BQ24030 Datasheet, PDF (12/20 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC (bqTINYI)

bq24030, bq24032, bq24035
SLUS618 – AUGUST 2004
Case 1: AC (PSEL = High)
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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, 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 6 V, Q1 turns off. For bq24032, 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× 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 and reach a steady state condition where the system gets its needed current and the battery
is charged with the remaining current. There is no active control to limit the current to the system. Therefore if the
system demands more current than the input can provide, the output voltage drops to the battery voltage and the
battery tries and supplement the input current to the system. There are three main advantages of DPPM.
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 3.0 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. There is a power savings using DPPM 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 are less power dissipation, lower system temperature and better
overall efficiency.
3. The DPPM’s function is to sustain the system voltage no matter what causes it to drop, if at all possible. It
does this by reducing the non-critical charging load while maintaining the maximum power output of the
adaptor.
Note that the DPPM voltage, V_(DPPM), is programmed as follows:
V_(DPPM) + I_(DPPM) R_(DPPM) SF
(1)
where
• R_DPPM is the external resistor connected between the DPPM and VSS pins
• I_(DPPM) is the internal current source
• SF is the scale factor as specified in the specification table
The safety timer is dynamically adjusted while in DPPM mode. The voltage on the ISET1 pin is directly
proportional to the programmed charging current. When the programmed charging current is reduced, due to
DPPM, the ISET1 voltage is reduced and the timer’s clock is proportionally slowed, extending the safety time.
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