LM27762: IC damaged when input battery is discharged – What Could Be the Cause?

danielb

Part Number: LM27762

Tool/software:

Hi everyone,

I'm using the LM27762 to generate dual rails of +3V and –2V, each supplying up to 100 mA. The input is a single-cell Li-ion battery, so the input voltage can range from about 4.2V down to something about 3.0V (or less) during discharge.

The LM27762 is damaged (no more +3V and –2V output voltages) when the battery is almost fully discharged. According to the datasheet:

The input voltage range is 2.7V to 5.5V
UVLO kicks in at 2.4V (off) and 2.6V (on)
The negative rail is generated via a charge pump + LDO, which has a dropout voltage of ~30 mV and output resistance of ~2.5Ω at 100 mA

I suspect the problem might be related to insufficient headroom for the negative rail or UVLO triggering, but I’d appreciate any insights from those with experience using this IC.

Has anyone encountered similar behavior with the LM27762?
Any suggestions on how to make the circuit more robust as the battery discharges?

Thanks in advance!

2 months ago

0 Febin 2 months ago

TI__Mastermind 25430 points

Hello,

How many devices were damaged?

What is the ambient temperature?

Could you share some scope plots?

Regards,

Febin

0 danielb 2 months ago in reply to Febin

Intellectual 270 points

Hi Febin,

Only the LM27762 is malfunctioning. The ambient temperature is around 23 degrees C. We don't have scope plots, but the output voltages measure by the voltmeter are wrong: 2.765V (correct is 3V) and 0.664V (correct is -2V). The curious thing is that today the circuit was working properly again for a couple of hours on a fully charged battery. Then it stopped again. How could we diagnose the circuit?

0 Febin 2 months ago in reply to danielb

TI__Mastermind 25430 points

Hi Daniel,

Looks like the device is not really damaged but does not get the sufficient input voltage due to the discharging.

Can you please measure the lowest Vin it reached during the discharge?

Thanks,

Febin

0 danielb 2 months ago in reply to Febin

Intellectual 270 points

Dear Febin,

We did not measure the lowest Vin yet, but it is sure it goes below 3V. My point is that the IC is not working properly anymore, even when the battery is fully charged (Vin=4.2V). Is there a way to "reset" the IC or is it really damaged?

0 Febin 2 months ago in reply to danielb

TI__Mastermind 25430 points

Hi Daniel,

Maybe the IC is damaged already. You can check the pin resistance to confirm...

Thanks,

Febin

0 danielb 2 months ago in reply to Febin

Intellectual 270 points

Thanks for the reply, Febin.

What is the pin's IC are you refering to?

Do you suggest any protection in the circuit to avoid damaging the IC when the battery is discharged?

0 Febin 2 months ago in reply to danielb

TI__Mastermind 25430 points

Hi Daniel,

The device will not be damaged because it hit UVLO...Maybe something else caused this...

You can measure all pins to GND to check the resistance. For eg: Vin to GND or Vout to GND etc

Thanks,

Febin

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LM27762: IC damaged when input battery is discharged – What Could Be the Cause?