BQ24171: Implementation of battery fuel gauge with battery charger

Akilarasan R

Part Number: BQ24171
Other Parts Discussed in Thread: BQ27426,

Hi,

I'm thinking about using BQ27426 (Fuel gauge) in my design along with BQ24171 battery charger. The following is the block diagram of my design.

Please clarify following doubts.

1. If adapter is present, path will be selected to adapter input. Our input will be 12V. We cannot give 12V to fuel gauge because fuel gauge input can accept max upto 6V.

2. If adapter is present, battery will get charged. Fuel gauge cannot determine battery capacity as adapter power path is selected.

Please tell me how I can implement BQ27426 (Fuel gauge) along with BQ24171 battery charger.

over 2 years ago

0 Jeff F over 2 years ago

TI__Guru**** 169756 points

Hi Akilarasan,

The fuel gauge only connects to and is powered by the battery. The ouptput of the BQ24171 charger, SRN, connects to the SRN pin of the of gauge as shown below:

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

But BQ24171's SRN pin is connected to battery as shown in below figure. If i connect gauge's SRN pin to charger's SRN pin, will it shortes both SRN and SRP pins as SRP of battery gauge is connected to battery also. Please give a rough block diagram for easy understanding

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

No. The charger and gauge use the same pin names but the only ones that are tied together are the SRN pins, not the SRP pins.

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

As you said, the following figure is the connection between battery charger and fuel gauge. As you can see, SRN pin of gauge is connected to SRN pin of charger. SRP pin of guage is connected battery pack+ and SRN pin of charger also connected to battery pack+. So, Battery gauge's SRP and SRN pin will get shorted together. How this will work?

0 Akilarasan R over 2 years ago in reply to Akilarasan R

Prodigy 240 points

Hi Jeff,

In typical application, it is mentioned as charger+ and charger- . What exactly are those pins in charger IC ( BQ24171 )

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

Charger+ = charger SRN pin. Charger- is GND.

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Please answer the previous question also.

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

Which question?

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

Please see below modified image from gauge datasheet.

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Please sent me as schematic diagram where charger and gauge is used together.

The above representation is not understandable. As battery's SRP pin and SRN pin are literally shorted together based what you are telling.

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

I do not have a schematic. The pins are not shorted together. There are 2 separate sense resistors, one for the charger and one for the gauge. The output of the charger (SRN and top FB resistor ) connects to the output (SRN) pin of the gauge. In high side sense gauge configuration, the gauge's SRP connects to the battery pack positive side. Positive current for the gauge is discharge current from the pack measured as current going into the SRP side of the sense resistor. Positive current for the charger is charge current going into the SRP side of the sense resistor.

Regards,

Jeff

0 Akilarasan R over 2 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Sorry for asking this question again.

I still have have one doubt. Please tell me about connection of battery gauge's series resistor.

0 Akilarasan R over 2 years ago in reply to Akilarasan R

Prodigy 240 points

Hi Jeff,

I have attached my schematic for your reference.

As you said the output of the charger (SRN and top FB resistor ) which is already connected to battery's positive side(VBATT) should be connected to the output (SRN) pin of the gauge and SRP connects to the battery pack positive side. Here you can see, both SRP and SRN of gauge is connected to same VBATT. Then, where will I connect series resistor?

Please clarify my doubt. I have been stuck at this for a month.

7853.BMS.pdf

0 Jeff F over 2 years ago in reply to Akilarasan R

TI__Guru**** 169756 points

Hi Akilarasan,

The charger has its own sense resistor and the gauge also has its own sense resistor. There are two sense resistors. One sense resistor cannot be shared by the charger and the gauge.

Regards,

Jeff