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Original question:

MSPM0G3507-Q1: MCU wakeup from Standby mode in BMS application BQ76907-Q1

BQ76907: Load sensing to exit SHUTDOWN mode (shipping mode)

Tirthraj Chandake
Prodigy 75 points
Part Number: BQ76907
Other Parts Discussed in Thread: BQ76942

Tool/software:

Hello Expert,

I want to implement shipping mode feature. When enter in shipping mode BQ76907 will be in shutdown. Then how to make wakeup functionality without any external switch or signal?

Can I make using load sensing? For example below schematic. LD Signal is used to interrupt MCU to wakeup MCU from shutdown and then MCU out voltage (Wake on TS voltage) on TS1 pin ? Will it work? Any other way? Any application note ?

  • 0
    TI__Expert 5090 points

    Hi Tirthraj,

    I'm not clear what part you are using.  The image shows BQ769x0, then in the text you mention BQ76907, but then you discuss the LD pin, which is on BQ76942/52/72.  What part are you using?

    Thanks,

    Terry

  • 0 in reply to -Terry
    Prodigy 75 points

    Hi Terry

    Sorry for confusion, I just used image from other application note to make understand concept. I want to use  BQ76907 which has TS pin to wake up from Shutdown. Idea is to detect load connect on PACK+ and PACK- and wake up BQ76907 from shutdown. Since I have MCU powered from battery I want to use it rather multiple MOSFET and diode show in application note SLUA769 (Figure 4 and 5). 

    I appreciate if you could share other ways as well based on your experience. 

    Note : Application is 12V auxiliary battery 

    Best Regards, 

    Tirthraj

  • 0 in reply to Tirthraj Chandake
    TI__Expert 5090 points

    Hi Tirthraj,

    Thanks for clarifying.  We unfortunately don't have a new app note on wakeup schemes for the BQ76907, but it is fairly similar to the BQ769x0, so the application note you referenced is probably the best document we have right now.

    You mention wanting to wake at load connect, you mean PACK+ and PACK- are open-circuit normally, vs you want to wake when a load is attached between PACK+ and PACK-, not a charger?

    What you describe above seems reasonable.  If there is no load, then PACK- is held fairly low by the diode and 20M resistance to gnd.  Then if a load is attached, PACK- is pulled up, which results in LD being pulled low by Q32, to wake the MCU.  Then as long as the MCU can output a voltage high enough to wake the part on TS, this seems fine.  Note if a load is attached but you do not want the FETs turned on, you will have a tiny trickle of current through D10 to VSS continuously.  However, this may be low enough to not be a concern for you.

    Thanks,

    Terry

  • 0 in reply to -Terry
    Prodigy 75 points

    Hi Terry 

    Thanks, 

    Is there way to detect charger as well?

    Best Regards,

    Tirthraj

  • 0 in reply to Tirthraj Chandake
    TI__Expert 5090 points

    Hi Tirthraj,

    I don't have an immediate recommendation for that case combined with your case above.  The above solution causes PACK- to lightly settle to ~0V (relative to battery pack) when no load is attached.  So PACK+/- would have the battery voltage across it.

    Assume that is 20V.  If you then have a charger attached which also puts out 20V, it would not change any voltages in any circuitry we attach.  If you assume the charger voltage will always be some level higher than the pack voltage (assuming the pack isn't fully charged), then when FETs are off and a charger is attached, the PACK- terminal will be driven below the AFE gnd level.  It is probably possible to rig up some circuitry that uses that to detect the charger and alert the MCU to wake the AFE.

    Thanks,

    Terry

  • +1 in reply to -Terry
    TI__Genius 17835 points

    Hello Tirthraj,

    I believe Section 4 Booting From an External Signal from the BQ769x0 Boot Switch Alternatives shows potentially how you can use the charger to do what you're asking that can also be applied similarly for the BQ76907. 

    Best Regards,
    Alexis