BQ24187 Datasheet, PDF (21/44 Pages) Texas Instruments – 1A USB-OTG Support

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Not Recommended for New Designs
bq24187
SLUSBM0 – APRIL 2014
Device Functional Modes (continued)
Where:
V_COLD = 0.60 × V_DRV
V_HOT = 0.30 × V_DRV
RCOOL =
RLO ´ RHI´ 0.564
RLO - RLO ´ 0.564 - RHI´ 0.564
(3)
RWARM =
RLO ´ RHI´ 0.383
RLO - RLO ´ 0.383 - RHI´ 0.383
(4)
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 Equation 3 and Equation 4.
DISABLE
VBAT(REG) 1 x Charge/
– 100 mV 0.5 x Charge
V_DRV
bq24187
TS COLD
+
TS COOL ₊
TS WARM ₊
TS HOT
+
V_DRV
RHI
TS
PACK+
TEMP
RLO
+
–
PACK–
Figure 11. TS Circuit
8.4.1.1.11 Thermal Regulation and Protection
During the charging process, to prevent overheating in the chip, bq24187 monitors the junction temperature, T_J,
of the die and reduces the input current once T_J reaches the thermal regulation threshold, T_REG. The input
current is reduced to zero when the junction temperature increases about 10°C above T_REG. Once the input
current is reduced to 0, the system current is reduced while the battery supplements the load to supply the
system. When the input current is completely reduced to 0 and T_J>125°C, this is may cause a thermal shutdown
of the bq24187 if the die temperature rises too high. At any state, if T_J exceeds T_SHTDWN, bq24187 stops charging
and disables the buck converter. During thermal shutdown mode, 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. The charge cycle resumes when T_J falls below T_SHTDWN by approximately 10°C.
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