bq76pl536q1 reading error

Chong Ding

Other Parts Discussed in Thread: BQ76PL536, BQ76PL536EVM-3, BQ76PL536A-Q1, BQ76PL536A, BQ76PL536-Q1

i recently build a board w/ referencing to the EVM-3 schematic. basically let the Bq measures a series of 6 battery's voltage. however, the voltage reading from the Bq doesn't seems to match the battery's actual voltage (measured w/ a DMM), the Bq's reading seems always about 50mV lower than the cell's actual voltage. i checked the Vref, REG50 w/ a DMM, which reads 2.5v and 5v as expected. has anyone seen the same?

i also got COV fault error in this setup where i set the COV threshold at 4.2V. how can it get triggered when the Bq reads only 4.13v? the actual voltage is about 4.18

over 10 years ago

0 Stephen Holland over 10 years ago

TI__Intellectual 2795 points

Can you please share which version of the datasheet you are working with?

There have been older revisions of the bq76PL536 datasheet that had recommended schematics that have since been updated in newer versions of the datasheet (use this one). One example difference is the connection of VC0 to GND and cell1-. The older schematics had a series 1k resistor and cap to VSS on the VC0 signal, whereas newer recommendations are to have a direct conenction of VC0 to cell1-, without a cap to VSS.

You could also share your schematic for me to review.

0 Chong Ding over 10 years ago in reply to Stephen Holland

Intellectual 410 points

i'm reference to the doc i found in this forum which seems to be the latest. 1538.HPA507E6 bq76PL536EVM-3 BINDER.

the VC0 is connected to vss (through a 0 ohm resistor). for the cap, do you mean there should be no cap connects between the vc0 and vss? i found there is one 0.1uf in both the above schematic and the evm3 board (C23)..

0 Stephen Holland over 10 years ago in reply to Chong Ding

TI__Intellectual 2795 points

That schematic shows a 1k resistor (R1) in series from VC0 to cell1-.

Please refer to the schematic in the datasheet linked above as the best recommendation.

0 Chong Ding over 10 years ago

Intellectual 410 points

that's interesting. the DS you shared is dated 2011 while the schematic i used was released around 2013 if i remember correctly and that matches with the actual evm3 board. one thing i noticed that, i'm using the latest version chip (bq76pl536q1) while on the evm3 board it seems to be the older bq76pl536.

0 Stephen Holland over 10 years ago in reply to Chong Ding

TI__Intellectual 2795 points

Neither of those are the latest version of the IC... The latest is bq76pl536A and bq76pl536A-Q1. The bq76pl536 and bq76pl536-Q1 are both not recommended for new designs.

The EVM is older and still has the older device on it.

Sorry for all of the confusion, but please just refer to the latest datasheets for the best recommendation.

0 Chong Ding over 10 years ago in reply to Stephen Holland

Intellectual 410 points

i tried VC0 -> Vss but still got the same result.

0 Stephen Holland over 10 years ago in reply to Chong Ding

TI__Intellectual 2795 points

What is the gauge and length of the connecting wire to your battery?

0 Chong Ding over 10 years ago in reply to Stephen Holland

Intellectual 410 points

my wire is 22 and about 7". but don't think it's relevant because when i say actual voltage, i measured it at the input of the chip not on the battery.

0 Stephen Holland over 10 years ago in reply to Chong Ding

TI__Intellectual 2795 points

I cannot say why it does not work for you... I have an EVM board setup here and I see only ~<2mV of error. Only a small error is expected, and that is only due to the harness, connector and external circuit influence.

I appears like a GND is potentially not connected properly. Is there any chance you can share your schematic or at least double check your board for any pins that may not be connected properly?

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bq76pl536q1 reading error