BQ77915: Using high-side control via charge pump gate drivers

Zac Blume

Part Number: BQ77915

Does anyone have experience converting the BQ77915 to high-side-base control, using NFETs (or PFETs)? I am finalizing a design and wanted additional input. My design will leave the shunt resistor at the pack negative, but switch the pack positive via Toshiba TCK401G charge pump gate drivers off the CHG/DIS pins. This is because I need to turn the pack outputs off/on often, but leave the GND referenced properly (for multiple obvious and not-so-obvious reasons). I'm using NFETs because the continuous current for this BMS design is 165A (24 FETs in total).

I'm also curious to know if the SRN/SRP ratings are referenced to each other, or VSS? It would vastly simplify my design to use high-side current monitoring, as well, without the complication of level-shifting the output to mimic low-side sensing. For now, I will leave it as low-side sensing.

over 5 years ago

0 Shawn Hinkle over 5 years ago

TI__Expert 7455 points

Hi,

Have you taken a look at this application note? https://www.ti.com/lit/an/slua910/slua910.pdf?ts=1597355411513&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ77905

This outlines how to convert to high-side implementation and you should find it very helpful.

0 Zac Blume over 5 years ago in reply to Shawn Hinkle

Prodigy 240 points

Hi Shawn,

Thanks for the reply. However, this AN covers using a high-side PFET for only the CHG protection, but I am also converting the DIS to high-side control. I'm particularly worried about post-protection wake (connecting a charger) to re-enable the drivers. To be specific, I'm not talking about the PRES (hibernate) wake function (that's powered from PACK+). Only the short-circuit, and UV, conditions.

0 Shawn Hinkle over 5 years ago in reply to Zac Blume

TI__Expert 7455 points

Hi,

To give you an idea for how you might be able to configure these pins, see the image I have attached. I would like to stress that this schematic has not been thoroughly tested and is just a suggestion. We cannot guarantee correct functionality using this configuration.

0 Zac Blume over 5 years ago in reply to Shawn Hinkle

Prodigy 240 points

Hi Shawn,

Thanks for the reply. Since our design is a 3s pack, my version of the LD circuit lacks the diodes for gate protection and stacking, but was otherwise the same as your idea. Glad to see we align on an LD solution. I will give this a go and see how it works.

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BQ77915: Using high-side control via charge pump gate drivers