LM46002: VOUT does not start when EN is on

Dice-K

Part Number: LM46002

Tool/software:

Hi support team,
It is used under the following conditions.

VIN: 9 ～32V
VOUT: 5V
BIAS: Supplied from VOUT

Power is constantly supplied to VIN.
When initially starting up with EN set to High, VOUT sometimes does not output.
If VIN is turned off once and then turned back on, VOUT will be output.

If VOUT is a negative voltage when EN is turned on, I think BIAS will become a negative voltage.
It is not an inverting buck-boost, but as per the following thread, will it cause malfunction if BIAS is a negative voltage?
I understand that less than -0.3V is outside the specifications.

Is the solution to insert a diode in series with the BIAS pin?

Regards,
Dice-K

11 months ago

0 Richard Fu22 11 months ago

TI__Mastermind 31165 points

Hi Dice-K,

Your application meets the requirement to power the BIAS from VOUT. And yes, you should avoid cases where bias can go negative, but it shouldn't happen with a standard buck converter.

Can you check that VCC voltage is not below UVLO and the EN trace is clean and above the threshold? That would be the first two things to check if output is not regulating at startup.

Schematic is also appreciated.

Thanks,

Richard

0 Dice-K 11 months ago in reply to Richard Fu22

Mastermind 7480 points

Hi Richard,
Thank you for your reply.

I send the schematic and waveforms via a private message.

Best regards,
Dice-K

0 Richard Fu22 11 months ago in reply to Dice-K

TI__Mastermind 31165 points

Hi Dice-K,

Understood. I'll take a look at it there. Let us continue the conversation here.

Thanks,

Richard

0 Richard Fu22 11 months ago in reply to Richard Fu22

TI__Mastermind 31165 points

Hi Dice-K,

As discussed since this situation is hard to replicate, I'll close the thread here and we can open a new thread if there is additional information.

Thanks,

Richard

Power management

Power management forum

LM46002: VOUT does not start when EN is on