LTC4372/LTC4373

14

Rev. 0

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APPLICATIONS INFORMATION

Using the LTC4372’s SHDN and 2UPU

When SHDN goes high, the LTC4372 enters shutdown

and asserts a 1mA pull-down between GATE and SOURCE

to turn off the external MOSFET. It also turns off most of

low with a 3μA pull-down to GND. If IN and SOURCE are

Shutting down the part does not interrupt forward current

flow as a path is still present through M1’s body diode. A

second MOSFET may be added to block the forward path

(see Figure 10). In this case, GATE and SOURCE are pulled

to GND during shutdown. The 3μA pull-down on GATE is

SHDN serves as an on/off control for the forward path,

as well as enabling the diode function. When SHDN is

driven low, the LTC4372 exits shutdown and re-enters

ideal diode operation.

If SHDN is not needed, connect it to GND. SHDN may

be driven with a 3.3V or 5V logic signal. It can also be

driven with an open-drain or collector output with SHDN

tied to 2UPU. 2UPU provides an internal pull up current

Figure 10. 24V Load Switch and Ideal Diode with Inrush Control

and Reverse Input Protection

Load Switching and Inrush Control

By adding a second MOSFET as shown in Figure 10, the

LTC4372/LTC4373 can be used to control power flow in

the forward direction while retaining ideal diode behav-

ior in the reverse direction. The body diodes of M1 and

M2 prohibit current flow when the MOSFETs are off. M1

serves as the ideal diode while M2 acts as a switch to

control forward power flow. ON/OFF control is provided

by SHDN or UV. C2 and R2 may be added to further reduce

inrush current. While C2 and R2 may be omitted if soft

starting is not needed. R1 is necessary to prevent MOSFET

parasitic oscillations and must be placed close to M2.

When SHDN is driven low or UV driven high and

C2, pulling up both MOSFET gates. M2 operates as a

source follower as shown in Equation 4.

C2

• 20µA

(4)

holds M1 and M2 off until the input exceeds the output by

30mV. In this way normal diode behavior of the circuit is

preserved, but with soft starting when the diode turns on.

When SHDN is driven high or UV driven low, GATE pulls

the MOSFET gates down quickly to SOURCE with a 1mA

pull-down. Both forward and reverse paths are cut off and

Configuring LTC4373’s UV and UVOUT for Voltage

Monitoring

With back-to-back MOSFETs, the LTC4373 can imple-

ment voltage monitoring at IN. Connect a resistive voltage

divider between IN and ground to bias UV. UV has a high

to low threshold of 1.191V with 15mV of hysteresis. The

When UV ramps high to low, the LTC4373 enters under-

voltage mode and asserts a 1mA pull-down between GATE

and SOURCE to turn off the external MOSFETs. It also turns

When UV ramps low to high, the LTC4373 exits under-

voltage mode and goes back into ideal diode operation.

R1

10

R2

1k

C1

100nF

M3

BSS138N

D3

SMAJ28A

28V

D2

SMAJ33A

33V

24V

10A

24V

10µF

C2

10nF

IN

2UPU

GND

SHDN

SOURCE

LTC4372

GATE

OUT

43723 F10

ON

OFF

M2

BSC026N08NS5

M1

BSC026N08NS5

to 10μA) or IN.