• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 65 subscribers
  • Views 186 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

BQ77216: Usage with BQ76952

FY AY
Prodigy 50 points
Part Number: BQ77216
Other Parts Discussed in Thread: BQ76952,

Tool/software:

Hi TI Team,

I have a question about usage BQ77216 with BQ76952. 

When I look the datasheet of BQ77216, at figure 9-4. It shows the usage them together. 

Its clearly seen that DOUT and COUT pins of the IC directly drives the low side to VSS level to disable high side power mosfets. At this time what will be the voltage at CHG and DSG pins with respect to Pack+ ? ( additionaly; what will be the behavior or BQ76952?) Is it dangerous the drive high side mosfets like this ? There will be current which is flowing through the zener diodes to VSS level. Am I wrong ?

Also, Could you please help me to select low side Cout and Dout mosfets resistors ( source gate, drain) ? What should we pay attention to?

Thanks,

Sincerely.

  • 0
    TI__Mastermind 40140 points

    Hello FY,

    In this particular figure, COUT/DOUT are also connecting to CFETOFF/DFETOFF, so that when the BQ77216 triggers its protection it will command the BQ76952 to turn-off the MOSFETs. If this is not done, the charge-pump will be overloaded and its voltage will collapse for both FET drivers.

    Regardless, the voltage the CHG/DSG pins may much lower than the BAT+/PACK+ pins, because you are pulling it low with the DOUT/COUT MOSFET. The MOSFET itself will be safe, because the Zener diode between the gate-source of the CHG/DSG FETs will be forward-biased, so the voltage across the FET will be a diode drop. You would want to ensure that the resistance to ground is low enough to limit the current flowing through the Zener.

    Now, I would actually recommend instead to simply connect COUT/DOUT to CFETOFF/DFETOFF (With a small level-shifter), and let the BQ76952 turn-off the MOSFETs by itself. You could also potentially use the FUSE pin (Of the BQ76952) as an input so that it can detect when COUT/DOUT goes high and the BQ76952 can make a decision.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 50 points

    Dear Luis, 

    Thank you for your answer. Where can I see the full design of these COUT/DOUT connection to CFETOFF/DFETOFF? I will use SPI connection so CFETOFF will be SPI_CS. I need to configure DFETOFF pin as BOTHOFF pin right ? 

    Edit: If I disable charge pump, Can I use these COUT/DOUT to disable high side fets as shown in figure 9-4? 

    Yes It'll be forward voltage drop of diode.

    For the fuse usage; should I configure the Fuse pin to detect high signal ? When I look the reference manual; I need to enable 2LVL ( Second Level Protector Permanent Fail) from Settings:Permanent Failure:Enabled PF B register. am I right? 

  • +1 in reply to FY AY
    TI__Mastermind 40140 points

    Hello FY,

    We currently do not have a design with this particular set-up.

    FY AY said:
    Where can I see the full design of these COUT/DOUT connection to CFETOFF/DFETOFF? I will use SPI connection so CFETOFF will be SPI_CS. I need to configure DFETOFF pin as BOTHOFF pin right ? 

    Correct, you would have to configure DFETOFF as BOTHOFF, both of COUT/DOUT may have output voltages of up-to 7-V, so you would want to have to step-down the voltage for the DFETOFF input.

    FY AY said:
    If I disable charge pump, Can I use these COUT/DOUT to disable high side fets as shown in figure 9-4? 

    Connecting COUT/DOUT to DFETOFF as BOTHOFF will disable the FET drivers, so that would be okay. However, there may be some mA of currents flowing from the BAT pin to the CHG pin to ground, as the CHG pin connects internally to the BAT pin when the CHG FET driver is OFF.

    FY AY said:
    For the fuse usage; should I configure the Fuse pin to detect high signal ? When I look the reference manual; I need to enable 2LVL ( Second Level Protector Permanent Fail) from Settings:Permanent Failure:Enabled PF B register. am I

    Correct.

    Best Regards,

    Luis Hernandez Salomon