FRDM-FXS-MULTI-B Li-Po charger LED never goes off.

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FRDM-FXS-MULTI-B Li-Po charger LED never goes off.

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bonzo
NXP Employee
NXP Employee

Hello,

The FRDM-FXS-MULTI-B uses a MC34673 to charge the internal Li-Po Battery.

But the CHG Green LED never turns off, even if charged overnight.  I tried removing J22, but that didn't help.

According to the MC34673 manual, this pin should go high (turning off the LED) once the battery is fully charged.

The PPR orange LED is on when I have the USB plugged in.

This sensor board is connected to a FRDM-KL25Z.  It all works great when communicating via BlueTooth to my Samsung Galaxy Tab.

Thanks,

Brad

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Joshevelle
Senior Contributor I

Hello Brad,

The green LED will turn off when the End-of-Charge (EOC) condition is meet.

The EOC threshold is set ~10% of the Ichg in the ISET pin. In the FRDM-FXS-MULTI-B a 22Kohm resistor is connected to the ISET pin of the MC34673, this pin is fixed to 1v, then the charge current is set to ~45mA, hence the EOC threshold is ~4.5mA. So the green LED will be ON as long as the current provided by the BAT pin in the MC34673 is higher than 4.5mA.

Please take a look at the schematics for the FRDM-FXS-MULTI-B, notice that SW1 connects the battery to the charger or to the FRDM system, what is the SW1 position when you charge the battery?

Do you have the header J19? if yest, is it in short circuit (AUTO-CHARGE option)? Please notice that if the header J19 is present and in short circuit, it means that the FRDM system would draw current from both, the battery and the charger, hence if the current provided by the charger is higher than 4.5mA, the green led would always be on.

- What is the revision number of your FRDM-KL25Z?

- Can you please measure the voltage in the ISET pin of the MC34673? it should be 1v.

- What is the voltage in the VIN pin of the MC34673? it should be 5v

Hope it helps.

Josh

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