RVG,
The part monitors battery temperature by measuring the voltage between the TS pin and GND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this voltage. The bq5105x compares this voltage against its internal thresholds to determine if charging is allowed. To initiate a charge cycle, the voltage on TS pin must be within the VT1 to VT4 (thresholds See DS). If VTS is outside of this range, the bq5105x suspends charge and waits until the battery temperature is within the VT1 to VT4 range.
If VTS is within the range of VT1 and VT2, the charge current is reduced to IBULK/2. If VTS is within the range of VT2 and VT3, the maximum charge voltage regulation is 4.25V. If VTS is within VT3 and VT4, the maximum charge voltage regulation is reduced back to 4.10V and charge current is reduced to IBULK/2. Figure 19 in th DS summarizes the operation.
The efficiency can be measured from coil to output. Effi=pout/pin=vout*iout/(Icoit*VCOIL in AC)
This app note is good reference.
http://www.ti.com/product/bq51050b
Thanks
Tahar