BQ76PL455A-Q1: bq76pl455a-Q1 Battery Monitoring chip NPN LDO is not working properly

Hi Suriyaprakasam,

Thank you for providing the circuit.... it seems as if it did not attach correctly. Can you try again?

Hi David Wiest,

Please find circuit diagram below

Thanks Suriyaprakasam,

Can you check your connections of VP and NPNB?

I think the schematic looks ok at a glance...unless I missed something, you followed our recommendations pretty well I think.

So, we move on to the next areas to look....

Now, I am concerned about NPNB (pin that drives the bjt) and VP (where voltage is "sampled" and input to BJT control loop).. this could be something layout related (noise coupling, parasitics, etc) causing problems, or manufacturing related (ie, poor solder connections/vias. etc).

Are you measuring the 8.5V at the pin of the BJT? or at the VP pin on the pl455? They should be the same, but i think that it is worth checking.

Regardless of how it happened...this IC is undoubtedly damaged. If VP is regulating at >8V, then VDIG and VIO will be fried, along with the internal circuits they support.

Is this a one-off, or something you are consistently seeing?

Hi David,

Thanks for your response.

Yes you are right i am getting constant 8.5V output at Vp, VDIG, VDIO

I have one more question on NPN LDO

BMU Wake up is required to Turn On NPN LDO? or VTOP voltage is suffuicient?

Can we measure the Die temperature of the Chip by reading a some of the special registers?

Thanks & Regards,

Suriyaprakasam C

Suriyaprakasam,

The VDIG and VIO circuits in the device will most definitely be damaged with a constant 8.5V, i would recommend replacing the IC.

VTOP should be present, but a wakeup pulse is required for the regulator to turn on.

You can measure both the digital die temp, as well as the analog die temp by including them as a part of the ADC measurements.

Setting bit 7 and bit 6 of the CHANNELS register includes the die temperature readings.