The source of the external MOSFET is connected to IN

and SOURCE while its drain is connected to OUT. The

LTC4372/LTC4373 control the gate of the MOSFET to

regulate the voltage drop across the pass transistor to

less than 30mV.

In the event of a rapid drop in input voltage, such as an

input short-circuit fault or negative-going voltage spike,

reverse current temporarily flows through the MOSFET.

This current is provided by any load capacitance and

by other supplies or batteries that feed the output in

diode-OR applications. The reverse current comparator

quickly responds to this condition by turning the MOSFET

off in 500ns. This fast turn-off prevents the reverse cur-

rent from ramping up to a damaging level, thus minimiz-

ing the disturbance to the output bus.

IN, SOURCE and GATE are protected against reverse

inputs of up to –28V. The negative comparator detects

negative input potentials at SOURCE and quickly connects

GATE to SOURCE, turning off the MOSFET and isolating

the load from the negative input.

For the LTC4372, driving SHDN high pulls the MOSFET

to 0.5μA for a back-to-back MOSFET configuration and

GATE is held low with a 3μA pull-down to GND. When

SHDN goes low, the LTC4372 ramps GATE up to turn on

which can be connected to SHDN to facilitate on/off con-

trol by a microcontroller’s open-drain output.

The LTC4373 can monitor the input voltage via an exter-

nal resistive voltage divider to UV. When UV goes below

1.191V, GATE pulls down to SOURCE with a 1mA pull-

back-to-back MOSFET configuration and GATE is held low

with a 3μA pull down to GND. When UV recovers above

the external MOSFET. An optional resistor can be con-

nected between UV and UVOUT to configure an external

LTC4372/LTC4373

9

Rev. 0

For more information www.analog.com

OPERATION

Blocking diodes are commonly placed in series with sup-

ply inputs for ORing redundant supplies and protecting

against supply reversal. The LTC4372/LTC4373 replace

the diodes such as in portable equipment and automo-

tive applications with N-channel MOSFETs acting as ideal

diodes. The forward voltage drop reduces as shown in

Figure 1, a feature that is readily appreciated at low input

voltages where headroom is tight.

Figure 1. Forward Voltage Drop Comparison Between MOSFET

and Schottky Diode

VOLTAGE (V)

MOSFET

(BSC026N08NS5)

SCHOTTKY DIODE

(SBG2040CT)

0.0

0

15

10

5

20

0.3

0.4

0.5

0.1

0.2

43723 F01

As a result of this lower forward voltage drop, there is a

dramatic reduction in power loss achieved in a practical

application as shown in the Typical Application curve on

Page 1. This represents significant savings in board area

by greatly reducing heat sinking requirements of the pass

device. In addition to these two desirable properties, the

LTC4372/LTC4373 feature a low operating current (5µA)

and shutdown current (0.5µA). This increases efficiency

in applications where the ideal diode is used for intermit-

tent loads or always on standby channels, making the

LTC4372/LTC4373 suitable for battery powered appli-

cations in the portable instrumentation, automotive and

renewable energy fields.