Datasheet

0mA
0mA
V
OUT
3.75V
3.55V
~3.1V
DPPM loop active
Supplement
Mode
I
BAT
USB
I
SYS
800mA
1800mA
2000mA
-200mA
1A
1500mA
~850mA
0mA
bq24270
bq24271
www.ti.com SLUSB10 –JUNE 2012
When the CE bit is a 0 and a valid source is connected to USB, the buck converter starts up and a charge cycle
is initiated. When V
(BAT)
is high enough that V
(SYS)
is > V
SYS(REG)
, the battery FET is turned on and the SYS
output is connected to BAT. If the SYS voltage falls to V
SYS(REG)
, it is regulated to that point to maintain the
system output even with a deeply discharged or absent battery. In this mode, the SYS output voltage is regulated
by the buck converter and the battery FET linearly regulates the charge current into the battery. The current from
the supply is shared between charging the battery and powering the system load at SYS. The dynamic power
path management (DPPM) circuitry of the devices monitor the current limits continuously and if the SYS voltage
falls to the V
(MINSYS)
voltage, it adjusts charge current to maintain the minimum system voltage and supply the
load on SYS. If the charge current is reduced to zero and the load increases further, the devices enter battery
supplement mode. During supplement mode, the battery FET is turned on and the battery supplements the
system load.
Figure 4. Example DPPM Response (V
(Supply)
= 5 V, V
(BAT)
= 3.1 V, 1.5 A Input Current Limit)
V
BAT(REG)
should never be programmed less than V
(BAT)
. If the battery is ever 5% above the regulation threshold,
the battery OVP circuit shuts the PWM converter off and the battery FET is turned on to discharge the battery to
safe operating levels. Battery OVP errors are shown in the I
2
C status registers.
Battery Only Connected
When a battery voltage > V
(BATUVLO)
is connected with no input source, the battery FET is turned on similar to
supplement mode. In this mode, the current is not regulated; however, there is a short circuit current limit. If the
short circuit limit is reached, the battery FET is turned off for the deglitch time. After the deglitch time, the battery
FET is turned on to test and determine if the short has been removed. If it has not, the FET turns off and the
process repeats until the short is removed. This process is to protect the internal FET from over current. If an
external FET is used for discharge, the body diode prevents the load on SYS from being disconnected from the
battery. If the battery voltage is less than V
(BATUVLO)
, the battery FET (Q3) remains off and BAT is high-
impedance. This prevents further discharging deeply discharged batteries.
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