• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 125 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76952: PCHG/PDSG Drive Desing for Common Source FET configuration

Oguzhan GUVERCIN
Prodigy 20 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQ76942

Tool/software:

Hi,

I'm designing a BMS for 24V lead acid replacement li-on battery. We are going to implement the design with BQ76952. But for thermal reasons we are going with common source back to fet configuration instead of common drain config. which is given in BQ76952 datasheet Figure 16-1 simplified schematic.

BQ76942 - Common Drain

Our common source design.

We will drive the fets with an isolated gate driver that has a supply referenced to this common source. And driving logic signals will be coming from BQ76942. So there is no problem with using CHG and DSG pins of  BQ76942.

But PCHG and PDSG pins creates some issues with common source config. I believe in order to drive the precharge FET given in figure 16-1 PCHG pin pulls the gate of precharge FET 8.4V below of PACK and to drive the predischarge FET given in figure 16-1 PDSG pin pulls the gate of precharge FET 8.4V below of BAT. Therefore creating the negative voltage needed to drive p channel fets.

Since I'm using a common source config. I can not connect this pins straight to my isolated gate driver input and expect it work. So I need to design a logic circuit that would change the PCHG and PDSG outputs into gate driver input logic signals. I think need to design the circuit referenced to PACK and BAT pins but I'm not really sure. 

Am I on the right track?

Has anyone designed this kind of circuit?

Any tips on how to approach this problem?

Thanks in advance. Best regards,

  • 0
    TI__Expert 5645 points

    HI,

    The BQ76952 FET drivers are designed for a common drain configuration.  It does not support a common source configuration, due to the voltage driven onto CHG when FETs are disabled and a load is still attached at PACK+. In addition the part has a body-diode protection feature which may not work properly if the source/drain are swapped. Given this all our test has been done with the drain tied together, and we have not tested this configuration, we cannot guaranteed it will work as intended and recommend to stay with our recommendation.  

    One good resource is to look into the multiple FETs app note "www.ti.com/.../sluaa09a.pdf" which provide different parallel configurations that might help with the thermal requirements. 

    Regards, 

    Arelis G. Guerrero 

  • 0 in reply to Arelis Guerrero
    Prodigy 20 points

    Hi Arelis,

    Thank you for your response. I know BQ76952 isn't meant for common source configuration. But I'm trying to find a work around for my unique requirements. 

    I appreciate the heads up on body diode protection feature. I'll keep that in my mind.

    Best regards,