BQ25071-Q1 Datasheet, PDF (11/22 Pages) Texas Instruments – Automotive Qualified

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bq25071-Q1
SLUSCD6 – APRIL 2016
8.3 Feature Description
8.3.1 Input Overvoltage Protection
The bq25071-Q1 contains an input overvoltage protection circuit that disables the LDO output and charging
when the input voltage rises above V_(OVP). This prevents damage from faulty adapters. The OVP circuitry
contains an 100 μs blanking period that prevents ringing on the input from line transients from tripping the OVP
circuitry falsely. If an adapter with an output greater than V_(OVP) is plugged in, the IC completes soft-start power
up and then shuts down if the voltage remains above V_(OVP) after 100 μs. The LDO remains off and charging
remains disabled until the input voltage falls below V_(OVP).
8.3.2 Undervoltage Lockout (UVLO)
The bq25071-Q1 remains in power down mode when the input voltage is below the undervoltage lockout
threshold (V_(UVLO)). During this mode, the control input (EN) is ignored. The LDO, the charge FET connected
between IN and OUT are off and the status output (CHG) is high impedance. Once the input voltage rises above
V_(UVLO), the internal circuitry is turned on and the normal operating procedures are followed.
8.3.3 External NTC Monitoring (TS)
The bq25071-Q1 features a flexible, voltage based external battery pack temperature monitoring input. The TS
input connects to the NTC thermistor in the battery pack to monitor battery temperature and prevent dangerous
over-temperature conditions. During charging, the voltage at TS is continuously monitored. If the voltage at the
TS pin is outside of the operating range (V_(HOT) to V_(COLD) for longer than the built in 25 ms deglitch time,
charging is suspended. When the voltage measured at TS returns to within the operation window, charging
resumes. When a battery pack temperature fault occurs charging is suspended, but the CHG output remains low
and continues to indicate charging.
The temperature thresholds are programmed using a resistor divider from LDO to GND with the NTC thermistor
connected to the center tap from TS to GND. See Figure 9 for the circuit example. The value of R1 and R2 are
calculated using the following equations:
R1 = ^{-R2 ´ RHOT ´ (0.125 - 1)}
0.125 ´ (R2 + RHOT)
(1)
R2 =
-RHOT ´ RCOLD ´ (0.125 - 0.250)
RHOT ´ 0.250 ´ (0.125 - 1) + RCOLD ´ 0.125 ´ (1 - 0.250)
(2)
RHOT is the expected thermistor resistance at the programmed hot threshold; RCOLD is the expected thermistor
resistance at the programmed cold threshold.
LDO
VCOLD
+
R1
TS
TEMP
PACK +
VHOT
+
R2
PACK -
bq25071-Q1
For applications that do not require the TS monitoring function, set R1 = 490 kΩ and R2 = 100 kΩ to set the TS
voltage at a valid level and maintain charging.
Figure 9. NTC Monitoring Function
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