bq24030, bq24031, bq24032,
bq24032A, bq24035, bq24038, bq24039
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SLUS618C–AUGUST 2004–REVISED JUNE 2005
CE Input (Chip Enable)
The CE (chip enable) digital input is used to disable or enable the IC. A high-level signal on this pin enables the
chip, and a low-level signal disables the device and initiates the standby mode. The bqTINY-III enters the
low-power standby mode when the CE input is low with either AC or USB present. In this suspend mode, internal
power FETs Q1 and Q3 (see block diagram) are turned off; the battery (BAT pin) is used to power the system via
Q2 and the OUT pin which also powers the LDO. This feature is designed to limit the power drawn from the input
supplies (such as USB suspend mode).
VBSEL INput (Battery Voltage Selection), bq24038
The VBSEL (battery voltage select) digital input pin can be used to set the charge voltage to 4.2 V typical
(VBSEL = low) or 4.36 V typical (VBSEL = high). If VBSEL is left open, an internal current source pulldown
ensures that the charge voltage is set to 4.2 V typical.
Charge Disable Functions
The DPPM input can be used to disable the charge process. This can be accomplished by floating the DPPM
mode. Note that this applies to both AC and USB charging.
Timer Fault Recovery
As shown in Figure 3, bqTINY-III 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: bqTINY-III 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 bqTINY-III 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 bqTINY-III 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 bqTINY-III disables the I(FAULT)
current and executes the recovery method described for condition 1. Once the battery falls below the recharge
threshold, the bqTINY-III 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 FETs (AC and USB) are
turned off. To recover from this state, a 500-Ω pullup resistor from each 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 FETs to be turned back on.
If the output drops 200 mV below the battery voltage, the battery FET 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 nV) / 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.
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