BQ24170 Datasheet, PDF (24/35 Pages) Texas Instruments – 1.6-MHz Synchronous Switch-Mode Li-Ion and Li-Polymer Stand-Alone Battery Charger

bq24170
bq24172
SLUSAD2A – NOVEMBER 2010 – REVISED NOVEMBER 2010
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TEMPERATURE QUALIFICATION
The controller continuously monitors battery temperature by measuring the voltage between the TS pin and
AGND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this
voltage. The controller compares this voltage against its internal thresholds to determine if charging is allowed.
To initiate a charge cycle, the battery temperature must be within the V_LTF to V_HTF thresholds. If battery
temperature is outside of this range, the controller suspends charge and waits until the battery temperature is
within the V_LTF to V_HTF range. During the charge cycle the battery temperature must be within the V_LTF to V_TCO
thresholds. If battery temperature is outside of this range, the controller suspends charge and waits until the
battery temperature is within the V_LTF to V_HTF range. The controller suspends charge by turning off the PWM
charge MOSFETss. Figure 22 summarizes the operation.
TEMPERATURE RANGE
TO INITIATE CHARGE
VREF
CHARGE SUSPENDED
VLTF
VLTFH
TEMPERATURE RANGE
DURING A CHARGE CYCLE
VREF
CHARGE SUSPENDED
VLTF
VLTFH
CHARGE at full C
CHARGE at full C
VHTF
CHARGE SUSPENDED
VTCO
CHARGE SUSPENDED
AGND
AGND
Figure 22. TS Pin, Thermistor Sense Thresholds
Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 23, the values of RT1 and RT2 can
be determined by using Equation 10 and Equation 11:
RT2 =
V_VREF
´ RTH_COLD ´ RTH_HOT
´
æ
ç
1
-
1
ö
÷
è ^VLTF ^VTCO ø
RTH_HOT
´
æ
ç
è
V_VREF
V_TCO
-
ö
1_÷
ø
-
RTH_COLD
´
æ
ç
V_VREF
- 1^ö÷
è ^VLTF ø
(10)
RT1 =
V_{VR EF}
V_{LT F}
-1
1
1
+
RT2 RTH_{CO LD}
(11)
Select 0°C to 45°C range for Li-ion or Li-polymer battery,
RTH_COLD = 27.28 kΩ
RTH_HOT = 4.911 kΩ
RT1 = 5.23 kΩ
RT2 = 30.1 kΩ
After select closest standard resistor value, by calculating the thermistor resistance at temperature threshold, the
final temperature range can be gotten from thermistor datasheet temperature-resistance table.
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