BQ24055

The absolute maximum ratings state that the maximum sink current for the /CHG (and the /PG although not stated) is 15mA.  So I suggest a resistor that results in no more than 10mA sink current.

Is termination disabled due to TS voltage or VINDPM being active?

I believe the termination is due to VINDPM being active.  Is there a formula to calculate the correct pull-up resistor value?  Or is this determine via trial and error?  The 10mA sink current is, the sinking input to the MCU pin correct?

The sink current is into the charge /CHG or /PG pins.  They are open drain FETs that sink current when active low.  The sink current is approximately (Vpullup - Vds) / Resistance.  Vds is the drain to source of the FET when operating as a switch and is needs to be lower the 0.3V. 

Is 3.3V power rail the Vpull- up? What is the value of Vds?  

The Vpull-up can be whatever rail you want that is less than the IC input voltage.  Vds is the internal FET drain to source voltage.  When used as a FET, it is the FET's saturation voltage and can't be higher than the /CHG, /PG low level maximum voltage.

What are you refereeing to “Vds is the internal FET drain to source voltage?” Do you mean this is inside the charging control?  Or do I need external MOSFET circuit?

The /PG and /CHG pins connect to the drains of FETs that are inside the charger IC.

“The sink current is approximately (Vpullup - Vds) / Resistance”, how do I determine the Vds value, where is Vds coming from?

Can someone reply to my questions please?

Vds is the minimum voltage required across the drain and source of a FET when it used as a switch.  It is typically around 0.1V-0.2V.  Since the VIL spec for the /PG and /CHG pins is 0.4V, the internal drive voltage for the FET will be enough to ensure that Vds stays below 0.4V as long the pull up resistor is sized to account for such a drop.

My Vpull-up is 3.3 and if Vds is 0.1-0.2V. To get the sink current < 10mA for the /PG and /CHG pins, the resistor value is ~340 ohms. This seems to be too low for Rpull-up. Am I missing something? Even thought the battery is fully charged, no change in status on MCU display.

Pull ups in the 1k to 10k range are typical. The IC would not be damaged with a 340 ohm pull up.

Regarding the status, unless termination is disabled due the TS pin voltage being out of normal charging range or due to the input voltage being too high or too low, the /CHG pin should go from low impedance to high impedance when the battery reaches regulation and the charge current drops below the termination current. 

The battery is fully charged, the charge current drops below the termination current, the CHG LED is off and the CHG pin goes to high impedance; however I am measuring 0.511V on the TS pin. Why is the TS pin not out of its normal charging range? 

As long as power is applied, the TS pin is sourcing current into the thermistor.  0.511V is in between the V(TS-10)=790mV and V(TS-45) = 278mV voltage thresholds, meaning the battery temperature is between 10C and 45C.  

I do not have a thermistor connected between TS and VSS pin. I have 10K resistor between TS and VSS pin. On your previous reply you mentioned “Regarding the status, unless termination is disabled due the TS pin voltage being out of normal charging range or due to the input voltage being too high or too low, the /CHG pin should go from low impedance to high impedance when the battery reaches regulation and the charge current drops below the termination current.” As I understand the statement, for the status to change the termination must be disable due to the TS pin voltage being out of normal charging range.  

The 10k thermistor is simulating a thermistor at 25C.  The TS feature is not limiting charge current.

What is consider low to high impedance on the CHG pin when the battery reaches regulation and the charge current drops below the termination current?

I am still not seeing change in status on the MCU display.

The /CHG pin is open drain of a nFET. HiZ means the nFET is not on and therefore pulling that pin to GND.  Is the battery voltage at the IC BAT pin above VBATREG-VRECH?  Is the battery current below the termination current value for the 29ms typical deglitch time (i.e., there are no load transients during this time)? 

Yes, the battery voltage is 4.19V and the current termination is set to 80mA which is 10% of the charging current (800mA) and yes the battery current is below the termination current value at 60mA.

If current is still flowing at 60mA, then you have not terminated.  The IC automatically disables termination if

1.  You are in USB100 mode (ISET2 is floating)

2.  The IC thermal regulation loop is active (i.e, the IC's internal junction temperature is above 125C)

3.  The input DPM loop is active (i.e, the IN pin voltage has dropped to the input DPM threshold of 4.3V-4.4V).