BQ24075T Datasheet, PDF(15/29 Page) Texas Instruments – 1.5A USB-Friendly Li-Ion Battery Charger and Power-Path Management IC

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BQ24075T Datasheet, PDF (15/29 Pages) Texas Instruments – 1.5A USB-Friendly Li-Ion Battery Charger and Power-Path Management IC

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bq24075T

bq24079T

SLUS937 â DECEMBER 2009

When the IN source is connected, priority is given to the system load. The DPPM and Battery Supplement

modes are used to maintain the system load. Figure 26 illustrates an example of the DPPM and supplement

modes. These modes are explained in detail in the following sections.

Input DPM Mode (VIN-DPM)

The bq2407xT utilizes the VIN-DPM mode for operation from current-limited USB ports. When EN1 and EN2 are

configured for USB100 (EN2=0, EN1=0) or USB500 (EN2=0, EN2=1) modes, the input voltage is monitored. If

VIN falls to VIN-DPM, the input current limit is reduced to prevent the input voltage from falling further. This prevents

the bq2407xT from crashing poorly designed or incorrectly configured USB sources. Figure 25 shows the

VIN-DPM behavior to a current limited source. In this figure, the input source has a 400mA current limit and the

device is in USB500 mode (EN1=1, EN2=0).

Figure 25. VIN-DPM Mode

DPPM Mode

When the sum of the charging and system load currents exceeds the maximum input current (programmed with

EN1, EN2 and ILIM pins), the voltage at OUT decreases. Once the voltage on the OUT pin falls to VDPPM, the

bq2407xT enters DPPM mode. In this mode, the charging current is reduced as the OUT current increases in

order to maintain the system output. Battery termination is disabled while in DPPM mode.

Battery Supplement Mode

While in DPPM mode, if the charging current falls to zero and the system load current increases beyond the

programmed input current limit, the voltage at OUT reduces further. When the OUT voltage drops below the

VBSUP1 threshold, the battery supplements the system load. The battery stops supplementing the system load

when the voltage at OUT rises above the VBSUP2 threshold.

During supplement mode, the battery supplement current is not regulated (BAT-FET is fully on), however there is

a short circuit protection circuit built in. demonstrate supplement mode. If during battery supplement mode, the

voltage at OUT drops VO(SC2) below the BAT voltage, the OUT output is turned off if the overload exists after

tDGL(SC2). The short circuit recovery timer then starts counting. After tREC(SC2), OUT turns on and attempts to

restart. If the short circuit remains, OUT is turned off and the counter restarts. Battery termination is disabled

while in supplement mode.

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