LMR14020: Sometimes it locked at 20V at output instead of 15V during a power-on event

Kaushik Prajapati

Part Number: LMR14020

Respected Sir,

I have used LMR14020 in one of my design. You can see it below-

PROBLEM: Normally, the PCBs are working fine but sometimes it gives 20V(OP) instead of 15V. Again I restart the Power supply again it is working fine.Randomly, Sometimes it is giving 20V at PP1.

I have checked EN voltage it was showing 1.9V which is enough to turn on my switcher.

At Pin 5 I got around 0.8V it was also correct. I don't understand why it locked at 20V(OP) sometimes during the power-on event.

over 7 years ago

0 Andy Chen over 7 years ago

TI__Mastermind 34185 points

There is resistor divider on EN pin, pls remove low side 10K and retest the circuit to see if problem solved.

B R

Andy

0 Varunesh Kumar over 7 years ago in reply to Andy Chen

Intellectual 940 points

Hi Andy
Thanks for your reply .

I've another two questions :
LMR 14020 has a Over Voltage Protection that switches off the High side MOSFET
when the Vref touches 109% ; and remains off till it drops to some 107% .
Why is that circuit not active when the nominal +15V goes to some 20 V ?
This is a potentially dangerous condition !!

Secondly ; removing that 10K disables the Enable function .
To keep the Enable function active ; what should one do ?
Decrease the Resistor Values from 10K / 100K to lower ?

Best regards
\
Varunesh

0 Andy Chen over 7 years ago in reply to Varunesh Kumar

TI__Mastermind 34185 points

Hi Varunesh,

Pls send me email at andy.chen@ti.com to have more detail discussion on this.

B R

Andy

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LMR14020: Sometimes it locked at 20V at output instead of 15V during a power-on event