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BQ25792: BQ25792

Shafeeq Muhammed
Expert 1200 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ24610, BQ24735, BQ24170, BQ24133

Hi,

We are planning to use BQ25792 in our design.

Please provide clarification on below points

  1. If we are giving an input of 24V input to the charger, what will be the output voltage at SYS? Whether the charger will regulate the voltage at SYS to ≤ 19?
  2. Can we set the voltage at SYS by writing registers via I2C?
  3. To enable ship mode, we have to use an external MOSFET which is controlled by SDRV. Can we enable Ship mode and Shutdown mode without using external MOSFET? By turning of BATFET alone?

Thanks & Regards,
Shafeeq

  • 0
    TI__Guru**** 166696 points

    Hi Shafeeq,

    Regarding 1, SYS regulates to a minimum voltage set by MINSYS register but then follows the battery up as it charges to VBATREG.  SYS then regulates slightly above BATREG.  SYS regulation is not independent of BAT regulation.  Also, the BQ25792 as input voltage OVP protection default set to 22V.  You will need to change that register to 26V if you want to use a 24V input rail.

    Regarding 2, see 1 above.

    Regarding 3, no.  The BATFET cannot be turned off.  You must have external MOSFET driven by SDRV in order to enter ship mode or shutdown mode.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1200 points

    Dear Jeff,

    Thanks for your reply.

    Just want to clarify the below point

    • If we set the OVP to 26V and provides 24V input, will we be getting 24V out on SYS?
    • If we use external FET and use shutdown mode when valid voltage is present at VBUS, will the charger turn off the out put to SYS? if yes, how to wake the IC from shutdown mode?

    Thanks and Regards,
    Shafeeq

  • 0 in reply to Shafeeq Muhammed
    TI__Guru**** 166696 points

    Hi Shafeeq,

    SYS is from the output of the converter, which is the higher of the MINSYS voltage setting or the battery voltage+ a few hundred millivolts.  The maximum voltage SYS will be the battery regulation voltage plus a few hundred millivolts.  We have charger's like BQ24610 standalone or BQ24735 SMBus controlled that pass the input voltage to the system. 

    Regarding the external FET, the charger cannot be in shutdown mode with a valid voltage at VBUS.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1200 points

    Hi,

    thanks for your reply.

    We are using BQ24610 in our current design.
    We are planning to change as the external components are more with it.
    Can you suggest any other modules with integrated FET?

    We are planning to use the charger for 2S cell. According to the datasheet, during the POR the IC will select the VSYSMIN in according to the PROG resistor.
    So in our case it will be 7V.
    As the VSYSMIN register is RW type, I think we can increase the VSYSMIN, But the question is till what voltage we can increase the register with a 2S battery setting?

    As we are using 2S Lithium battery, I think we may not be able to increase battery regulation voltage more than 8.4V. is my understanding correct?

    Thanks & Regards,
    Shafeeq

  • 0 in reply to Shafeeq Muhammed
    TI__Guru**** 166696 points

    Hi Shafeeq,

    You can increase SYSMIN slightly above BATREG in each of the 1S,2S,3S,4S configurations but there is an eventual clamp when you start to enter the next configuration.  The drawback to having SYSMIN>BATREG is that the charger stays in linear mode during the entire charge time instead only when the battery is deeply discharged. Linear mode charging across the BATFET is not efficient as PWM charging so the charger gets hot.  In thermal regulation, the charger auto scales back the output power to keep the IC die temp below the selected value.  This results in longer charge time.

    BQ24133 and BQ24170 have integrated converter FETS but external input FETs (for passing the input power to the system) and battery FETs. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1200 points

    Hi Jeff,

    Thanks for your reply.

    The both charger IC that you have suggested is having maximum input of 17V.
    Can you suggest any other Charger ICs with at least 24V input support.

    Regards,
    Shafeeq 

  • 0 in reply to Shafeeq Muhammed
    TI__Guru**** 166696 points

    Hi Shafeeq,

    TI does not have any other 24V-input, integrated FET chargers, than I have mentioned above.

    Regards,

    Jeff