BQ40Z50-R2: Current sense/Gas Guage

Jeffrey Wright

Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50, BQ40Z80, BQ78350-R1

Hello; I see that the device includes a "Scale Factor" register where I can support my 100AH application, but in section 18.27 it says IPScale Not supported by the gas gauge ?

Also, we use a 100uOhm shunt whereas the datasheet says the device is designed to support 1mOhm to 3mOhm. Can we merely use our high-side current sense amp to drive the current sense pins to +/- 100mV?

Thanks

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

Hi Jeffrey,

No, we don't have scaling in the device. Also the design of the bq40z50 is suitable only for an rsns of 1-3mOhm.

For your applicaftion, we suggest that you use the bq40z80 or the bq78350-R1.

0 Antonio Fadhel over 6 years ago in reply to Batt

TI__Genius 9410 points

Hi Batt,

Even if it's not a built-in feature, could scaling be implemented as described in the following threads?:

https://e2e.ti.com/support/power-management/f/196/t/652759

https://e2e.ti.com/support/power-management/f/196/t/550004

Thanks,

Antonio

0 Jeffrey Wright over 6 years ago in reply to Batt

Expert 2875 points

Hi Batt. I see that the bq78351 supports the current range we need, but the 40z80 still say 1mOhm. I'm unclear as to why a smaller shunt R cannot be used. Will you please replace my ignorance with knowledge on this? I'd surely appreciate it

Thanks!

0 Batt over 6 years ago in reply to Antonio Fadhel

TI__Mastermind 42535 points

Hi Antonio,

Yes, that can technically be done so as to keep voltages below sense threshold.

0 Batt over 6 years ago in reply to Jeffrey Wright

TI__Mastermind 42535 points

Hi Jeffrey,

We are highly dependent on the linearity of the sense resistor for current accuracy. Adding shunts would introduce non linearities in the circuit that can't be easily compensated given the low voltages we use.

However, as Antonio suggested, you can use scaling by artificially calibrating current at 2x or 4x scale. However as mentioned there you need to watch out for AFE protections.

Power management

Power management forum

BQ40Z50-R2: Current sense/Gas Guage