BQ24187 Datasheet, PDF (20/44 Pages) Texas Instruments – 1A USB-OTG Support

bq24187
SLUSBM0 – APRIL 2014
Not Recommended for New Designs
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Device Functional Modes (continued)
8.4.1.1.10 External NTC Monitoring (TS)
The I²C interface allows the user to easily implement the JEITA standard for systems where the battery pack
thermistor is monitored by the host. Additionally, the bq24187 provides a flexible, voltage based TS input for
monitoring the battery pack NTC thermistor. The voltage at TS is monitored to determine that the battery is at a
safe temperature during charging. The JEITA specification is shown in Figure 10.
1.0 C
Charging Current 0.5 C
4.25 V
V_BAT 4.15 V
4.1 V
Portion of spec not covered by TS
Implementation on bq24187
T1
(0°C)
Cold
T2
(10°C)
Cool
T3 T4
(45°C) (50°C)
Warm
T5
(60°C)
Hot
Figure 10. Charge Current During TS Conditions
To satisfy the JEITA requirements, four temperature thresholds are monitored; the cold battery threshold (T_NTC <
0°C), the cool battery threshold (0°C < T_NTC < 10°C), the warm battery threshold (45°C < T_NTC < 60°C) and the
hot battery threshold (T_NTC > 60°C). These temperatures correspond to the V_COLD, V_COOL, V_WARM, and V_HOT
thresholds in the EC table. Charging is suspended and timers are suspended when V_TS < V_HOT or V_TS > V_COLD.
When V_COOL < V_TS < V_COLD, the charging current is reduced to half of the programmed charge current. When
V_HOT < V_TS < V_WARM, the battery regulation voltage is reduced by 140mV from the programmed regulation
threshold. The TS function is disabled by connecting TS directly to DRV (V_TS > V_TSOFF).
The TS function is voltage based for maximum flexibility. Connect a resistor divider from DRV to GND with TS
connected to the center tap to set the threshold. The connections are shown in Figure 11. The resistor values are
calculated using the following equations:
RLO =
V_DRV
´ RCOLD
´ RHOT
´
é
ê
ë
1
V_COLD
1^ù
-
V_HOT
ú
û
RHOT
´
é
ê
ë
V_DRV
V_HOT
-
1^ùú
û
-
RCOLD
´
é
ê
ë
VDRV
V_COLD
- 1^ùú
û
(1)
RHI =
V_DRV
V_COLD
-1
1
1
RLO ⁺ RCOLD
(2)
20
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