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BQ27531 and BQ24190 - Shipping Mode

Andrew Stewart82
Prodigy 60 points
Other Parts Discussed in Thread: BQ27531EVM, BQ24192, BQSTUDIO

How do we enable ship mode in the following circuit?

We're using the BQ27531YZFT-G1 and BQ24190RGET.  The datasheet for the BQ27531 isn't very enlightening, the technical reference manual is a little better.

If we send a shipmode_enable command to the fuel gauge we are able to enter shipping mode.  But when we plug in VBUS our microcontroller will boot but as soon as vbus is unplugged the circuit powers down.  Do we need to re-enable the watchdog and enable the BATFET?

  • 0
    Prodigy 60 points

    VIN powers our whole design. When we enter Shipping mode we have disabled most of our design (load switch) and this rail very slowly drops in voltage.  Could this slow drop be causing our problem?

    What happens when we request to enter Shipping mode with VBUS disconnected, Battery 90%+.  BATFET is disconnected but VIN stays high and very slowly drops to zero.

  • 0
    Prodigy 30 points

    We have also tested using the TI bq27531EVM with the bq24192 charger. As you can see from this setup we have a large capacitor attached to the Sys pins along with a USB detector and a dummy current sink. Similar to our end product. (Capacitor is not shown in the schematic above). The system will enter Shipmode, but when connecting the adapter to exit from ship mode we can see that the charger and fuel gauge turn back on but the BATFET doesn't reconnect (i.e. the battery doesn't charge and removing the USB adapter power causes the system to shut down). Is it possible to force the BATFET on? reading the charger registers show that the BATFET_DIS is set to zero, but still it does not wake up.

  • 0 in reply to Evan Fitzpatrick
    TI__Guru 55806 points

    Did you send SHIPMODE_DISABLE after connecting the adapter?

  • 0 in reply to Dominik Hartl11
    Prodigy 30 points

    Yes we have tried this but it does nothing. reading the charger_status register returns 0x00, if that helps. i.e. shipmode is not set,

  • 0 in reply to Evan Fitzpatrick
    TI__Guru 55806 points
    Your schematics look ok. What is connected to the BSCL and BSDA signals? There are nets connected to these signals in your schematics but it doesn't show the actual circuit.

    Here are the steps that I use to test shipmode on the EVM (default jumper settings):

    1. connect a charged battery to pack+ and pack-.
    2. launch bqstudio.
    3. set bit 0 (Bypass) in Charger Options (Data Memory->Charger->Charger Control Information->Charger Options->Bypass = 1) to enable direct charger control.
    4. clear bit 4 and bit 5 (WATCHDOG_0 and WATCHDOG_1) to disable the charger watchdog.
    5. clear bit 0 (Bypass) in Charger Options to disable direct charger control.
    6. issue SHIPMODE_ENABLE command.

    After the programmable delay, the BATFET switches off and SYS changes to 0V.

    After a short pulse of 5V on VBUS, the BATFET swtiches on and SYS changes to BAT and stays at BAT. The gauge is enabled and the charger is reset (=you must disable the watchdog if you want to enable shipmode again).
  • 0 in reply to Dominik Hartl11
    Prodigy 60 points

    BSCL and BSDA are connected to test points, just pads.

    We use a "470mF" connected to the SYS output of the circuit. 

    When we go into SHIPMODE with this capacitor in place and applying a short 5V pulse doesn't bring us out of shipmode.  When the capacitor is removed we don't have a problem.  Is this an expected behaviour we need to design around?

    Andrew

  • 0 in reply to Andrew Stewart82
    TI__Guru 55806 points
    If this capacitor is totally discharged, its current draw through the BATFET (BAT to SYS) will likely exceed the max. current when you turn on the charger. I(BATFET_OCP) is 6A (see page 8 in the charger datasheet).

    I would connect the capacitor to BAT instead so that it stays charged when your system is off.
  • 0 in reply to Andrew Stewart82
    TI__Guru 71526 points
    Andrew, Did connecting cap to BAT solve this issue?
  • 0 in reply to LeonardEllis
    Prodigy 30 points
    Unfortunately we cannot attempt this right away. But hopefully next week we will try this and get back with a response. Thanks,
    Evan