BQ24070RHLRG4 Datasheet, PDF (12/31 Pages) Texas Instruments – SINGLE-CHIP LI-ION CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24070
bq24071
SLUS694F – MARCH 2006 – REVISED DECEMBER 2009
www.ti.com
Autonomous Power Source Selection, Mode Control Pin
With the MODE input low, the bq24070/1 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 bq24070/1 offers a proprietary boot-up
sequence. On the first application of power to the bq24070/1, 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 bq24070/1 implement CE and ISET2 input settings. Table 1 indicates when this feature is enabled.
See Figure 9.
Power-Path Management
The bq24070/1 powers the system while independently charging the battery. This feature 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
IN
VDC
(2)
OUT
GND
System
Q1
PACK+
40 mΩ
BAT
+
PACK−
Q2
bq24070/1
UDG−04082
Figure 5. Power-Path Management
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 5). The output is regulated at 4.4 V (bq24070). 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.
1. This feature allows the designer to select a lower power wall adapter, if the average system load is moderate
compared to its peak power. For example, if the peak system load is 1.75 A, average system load is 0.5 A
and battery fast-charge current is 1.25 A, the total peak demand could be 3 A. With DPPM, a 2-A adaptor
could be selected instead of a 3.25-A supply. During the system peak load of 1.75 A and charge load of 1.25
A, the smaller adaptor’s voltage drops until the output voltage reaches the DPPM regulation voltage
threshold. The charge current is reduced until there is no further drop on the output voltage. The system gets
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