BQ24072 Datasheet, PDF (18/38 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
OVERVOLTAGE PROTECTION (OVP)
The bq2407x accepts inputs up to 28V without damage. Additionally, an overvoltage protection (OVP) circuit is
implemented that shuts off the internal LDO and discontinues charging when V_IN > V_OVP for a period long than
t_DGL(OVP). When in OVP, the system output (OUT) is connected to the battery and PGOOD is high impedance.
Once the OVP condition is removed, a new power on sequence starts (See the SubSec2 0.1 section). The safety
timers are reset and a new charge cycle will be indicated by the CHG output.
DYNAMIC POWER-PATH MANAGEMENT
The bq2407x features an OUT output that powers the external load connected to the battery. This output is
active whenever a source is connected to IN or BAT. The following sections discuss the behavior of OUT with a
source connected to IN to charge the battery and a battery source only.
INPUT SOURCE CONNECTED (ADAPTER or USB)
With a source connected, the dynamic power-path management (DPPM) circuitry of the bq2407x monitors the
input current continuously. The OUT output for the bq24073/ 74/ 75 is regulated to a fixed voltage (V_O(REG)). For
the bq24072, OUT is regulated to 200mV above the voltage at BAT. When the BAT voltage falls below 3.2V,
OUT is clamped to 3.4V. This allows for proper startup of the system load even with a discharged battery. The
current into IN is shared between charging the battery and powering the system load at OUT. The bq2407x has
internal selectable current limits of 100mA (USB100) and 500mA (USB500) for charging from USB ports, as well
as a resistor-programmable input current limit.
The bq2407x is USB IF compliant for the inrush current testing. The USB spec allows up to 10µF to be hard
started, which establishes 50µC as the maximum inrush charge value when exceeding 100mA. The input current
limit for the bq2407x prevents the input current from exceeding this limit, even with system capacitances greater
than 10µF. Note that the input capacitance to the device must be selected small enough to prevent a violation
(<10µF), as this current is not limited. Figure 35 demonstrates the startup of the bq2407x and compares it to the
USB-IF specification.
10 μC
50 μC
100 μs/div
Figure 35. USB-IF Inrush Current Test
The input current limit selection is controlled by the state of the EN1 and EN2 pins as shown in Table 1. When
using the resistor-programmable current limit, the input current limit is set by the value of the resistor connected
from the ILIM pin to VSS, and is given by the equation:
I_IN-MAX = K_ILIM/R_ILIM
The input current limit is adjustable up to 1.5A. The valid resistor range is 1.1 kΩ to 8 kΩ.
When the IN source is connected, priority is given to the system load. The DPPM and Battery Supplement
modes are used to maintain the system load. Figure 37 and Figure 38 illustrate examples of the DPPM and
supplement modes. These modes are explained in detail in the following sections.
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