BQ25890H Datasheet, PDF (29/66 Pages) Texas Instruments – I2C Controlled Single Cell 5-A Fast Charger

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8.2.13 Input Current Limit on ILIM
BQ25890H
SLUSCC5 – SEPTEMBER 2016
For safe operation, the device has an additional hardware pin on ILIM to limit maximum input current on ILIM pin.
The input maximum current is set by a resistor from ILIM pin to ground as:
I_INMAX
=
K_ILIM
R_ILIM
(3)
The actual input current limit is the lower value between ILIM setting and register setting (IINLIM). For example, if
the register setting is 111111 for 3.25 A, and ILIM has a 260-Ω resistor (KILIM = 390 max.) to ground for 1.5 A,
the input current limit is 1.5 A. ILIM pin can be used to set the input current limit rather than the register settings
when EN_ILIM bit is set. The device regulates ILIM pin at 0.8 V. If ILIM voltage exceeds 0.8 V, the device enters
input current regulation (Refer to Dynamic Power Management section).
The ILIM pin can also be used to monitor input current when EN_ILIM is enabled. The voltage on ILIM pin is
proportional to the input current. ILIM pin can be used to monitor the input current following Equation 4:
I_IN
=
K_ILIM
R_ILIM
x
x
V_ILIM
0.8 V
(4)
For example, if ILIM pin is set with 260-Ω resistor, and the ILIM voltage is 0.4 V, the actual input current 0.615 A
- 0.75 A (based on KILM specified). If ILIM pin is open, the input current is limited to zero since ILIM voltage
floats above 0.8 V. If ILIM pin is short, the input current limit is set by the register.
The ILIM pin function can be disabled by setting EN_ILIM bit to 0. When the pin is disabled, both input current
limit function and monitoring function are not available.
8.2.14 Thermal Regulation and Thermal Shutdown
8.2.14.0.1 Thermal Protection in Buck Mode
The device monitors the internal junction temperature T_J to avoid overheat the chip and limits the IC surface
temperature in buck mode. When the internal junction temperature exceeds the preset thermal regulation limit
(TREG bits), the device lowers down the charge current. The wide thermal regulation range from 60ºC to 120ºC
allows the user to optimize the system thermal performance.
During thermal regulation, the actual charging current is usually below the programmed battery charging current.
Therefore, termination is disabled, the safety timer runs at half the clock rate, and the status register
THERM_STAT bit goes high.
Additionally, the device has thermal shutdown to turn off the converter and BATFET when IC surface
temperature exceeds T_SHUT. The fault register CHRG_FAULT is set to 10 and an INT is asserted to the host. The
BATFET and converter is enabled to recover when IC temperature is below T_{SHUT_HYS}.
8.2.14.0.2 Thermal Protection in Boost Mode
The device monitors the internal junction temperature to provide thermal shutdown during boost mode. When IC
surface temperature exceeds T_SHUT, the boost mode is disabled (converter is turned off) by setting
OTG_CONFIG bit low and BATFET is turned off. When IC surface temperature is below T_{SHUT_HYS}, the BATFET
is enabled automatically to allow system to restore and the host can re-enable OTG_CONFIG bit to recover.
8.2.15 Voltage and Current Monitoring in Buck and Boost Mode
8.2.15.1 Voltage and Current Monitoring in Buck Mode
The device closely monitors the input and system voltage, as well as HSFET current for safe buck and boost
mode operations.
8.2.15.1.1 Input Overvoltage (ACOV)
The input voltage for buck mode operation is V_{VBUS_OP}. If VBUS voltage exceeds V_ACOV, the device stops
switching immediately. During input over voltage (ACOV), the fault register CHRG_FAULT bits sets to 01. An INT
is asserted to the host..
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