BQ25171-Q1: resistor for VSET

Hi Ohashi

We do not recommend this configuration. 

What are the customer requirements and why are they considering 11k setting?

Hi John

Belows are the customer's use case.

[Use case]
・Configuration: 2 series lithium-ion battery for backup power supply
・Vin: 8V(7.79～8.53V)
・charging voltage: 7V
・charging current: 800mA
・discharging current: max650mA
・discharging time: 40sec
・battery capacity: 7.22mAh 

They would like to set the charging voltage to 7V with 2 series Li-ion battery configuration. So, they thought that they should place 11k ohm resistor to VSET.

Regards,

Ohashi

Hi Ohashi

Let me check on this and get back to you.

Hi Ohashi

We think it will work form the BQ25171 standpoint:

The batteries will charge to 7V and current will decrease to termination value and unit will enter charge complete --- 171 will see what it expects from a LiFePO4 for charge cycle.

V-BAT_LOWV  2.0V vs 2.8V.

V-BAT_SHORT 1.2V vs 2.2V.

V-OUT_OVP 104% of VSET – when the battery is inserted it could indicate a fault (4.2V vs 3.0V).

BUT not sure how the battery will preform only charged to 3.5V per cell -- need to evaluate this. 

Is battery capacity 7.22mAh or 7.22Ah?

Hi Johns

Thanks for the comments.

"V-BAT_LOWV  2.0V vs 2.8V."

Does this vs mean: V-BAT_LOWV is 2.0V for LiFePO4 and 2.8V for Li-ion battery?

For your question, the battery capacity is 7.22mAh.

Regards,

Ohashi

Hi Ohashi

Yes -- "V-BAT_LOWV is 2.0V for LiFePO4 and 2.8V for Li-ion battery?"

Hi Bill,

Thanks for your reply.

BTW, what would be the other recommended battery charger when they fail to use BQ25171-Q1?

[Use case]
・Configuration: 2 series lithium-ion battery for backup power supply
・Vin: 8V(7.79～8.53V)
・charging voltage: 7V  (< 7.365V = Vin_min:7.79V – VDD_typ:0.425V)
・charging current: 800mA
・discharging current: max650mA
・discharging time: 40sec
・battery capacity: 7.22mAh

Regards,

Ohashi