LMR38020SDDAR will generate a pulse when power loss

Andy Li

Prodigy 10 points

Other Parts Discussed in Thread: LMR38020

Yellow: input of LMR38020, waveform of capacitor, 24VDC

Green: Output of LMR38020, 5V output

Blue: TPS5432DDAR's output, 3.3V

we can see the input of LMR38020's capacitor is charging when power loss. it is very strange, why? what's the loop of charging?

over 1 year ago

0 Hongjia-Wu over 1 year ago

TI__Expert 5280 points

Hi，

I suppose you are talking about power off. Can you zoom in the 3 voltage peaks and see what is the amplitude respectively? Also can you share the circuit schematic?

Regards,

Hongjia

0 Andy Li over 1 year ago

Prodigy 10 points

Sorry I could not public schematic here according to our policy

0 Hongjia-Wu over 1 year ago in reply to Andy Li

TI__Expert 5280 points

Hi,

If that is the case, I can only share with you my guess. There might be large parasitic inductance on the input supply line, and when the power is off, there is no other way that the energy can go and the input cap is charged to make the device on for a short while.

Regards,

Hongjia

Power management

Power management forum

LMR38020SDDAR will generate a pulse when power loss