BQ24070 Datasheet, PDF(14/26 Page) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

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BQ24070 Datasheet, PDF (14/26 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

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bq24070

SLUS694A â MARCH 2006 â REVISED MARCH 2006

www.ti.com

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(DPPMâREG) + I(DPPM) R(DPPM) SF

(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 (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 Ã 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.

VAC

VOUT

VOUT Reg. @ 4.4 V (bq24070)

VDPPM â OUT = 4.26 V, DPPM Mode

, VOUT â VOUT BAT Supplement Mode

ICHG

IOUT

Figure 5. DPPM and Battery Supplement Modes

Figure 6 illustrates when Mode is toggled low for 500 Âµs. Power transfers from AC to USB to AC; channel 1

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