LTC4372/LTC4373

13

Rev. 0

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APPLICATIONS INFORMATION

Figure 7. LTC4372/LTC4373 Handling Reverse Input

Figure 8. Redundant Power Supplies

LTC4372

U1A

OUT

GATE

INA

SOURCE

IN

43723 F08

M1A

Si4190ADY

POWER

SUPPLY

A

100µF

LTC4372

U1B

OUT

GATE

INB

SOURCE

IN

M1B

Si4190ADY

POWER

SUPPLY

B

+

–

+

–

GND

2UPU

2UPU

100

C1B

100nF

GND

100

C1A

100nF

Figure 9. Load Transition of Redundant Power Supplies

MOSFET. The LTC4372/LTC4372 sense this reverse cur-

rent and activate a fast pull-down to quickly turn off the

MOSFET.

If all the load current was supplied by the channel that

suffered the short, the output will fall until the body diode

of the next MOSFET conducts. Meanwhile, the LTC4372/

LTC4372 charge the MOSFET gate with 20μA until the

forward drop is reduced to 30mV. If this supply was shar-

ing load current at the time of the fault, its associated

ORing MOSFET was already servoed to less than 30mV

drop. In this case, the LTC4372/LTC4372 will simply drive

the MOSFET gate higher to maintain a drop of 30mV at

full load.

Load sharing can be accomplished if both power sup-

ply output voltages and source impedances are nearly

equal. The 30mV regulation technique allows load sharing

between outputs. The degree of sharing is a function of

and their initial output voltages.

1s/DIV

43723 F07

I(M1)

2A/DIV

SOURCE

20V/DIV

GATE

20V/DIV

OUT

1V/DIV

10V/DIV

INA, INB

50mV/DIV

GATEA,

GATEB

2V/DIV

5V

5V

50ms/DIV

INA

INB

GATEA

GATEB

43723 F09a

50ms/DIV

43723 F09b

I(M1A)

0.5A/DIV

I(M1B)

0.5A/DIV

OUT

50mV/DIV

5V

0A

0A

(a)

(b)

Paralleling Supplies

Multiple LTC4372/LTC4373’s can be used to combine the

outputs of two or more supplies for redundancy or for

droop sharing, as shown in Figure 8. For redundant sup-

plies, the supply with the highest output voltage sources

most or all of the load current. Figure 9a and Figure 9b

show the load transition between the two redundant

power supplies.

If the higher supply’s input is shorted to ground while

delivering load current, the flow of current temporarily

reverses and flows backwards through the higher supply’s