BQ40Z50-R2: Grounding Scheme; AGND/CHGND/GND

Christopher Timperio

Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50

Hello,

I am designing a power management module with the BQ40z50 IC and am trying to determine how to keep the specified grounds performing well. It seems that there are 3 main grounds; AGND, CHGND, and GND. I understand for CHGND and GND they should be kept separate and that together with PACK+; CHGND is essentially your PACK- reference.

However, for AGND, should this also be totally isolated from any board grounds and IC ground (GND and CHGND)? Or is there another way to connect this to your system, through a 0ohm resistor to GND for instance?

Thanks

Chris

over 5 years ago

0 Damian Lewis over 5 years ago

TI__Mastermind 34775 points

Hello Chris,

Yes AGND should be connected to GND with 0-ohm resistor with power rating that can handle the current to blow the fuse, if fuse is used. IN the case you don't want to have 3 grounds, AGND can be combined with GND.

0 Christopher Timperio over 5 years ago in reply to Damian Lewis

Prodigy 120 points

Hi Damian, thanks for the info. What are the consequences of connecting AGND to GND? Is it slightly more noisy or have some other influence?

0 Damian Lewis over 5 years ago in reply to Christopher Timperio

TI__Mastermind 34775 points

Hello Chris,

There's no consequence, since GND should be a quiet ground as well. We have combined AGND and GND on new designs with out any issues. The separate AGND was to ensure noise on the ground doesn't falsely turn on the NMOS and blow the fuse. That's extremely unlikely as NMOS gate drivers' ground reference is GND. There's a pulldown resistor and cap as extra insurance against falsely blowing the fuse. When the fuse is blown, a catastrophic event already occurred and pack is about to be bricked.

0 Christopher Timperio over 5 years ago in reply to Damian Lewis

Prodigy 120 points

Ok thank you Damian. Makes sense.

Power management

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BQ40Z50-R2: Grounding Scheme; AGND/CHGND/GND