BQ24750_07 Datasheet, PDF (22/38 Pages) Texas Instruments – Host-controlled Multi-chemistry Battery Charger with Integrated System Power Selector and AC Over-Power Protection

bq24750
SLUS735 – DECEMBER 2006
www.ti.com
L_MIN = minimum output inductor
The ISYNSET comparator, or charge undercurrent comparator, compares the voltage between SRP-BAT and
internal threshold on the cycle-to-cycle base. The threshold is set to 13 mV on the falling edge, with an 8-mV
hysteresis on the rising edge with a 10% variation.
High Accuracy IADAPT Using Current Sense Amplifier (CSA)
An industry-standard, high-accuracy current-sense amplifier (CSA) allows a host processor or discrete logic to
monitor the input current through the analog voltage output of the IADAPT pin. The CSA amplifies the input
sensed voltage of ACP – ACN by 20× through the IADAPT pin. The IADAPT output is a voltage source 20× the
input differential voltage. When PVCC is above 5V and ACDET is above 0.6V, IADAPT no longer stays at
ground, but becomes active. If the designer needs to lower the voltage, a resistor divider from IOUT to AGND
can be used, while still achieving accuracy over temperature as the resistors can be matched for their thermal
coefficients.
A 200-pF capacitor connected on the output is recommended for decoupling high-frequency noise. An additional
RC filter is optional, after the maximum 200-pF capacitor, if additional filtering is desired. Note that adding
filtering also adds additional response delay.
Input Overvoltage Protection (ACOV)
ACOV provides protection to prevent system damage due to high input voltage. The controller enters ACOV
when ACDET > 3.1 V. Charge is disabled, the adapter is disconnected from the system by turning off ACDRV,
and the battery is connected to the system by turning on BATDRV. ACOV is not latched—normal operation
resumes when the ACDET voltage returns below 3.1 V. ACOV threshold is 130% of the adapter-detect
threshold.
Input Undervoltage Lockout (UVLO)
The system must have 5 V minimum of PVCC voltage for proper operation. This PVCC voltage can come from
either the input adapter or the battery, using a diode-OR input. When the PVCC voltage is below 5 V, the bias
circuits REGN, VREF, and the gate drive bias to ACFET and BATFET stay inactive, even with ACDET above
0.6 V.
Battery Overvoltage Protection
The converter stops switching when BAT voltage goes above 104% of the regulation voltage. The converter will
not allow the high-side FET to turn on until the BAT voltage goes below 102% of the regulation voltage. This
allows one-cycle response to an overvoltage condition, such as when the load is removed or the battery is
disconnected. A 10-mA current sink from BAT to PGND is on only during charge, and allows discharging the
stored output-inductor energy into the output capacitors.
Charge Overcurrent Protection
The charger has a secondary overcurrent protection feature. It monitors the charge current, and prevents the
current from exceeding 145% of regulated charge current. The high-side gate drive turns off when the
overcurrent is detected, and automatically resumes when the current falls below the overcurrent threshold.
Thermal Shutdown Protection
The QFN package has low thermal impedance, providing good thermal conduction from the silicon to the
ambient, to keep junction temperatures low. As an added level of protection, the charger converter turns off and
self-protects when the junction temperature exceeds the TSHUT threshold of 155°C. The charger stays off until
the junction temperature falls below 135°C.
Status Register (ACGOOD, DPMDET Pins)
Two status outputs are available, and both require external pullup resistors to pull the pins to the system digital
rail for a high level.
ACGOOD goes low when ACDET is above 2.4 V and the 700-ms delay time is over. It indicates that the adapter
voltage is high enough.
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