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[FAQ] BQ25890: Why VSYS does not start up normally when there is a loading on the SYS and the battery is not present for BQ25890, BQ25890H, BQ25892, BQ25895, BQ25895M, BQ25896, BQ25898, BQ25898D, BQ25898C, BQ24190, BQ24192, BQ24192I, BQ24195, BQ24292I...

Ning T
Guru 54131 points
Part Number: BQ25890
Other Parts Discussed in Thread: BQ24190, BQ25898, BQ24296, BQ24192I, BQ25895, BQ25896, BQ24193, BQ24192, BQ24292I, , BQ24295, BQ24298, BQ25898C, BQ25898D, , BQ24259, BQ25895M, BQ25892, BQ24296M, BQ24195, BQ24196, BQ24297, BQ24195L

Hi,

It was observed that VSYS could not start up normally with some loading on SYS when the battery is not present . This applies for BQ25890, BQ25890H, BQ25892, BQ25895, BQ25895M, BQ25896, BQ25898, BQ25898D, BQ25898C, BQ24190, BQ24192, BQ24192I, BQ24193, BQ24195, BQ24195L, BQ24196, BQ24292I, BQ24295, BQ24296, BQ24297, BQ24296M, BQ24259, BQ24298. The reasons are listed below:

  • Referring to the charger IC datasheet, the input current limit is set to IIN(START) internally if the voltage on SYS pin VSYS is less than the typical 2.2V. As shown by the BQ25895 and BQ25898D datasheet below as an example below, the input is limited to 200mA maximum.

            As shown by the BQ24192 or BQ24296 datasheets, the input current is limited to 100mA typical.

  • When the charger is powered up without the battery’s presence, VSYS will start from 0V and the input current is limited. If the SYS load tries to pull more than IIN(START) input current, VSYS may be current-limited so that VSYS can’t start up normally.
  • In order to start up VSYS normally, the system loading on SYS pin should be applied after the SYS voltage has been ramped up above 2.2V.