bq40z60 ACP current draw

Jim OSullivan

Other Parts Discussed in Thread: BQ40Z60

I'm using a bq40z60 in a custom circuit based on the EVM design. When the charger is disabled, the voltage applied to VAC is reflected accurately in the AC adapter voltage register (after calibration). However, when the charger is enabled, the voltage across the 10k resistor (R14 in the EVM) drops by about 4.7V, from 16.3 to under 12v.

I haven't been able to find a specification for current drain on the 40z60 ACP pin. Can anyone shed light on this?

Should the ACP input resistor (EVM R14) be a lower value?

Thanks.

over 9 years ago

0 ThomasCosby over 9 years ago

TI__Guru 73830 points

Jim
I will check this and get back with you.

Tom

0 Brad Bushard14 over 9 years ago

Prodigy 210 points

Jim,

I see similar behavior with the bq40z60 with variability of 'AC Adapter Voltage' (VACP) when the bq changes modes. It seems when FETs are energized or de-energized there is a jump in ACP voltage, specifically ACFET and CHRG FET seems to influence ACP. My board does not change as dramatic as yours (4.7 V) where I normally see ~1.2 V change.

0 Jim OSullivan over 9 years ago in reply to Brad Bushard14

Intellectual 375 points

Hi Brad - thanks for posting that. Good to know it's not just on our system.

Tom - any news on this? Won't this affect operation of the charger as the VAC voltage gets close to the cutoff voltage?

Thanks.

0 ThomasCosby over 9 years ago in reply to Jim OSullivan

TI__Guru 73830 points

Jim

I do not see this voltage drop on my EVM. I can work with your board.

Tom

0 Austin Hendrix over 9 years ago in reply to ThomasCosby

Prodigy 125 points

Page 8 of the BQ40Z60 datasheet indicates that there is a 30-50k pull-down on the ACP pin. That seems reasonably consistent with the voltage drop you're seeing across R14

0 ThomasCosby over 9 years ago in reply to Austin Hendrix

TI__Guru 73830 points

Austin
The 40 kohm pull-down resistor is only active when the gauge is trying to enter shutdown. I do not see a drop on the ACFET, but I do see a drop across the 10 kohm series resistor in the ACP signal path. This drop is due to the ACFET charge pump.
Tom

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bq40z60 ACP current draw