Datasheet

50 μC10 μC
100 μs/div
20mA/div
USB100CurrentLimit
bq24230
bq24232
www.ti.com SLUS821E –OCTOBER 2008–REVISED JANUARY 2014
Figure 26. USB-IF Inrush Current Test
The input current limit selection is controlled by the state of the EN1 and EN2 pins as shown in Table 1. When
using the resistor-programmable current limit, the input current limit is set by the value of the resistor connected
from the ILIM pin to VSS and is given by the Equation 1:
I
IN-MAX
= K
ILIM
/R
ILIM
(1)
The input current limit is adjustable up to 500 mA. The valid resistor range is 2.75 kΩ to 8.4 kΩ.
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 27 illustrates examples of the DPPM and supplement
modes. These modes are explained in detail in the following sections.
Input DPM Mode, V
IN
-DPM
The bq2423x uses 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 bq2423x from crashing poorly designed or incorrectly configured USB sources.
DPPM Mode
When the sum of the charging and system load currents exceeds the preset 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 bq2423x enters DPPM mode. In this mode, the charging current is reduced as the OUT
current goes up 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
battery voltage by V
BSUP1
, the battery supplements the system load. The battery stops supplementing the system
load when the voltage on the OUT pin rises above the battery voltage by V
BSUP2
.
During supplement mode, the battery supplement current is not regulated; however, a short-circuit protection
circuit is built in. If during battery supplement mode, the voltage at OUT drops 250 mV 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.
Copyright © 2008–2014, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: bq24230 bq24232