BQ24315 Datasheet, PDF (9/20 Pages) Texas Instruments – OVERVOLTAGE AND OVERCURRENT PROTECTION IC AND Li+ CHARGER FRONT-END PROTECTION IC

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TYPICAL APPLICATION CIRCUIT
V_OVP = 5.85V, I_OCP = 1000mA, BV_OVP = 4.35V
AC Adapter
VDC
GND
1 ^IN
C_IN
1 mF
OUT ₈
1 mF
C_OUT
bq24315
VBAT ₆
R_BAT
100 kW
7
R_ILM
FAULT ₄
CE ₅
2
bq24080
Charger IC
V_PU
R_PU 47 kW
47 kW
R_FAULT
47 kW
R_CE
bq24315
SLUS817 – MARCH 2008
SYSTEM
Host
Controller
Figure 20.
DETAILED FUNCTIONAL DESCRIPTION
The bq24315 is an integrated circuit designed to provide protection to Li-ion batteries from failures of the
charging circuit. The IC continuously monitors the input voltage, the input current and the battery voltage. For an
input overvoltage condition, the IC immediately removes power from the charging circuit by turning off an internal
switch. For an overcurrent condition, it limits the system current at the threshold value, and if the overcurrent
persists, switches the pass element OFF after a blanking period. If the battery voltage rises to an unsafe level,
the IC disconnects power from the charging circuit until the battery voltage returns to an acceptable value.
Additionally, the IC also monitors its own die temperature and switches off if it exceeds 140°C. The input
overcurrent threshold is user-programmable. 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. The FET Q1 connected between 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. All internal counters and
other circuit blocks are reset. The IC then waits for duration t_DGL(PGOOD) for the input voltage to stabilize. If, after
t_DGL(PGOOD), the input voltage and battery voltage are safe, FET Q1 is turned ON. The IC has a soft-start feature
to control the inrush current. The soft-start minimizes the ringing at the input (the ringing occurs because the
parasitic inductance of the adapter cable and the input bypass capacitor form a resonant circuit). Because of the
deglitch time at power-on, if the input voltage rises rapidly to beyond the OVP threshold, the device will not
switch on at all, instead it will go into protection mode and indicate a fault on the FAULT pin.
OPERATION
The device continuously monitors the input voltage, the input current, and the battery voltage as described in
detail in the following sections.
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): bq24315
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