bq24070
bq24071
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SLUS694B–MARCH 2006–REVISED AUGUST 2006
Charge Disable Functions
The DPPM input can be used to disable the charge process. This can be accomplished by floating the DPPM
pin.
Timer Fault Recovery
As shown in Figure 3, bq24070/1 provides a recovery method to deal with timer fault conditions. The following
summarizes this method:
Condition 1: Charge voltage above recharge threshold (V(RCH)) and timeout fault occurs.
Recovery Method: bq24070/1 waits for the battery voltage to fall below the recharge threshold. This could
happen as a result of a load on the battery, self-discharge, or battery removal. Once the battery falls below the
recharge threshold, the bq24070/1 clears the fault and starts a new charge cycle. A POR or CE toggle also
clears the fault.
Condition 2: Charge voltage below recharge threshold (V(RCH)) and timeout fault occurs.
Recovery Method: Under this scenario, the bq24070/1 applies the I(FAULT) current. This small current is used to
detect a battery removal condition and remains on as long as the battery voltage stays below the recharge
threshold. If the battery voltage goes above the recharge threshold, then the bq24070/1 disables the I(FAULT)
current and executes the recovery method described for condition 1. Once the battery falls below the recharge
threshold, the bq24070/1 clears the fault and starts a new charge cycle. A POR or CE toggle also clears the
fault.
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 {Rload > 1 V × 500 Ω/ (Vin–Vout)} 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 (Vout<Vbat-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 VDPPM 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 VDPPM rise time is a function of the 100-µA DPPM current
source, the DPPM resistor, and the capacitor added.
VREF
The VREF 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 VREF pin. For internal compensation, the VREF pin
requires a minimum 0.1-µF ceramic capacitor. The VREF capacitor should not exceed 1 µF.
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