input current bandwidth of the BQ34z100

todd johnson

Other Parts Discussed in Thread: BQ34Z100, BQ76920, BQ27200, BQ2083, BQ26231

concern about the current sensing input bandwidth of the bq34z100. A/D conversion update is approx. 1sec. The changes in the current could be in the 10's of Hz ( e bike motor controller) and contribute to SOC of the battery. Chip uses a delta sigma for the a/d and is continuously running. Not that familiar with this type, but never seen a sample&hold used with them like with SAR types. Will the bandwidth of the current signals be limited to the conversion rate and lower missing the higher frequency content? or during that 1sec conversion, signals in the 10's of Hz be averaged in the result. Understand that much higher frequencies need to be filtered.

over 10 years ago

0 ThomasCosby over 10 years ago

TI__Guru 73830 points

Todd,

The gauge does accumulate the charge over the 1 second period and reported as the Current. Spikes will contribute to the charge, but the magnitude of the spikes will not get captured.

Tom

0 todd johnson over 10 years ago in reply to ThomasCosby

Prodigy 70 points

Thanks Thomas for the quick response. Much appreciated. Todd

0 todd johnson over 10 years ago in reply to ThomasCosby

Prodigy 70 points

Hi Tom,
could i do better in performance (resolution and temperature drift) if i used one of your 24bit delta sigmas, precision reference, and amp gain block to amplify the 200mv across the current sense resistor to scale to reference? just after the current value. thanks - todd

0 ThomasCosby over 10 years ago in reply to todd johnson

TI__Guru 73830 points

Todd,

I have not seen anyone do that and I am not sure that it will improve. You could try it and see how it works. We have seen hall sensors used for high current applications.

Tom

0 todd johnson over 10 years ago in reply to ThomasCosby

Prodigy 70 points

Hi Tom,

Plan on using the BQ76920 just for the coulomb counter, nothing else, no cells will be connected. As far as I can see, if I connect the Vbat terminal to a minimum of 6 volts, that should be enough to power the chip. Is there anything I should be aware of? It will interface to a PIC power by 5 volts. trying to short out the signals levels between the two.

Thanks Tom,

Todd

0 WM5295 over 10 years ago in reply to todd johnson

TI__Guru 54715 points

The bq76920 ADC can be turned off and the VCX inputs can be left at 0V safely. The part is not characterized to operate in that manner but should be able to operate that way. The temperature measurement also stops when the ADC is turned off.
The CC is a 16 bit integrating system as described in the datasheet, it can run independent of the current protection thresholds and the voltage measurement ADC.

0 todd johnson over 10 years ago in reply to WM5295

Prodigy 70 points

Does TI make a part that is solely for coulomb counting independent individual cell connections that might be better suited for my application? The battery pack can range between 48volts to 400volts.

0 ThomasCosby over 10 years ago in reply to todd johnson

TI__Guru 73830 points

If you just want a coulomb counter, then the bq26231 may work. We also have a few CEDV type gauges that just use coulomb counters. The bq27200 and bq2083 can be configured for multi-cell.

Power management

Power management forum

input current bandwidth of the BQ34z100