BQ24750_14 Datasheet, PDF (22/39 Pages) Texas Instruments – AC Overpower Protection

bq24750
SLUS735D – DECEMBER 2006 – REVISED MARCH 2009............................................................................................................................................... www.ti.com
where:
V_IN = adapter voltage
V_BAT = BAT voltage
f_{S =} switching frequency
L = output inductor
D = duty-cycle
I_{RIPPLE_MAX} Happens when the duty-cycle(D) is mostly near to 0.5 at given V_IN, f_s, and L.
The ISYNSET comparator, or charge undercurrent comparator, compares the voltage between SRP-SRN and
internal threshold. 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.
NOTE:
The bq24750 will not allow ACDRV to turn on in the unique condition that ACP<3V
and PVCC>UVLO. In this condition, the break-before-make protection latch gets stuck
in a state that it thinks the BATDRV is ON, and does not allow the ACDRV to turn on.
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.
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.
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