BQ24232HA Datasheet, PDF (18/36 Pages) Texas Instruments – USB-Friendly Lithium-Ion Battery Charger

bq24232HA
SLUSCG4 – MAY 2016
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Feature Description (continued)
7.3.5 Battery Pack Temperature Monitoring
The bq24232HA features an external battery pack temperature monitoring input. The TS input connects to the
NTC resistor in the battery pack to monitor battery temperature and prevent dangerous over-temperature
conditions. Using the basic connection as shown in the Typical Application Circuit example, a nominal range of
0°C to 50°C is achieved using a standard 103AT – 2 type thermistor (ß = 3435) with no additional external
components.
During charging, INTC 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
7.3.5.1 Modifying and Extending the Allowable Temperature Range for Charging
The nominal temperature range to allow charging is 0°C to 50°C when using a typical 103AT-2 type thermistor.
However, the user can increase the range by adding two external resistors. See Figure 13 for the circuit. 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
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: Hot Trip Threshold of the IC = 0.3 V nominal
• V_C: Cold Trip Threshold of the IC = 2.1 V nominal
• I_TS: Output Current Bias of the IC = 75 µA nominal
• NTC Thermsitor Semitec 103AT-2 Type or equivalent
(3)
Table 2 provides examples of the thermistor resistance at different temperatures and suggested typical Rs and
Rp values, using 1% tolerance resistors that can extend the allowable temperature range beyond the standard
0°C – to – 50° C window.
Table 2. Example Thermistor Resistance and Suggested Typical Rs and Rp 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
18
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