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STBC08 charger state outputs, GPIO, pullups

Question asked by Eliot Stock on Oct 9, 2017

Hi.

 

I have an STBC08 charger IC on a board here. It has two open drain output pins for state: CHARGE and POWER ON. It's this part:

 

STBC08 - 800mA STANDALONE LINEAR Li-Ion Battery charger with thermal regulation - STMicroelectronics 

 

The datasheet for the part has this to say about these two pins when they're in the "1" state:

 

"Output pin in high impedance (external pull-up needed)."

 

I have both these pins connected to a micro on which I've configured GPIO input pins with a pullup resistor. VDD on that micro is 3.0V. But when the pins go high on the STBC08, the micro does not see the input go high. The voltage on the output is about 1.2V, so, less than half of VDD for the micro. The micro is a Nordic Semiconductor nRF 52 series.

 

What could be the cause of this?

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