BQ77915: Ground referencing the BQ77915 battery protector IC

Tony Bisconti

Part Number: BQ77915

Hello,

I'm looking for a three cell (LiPo) charge balancing solution for my project. I found quite a few potential IC's however, none of them

will support a ground referenced battery. My system and the battery are both ground referenced.

I started looking at the BQ77915 and with a few modifications I should be able to make it work in my application.

I'm mainly interested in the charge balancing portion of the chip. My system will take care of the other protections (UV, overcurrent, etc).

I had to remove all the ground based components. I removed the ground side FET switches. My system already contains high side switches (the system controls the discharge).

Also removed the current sense resistor (Rsns). I'm sending a fake signal to SRP and SRN to activate the charge cycle.

Several variants of this part listed in the data sheet have some protections disabled. Will they work best for me?

I found I slight typo in the data sheet. Rcb is used as the external discharge FET series resistor and also the CBI grounding resistor.

After all 10K resistors for the discharge FETs are way too large.

I attached a schematic of my design. Could someone please review it and verify if it will work, or not.

Or If someone could point me to a ground referenced solution that might be best.

Thanks

Tony

0044.BQ77915_Schematic.pdf

8 months ago

0 Tony Bisconti 8 months ago

Prodigy 50 points

I wrote "I'm sending a fake signal to SRP and SRN to activate the charge cycle." Sorry wrong pin. Divider should be connected to "SRP". see updated schematic.

81404.BQ77915_Schematic.pdf

0 Maxwell Verboncoeur 8 months ago in reply to Tony Bisconti

TI__Mastermind 20980 points

Hi Tony,

This looks like it should work. One comment I have is that 10k for the balancing resistors is likely going to be too large to see any decent balancing current.

Regards,

Max Verboncoeur

0 Tony Bisconti 8 months ago in reply to Maxwell Verboncoeur

Prodigy 50 points

Hi Max,

Thanks for the quick response.

I wish there was a way to simulate my changes before I commit to hardware. I guess I just have to "go for it".

I know about the 10K resistors. That's why they are question marked.

"I found a slight typo in the data sheet. Rcb is used as the external discharge FET series resistor and also the CBI grounding resistor."

If you look on page 6 of the data sheet Table 8.3 "Recommended Operating Conditions (continued)" towards the bottom of the table

Rcb is also defined as the CBI resistor listed as 10K. Table 8.3 and figure 9.3 conflict.