LTC4354 データシートの表示（PDF） - Linear Technology

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LTC4354

UV, OV and Reverse Supply Protection Controller

Linear Technology 

LTC4365

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 VIN to

VOUT as long as the voltage at VIN is between 3.5V and

VIN

12V NOMINAL

SI4946

60V DUAL

M1

M2

VOUT

3.5V TO 18V

+ COUT

100μF

R5

100k

R3

1820k

R2

243k

R1

59k

GATE

VIN

VOUT

LTC4365

SHDN

UV

FAULT

OV

GND

4365 F01

OV = 18V

UV = 3.5V

18V. Voltages at VIN 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 VIN 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 VOUT to the supply at VIN.

GATE Drive

The LTC4365 turns on the external N-channel MOSFETs

by driving the GATE pin above VOUT. The voltage differ-

ence between the GATE and VOUT pins (gate drive) is a

function of VIN and VOUT.

Figure 1. LTC4365 Protects Load from –40V to

60V VIN Faults

4365f

8

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