BQ24273 Datasheet, PDF (12/27 Pages) Texas Instruments – 2.5A, Single Input, Single Cell Switchmode Li-Ion Battery Charger with Integrated Current Sense

bq24273
SLUSB08 – JUNE 2012
www.ti.com
LDO Output (DRV)
The bq24273 contains a linear regulator (DRV) that is used to supply the internal MOSFET drivers and other
circuitry. Additionally, DRV supplies up to 10mA external loads to power the STAT. The maximum value of the
DRV output is 5.45V. The LDO is on whenever a supply is connected to the IN input of the bq24273. The DRV is
disabled under the following conditions:
1. V_SUPPLY < UVLO
2. V_SUPPLY < V_SLP
3. Thermal Shutdown
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 bq24273 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 bq24273 enable the user to easily implement the JEITA standard for
charging temperature. The JEITA specification is shown in Figure 4.
1.0C
0.5C
4.25V
4.15V
4.1V
Portion of spec not covered by TS
Implementation on bq24273
T1
(0ºC)
T2
(10ºC)
T3
T4
(45ºC) (50ºC)
T5
(60ºC)
Figure 4. 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 < TNTC < 60°C) and the
hot battery threshold (TNTC > 60°C). These temperatures correspond to the V_COLD, V_COOL, V_WARM, and V_HOT
thresholds. Charging is suspended and timers are suspended when V_TS < V_HOT or V_TS > V_COLD. When V_HOT <
V_TS < V_WARM, the battery regulation voltage is reduced by 140mV from the programmed regulation threshold.
When V_COOL < V_TS < V_COLD, the charging current is reduced to half of the programmed charge current.
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 5. The resistor values are
calculated using the following equations:
RLO =
V_DRV
´ RCOLD
´
RHOT ´
é₁
ê
ë
V_COLD
-
1
V_HOT
ù
ú
û
RH
OT
´
é
ê
ë
V_DRV
V_HOT
ù
- 1_ú
û
-
R
COLD
´
é
ê
ë
V_DRV
V_COLD
ù
-1_ú
û
(1)
12
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