6
LTC4411
4411fa
APPLICATIO S I FOR ATIO
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INTRODUCTION
The LTC4411 is intended for power control applications
that include low loss diode ORing, fully automatic
switchover from a primary to an auxiliary source of power,
microcontroller controlled switchover from a primary to
an auxiliary source of power, load sharing between two or
more batteries, charging of multiple batteries from a
single charger and high side power switching.
Figure 4. State Transition Diagram
CONSTANT R
ON
REGULATION
CONSTANT I
ON
REGULATION
CONSTANT V
ON
REGULATION
REVERSE
BIASED
V
IN
– V
OUT
< V
FWD
I
OUT
> I
FWD
I
OUT
< I
FWD
I
OUT
> I
MAX
I
OUT
< I
MAX
V
IN
– V
OUT
> V
FWD
I
STAT
= 0
DIODE ON
I
STAT
= 10µA
DIODE OFF
I
STAT
= 0
DIODE OFF
I
STAT
= 0
DIODE OFF
I
STAT
= 10µA
DIODE OFF
I
STAT
= 0
DIODE ON
I
STAT
= 0
DIODE ON
CONTROL
SHUTDOWN
UNDER
VOLTAGE
LOCK-OUT
OVER
TEMPERATURE
SHUTDOWN
T
J
< 140°C
T
J
> 150°C
V
DD
> 2.4
V
DD
< 2.3
V
CTL
< V
IL
4411 F04
NORMAL OPERATION
V
CTL
> V
IH
WHERE:
V
DD
= MAX {V
IN
, V
OUT
}
V
IL
= V
TH
– V
HYST
/2
V
IH
= V
TH
+ V
HYST
/2
When the load current exceeds I
MAX
, an over current
condition is detected and the LTC4411 will limit the output
current. This will cause the output voltage to drop as the
load current exceeds the amount of current that the
LTC4411 can supply. This condition will increase the
power consumption within the LTC4411.
When an alternate power source is connected to the
output, the LTC4411 will sense the increased voltage at
OUT, and the amplifier (A) will increase the voltage at
V
GATE
. When V
OUT
is higher than V
IN
+
V
RTO
, the internal
power source for the LTC4411 (V
DD
) will be diverted to
source current from the OUT pin. At the same time V
GATE
will be pulled to V
DD
, which will turn off P1. The system is
now in the reverse turn-off mode. Power to the load is
being delivered from an alternate supply, and only a small
OPERATIO
U
current is drawn from IN to sense the potential V
IN
. During
reverse turn-off mode the STAT pin will sink 10µA to
indicate that the diode is not conducting.
When the CTL input is asserted (high), P1 will have its gate
voltage pulled high, and the STAT pin will sink 10µA. A 3µA
pull-down current on the CTL pin will ensure a low level at
this input if it is left open circuited.
The overtemperature condition is detected when the
internal die temperature increases beyond 150°C. The
overtemperature condition will cause the gate amplifier
(A) as well as P1 to be shut off. When the internal die
temperature cools to below 140°C, the amplifier will turn
on and revert to normal operation. Note that prolonged
operation under overtemperature conditions will degrade
reliability.
Automatic PowerPath Control
Figure 1 illustrates an application circuit for automatic
switchover of a load between a battery and a wall adapter
or other power input. With initial application of the battery,
the load will be charged up as the LTC4411 turns on. The
LTC4411 will control the gate voltage of its internal MOSFET
to reduce the MOSFET’s voltage drop to a low forward
voltage (V
FWD
). The system is now in the forward regula-
