LM22680: Current Rise to 3.1A when start up

Zhihong Huang

Part Number: LM22680

Hi team,

After the testing the current in the point shown below, it was found that the current rushed to 3.1A for a short period of time when the power was just started and the duration was 173.5uS.

1. Is the current waveform normal at this point? Why does it rush to 3.1A?

2. What risks does it cause if it is abnormal? What can be done to solve this problem？

The current waveform part is enlarged as follows：

Best Regards,

Wesley Huang

Email: wesley-huang@ti.com

over 4 years ago

0 Andy Chen over 4 years ago

TI__Mastermind 27045 points

Hi Zhihong,

The circuit startup voltage is about 15V with 120K and 20K divider on EN pin, output is zero at startup point, so the converter will switch at Ton-min for several cycles to regulate the output to track SS pin voltage, you can see the Ton is 78ns and current peak is 2.8A which match data sheet spec. well.

if the loop is unstable for Vin=15V to Vout=1V or lower conversion, then the duty cycle may be unstable as you observed.

You can test it by removing R218 and R220 to see if any improvement

B R

Andy

0 Zhihong Huang over 4 years ago in reply to Andy Chen

TI__Intellectual 1550 points

Hi Andy,

Thanks for your reply.

I can't understand " output is zero at startup point, so the converter will switch at Ton-min for several cycles to regulate the output to track SS pin voltage, " and I also can't see any description about the start up in the datasheet.

Could you please explain this sentence more specifically?

Best Regards,

Wesley Huang

Email: wesley-huang@ti.com

0 Andy Chen over 4 years ago in reply to Zhihong Huang

TI__Mastermind 27045 points

Hi Wesley,

I will close this thread after we talking on phone.

B R

Andy

Power management

Power management forum

LM22680: Current Rise to 3.1A when start up