BQ24070RHLRG4 Datasheet, PDF (20/31 Pages) Texas Instruments – SINGLE-CHIP LI-ION CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24070
bq24071
SLUS694F – MARCH 2006 – REVISED DECEMBER 2009
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Short-Circuit Recovery
The output can experience two types of short-circuit protection, one associated with the input and one with the
battery.
If the output drops below ~1 V, an input short-circuit condition is declared and the input FET, Q1 is turned off. To
recover from this state, a 500-Ω pullup resistor from the input is applied (switched) to the output. To recover, the
load on the output has to be reduced {R_load > 1 V × 500 Ω/ (V_in–V_out)} such that the pullup resistor is able to lift
the output voltage above 1 V, for the input FET to be turned back on.
If the output drops 200 mV below the battery voltage, the battery FET, Q2 is considered in short circuit and the
battery FET turns off. To recover from this state, there is a 10-mA current source from the battery to the output.
Once the output load is reduced, such that the 10-mA current source can pick up the output within 200 mV of the
battery, the FET turns back on.
If the short is removed, and the minimum system load is still too large [R<(VBat-200 mV) / 10 mA], the
short-circuit protection can be temporarily defeated. The battery short-circuit protection can be disabled
(recommended only for a short time) if the voltage on the DPPM pin is less than 1 V. Pulsing this pin below 1 V,
for a few microseconds, should be enough to recover.
This short-circuit disable feature was implemented mainly for power up when inserting a battery. Because the
BAT input voltage rises much faster than the OUT voltage (V_out<V_bat-200 mV), with most any capacitive load on
the output, the part can get stuck in short-circuit mode. Placing a capacitor between the DPPM pin and ground
slows the V_DPPM rise time, during power up, and delays the short-circuit protection. Too large a capacitance on
this pin (too much of a delay) could allow too-high currents if the output was shorted to ground. The
recommended capacitance is 1 nF to 10 nF. The V_DPPM rise time is a function of the 100-μA DPPM current
source, the DPPM resistor, and the capacitor added.
V_REF
The V_REF is used for internal reference and compensation (3.3 V typ). Additionally, it can be used to disable the
safety timer and termination by connecting the TMR to the V_REF pin. For internal compensation, the V_REF pin
requires a minimum 0.1 μF ceramic capacitor. The V_REF capacitor should not exceed 1 μF.
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