Datasheet

0mA
0 mA
V
OUT
3.75 V
~3.1 V
DPPM loop active
Supplement
Mode
I
BAT
I
IN
I
SYS
800 mA
1800 mA
2000mA
-200mA
1A
1500mA
~850 mA
0 mA
3.55 V
bq24272
SLUSB09 –JUNE 2012 www.ti.com
management (DPPM) circuitry of the bq24272 monitors 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 bq24272 enters battery
supplement mode. During supplement mode, the battery FET is turned on and the battery supplements the
system load.
Figure 3. Example DPPM Response (V
Supply
=5V, VBAT = 3.1V, 1.5A 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 see 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.
Battery Discharge FET (BGATE)
The bq24272 contains a MOSFET driver to drive an external discharge FET between the battery and the system
output. This external FET provides a low impedance path when supplying the system from the battery. Connect
BGATE to the gate of the external discharge MOSFET. BGATE is on under the following conditions:
1. No input supply connected.
2. HZ_MODE = 1
3. CD pin connected high
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