BQ24171 Datasheet, PDF (22/35 Pages) Texas Instruments – JEITA Compliant Stand-Alone Switch-Mode Li-Ion and Li-Polymer Battery Charger with Integrated MOSFETs and Power Path Selector

bq24171
SLUSAF2A – FEBRUARY 2011 – REVISED MAY 2011
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TEMPERATURE QUALIFICATION AND JEITA GUIDELINE
The controller continuously 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 controller 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 V_T1 to V_T5 thresholds. If V_TS is outside of this
range, the controller suspends charge and waits until the battery temperature is within the V_T1 to V_T5 range.
During the charge cycle the battery temperature must be within the V_T1 to V_T5 thresholds. If battery temperature
is outside of this range, the controller suspends charge and waits until the battery temperature is within the V_T1 to
V_T5 range. The controller suspends charge by turning off the PWM charge FETs. If V_TS is within the range of V_T1
and V_T2, charge voltage regulation on FB pin is 2.1 V and the charge current is reduced to I_CHARGE/2 (To avoid
early termination during V_T1 and V_T2 range, fast charge current need to be bigger than 2 times of termination
current); if V_TS is within the range of V_T2 and V_T3, the charge voltage regulation on FB pin is 2.1 V; if V_TS is within
V_T3 and V_T4, the charge voltage regulation on FB pin is reduced back to 2.05 V; and if V_TS is within V_T4 and V_T5,
the charge voltage regulation on FB pin is further reduced to 2.025 V. Figure 20 below summarizes the
operation. See the Li-ion battery-charger solutions for JEITA compliance, SLYT365
Charge Voltage
VFB=2.1 V
VFB=2.05 V
VFB=2.025 V
Charge Current
Charge
Suspended
ICharge
ICharge/2
Temperature
Charge
Suspended
0 °C
10 °C
(T1)
(T2)
45 °C 50°C
(T3) (T4)
Temperature
60 °C
(T5)
Figure 20. TS Pin, Thermistor Sense Thresholds
Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 21, the values of RT1 and RT2 can
be determined by using Equation 9 and Equation 10:
RT2 =
V_VREF
´
RTH_COLD
´
RTH_HOT
´
æ1
ç
è
VT1
-
1ö
VT5
÷
ø
RTH_HOT
´
æ
ç
è
V_VREF
VT5
-1^ö÷ - RTH_COLD
ø
´
æ
ç
è
V_VREF
VT1
- 1^ö÷
ø
(9)
V_{VREF -1}
RT1 =
VT1
1
1
+
RT2 RTH_COLD
(10)
22
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