LTC4365
8
4365f
OPERATION
Many of today’s electronic systems get their power from
external sources such as a wall wart adapter, batteries
and custom power supplies. These power sources are
often unreliable, wired incorrectly, out of spec, or just
plain wrong. This can lead to supply voltages that are too
high, too low, or even negative. If these power sources
are applied directly to the electronic systems, the systems
could be subject to damage. The LTC4365 is an input
voltage fault protection N-channel MOSFET controller.
The part isolates an input supply from its load to protect
the load from unexpected supply voltage conditions, while
providing a low loss path for qualified power.
To protect electronic systems from improperly connected
power supplies, system designers will often add discrete
diodes, transistors and high voltage comparators. The
high voltage comparators enable system power only if
the input supply falls within a desired voltage window.
A Schottky diode or P-channel MOSFET typically added
in series with the supply protects against reverse supply
connections.
The LTC4365 provides accurate overvoltage and
undervoltage comparators to ensure that power is ap-
plied to the system only if the input supply meets the user
selectable voltage window. Reverse supply protection
circuits automatically isolate the load from negative input
voltages. During normal operation, a high voltage charge
pump enhances the gate of external N-channel power
MOSFETs. Power consumption is 10μA during shutdown
and 125μA while operating. The LTC4365 integrates all
these functions in tiny TSOT-23 and 3mm × 2mm DFN
packages.
APPLICATIONS INFORMATION
The LTC4365 is an N-channel MOSFET controller that
protects a load from faulty supply connections. A basic
application circuit using the LTC4365 is shown in Figure 1.
The circuit provides a low loss connection from V
IN
to
V
OUT
as long as the voltage at V
IN
is between 3.5V and
V
IN
UV
OV
SHDN
OV = 18V
UV = 3.5V
4365 F01
V
OUT
FAULT
GATE
V
IN
12V NOMINAL
V
OUT
3.5V TO 18V
SI4946
60V DUAL
GND
LTC4365
R5
100k
C
OUT
100μF
R3
1820k
R2
243k
R1
59k
+
M1
M2
Figure 1. LTC4365 Protects Load from –40V to
60V V
IN
Faults
18V. Voltages at V
IN
outside of the 3.5V to 18V range are
prevented from getting to the load and can be as high as
60V and as low as –40V. The circuit of Figure 1 protects
against negative voltages at V
IN
as shown. No other ex-
ternal components are needed.
During normal operation, the LTC4365 provides up to
9.8V of gate enhancement to the external back-to-back
N-channel MOSFETs. This turns on the MOSFET, thus
connecting the load at V
OUT
to the supply at V
IN
.
GATE Drive
The LTC4365 turns on the external N-channel MOSFETs
by driving the GATE pin above V
OUT
. The voltage differ-
ence between the GATE and V
OUT
pins (gate drive) is a
function of V
IN
and V
OUT
.
