BQ24382 Datasheet, PDF (9/18 Pages) Texas Instruments – Overvoltage and Overcurrent Protection IC and Li+ Charger Front-End Protection IC With LDO Mode

bq24380
bq24381
bq24382
www.ti.com......................................................................................................................................................... SLUS805B – APRIL 2008 – REVISED MARCH 2009
DETAILED FUNCTIONAL DESCRIPTION
The bq2438x is a highly integrated circuit designed to provide protection to Li-ion batteries from failures of the
charging circuit and the input source. The IC continuously monitors the input voltage and the battery voltage. The
device operates like a linear regulator, maintaining a 5.5-V (bq24380) or 5-V (bq24381, bq24382) output with
input voltages up to the input overvoltage threshold (V_OVP). If the input voltage exceeds V_OVP, the IC shuts off the
pass FET and disconnects the system from input power. Additionally, if the battery voltage rises above 4.35 V,
the IC switches off the pass FET, removing the power from the system until the battery voltage falls to safe
levels. The IC also monitors its die temperature and switches the pass FET off if it exceeds 140°C.
The IC can be controlled by a processor, and also provides status information about fault conditions to the host.
POWER DOWN
The device remains in power-down mode when the input voltage at the IN pin is below the undervoltage
threshold (UVLO) of 2.8 V. The FET connected between the IN and OUT pins is off, and the status output,
FAULT, is set to HI-Z.
POWER ON RESET
The device resets when the input voltage at the IN pin exceeds the UVLO threshold. During power-on reset, the
IC waits for duration t_DGL(PGOOD) for the input voltage to stabilize. If, after t_DGL(PGOOD), the input voltage and battery
voltage are within operation limits, the pass FET is turned ON. The IC has a soft-start feature to control the
inrush current. The soft-start minimizes the ringing at the input due to the resonant circuit formed by the parasitic
inductance of the adapter cable and the input bypass capacitor. During the soft-start time, t_SStart, the current limit
is stepped up in 8 equal steps every 625µs. Each step is 1/8 of the I_O(SC). After the soft-start sequence is over,
the IC samples the load current. If the load current exceeds I_O(SC), the IC initiates short circuit protection. See the
Startup Short-Circuit Protection section for details. If no overcurrent event is measured, the current monitoring
circuitry is disabled for normal operation.
In the event a short-circuit is detected at power-on, to prevent the input voltage from spiking up when the pass
FET is switched off (due to the inductance of the input cable), The pass FET is turned off by gradually reducing
its gate-drive, resulting in a soft-stop (t_SStop).
DETAILED FUNCTIONAL DESCRIPTION
The device continuously monitors the input voltage and the battery voltage as described in detail below:
Input Overvoltage Protection
The OUT output of the bq2438x operates similar to a linear regulator. While the input voltage is less than
V_O(REG), and above the UVLO, the output voltage tracks the input voltage (less the drop caused by R_DS(on) of the
pass FET). When the input voltage is greater than V_O(REG) (plus the R_DS(on) drop) and less than V_OVP, the output
voltage is regulated to V_O(REG). V_O(REG) is 5.5 V for the bq24380, and 5 V for the bq24381 and bq24382. If the
input voltage is increased above V_OVP, the internal pass FET is turned off, removing power from the charging
circuitry connected to OUT. The FAULT output is then asserted low. When the input voltage drops below V_OVP –
V_hys(OVP) (but is still above UVLO), the pass FET is turned on after a deglitch time of t_REC(OVP). The deglitch time
ensures that the input supply has stabilized. The condition 5 in Figure 18 illustrates an input overvoltage event.
Battery Overvoltage Protection
The battery overvoltage threshold BV_OVP is internally set to 4.35 V for the bq2438x. Condition 3 in Figure 18
illustrates a battery overvoltage event. If the battery voltage exceeds the BV_OVP threshold for longer than
t_DGL(BVovp), the pass FET is turned off (using soft-stop), and FAULT is asserted low. The pass FET is turned on
(using the soft-start sequence) once the battery voltage drops to BV_OVP – V_hys(BVovp).
Thermal Protection
If the junction temperature of the device exceeds T_J(OFF), the pass FET is turned off, and the FAULT output is
asserted low. The FET is turned on when the junction temperature falls below T_J(OFF) – T_J(OFF-HYS).
Copyright © 2008–2009, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Link(s): bq24380 bq24381 bq24382