TPS92641: Is there a work around to achieve soft start when enable UDIM?

Rocky Chen

Part Number: TPS92641

We found an issue when debugging TPS92641 to drive LED strings. To eliminate the output capacitors audible noise, we put small value ceramic caps after Inductor. But it was found a big overshoot current on LED (20A peak. Then stable to 16A as designed LED current) when UDIM from low to high.

To decrease the LED overshoot current, adding more caps after inductor helps. Though it may make some irush current to the cap, but the LED overshoot current did decrease a lot. But adding caps here will bring audible noise.

So we are troubled here........Would you please help advise some ways? If there is a soft start scheme, it should be perfect!

Thanks!

-Rocky

over 7 years ago

0 Irwin Nederbragt over 7 years ago

TI__Mastermind 28655 points

Hello,

You may be able to use the Iadj pin to create a soft-start. The other option is to look at the control loop and improve it.

Regards,

0 Rocky Chen over 7 years ago in reply to Irwin Nederbragt

TI__Expert 8860 points

Hi Irwin

Thanks, Could you share how to improve it via tuning control loop? There is only a Ccomp that could be tuned. Currently, it is 470nF, which is maximum value recommended. So we can only tune it with smaller value to try?

0 Irwin Nederbragt over 7 years ago in reply to Rocky Chen

TI__Mastermind 28655 points

Hello Rocky,

To drastically change it you would need more than just a capacitor. You can try lowering the capacitor, try 0.1 uF or maybe lower and see what it does however it would be best to measure loop stability if you are going to change it significantly.

Regards,

Power management

Power management forum

TPS92641: Is there a work around to achieve soft start when enable UDIM?