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BQ25858B-Q1: APPLICATION ISSUES

Colt Zhang
Expert 4985 points
Part Number: BQ25858B-Q1
Other Parts Discussed in Thread: BQ25858-Q1, BQ25856-Q1

Tool/software:

hi expert,

my customer have some question about BQ25858-Q1:

1 With regard to the ACUV and ACOV pins, they understand that when the input power is present and is greater than a certain value, Ability to automatically stop reverse mode, automatically turn on reverse mode when input power is not present or less than a certain value, does not know if they understand it correctly


2, the following formula does not understand, what does this target voltage mean? How should I determine this target voltage


3, because their products have sleep function, when sleep, the sleep current needs to be less than 100uA, In order to achieve this current value, they shut off the 5V output during sleep, that is, the MCU power down, this time there is no 5V level to pull up the CE pin. That IC will charge the supercapacitor behind it
Now they want to ask you if you can use the REGN that comes with this IC, which is an LDO for CE, PG, STAT, Pull up with INT

4, in addition to the 3 described, this device needs to be configured to enter the low power mode.

  • 0
    TI__Expert 5785 points

    Hi,

    Colt Zhang said:
    1 With regard to the ACUV and ACOV pins, they understand that when the input power is present and is greater than a certain value, Ability to automatically stop reverse mode, automatically turn on reverse mode when input power is not present or less than a certain value, does not know if they understand it correctly

    The BQ25858-Q1 can automatically enter reverse mode operation when the input voltage drops below the threshold of ACUV by setting the register bit EN_AUTO_REV = 1 through I2C.

    The BQ25858-Q1 cannot automatically exit reverse mode. This needs to be done by setting EN_AUTO_REV = 0 and EN_REV = 0 through I2C.

    There is a section for this functionality in the BQ25856-Q1 datasheet. I am unsure why it is not in the BQ25858-Q1 datasheet.

    Colt Zhang said:
    2, the following formula does not understand, what does this target voltage mean? How should I determine this target voltage

    The target voltage is dependent on your application. VACUV_TARGET is the voltage you want for your input undervoltage protection, and it is usually the lower limit of the input voltage source in the design. VACOV_TARGET is the voltage for input overvoltage protection. For a 12V nominal input voltage, choosing 8V for VACUV_TARGET and 16V for VACOV_TARGET will limit the operating range of the device between 8V and 16V.

    This FAQ page for the ACUV and ACOV pins might explain things a little clearer.

    Colt Zhang said:
    3, because their products have sleep function, when sleep, the sleep current needs to be less than 100uA, In order to achieve this current value, they shut off the 5V output during sleep, that is, the MCU power down, this time there is no 5V level to pull up the CE pin. That IC will charge the supercapacitor behind it
    Now they want to ask you if you can use the REGN that comes with this IC, which is an LDO for CE, PG, STAT, Pull up with INT

    I believe that this is possible. The maximum voltage rating on these pins is 6V so the REGN LDO should not harm these pins. The main concern would be drawing too much current from the LDO while it is trying to power the switching. The REGN LDO will turn off when the charging is disabled, however. Using it to pull CE pin high will shut it off which will likely drive the pin low again.

    Colt Zhang said:
    4, in addition to the 3 described, this device needs to be configured to enter the low power mode.

    I would recommend using an external LDO to pull the CE pin high to enter the low power mode.

    Best regards,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 30 points

    hi，expert

    1. Can I refer to the datasheet of BQ25856 - Q1?
    2. The operating voltage of our product is 9~16V. ACOV means that after exceeding 16V, and after setting EN_AUTO_REV = 0 and EN_REV = 0 through I2C, can it support the automatic - off reverse mode?
    3. ACUV and ACOV are related to the reverse mode. The operating voltage of our product is 9~16V. Now it is necessary to configure the window voltages of ACUV and ACOV through resistors. How should it be configured? For example, when ACUV is reduced to 7V, the reverse mode is automatically turned on.
    4. Because the current consumption of this device in the low - power mode is relatively large, which is 0.75mA. The current hardware design is to turn off the VAC input after entering sleep, with only battery power supply, REGN is turned off, and CE is in a floating state. In this case, can the REGN LDO be used as the pull - up for CE, PG, STAT and INT?
  • 0 in reply to ? ?
    TI__Expert 5785 points

    Hi,

    ? ? said:
    Can I refer to the datasheet of BQ25856 - Q1?

    The datasheet is here:

    The auto reverse section of this datasheet should be applicable to the BQ25858-Q1.

    ? ? said:
    The operating voltage of our product is 9~16V. ACOV means that after exceeding 16V, and after setting EN_AUTO_REV = 0 and EN_REV = 0 through I2C, can it support the automatic - off reverse mode?

    What do you mean by "automatic - off reverse mode?" Reverse mode will not automatically turn off on the BQ25856-Q1.

    ? ? said:
    ACUV and ACOV are related to the reverse mode. The operating voltage of our product is 9~16V. Now it is necessary to configure the window voltages of ACUV and ACOV through resistors. How should it be configured? For example, when ACUV is reduced to 7V, the reverse mode is automatically turned on.

    This design calculator should help choose the values for ACUV and ACOV:

    ? ? said:
    Because the current consumption of this device in the low - power mode is relatively large, which is 0.75mA. The current hardware design is to turn off the VAC input after entering sleep, with only battery power supply, REGN is turned off, and CE is in a floating state. In this case, can the REGN LDO be used as the pull - up for CE, PG, STAT and INT?

    REGN LDO should not be used as the pullup for CE. When the CE pin goes high, REGN will turn off and CE will then become low which will turn on REGN again.

    Best,
    Michael