BQ24273 Datasheet, PDF (13/27 Pages) Texas Instruments – 2.5A, Single Input, Single Cell Switchmode Li-Ion Battery Charger with Integrated Current Sense

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bq24273
SLUSB08 – JUNE 2012
V_{DRV - 1}
RHI = ^VCOLD
1₊ 1
RLO RCOLD
(2)
Where:
V_COLD = 0.60 × V_DRV
V_HOT = 0.30 × V_DRV
Where RHOT is the NTC resistance at the hot temperature and RCOLD is the NTC resistance at cold
temperature.
The WARM and COOL thresholds are not independently programmable. The COOL and WARM NTC
resistances for a selected resistor divider are calculated using the following equations:
RCOOL =
RLO ´ 0.564 ´ RHI
RLO - RLO ´ 0.564 - RHI´ 0.564
(3)
RWARM =
RLO ´ 0.383 ´ RHI
RLO - RLO ´ 0.383 -RHI ´ 0.383
(4)
DISABLE
VBAT( REG) 1 x Charge/
– 140mV 0.5 x Charge
V_DRV
bq242702
TS COLD
+
TS COOL ₊
TS WARM ₊
TS HOT
+
V_DRV
RHI
TS
TEMP
PACK +
RLW
PACK-
Figure 5. TS Circuit
Thermal Regulation and Protection
During the charging process, to prevent chip overheating, bq24273 monitors the junction temperature, T_J, of the
die and begins to taper down the charge current once T_J reaches the thermal regulation threshold, T_REG. The
charge current is reduced to zero when the junction temperature increases about 10°C above T_REG. Once the
charge current is reduced, the system current is reduced while the battery supplements the load to supply the
system. This may cause a thermal shutdown of the bq24273 if the die temperature rises too high. At any state, if
T_J exceeds T_SHTDWN, bq24273 suspends charging and disables the buck converter. During thermal shutdown
mode, the PWM is turned off, all timers are suspended, and a single 128μs pulse is sent on the STAT and INT
outputs and the STATx and FAULT_x bits of the status registers are updated in the I²C. A new charging cycle
begins when T_J falls below T_SHTDWN by approximately 10°C.
Copyright © 2012, Texas Instruments Incorporated
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