BQ25071-Q1 Datasheet, PDF (14/22 Pages) Texas Instruments – Automotive Qualified

bq25071-Q1
SLUSCD6 – APRIL 2016
www.ti.com
Device Functional Modes (continued)
8.4.2 Programmable Input Current Limit (ISET)
When the charger is enabled, and the user programmable current limit is selected by the EN input, internal
circuits generate a current proportional to the input current at the ISET input. The current out of ISET is 1/1000
(±10%) of the charge current. This current, when applied to the external charge current programming resistor, R1
( Figure 11), generates an analog voltage that is regulated to program the fast charge current. Connect a resistor
from ISET to GND to program the input current limit using the following equation:
I_{(IN_LIM)}
=
K_(ISET)
R_(ISET)
= ^{1000A ´ W}
R_(ISET)
(3)
I_{(IN_LIM)} is programmable from 100 mA to 1 A. The voltage at ISET can be monitored by an external host to
calculate the charging current to the battery. The input current is related to the ISET voltage using the following
equation:
I_IN
=
V_(ISET)
´
1000
R_(ISET)
(4)
Monitoring the ISET voltage allows for the host to calculate the actual charging current and therefore perform
more accurate termination. The input current to the system must be monitored and subtracted from the current
into the bq25071-Q1 which is show by V_(ISET).
8.4.3 Sleep Mode
If the IN pin voltage is between V_(UVLO) and V_(BAT)+ V_IN(SLP), the charge current is disabled, the safety timer
counting stops (not reset) and the CHG pin is high impedance. As the input voltage rises and the charger exits
sleep mode, the safety timer continues to count, charge is enabled and the CHG pin returns to its previous state.
8.4.4 Thermal Regulation and Thermal Shutdown
The bq25071-Q1 contains a thermal regulation loop that monitors the die temperature continuously. If the
temperature exceeds T_J(REG), the device automatically reduces the charging current to prevent the die
temperature from increasing further. In some cases, the die temperature continues to rise despite the operation
of the thermal loop, particularly under high V_IN conditions. If the die temperature increases to T_J(OFF), the IC is
turned off. Once the device die temperature cools by T_J(OFF-HYS), the device turns on and returns to thermal
regulation. Continuous overtemperature conditions result in the pulsing of the load current. If the junction
temperature of the device exceeds T_J(OFF), the charge FET is turned off. The FET is turned back on when the
junction temperature falls below T_J(OFF) – T_J(OFF-HYS).
Note that these features monitor the die temperature of the bq25071-Q1. This is not synonymous with ambient
temperature. Self heating exists due to the power dissipated in the IC because of the linear nature of the battery
charging algorithm.
14
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