BQ40Z60: Understanding GND vs PGND

Mathias Koch

Part Number: BQ40Z60

Hi TI.

I am working on a design using the BQ40Z60 as an in-circuit battery gauge, management and charger. In regards to this, I am not quite sure i understand how PGND vs GND works.

I have attached a schematic of my design, but the question at hand is: Looking at the EVM schematics, i have followed the PGND and GND setup, but i am unsure whether all of the system load (computer, motors etc.) should be referenced to PGND or GND, where GND is directly the battery pack negative.

While I am at it, does my design look like it could work? Did i do anything wrong? It is designed to work with a 3s LIPO battery.

I think im gonna need a hot-plug filter on the DC adapter, but other than that?

Thank you so much,

Mathias Koch4628.Schematics.pdf

over 8 years ago

0 Onyx Ahiakwo over 8 years ago

TI__Guru* 76230 points

Most folks are out for the July 4th Holidays. We should get back to you after the break.

0 Onyx Ahiakwo over 8 years ago in reply to Onyx Ahiakwo

TI__Guru* 76230 points

hi Mathias,
PGND and GND are the differnent grounds for the gauge and the charger/load. You wouldn't want the charger and the gauge portion to have the same ground other wise you will short out the current sense resistor of the gauge and will be unable to measure current as a result.
thanks
Onyx

0 Mathias Koch over 8 years ago in reply to Onyx Ahiakwo

Prodigy 165 points

Hi Onyx

Thank you for your reply.

Looking at my attached schematic, could you point me in the direction of where i have done that? If I actually did, and it wasn't just a general rule :)

Thank you!

Mathias

0 Onyx Ahiakwo over 8 years ago in reply to Mathias Koch

TI__Guru* 76230 points

Hi Mathias,
I was responding to your question on understanding how pgnd and gnd works.

thanks
Onyx

0 Mathias Koch over 8 years ago in reply to Onyx Ahiakwo

Prodigy 165 points

Alright.

So just to be 100% sure.

PGND is the ground related to the charging part (Charging adapter input, switching FETS, BQ40Z60)

GND is the ground reference related to the gauging, and is as such the one to reference for all load in the system (computer, motors etc.)?

Does that sound about right?

Cheers,

Mathias

0 Onyx Ahiakwo over 8 years ago in reply to Mathias Koch

TI__Guru* 76230 points

Hi Mathias,

No, that is not correct. Typically you want all current flowing into or out of the battery to go through the sense resistor so the gauge can measure current. So that mean your load and charger will have the same ground (pgnd), different from the ground of the gauge and battery (gnd)

thanks
Onyx

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BQ40Z60: Understanding GND vs PGND