bq24070
bq24071
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SLUS694B–MARCH 2006–REVISED AUGUST 2006
FUNCTIONAL DESCRIPTIONS (continued)
Dynamic Power-Path Management (DPPM)
The theory of operation is the same as described in CASE 1, except that Q1 is restricted to the USB current
level selected by the ISET2 pin.
Note that the DPPM voltage, V(DPPM), is programmed as follows:
V
+ I
R
SF
(DPPM−REG)
(DPPM)
(DPPM)
(2)
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.
Feature Plots
Figure 5 illustrates DPPM and battery supplement modes as the output current (IOUT) is increased; channel 1
(CH1) VAC = 5.4 V; channel 2 (CH2) VOUT; channel 3 (CH3) IOUT = 0 to 2.2 A to 0 A; channel 4 (CH4) VBAT
=
3.5 V; I(PGM-CHG) = 1 A. In typical operation, bq24070/1 (VOUT = 4.4 Vreg), through an AC adaptor overload
condition and recovery. The AC input is set for ~5.1 V (1.5 A current limit), I(CHG) = 1 A, V(DPPM-SET) = 3.7 V,
V(DPPM-OUT) = 1.15 × V(DPPM-SET) = 4.26 V, VBAT = 3.5 V, Mode = H, and USB input is not connected. The output
load is increased from 0 A to ~2.2 A and back to 0 A as shown in the bottom waveform. As the IOUT load
reaches 0.5 A, along with the 1-A charge current, the adaptor starts to current limit, the output voltage drops to
the DPPM-OUT threshold of 4.26 V. This is DPPM mode. The AC input tracks the output voltage by the dropout
voltage of the AC FET. The battery charge current is then adjusted back as necessary to keep the output
voltage from falling any further. Once the output load current exceeds the input current, the battery has to
supplement the excess current and the output voltage falls just below the battery voltage by the dropout voltage
of the battery FET. This is the battery supplement mode. When the output load current is reduced, the operation
described is reversed as shown. If the DPPM-OUT voltage was set below the battery voltage, during input
current limiting, the output falls directly to the battery's voltage.
Under USB operation, when the loads exceeds the programmed input current thresholds a similar pattern is
observed. If the output load exceeds the available USB current, the output instantly goes into the battery
supplement mode.
V
AC
V
OUT
V
V
Reg. @ 4.4 V (bq24070)
OUT
= 4.26 V, DPPM Mode
DPPM − OUT
VOUT ≈ VOUT, BAT Supplement Mode
I
I
CHG
OUT
Figure 5. DPPM and Battery Supplement Modes
Figure 6 illustrates when Mode is toggled low for 500 µs. Power transfers from AC to USB to AC; channel 1
14
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