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BQ24780SEVM-583: hybrid boost mode behavior

Prabhat Kumar31
Prodigy 195 points
Part Number: BQ24780SEVM-583
Other Parts Discussed in Thread: BQ24780S

Hi,

We are testing transient behavior when hybrid boost mode kicks in. We notice that in hybrid boost mode battery kicks in and then kicks out for short duration and then comes back again. Is this expected behavior?

I have attached scope screen shots:

Screenshot #1: Input supply provide all the power and simulated battery is in charging state

Screenshot #2: Transient behavior when Battery charger is in hybrid boost mode.

I have 12V input supply. System load is 1.5A or higher. Battery supplying rest of the power needed by the system. Charge Voltage set at 8.2V, Charge Current at 1.024A and input current limiting at 1.024A. I have shunt resistors connected on the low side of the loads for transient measurement. The scope plots are for currents.

I also notice sometimes hybrid power boost mode does not get triggered at all. I have enable the hybrid power mode and disable the watchdog timer.  Am I missing any setting/state that can cause that?

Thanks

  • 0
    TI__Guru 56650 points

    "We are testing transient behavior when hybrid boost mode kicks in. We notice that in hybrid boost mode battery kicks in and then kicks out for short duration and then comes back again. "
    It is expected behavior. Charger still checks the hybrid boost mode condition every 175ms even the watch dog timer is disabled. When bq24780S checks the boost mode condition, you can see a short kicks in and out.
     
    "I also notice sometimes hybrid power boost mode does not get triggered at all" ; "input current limiting at 1.024A"
    Please set the input current register value higher than 1536 (see datasheet page 22): To support hybrid power boost mode, input current must be set higher than 1536 mA for 10 mΩ input current sensing resistor.

  • 0 in reply to Wang5577
    Prodigy 195 points
    "It is expected behavior. Charger still checks the hybrid boost mode condition even the watch dog timer is disabled."
    How does normal mode to boost mode switching works in terms of timing?
    Is this correct? Charger checks whether hybrid boost mode is enabled when the input current hits the lmit 1.024A. I am guessing, at this stage the battery kicks in and starts supplementing current when system load increases and the charger goes into hybrid boost mode. When does the charger kicks out the battery for short duration?

    "Please set the input current register value higher than 1536 (see datasheet page 22): To support hybrid power boost mode, input current must be set higher than 1536 mA for 10 mΩ input current sensing resistor."
    I have changed the input sense resistance to 20mΩ and setting the input current limit to 2048mA (which is 1024mA in my case).
  • 0 in reply to Prabhat Kumar31
    TI__Guru 56650 points
    If the watchdog timer is not disable, "The bq24780S device includes a watchdog timer to terminate charging or hybrid power boost mode if the charger does not receive a write ChargeVoltage() or write ChargeCurrent() command within 175 s (adjustable through 0x12[14:13] command)." (see datasheet page 20.)
    If the watchdog time is disable, the bq24780S will keep hybrid power boost mode without ChargeVoltage() or write ChargeCurrent() command. But, it will check the boost mode condition (Iin>Iin_dpm...) every 175ms which is in and out hybrid mode. The charger is not kicked out from hybrid. It proactively checks the boost mode condition every 175ms.

    "I also notice sometimes hybrid power boost mode does not get triggered at all."
    According to your first question, you can run into hybrid mode. How did you run the hybrid mode to check hybrid boost mode battery kicks in and then kicks out issue?
  • 0 in reply to Wang5577
    Prodigy 195 points
    Setup:
    Input voltage: 12V (modified voltage divider resistor at ACDET pin)
    Input sense resistor: 20m ohms ( changed on the board)
    Input current limit: 2048mA/2 = 1024mA (setting it to 2048mA using BQ studio)
    Charge current:1024mA
    Charge Voltage: 8.2V
    Watch dog timer disabled.
    Enabled Hybrid boost mode
    Connected 1.2 A load as system load.

    Also connected shunt load to measure currents on the low side of input, output(system load) and battery. I am using power supply to simulate battery. Hybrid boost mode kicks in when 1.2A system load is applied. I can also read "boost voltage indication" register changing to 1 in BQ studio.

    Normal operation is shown in screenshot #1. Screenshot #2 when 1.2A load is applied at the output (system load). Screenshot # 2 shows that the battery current goes back to zero and stays zero for about 800ms. After that battery is supplementing current again. I was expecting current drawn from battery and no transition. As seen in screen shot#2, battery (blue) supplements current and then goes to zero and back again to supplementing current.
  • 0 in reply to Prabhat Kumar31
    TI__Guru 56650 points
    Battery running into hybrid mode is decided by the Isys and Iin-dpm setting. Can you measure the system load current and input current?
    Also, can you share your schematic with us?
  • 0 in reply to Wang5577
    Prodigy 195 points

    Hybrid mode:

    Isys = 1.222A

    Iinput = 1.043A

    Simulated Battery supplementing the rest  = 303mA @ 7.86V

    I made the two changes on the evaluation board itself. I do not have custom schematic. Please see attached schematic below

  • 0 in reply to Prabhat Kumar31
    TI__Guru 56650 points
    Hybrid mode:

    Isys = 1.222A

    Iinput = 1.043A

    Simulated Battery supplementing the rest = 303mA @ 7.86V

    Those information cannot help you or me to understand "I also notice sometimes hybrid power boost mode does not get triggered at all".
    Those information tell me Hybrid mode is normal.
  • 0 in reply to Wang5577
    Prodigy 195 points
    /TB_STAT is high and Hybrid boost mode is enabled.
    The EVM board does not go in hybrid mode.
    What can cause EVM not to go in hybrid boost mode?

    Input sense resistor: 20m ohms ( changed on the board)
    Input current limit: 2048mA/2 = 1024mA (setting it to 2048mA using BQ studio)
  • 0 in reply to Prabhat Kumar31
    TI__Guru 56650 points

    Please step and step follow the EVM test procedure or user's guide. And, please let me know on which step do you have an abnormal condition?

  • 0 in reply to Wang5577
    Prodigy 195 points
    EVM board stop working. Getting a new one.