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bq24618

Perico Eldelospalotes
Intellectual 505 points
Other Parts Discussed in Thread: BQ24618, BQ24296

Hi.

I have been reading bq24618 datasheet. I want to use this charger with either USB or WALL ADAPTER. I have seen that a pin is used to set the charging current (ISET1). Imagine we want to power the system and charge the battery via USB. Imagine too that the maximum current avaliable from the USB port is 100 mA. Imagine my system needs, for example, 50 mA. The ISET1 has been set to 1A charging current. What will happens? The current to the system will be 50 mA and the remaining current will go to the battery despite the charging current has been set to 1A?

Thank you in advance.

  • 0
    TI__Expert 5565 points

    Hi Perico,

    If you set the charge current to 1A, then the battery charger will try to charge with 1A as long as the input voltage to the charger is >150mV higher than the VCC voltage. However, in this case since the USB supply can only supply 100mA, the input voltage will crash (mostly like the battery voltage) which will trigger sleep mode (sleep mode is when VCC - SRN < 150mV).

    I highly recommend against setting charging current to 1A if your supply is only 100mA. Is your application designed to draw the maximum current from the USB port (USB2 = 500mA max, USB3 = 900mA max)? If your input supply current could vary, but you want to make sure your charging current doesn't cause the USB voltage to crash, I recommend one of the following solutions:

    1. If you have a host controller (like an MCU) in your system - upon detection of USB type (1, 2, or 3), have the MCU drive a FET to change the resistor divider on the ISET1 pin (which will change V_ISET1). This will change your charging current for the USB port you are plugged into. You can do this with ACSET pin as well (which I recommend) which will change your input current limit accordingly (and your system + battery current will not exceed your input current). The battery charging current will be reduced (to 0mA if necessary) so that the system load is prioritized.
    2. Take a look at the bq24296 - if you have a host controller with I2C master capability, you can change the input current limit via I2C upon detection of your USB port.