Datasheet

bq24072T
bq24075T, bq24079T
SLUS937A –DECEMBER 2009–REVISED APRIL 2010 www.ti.com
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 30 illustrates an example of the DPPM and supplement
modes. These modes are explained in detail in the following sections.
Input DPM Mode (V
IN
-DPM)
The bq2407xT utilizes the V
IN
-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
V
IN
falls to V
IN-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 29 shows the
V
IN
-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 29. 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 V
DPPM
, 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
V
BSUP1
threshold, the battery supplements the system load. The battery stops supplementing the system load
when the voltage at OUT rises above the V
BSUP2
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 V
O(SC2)
below the BAT voltage, the OUT output is turned off if the overload exists after
t
DGL(SC2)
. The short circuit recovery timer then starts counting. After t
REC(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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