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[FAQ] BQ25731: Could I replace BQ25731 with BQ25730 in non-power-path applications?

Part Number: BQ25731
Other Parts Discussed in Thread: BQ25730,

BQ25730 and BQ25731 are buck-boost charge controllers, with same package, same pinout and similar functions. BQ25731 is specially designed for non-power-path applications. No battery MOSFET (BATFET) saves cost and increases efficiency.

Although both parts are similar in functions, there are a few register setting differences, for example the EN_LDO mode and default charge current for auto wakeup. Moreover, the BQ25731 is specially designed to handle the startup without BATFET. Therefore, we do not recommend to replace BQ25731 with BQ25730. They are not interchangeable parts. 

  • Still not convinced? You are advised of the following instructions before proceeding.

    When BATFET is removed, the system node VSYS is shorted to SRP. Before the converter starts operation, LDO mode needs to be disabled. The following sequence is required to configure charger without BATFET.

    1. Before adapter plugs in, put the charger into HIZ mode. (either pull pin 6 ILIM_HIZ to ground, or set REG0x35[7] to 1)
    2. Set 0x00[2] to 0 to disable LDO mode.
    3. Check if battery voltage is properly programmed (REG0x05/04)
    4. Set pre-charge/charge current (REG0x03/02)
    5. Put the device out of HIZ mode. (Release ILIM_HIZ from ground and set REG0x35[7]=0).

    In order to prevent any accidental SW mistakes, the host sets low input current limit (a few hundred milliamps) when device is out of HIZ.