vs. LL

PGOOG vs. LL

VBST vs. LL

VIN vs. LL

VOUT vs. LL

MODE vs. LL

TRIP vs. LL

VREG

0 JohnTucker over 11 years ago in reply to Denny Ambrosini

TI__Guru**** 191445 points

Those waveforms do not look at all normal. If I read this correctly, the horizontal resolution is 250 usec per division. You should see a regular pulse train of 500 kHz for LL signal. It should be rectangular pulses of duty cycle = Vout/Vin. You may have to start over with your layout. i would recommend prototyping your design on an EVM with a known good layout.