BQ24617: IS bq24617 is limiting to set lower cut-off threshold of battery to be charged due to V LOWV=1.55V fixed

PRAKASH VISHWAKARMA

Part Number: BQ24617
Other Parts Discussed in Thread: BQ24650, BQ24610, BQ24172, BQ24600, BQ24171, BQ24616, BQ24618

I am using bq24617 IC to charge RRC2020 battery pack and this battery pack is allowing to set battery regulation voltage of 13V. Now, for the designed resistive feedback at VFB pin for 13V regulation voltage the lower cut-off voltage of battery ( Which i need to take care) is somewhere 9.6V due to V LOWV ( Precharge to fast-charge transition threshold) 1.55V (fixed) at VFB pin but actual battery lower cut-off voltage is 8.1V.

Now suppose if i discharge the battery till 8.5V and putted for charging. In this case if VFB pin voltage is not crossing V LOWV threshold during precharge time (30 min) then charger will declare fault. on an whole i won't be able to utilize the full battery capacity (100WH) due to V LOWV=1.55V fixed in side the IC instead of allowing user to set externally.

Kindly suggest me some way to overcome above limitation.

over 7 years ago

0 Steven Bangdiwala over 7 years ago

TI__Expert 8690 points

Hi Prakash,

You would need a comparator to measure if your battery is below 10V, then use the output of the comparator to turn on/off a FET which modifies the VFB resistor ratio.

Regards,
Steven

0 PRAKASH VISHWAKARMA over 7 years ago in reply to Steven Bangdiwala

Prodigy 60 points

Hello Sir, request you to share some sample circuit (Schematics) to understand the operation better.

0 Steven Bangdiwala over 7 years ago in reply to PRAKASH VISHWAKARMA

TI__Expert 8690 points

Hi Prakash,

I have found a simpler and easier way to reduce the precharge region. Please follow this app note carefully. www.ti.com/.../slva473.pdf . It is for the bq24650, but the same can be applied for bq24617 because the battery voltage sensing is similar.

Regards,
Steven

0 PRAKASH VISHWAKARMA over 7 years ago in reply to Steven Bangdiwala

Prodigy 60 points

Sir, I have gone through the app note and it is really very simpler scheme. Thanks for your support. The only last one thing i would like to confirm is that whether this scheme can be be used in "bq24610" also or not. Request you to comment on this.

0 Steven Bangdiwala over 7 years ago in reply to PRAKASH VISHWAKARMA

TI__Expert 8690 points

Prakash,

Yes it will also work for bq24610. Any device which uses a VFB resistor network and precharge threshold can use this type of solution. (bq24610, bq24616, bq24617, bq24618, bq24600, bq24650, bq24171, bq24172)

Regards,
Steven

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BQ24617: IS bq24617 is limiting to set lower cut-off threshold of battery to be charged due to V LOWV=1.55V fixed