BQ24072 Datasheet, PDF (16/38 Pages) Texas Instruments – 1.2A USB-FRIENDLY Li-Ion BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24072, bq24073
bq24074, bq24075
SLUS810A – SEPTEMBER 2008 – REVISED DECEMBER 2008...................................................................................................................................... www.ti.com
DETAILED FUNCTIONAL DESCRIPTION
The bq2407x devices are integrated Li-Ion linear chargers and system power path management devices targeted
at space-limited portable applications. The device powers the system while simultaneously and independently
charging the battery. This feature reduces the number of charge and discharge cycles on the battery, allows for
proper charge termination and enables the system to run with a defective or absent battery pack. It also allows
instant system turn-on even with a totally discharged battery. The input power source for charging the battery
and running the system can be an AC adapter or a USB port. The devices feature Dynamic Power Path
Management (DPPM), which shares the source current between the system and battery charging, and
automatically reduces the charging current if the system load increases. When charging from a USB port, the
input dynamic power management (V_IN-DPM) circuit reduces the input current if the input voltage falls below a
threshold, preventing the USB port from crashing. The power-path architecture also permits the battery to
supplement the system current requirements when the adapter cannot deliver the peak system currents.
UNDERVOLTAGE LOCKOUT (UVLO)
The bq2407X family remains in power down mode when the input voltage at the IN pin is below the undervoltage
threshold (UVLO).
During the power down mode the host commands at the control inputs (CE, EN1 and EN2) are ignored. The Q1
FET connected between IN and OUT pins is off, and the status outputs CHG and PGOOD are high impedance.
The Q2 FET that connects BAT to OUT is ON. (If SYSOFF is high, Q2 is off). During power down mode, the
V_OUT(SC2) circuitry is active and monitors for overload conditions on OUT.
POWER ON
When V_IN exceeds the UVLO threshold, the bq2407x powers up. While V_IN is below V_BAT + V_IN(DT), the host
commands at the control inputs (CE, EN1 and EN2) are ignored. The Q1 FET connected between IN and OUT
pins is off, and the status outputs CHG and PGOOD are high impedance. The Q2 FET that connects BAT to
OUT is ON. (If SYSOFF is high, Q2 is off). During this mode, the V_OUT(SC2) circuitry is active and monitors for
overload conditions on OUT.
Once V_IN rises above V_BAT + V_IN(DT), PGOOD is driven low to indicate the valid power status and the CE, EN1,
and EN2 inputs are read. The device enters standby mode if (EN1 = EN2 = HI) or if an input overvoltage
condition occurs. In standby mode, Q1 is OFF and Q2 is ON so OUT is connected to the battery input. (If
SYSOFF is high, FET Q2 is off). During this mode, the V_OUT(SC2) circuitry is active and monitors for overload
conditions on OUT.
When the input voltage at IN is within the valid range: V_IN > UVLO AND V_IN > V_BAT + V_IN(DT) AND V_IN < V_OVP, and
the EN1 and EN2 pins indicate that the USB suspend mode is not enabled [(EN1, EN2) ≠ (HI, HI)] all internal
timers and other circuit blocks are activated. The device then checks for short-circuits at the ISET and ILIM pins.
If no short conditions exists, the device switches on the input FET Q1 with a 100mA current limit to checks for a
short circuit at OUT. When V_OUT is above V_SC, the FET Q1 switches to the current limit threshold set by EN1,
EN2 and R_ILIM and the device enters into the normal operation. During normal operation, the system is powered
by the input source (Q1 is regulating), and the device continuously monitors the status of CE, EN1 and EN2 as
well as the input voltage conditions.
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