BQ24061 - Behavior when Charge Timer is Disabled?

Q: BQ24061 - Behavior when Charge Timer is Disabled? A

"We have a 2500mAHr battery and will be charging it through the USB port.  USB will limit our power to either 100mA or 500mA.  At 100mA the charging could take >25 hours. The TMR pin sets a charge timeout but it is limited to about 10 hours.  R(TMR)max is 100K.  If we leave the TMR pin floating this disables the charge timer, puts the part in LDO mode, and disables the charging termination circuit (page 13 - LDO Mode Operation).  In this mode is the part acting as a battery charger (CC and CV modes) without the charge termination circuits enabled? I'm somewhat confused by the datasheet."


A: Re: BQ24061 - Behavior when Charge Timer is Disabled?

Not sure what your confusion is....the term LDO in my opinion is a loosely used term for a low drop out device. A switcher could be a low drop out switcher.  Typically a LDO is always on if powered.  Removing the termination/timer feature allows this low drop out linear device to stay on.  In our LDO case the LDO (charger) has a current limit (fast charge and precharge) in addition to the regulated output voltage.  So no, LDO does not mean no current limit.

One can use a much higher resistor as long as the voltage does not get close to the termination disable threshold (2.5V minimum).  The reason the 10 hour spec is used is the the timer tolerance gets a little loose the wider the range and 10 hours is typically more than enough.

I would program it for 25 hours and see how it works. 
Always test 25% out side of the desired setting to see if the part still works or if one is up against some threshold.  If 31 hours still works then I would think that 25 hours would always work, but may have a sloppier accuracy.