BQ24030_07 Datasheet, PDF (14/38 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC (bqTINY)

bq24030, bq24031, bq24032A
bq24035, bq24038
SLUS618F – AUGUST 2004 – REVISED NOVEMBER 2006
www.ti.com
AC Adapter
USB Port
D+
D−
VBUS
VDC
GND
GND
AC
(2)
OUT
Q1
USB
40 mΩ
BAT
Q3
Q2
bq2403x
Figure 4. Power-Path Management
PACK+
+
PACK−
System
UDG−04082
Case 1: AC Mode (PSEL = High)
System Power
In this case, the system load is powered directly from the AC adapter through the internal transistor Q1 (see
Figure 4). For bq24030/31, Q1 acts as a switch as long as the AC input remains at or below 6 V (V_O(OUT-REG)).
Once the AC voltage goes above 6 V, Q1 starts regulating the output voltage at 6 V. For bq24035, once the AC
voltage goes above V_CUT-OFF (~6.4 V), Q1 turns off. For bq24032A/38, the output is regulated at 4.4 V from the
AC input. Note that switch Q3 is turned off for both devices. If the system load exceeds the capacity of the
supply, the output voltage drops down to the battery's voltage.
Charge Control
When AC is present, 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-SET) × 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
its 1.75-A charge and the battery charge current is reduced from 1.25 A to 0.25 A. When the peak system
load drops to 0.5 A, the charge current returns to 1 A and the output voltage returns to its normal value.
2. Using DPPM provides a power savings compared to configurations without DPPM. Without DPPM, if the
system current plus charge current exceed the supply’s current limit, then the output is pulled down to the
battery. Linear chargers dissipate the unused power (V_IN-V_OUT) × I_LOAD. The current remains high (at current
limit) and the voltage drop is large for maximum power dissipation. With DPPM, the voltage drop is less
(V_IN-V_(DPPM-REG)) to the system which means better efficiency. The efficiency for charging the battery is the
same for both cases. The advantages include less power dissipation, lower system temperature, and better
overall efficiency.
3. The DPPM sustains the system voltage no matter what causes it to drop, if at all possible. It does this by
reducing the noncritical charging load while maintaining the maximum power output of the adaptor.
Note that the DPPM voltage, V_(DPPM-REG), is programmed as follows:
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