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bq24192I - Safety Timer

Dice-K
Mastermind 7642 points
Other Parts Discussed in Thread: BQ24192I

Hello,

I use bq24192I. And I have two questions about the behavior of Safety Timer.

 

1. Are "start condition of Safety Timer" and "the state of the stop" correct, in follows?

(Conditions: VBUS=9V, VBAT=3.7V, the register setting of bq24192I is default)

 - When /CE becomes Low(charge enable), the counter of the Timer starts.

 - When the Timer is expired, EN_HIZ(REG00[7]) is set to "1" and the buck converter stops.

 

2. About restart processing after Safety Timer stop

 - When /CE is changed from High(charge disable) to Low(charge enable), is the Timer cleared ?

   Does the charging restart?

 - If REG00[7] is set to "0", does the charging restart?

 

Regards,

Daisuke

  • 0
    TI__Guru 59361 points
    1. Your understanding is correct in default mode.
    2. When /CE is changed from High to Low, the timer restarts. When REG00[7] is changed from "1" to "0", HIZ mode will be disabled, but it does not mean charging will restart and the timer will reset. Referring to p21 of the d/s:
    The following actions restart the safety timer:
    • At the beginning of a new charging cycle
    • Toggle the CE pin HIGH to LOW to HIGH (charge enable)
    • Write REG01[5:4] from 00 to 01 (charge enable)
    • Write REG05[3] from 0 to 1 (safety timer enable)

    Thanks,

    Ning.
  • 0 in reply to Ning T
    Mastermind 7642 points

    Hello Ning,

    Thank you for your reply.

    I have three questions.

     

    1.

    I summarized a flow in this file.

    Is it correct?

    timer_behavior.xls

     

    2.

    In the condition of charging restart "Toggle the CE pin HIGH to LOW to HIGH (charge enable)".

    Is the timer not reset when I do not control HIGH -> LOW -> HIGH after the timer stop?

    Is "/CE=HIGH" not "charge disable"?

     

    3.

    For "At the beginning of a new charging cycle"

    what kind of control is necessary?

    If I do three following work, does a new charging cycle begin?

      - Toggle the CE pin HIGH to LOW to HIGH (charge enable)

      - Write REG01[5:4] from 00 to 01 (charge enable)

      - Write REG05[3] from 0 to 1 (safety timer enable)

     

    Best regards,
    Daisuke

  • 0 in reply to Dice-K
    TI__Guru 59361 points

    Please see below for my comments:

    1. Both  I2C register bit (REG01[5:4]) = 01 and CE is low are necessary to enable charging. Please note that the device may work in default mode and host mode (p27 of d/s). REG00[7] behaves differently for the two modes.

    2. The safety timer will not reset if one of the actions mentioned earlier is not taken to restart the safety timer.

    If CE/=High, charge is disabled.

    3. Referring to p18, A new charge cycle starts when the following conditions are valid:

    • Converter starts

    • Battery charging is enabled by I2C register bit (REG01[5:4]) = 01 and CE is low

    • No thermistor fault on TS1 and TS2

    • No safety timer fault

    • BATFET is not forced to turn off (REG07[5])

    Enabling charging does not mean charging will start. The battery voltage also needs to fall below the recharge threshold.

     

    Please read through the complete d/s. The best way to understand is to order an EVM and do evaluations.

     

    Thanks,

    Ning.