BQ76PL536A: Multi-Drop System GND problem?

Troy.Tsai

Part Number: BQ76PL536A

Hello,

I'm developing a multi-slave BMS now.and I'm using Multi-Drop system with CAN (without ISOLATER).

But when I saw reference design (tidub04.pdf -- Page 19), something weird.

The schematic connect two BQ76PL536A GND together, I don't know how to push Internal LDO(Top IC), where is reference GND of Top IC?

Where can I get full Multi-Drop system reference design schematic? (Contain VSS, VSSD, VBAT connection)

My question:

1.Which Pin is VBAT's GND?

2.Can I connect 2 IC GND together?(As shown below, looks really dangerous)

P.S. My MCU will use daisy chain to connect all of MCU(CAN) and without any isolation.

over 8 years ago

0 Troy.Tsai over 8 years ago

Intellectual 365 points

Roger Hwang Do you have any suggestion?
Thanks.

0 David Wiest Jr over 8 years ago in reply to Troy.Tsai

TI__Genius 11480 points

Hi Troy,

I can step in.

It looks like it was just a limitation of our drawing software - sharing a ground while stacking cells will certainly violate ABSMAX for almost every pin. They should be separate grounds...good catch.

Reference ground of the top ic would be the bottom of the lowest cell in the top module (if that makes sense)

Hope that helps

0 Roger Hwang over 8 years ago in reply to Troy.Tsai

TI__Genius 10785 points

Hi Troy,

You need to have two completely separate GNDS.
IC1 GND and IC2 GND should be separated.
The schematic only shows that cells are connected. It doesn't shows layout.
Even daisy-chain configuration, GNDs should not be connected.

you should treat as two separate board.
I don't quite understand where two gnds are connected together from the schematic.

0 Troy.Tsai over 8 years ago in reply to David Wiest Jr

Intellectual 365 points

First, thank you for your replay.

I see.

So I still need to add an isolater between MCU and PL536A right? because I wanna use CAN bus..need a GND for all CAN Transceiver.

Troy

0 Troy.Tsai over 8 years ago in reply to Roger Hwang

Intellectual 365 points

Thank you for your reply too!

Well...David got the point..drawing software limitation.Looks like top IC GND connect to bottom IC GND(Same symbol).

Do you have any recommendation to connect all device(MCU with CAN Transceiver) without isolater? or I must put an isolater on each board?

Troy

0 Roger Hwang over 8 years ago in reply to Troy.Tsai

TI__Genius 10785 points

Ah,, I see... Good catch. They should be diff gnd.

No, there is no WAY of connecting MCU and CAN transceiver without the isolators.
Daisy chain is way to go. You only need 1 or NO isolator but I recommend to isolate HV and LV...

0 Troy.Tsai over 8 years ago in reply to Roger Hwang

Intellectual 365 points

Thank you for your reply.

I'll reference to EVM schematic to isolate HV and LV.

Really useful.

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BQ76PL536A: Multi-Drop System GND problem?