LTC4365

13

4365f

Select Between Two Input Supplies

driven by separate power supplies. The LTC4365 then

automatically drives the GATE pin just below the lower of

the two supplies, thus turning off the external back-to-back

MOSFETs. The application of Figure 11 uses two LTC4365s

to select between two power supplies. Care should be taken

to ensure that only one of the two LTC4365s is enabled

at any given time.

APPLICATIONS INFORMATION

Figure 11. Selecting One of Two Supplies

V2

SHDN

4365 F11

GATE

LTC4365

V1

SEL

0

1

OUT

V1

V2

OUT

M2

M1

M2

M1

SEL

SHDN

GATE

LTC4365

Limiting Inrush Current During Turn-On

The LTC4365 turns on the external N-channel MOSFET

with a 20μA current source. The maximum slew rate at

the GATE pin can be reduced by adding a capacitor on

the GATE pin:

Slew Rate

=

20µA

Since the MOSFET acts like a source follower, the slew

Therefore, inrush current is given by:

I

•20µA

For example, a 1A inrush current to a 330μF output

capacitance requires a GATE capacitance of:

20µA • 330µF

1A

= 6.6nF

Figure 13 limits the inrush current to approximately 1A.

turn off characteristics during UV/OV faults, or during

frequency oscillations with the external N-channel MOSFET

and related board parasitics.

UV

OV

SHDN

OV = 30V

4365 F12

FAULT

GATE

24V

SI7120DN

60V

GND

LTC4365

R2

2370k

R1

40.2k

100μF

+

Figure 12. Small Footprint Single MOSFET Application

Protects Against 60V

Single MOSFET Application

external N-channel MOSFET is necessary. The applica-

components.

4365 F13

R4B

10Ω

R4A

10Ω

330μF

GATE

LTC4365

5.1k

6.8nF

+

M2

M1