Datasheet

LTC4413-1/LTC4413-2
14
441312fd
Soft-Start Overvoltage Protection
In the event that a low power external PFET is used for
the external overvoltage protection device, care must be
taken to limit the power dissipation in the external PFET.
The operation of this circuit is identical to the “Automatic
Switchover from a Battery to a Wall Adapter” application
shown on the fi rst page of this data sheet. Here, however,
the ideal diode from INA to INB is disabled by pulling up
on ENBA whenever an overvoltage condition is detected.
This channel is turned-off using a resistor connected to
OVP along with a 5.6V Zener diode, ensuring the abso-
lute maximum voltage at ENBA is not exceeded during
an overvoltage event. When the overvoltage condition
ends, the OVP voltage drops slowly, depending on the
gate charge of the external PFET. This causes the external
PFET to linger in a high R
DS(ON)
region where it can dis-
sipate a signifi cant amount of heat depending on the load
current. To avoid dissipating heat in the external PFET, this
application delays turning on the ideal diode from INA to
OUTA, until the gate voltage of the external PFET drops
below V
ENBIL
, where the external PFET should safely be
out of the high R
DS(ON)
region. This soft-start scheme can
be used on either channel of the LTC4413-2.
APPLICATIONS INFORMATION
INA
IDEAL
FDR8508
LTC4413-2
INB
IDEAL
BAT
D2
5.6V
ENBA
GND
ENBB
OUTA
OUTB
STAT
R
STAT
470k
C
OUT
4.7μF
441312 F07
STAT
STAT IS HIGH WHEN WALL ADAPTER IS
SUPPLYING LOAD CURRENT
OVP IS HIGH WHEN WALL ADAPTER
VOLTAGE > 6V
C1: C0805C106K8PAC
C2: C0403C103K8PAC
C
OUT
: C1206C475K8PAC
OVP
TO LOAD
V
CC
OVI
OVP
+
C1
10μF
C2
10nF
D1
OPTIONAL
WALL
ADAPTER
INPUT
1Ω
0.1μF
R
ENBA
560k
Figure 7