Datasheet

LTC4361-1/LTC4361-2
9
436112fb
applicaTions inFormaTion
ON Input
ON is a CMOS compatible, active low enable input. It has
a default 5µA pull-down to ground. Connect this pin to
ground or leave open to enable normal device operation.
If it is driven high while the external MOSFET is turned on,
GATE is pulled low with a weak pull-down current (40µA)
to turn off the external MOSFET gradually, minimizing
input voltage transients. The LTC4361 then goes into a low
current sleep mode, drawing only 1.5µA at IN. When ON
goes back low, the part restarts with a 130ms delay cycle.
GATEP Control
GATEP has a 2M resistive pull-down to ground and a 5.8V
Zener clamp in series with a 200k resistor to IN. It con-
trols the gate of an optional external P-channel MOSFET
to provide negative voltage protection. The 2M resistive
pull-down turns on the MOSFET once V
IN
– V
GATEP
is
more than the MOSFET gate threshold voltage. The IN to
GATEP Zener protects the MOSFET from gate overvoltage
by clamping its V
GS
to 5.8V when V
IN
goes high.
MOSFET Configurations and Selection
The LTC4361 can be used with various external MOSFET
configurations (see Figure 3). The simplest configuration
is
a single N-channel MOSFET. It has the lowest R
DS(ON)
and voltage drop and is thus the most power efficient
solution. When GATE is pulled to ground, the N-channel
MOSFET can isolate OUT from a positive voltage at IN up
to the BV
DSS
of the N-channel MOSFET. However, reverse
current can still flow from OUT to IN via the parasitic body
diode of the N-channel MOSFET.
For near zero reverse-leakage current protection when GATE
is pulled to ground, back-to-back N-channel MOSFETs
can be used. Adding an additional P-channel MOSFET
controlled by GATEP provides negative input voltage
protection down to the BV
DSS
of the P-channel MOSFET.
Another configuration consists of a P-channel MOSFET
controlled by GATEP and a N-channel MOSFET controlled
by GATE. This provides protection against overvoltage and
negative voltage but not reverse current.
Figure 3. MOSFET Configurations
GATEP
OVERVOLTAGE, REVERSE-
CURRENT PROTECTION
NEGATIVE
VOLTAGE
PROTECTION
GATE
OVERVOLTAGE, REVERSE-
CURRENT PROTECTION
GATE
GATE
GATEP
SUPPLY
SUPPLY
SUPPLY
SUPPLY
436112 F03
OVERVOLTAGE
PROTECTION
OVERVOLTAGE
PROTECTION
M1
M1 M3
M1M2
M1M2
M3
NEGATIVE
VOLTAGE
PROTECTION
GATE
OUT
OUT
OUT
IN
R
SENSE
SENSE
OUT
IN
R
SENSE
SENSE
IN
R
SENSE
SENSE
IN
R
SENSE
SENSE