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BQ24250 eval board queries

Srijan Ashok
Intellectual 1045 points
Other Parts Discussed in Thread: BQ24250

Hi Folks,

As discussed with you, we have done some experiments using the BQ24250 Eval board and have few queries based on the testing as below:

 

  • How SYSREG will be maintained at the output when fully drained battery is connected.
    • What is the Min SYSREG output voltage? In datasheet under power path management section it is mentioned that the VSYSREG voltage will be MinSYS-200mV[3.5-0.2=3.3V]. Is that correct ?
    • If so do you have any other part which gives SYS output of Min 3.5V ?

 

  • With following settings in EVK we observed that the SYS output voltage drops below 3.5V
    • In standalone mode->EN1 and EN2=100mA, fully drained battery is connected at BATT pin and even without any load at SYS pin we are seeing a voltage of less than 3.5V.
    • Will there be any issues, if we apply a voltage at the BQ24250 LDO pin i.e. only when 5V is not connected.
    • How can the charge termination current be set when BQ24250 is in standalone mode.

      Thanks

    • Srijan

  • 0
    TI__Expert 7730 points
    Hello Srijan,

    If the IC is NOT in DPM mode, the system voltage will be regulated to 3.5V. In DPM mode, the input power is not enough to supply the output, so that the input current is reduced to prevent the input voltage from collapsing.

    Can you let me know what is the exact bat voltage, vin and sysreg voltage when you saw Vsys is below 3.5V?
    If a voltage is apply to LDO pin, some of the internal circuits will be activated. However, this is an output pin and should not be applied a voltage even without VIN.
    In standalone mode, the termination current is always 10% of the charge current.

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 10 points

    Hello All,

    For the following question, Can you let me know what is the exact bat voltage, vin and sysreg voltage when you saw Vsys is below 3.5V?

    [Sling_7thJan2015]: BATT voltage, SYS voltage and input voltage are as mentioned below.

    BATT Voltage = 3.12V ; SYS Voltage = 3.32V ; Vin = 5V

    EN1 and EN2 are configured to draw not more than 100mA from input[which will be the maximum current we can draw from 5V rail before enumeration].

    During this test no additional load is applied at SYS output.

    We have few additional questions as below:

    1. Please let us know what does No DPM means? How is the configuration for this is to be done?

    2. When 5V input is applied and battery is drained, we want Min SYS output of 3.5V at SYS pin of BQ24250. Please let us know can this be achieved using this part?

    Regards,

    Ranjana

  • 0 in reply to Ranjana Naik
    TI__Expert 7730 points
    In the spec that you attached in the first post, please notice that in MINSYS stage (DPM or DPPM active), the system voltage will be regulated at VMINSYS-200mV which is 3.3V as you observed.

    DPM loop will be active when the system and battery is trying to draw more power than what the input can provide, so the DPM loop will reduce the input current to prevent the further drop of the input voltage.

    DPPM loop will be active when the charge current is higher than the input current limit.

    If either of the above loop is active, the system voltage will be VMINSYS-200mV. In your case, because ILIM is limited to 100mA, if Ichg is above 100mV, then the DPPM loop is taking the control and that is why you are seeing 3.3V instead of 3.5V at system.

    To be able to get 3.5V output, you can change the ILIM setting to 500mA or some other value that is higher than your programmed charge current, or reduce your charge current to below 100mA before enumeration.

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 70 points
    Hi Wenjia,

    Thank you for your quick response.
    Based on your response it looks like there are two options to keep SYS voltage at 3.5V.

    Option 1
    1. Setting input current limit to 500mA.
    This option is not feasible as because we can’t draw more than 100mA before enumeration. For enumeration to happen I need min of 3.5V at SYS pin.

    Option 2
    2. Setting charge current below 100mA.
    Can this be done in standalone mode ?
    Our SOC will not send any I2C signal as long as device gets enumerated so can we set the charge current below 100mA in standalone mode ?
    please note that we don’t want to disconnect battery from SYS output as because my system needs continuous supply at SYS pin to Run RTC.

    Regards,
    Vikram
  • 0 in reply to vikram B
    TI__Expert 7730 points

    Vikram,

    Your understanding is correct.

    In option 2, you can program the charge current through ISET pin resistor. The formula is Ichg = 250/RISET. For example, to set 100mA charge current, the RISET should be 2.5 kohm. I2C command can overwrite the external charge current setting if you want to change the value later.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 70 points

    Hi Wenjia,

    It is good to know that we can set the charge current below 100mA in standalone mode.please let us know what is the min value we can set ?

    In Datasheet under Electrical characteristics why Fast charge current is mentioned as 500mA to 2A ?

    Regards,

    Vikram

  • 0 in reply to vikram B
    TI__Expert 7730 points

    Vikram,

    500mA to 2A is the recommended current range that we guaranteed with the accuracy on datasheet. In reality, the ICHG is linear with the resistor value on ISET pin and can be programmed to below 100mA.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 70 points

    Wenjia,

    I am going to set it to ~5mA in my design by using R value of 49.9K. please confirm is it is fine ?

    Also confirm the min value that we can set.

    Regards,

    Vikram 

  • 0 in reply to vikram B
    TI__Expert 7730 points

    Vikram,

    The minimum charge current that we've verified is 80mA.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 70 points

    Wenjia,

    We have one BQ24250 EVM and in that i could set it to 5mA by changing R-ISET to 49.9K.

    Please confirm will there be any issues if i use this value in our design ?

     

  • 0 in reply to vikram B
    TI__Expert 7730 points

    Vikram,

    We have not simulated or tested the charge current at this low level so the accuracy and stability is not guaranteed. Besides, with 5mA charge current, the termination current should be 10% of it, which is 500uA. However, I'm pretty sure this IC cannot terminated accurately at this level. Is there a reason you need to set the current this low? I thought you just need to keep it below what the input current limit can provide.

    Thanks,

    Wenjia