BQ24075-Q1 Datasheet, PDF (25/36 Pages) Texas Instruments – 1.5A USB-FRIENDLY Li-Ion BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24075-Q1
www.ti.com
SLUSAU3B – FEBRUARY 2012 – REVISED MARCH 2012
BATTERY PACK TEMPERATURE MONITORING
The bq24075-Q1 features an external battery pack temperature monitoring input. The TS input connects to the
NTC thermistor in the battery pack to monitor battery temperature and prevent dangerous over-temperature
conditions. During charging, I_NTC is sourced to TS and the voltage at TS is continuously monitored. If, at any
time, the voltage at TS is outside of the operating range (V_COLD to V_HOT), charging is suspended. The timers
maintain their values but suspend counting. When the voltage measured at TS returns to within the operation
window, charging is resumed and the timers continue counting. When charging is suspended due to a battery
pack temperature fault, the CHG pin remains low and continues to indicate charging.
For applications that do not require the TS monitoring function, connect a 10kΩ resistor from TS to VSS to set
the TS voltage at a valid level and maintain charging.
The allowed temperature range for 103AT-2 type thermistor is 0°C to 50°C. However, the user may increase the
range by adding two external resistors. See Figure 31 for the circuit details. The values for Rs and Rp are
calculated using the following equations:
-(R_TH + R_TC ) ±
æ
ççè (R_TH+R_TC
)²
-
4
ì
íî^RTH
´
R_TC + _(VH
V_H ´ V_C
- V_C ) ´
I_TS
´ (R_TC
üö
-
R_TH
)_ý
þ
÷÷ø
Rs =
2
(2)
( ) _{Rp =} V_H ´ R_TH + R_S
( ) I_TS ´ R_TH + R_S - V_H
(3)
Where:
R_TH: Thermistor Hot Trip Value found in thermistor data sheet
R_TC: Thermistor Cold Trip Value found in thermistor data sheet
V_H: IC's Hot Trip Threshold = 0.3V nominal
V_C: IC's Cold Trip Threshold = 2.1V nominal
I_TS: IC's Output Current Bias = 75µA nominal
NTC Thermsitor Semitec 103AT-4
Rs and Rp 1% values were chosen closest to calculated values
Cold Temp Resistance and
Trip Threshold; Ω (°C)
28000 (–0.6)
28480 (–1)
28480 (–1)
33890 (–5)
33890 (–5)
33890 (–5)
Hot Temp Resistance and Trip
Threshold; Ω (°C)
4000 (51)
3536 (55)
3021 (60)
4026 (51)
3536 (55)
3021 (60)
External Bias Resistor, Rs (Ω)
0
487
1000
76.8
576
1100
External Bias Resistor, Rp (Ω)
∞
845000
549000
158000
150000
140000
Copyright © 2012, Texas Instruments Incorporated
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