BQ24070 Datasheet, PDF (12/26 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24070
SLUS694A – MARCH 2006 – REVISED MARCH 2006
www.ti.com
FUNCTIONAL DESCRIPTIONS (continued)
Autonomous Power Source Selection, Mode Control Pin
With the MODE input low, the bq24070 defaults to USB-mode charging, and the supply current is limited by the
ISET2 pin (100 mA for ISET2 = Low, 500 mA for ISET2 = High). If an input source is not available, then the
battery is selected as the source.
Boot-Up Sequence
In order to facilitate the system start-up and USB enumeration, the bq24070 offers a proprietary boot-up
sequence. On the first application of power to the bq24070, this feature enables the 100-mA USB charge rate
for a period of approximately 150 ms, (t_(BOOT-UP)), ignoring the ISET2 and CE inputs setting. At the end of this
period, the bq24070 implements CE and ISET2 inputs settings. Table 1 indicates when this feature is enabled.
See Figure 8.
Power-Path Management
The bq24070 powers the system while independently charging the battery. This features reduces the charge and
discharge cycles on the battery, allows for proper charge termination, and allows the system to run with an
absent or defective battery pack. This feature gives the system priority on input power, allowing the system to
power up with a deeply discharged battery pack. This feature works as follows.
AC Adapter
VDC
GND
IN
(2)
OUT
Q1
40 mΩ
Q2
bq24070
BAT
PACK+
+
PACK−
Figure 4. Power-Path Management
System
UDG−04082
Case 1: AC Mode (Mode = High)
System Power
In this case, the system load is powered directly from the AC adapter through the internal transistor Q1 (see
Figure 4). The output is regulated at 4.4 V. If the system load exceeds the capacity of the supply, the output
voltage drops down to the battery's voltage.
Charge Control
When in AC mode the battery is charged through switch Q2 based on the charge rate set on the ISET1 input.
Dynamic Power-Path Management (DPPM)
This feature monitors the output voltage (system voltage) for input power loss due to brown outs, current limiting,
or removal of the input supply. If the voltage on the OUT pin drops to a preset value, V_(DPPM) × SF, due to a
limited amount of input current, then the battery charging current is reduced until the output voltage stops
dropping. The DPPM control tries to reach a steady-state condition where the system gets its needed current
and the battery is charged with the remaining current. No active control limits the current to the system;
therefore, if the system demands more current than the input can provide, the output voltage drops just below
the battery voltage and Q2 turns on which supplements the input current to the system. DPPM has three main
advantages.
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