Datasheet

4ms/div
500mV/div
USB5 CurrentLimit00
200mA/div
200mA/div
200mA/div
I
OUT
I
IN
V
IN
(5V)
I
BAT
Inputcollapses
Inputcurrentlimitis
reducedtoprevent
crashingthesupply
InputregulatedtoV
IN_DPM
bq24072, bq24073
bq24074, bq24075, bq24079
www.ti.com SLUS810I –SEPTEMBER 2008–REVISED JANUARY 2014
Input DPM Mode (V
IN
-DPM)
The bq2407x 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 bq2407x from crashing poorly designed or incorrectly configured USB sources. Figure 36 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 36. V
IN
-DPM Waveform
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
bq2407x 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. Figure 5 demonstrates 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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