BQ25892: VSYS below 3.5 V when VBAT<3.5 V

Stefan Caps-Kuhn

Part Number: BQ25892

Hi, im designing a charging circuit with the BQ25892. However, when the battery voltage drops below 3.5 V, VSYS is not regulated above 3.5 V. VSYS has unfortunately the exact same voltage level as the battery.

I measured the following voltage levels at the GPIOs:

QON: 2.84 V
OTG: low
CE: low
PG: low, when Walladapter connected
STAT: low, when charging
PSEL: low
ILIM: 0.143V
REGN: 4.57 V, when Walladapter is connected
INT: 2.84 V

What could be the reason for VSYS to be <3.5 V?

over 2 years ago

+1 Garrett Kreger over 2 years ago

TI__Mastermind 31180 points

Hello,

Anytime your wall adapter input is not connected the SYS pin voltage will be the same as the voltage level of the battery. The buck converter in the BQ25892 must be switching for VSYS to be regulated above the Vsys_min setting. Vsys_min is default 3.5V and is set via bits 3-1 in REG03.

Assuming the input supply is connected VSYS will be <3.5V when SYS_MIN setting is changed to a lower value than default.

Best Regards,

Garrett

0 Stefan Caps-Kuhn over 2 years ago in reply to Garrett Kreger

Prodigy 10 points

Hello Garret,

thank you for your answer. So as i understand it is not possible to regulate VSYS to be >3.5 V, when VBAT<3.5 V, when the walladapter is not connected and therfore VBUS=0V?

Best Regards,

Stefan

+1 Garrett Kreger over 2 years ago in reply to Stefan Caps-Kuhn

TI__Mastermind 31180 points

Hi Stefan,

Your understanding is correct.

Best Regards,

Garrett

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BQ25892: VSYS below 3.5 V when VBAT<3.5 V