BQ34Z100: Different ground system

Bhanu Indu Sekhar Muppalla

Part Number: BQ34Z100

Hello Team,

We wanted to integrate the BQ34Z100 IC into our BMS board. We are having some confusion about the different ground system.

We are using a 4 layer board.

BAT- will be a copper pour on front copper and Pack - will be a copper pour on front copper connected to the BMS ground(Internal Layer) through VIA .

The BMS Ground has the charger ground and load ground.

We wanted to know if the grounds shown in the BQ34Z100 Circuit also connect to the BMS Ground or should it be an isolated ground .

1) If they connect to the same BMS GROUND , what happens to the net tie

Would really appreciate the help

Thanks

over 2 years ago

0 Shirish over 2 years ago

TI__Guru 57697 points

The ground of bq34z100 is connected to Bat-

There is a sense resistor between PAck- and Bat-, therefore cannot connect to same ground

0 Bhanu Indu Sekhar Muppalla over 2 years ago in reply to Shirish

Intellectual 400 points

Hello Shirish,

So all the grounds shown in the schematic of Bq34z100

1) will have its own separate ground from the BMS Ground and the BQ34Z100 Ground will connect to BAT-

Is this right?

2) Also is it necessary to use separate analog and digital ground for the schematic or is one ground plane enough

Thanks

0 Bhanu Indu Sekhar Muppalla over 2 years ago in reply to Bhanu Indu Sekhar Muppalla

Intellectual 400 points

Hello Shirish,

just wanted to confirm this. Could you kindly give me an update on this

Thanks

0 Steven Yao over 2 years ago in reply to Bhanu Indu Sekhar Muppalla

TI__Genius 12215 points

Hi, Bhanu

Yes, the BAT- shall be used as GND for BMS circuit and bq34z100, and it is always a good practice to separate GND for analog and digital circuit and connect them in a single point

0 Bhanu Indu Sekhar Muppalla over 2 years ago in reply to Steven Yao

Intellectual 400 points

Hi Steven,

Ok so BAT- is the ground for the BQ34Z100 Circuit and PACK- is the ground for the charger and load

But if we use BAT- as the ground for the BQ34Z100 then the SDA and SCL lines will have to cross a split between BAT- GND and PACK- GND as the BMS MCU would be connected to PACK- GND.

Could you kindly help me figure this issue out

Thanks

0 Steven Yao over 2 years ago in reply to Bhanu Indu Sekhar Muppalla

TI__Genius 12215 points

Bhanu

If the load is powered by the battery, then all current should always return to BAT-. If the load is power by another power supply and the I2C pull up is at the system side, and external power is charging the battery, then the current flow through the pull up resistor should return to the external power supply.

0 Bhanu Indu Sekhar Muppalla over 2 years ago in reply to Steven Yao

Intellectual 400 points

Hi Steven,

On our BMS board we have load power connection and charger connection. So the current needs to flow from BAT- to PACK- through the sense resistor right?

0 Steven Yao over 2 years ago in reply to Bhanu Indu Sekhar Muppalla

TI__Genius 12215 points

For the current to flow from BAT- to PACK-, This is the case when the battery is being charged, but the current for I2C pull up is not included under this scenario. And the pull up current is so minor to cause any error to the gas gauging

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BQ34Z100: Different ground system