pgood¶

Reads the state of the PGOOD pin on the bq24074.

Sketch¶

The sketch can be found here.

Hypothesis¶

The PGOOD pin is pulled to GND when the LiPo battery on the bq24074 is fully charged. The Feather can be used to read the state of that pin to determine if the battery is fully charged.

One potential problem is that the pulled high resistor on pin 14 can cause issues to the PGOOD pin.

This method theoretically can use the Feather to also read the state of the CHG pin on the bq24074 which indicates when the LiPo battery is charging.

Assumptions¶

The pulled high resistor on pin 14 does not cause an issue with the PGOOD pin.

Procedure¶

Circuit¶

Connect a LiPo battery to the LiPo Batt JST connector on the bq24074.
Connect the JST connector on the Feather to the LIPO and GND pins on bq24074 so that the Feather is powered by bq24074 and that there is a common ground.
Add a 10kΩ pull up resistor to pin 14 on the Feather and pin 3.3V.
Connect pin 14 on the Feather to the PGOOD pin on the bq24074.
Plug in the USB port on the bq24074 to 5V power.

Circuit made with Circuit Diagram

Code¶

The sketch reads the opposite of pin 14 so when the PGOOD pin is open, pin 14 is pulled high and the value of pin 14 is 0. When PGOOD is pulled to GND (open drain), pin 14 is also pulled to GND but the output value is read as 1.

Output¶

test title=Typical Output test: pgood Digial Read: Pin: 14 Value: 0 Digial Read: Pin: 14 Value: 1

When the USB power supply is not plugged into the bq24074, the PGOOD green LED is off and the value of pin 14 is 0. The built in red LED on the Feather is off.

When the USB power supply is plugged into the bq24074, the PGOOD green LED turns on if the LiPo battery is full and the value of pin 14 is 1. The built in red LED on the Feather is blinking.

Analysis¶

Everything worked as expected. The value of pin 14 was correct when the green LED was on or off. The built in red LED on the Feather blinked when the green LED was on and off when the green LED was off.

Conclusion¶

The Feather can be used to read the state of PGOOD pin and therefore the state of the CHG pin as well.