LTC4413-1/LTC4413-2
13
441312ff
For more information www.linear.com/LTC4413-1
Automatic Switchover from a Battery to an Auxiliary
Supply, or a Wall Adapter with Overvoltage Protection
Figure 4 illustrates an application circuit where the
LTC4413-2 is used to automatically switch over between
a battery, an auxiliary power supply and a wall adapter.
When the battery is supplying load current, OVP is at GND
and STAT is high. If a higher supply is applied to AUX, the
BAT will be disconnected from the load and the load is
powered from AUX. When a wall adapter is applied, the
body diode of MP2 forward biases. When the load voltage
exceeds the AUX (or BAT) voltage, the LTC4413-2 senses
this higher voltage and disconnects AUX (or BAT) from
the load. At the same time it pulls the STAT voltage to
GND, thereby turning on MP2. The load current is now
supplied from the wall adapter. If the wall adapter voltage
exceeds the OVI rising threshold, the OVP voltage rises
and turns off MP1, disconnecting the wall adapter from
the load. The output voltage collapses down to the AUX
(or BAT) voltage and the LTC4413-2 reconnects the load
to AUX (or BAT).
APPLICATIONS INFORMATION
Capacitor C2 is required to dynamically pull up on the
gate of MP1 if a fast edge occurs at the wall adapter input
during a hot plug. If the wall adapter voltage is precharged
when an overvoltage spike occurs, the OVP voltage may
not discharge capacitor C2 in time to protect the output.
In this event, a Zener diode is recommended to protect
the output node until MP1 is turned off.
Multiple Battery Charging
Figure 5 illustrates an application circuit for automatic dual
battery charging from a single charger. Whichever battery
has the lower voltage will receive the larger charging cur
-
rent until both battery voltages are equal, then both are
charged. While both batteries are charging simultaneously,
the higher capacity battery gets proportionally higher cur
-
rent from the charger. For Li-Ion batteries, both batteries
achieve the float voltage minus the forward regulation
voltage of 15mV. This concept can apply to more than
two batteries. The STAT pin provides information as to
when the battery at OUTA is being charged. For intelligent
control, the ENBA/ENBB input pins can be used with a
microcontroller as shown in Figure 3.
INA
IDEAL
MP1
IRLML6402
MP2
IRLML6402
LTC4413-2
INB
IDEAL
ENBA
C1: C1206C106K8PAC
C2: C0403C103K8PAC
C
OUT
: C1206C475K8PAC
GND
ENBB
OUTA
1
4
5
2
AUX
470k
470k
3
10
7
9
6
8
OUTB
STAT
C
OUT
4.7µF
C2
10nF
441312 F04
STAT
R
STAT
560k
OVP
TO LOAD
OVI
OVP
BAT
C1
0.10µF
WALL
ADAPTER
INPUT
JACK
R1
1Ω
+
OPTIONAL
6.2V
DFLZ6V2-7
10nF
INA
IDEAL
LTC4413-1
INB
IDEAL
ENBA
GND
ENBB
OUTA
1
3
4
5
2
10
STAT IS HIGH
WHEN BAT1 IS
CHARGING
V
CC
9
470k
BAT2
6
OUTB
STAT
BATTERY
CHARGER
INPUT
441312 F05
LOAD
LOAD
+
BAT1
+
Figure 4 Figure 5
