LM2575HV: ON/OFF pin question

Mike Jung

Part Number: LM2575HV

Dear all.

I have a question about on/off pin.

when configured as shown in the attached schematic, the output is intermittent when the switch is turned on and the on/off pin is low.

removing 1M of the Vin will eliminate the problem and will not be output when 100k is applied.

I would like to ask you if there are any problems with the schematic

Thanks.

0 Neal Zhang over 4 years ago

Hi,

What's Sig_key_on when the problem happens?

I guess the gate voltage of Q2 is low, so Q2 is not fully turn on, which result the problem.

0 Mike Jung over 4 years ago in reply to Neal Zhang

Hi,

Sig_key_on sends DC 24V to the MCU as divider resistor.

It occurs in some ICs, and removing R33 or R37 eliminates the problem.

Thanks.

0 Neal Zhang over 4 years ago in reply to Mike Jung

Hi,

Yes, I think the reason is Q2 is not fully turned on off as we wanted, because the gate voltage is not high enough.

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