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BQ76920: Boot sequence

Dejan Hrovatin
Intellectual 360 points
Part Number: BQ76920

Hi,

I would like to use your BQ76920 IC just for monitoring voltages of 4 Li-ion battery cells. I don't need hardware protection features (Overcurrent in discharge, Short circuit in discharge, Overvoltage and Undervoltage) and also I don't need a thermistor at this moment. Mentioned functions are realized on the other way. I don't understand datasheet clear, but for properly working is OK if:
- pin CHG and DSG are connected to ground (via 1MOhm resistor) ?
- pin TS1 is connected to VSS with 10kOhm resistor?

If I right understand, on start-up, IC goes in to the SHIP mode and after boot sequence (voltage on TS1> 1 V) it goes in the NORMAL mode. I would like to use this IC always in normal mode. Which is the best option to achieve this if I don't want to use push button switch (or maybe PMOS transistor)? Via I2C communication is also possible to switch IC from NORMAL to SHIP mode and not also vice versa?

Thank you for this answer!
Dejan.

  • 0
    TI__Expert 6085 points

    Dear user,

    NORMAL to SHIPMode is commanded by 2-registers ( SHUT_A, SHUT_B) writes via the I2C.

    SHIPmode to Normal is ALWAYS via an external WAKE on the TS1.

    The reason being, in SHIPmode al the regulators ( except for SLEEP/WAKE latch circuit is kept Active) are OFF inside the IC.

    hence the communication circuit is also OFF until the REGOUT is up.

    The boot sequence power is, WAKE( >1V on TS1)---> CAP1-->REGOUT-->SCLK/SDATA-->CAP2--CAP3

  • 0 in reply to Vish Nadarajah
    Intellectual 360 points
    Hi,

    what way is the best to "terminate" CHG, DSG, SRP and SRN if they are not in use? I connected CHG pin via 1 MOhm resistor to VSS, DSG via 1 MOhm resistor to VSS and I left SRP and SRN floating. Is this OK?
    What do you mean with: "hence the communication circuit is also OFF until the REGOUT is up" ...REGOUT is 3v3/2v5 LDO...

    Thank you!
    with best regards.
  • 0 in reply to Dejan Hrovatin
    TI__Expert 4640 points

    Hi,

    You should ground your SRP and SRN if you are not going to use them and you should leave floating the CHG and DSG pins, but you can do what you did which was to tie the CHG and DSG pins to 1Mohm then ground them. Keep in mind that then your battery pack is no longer protecting unless you are using the MCU to drive FETs. Also you aren't using the hardware comparaters the device has for better protection.

    Thx

    M