LT4351CMS datasheet(13/20 Pages) LINER

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LT4351

sn4351 4351fs

STATUS

The STATUS pin sinks current when the input (VIN) is

above output (OUT) by 15mV and GATE is above VIN by

0.7V. This will normally indicate that power is being

passed though the MOSFETs.

In the event of a nonfunctional MOSFET, the GATE voltage

will be driven high (to the GATE clamp voltage). If VIN is

greater than OUT by more than 0.21V, the FAULT pin will

sink current to signal the potential problem.

There is no direct measurement or confirmation of current

flowing in the MOSFETs. Current is shared between sources

based on their voltage and series resistance. If precision

load sharing is desired, the LTC4350 may be a more

suitable part.

Redundant Supplies

The LT4351 is an improved solution for ORing redundant

supplies because of its lower forward drop versus conven-

tional diodes. The lower forward drop significantly im-

proves overall efficiency, improves the voltage tolerance

at the load and provides for a more accurate transition

from supply to supply and more accurate load sharing

between supplies.

APPLICATIO S I FOR ATIO

ORing can be done either at the load or at the source.

Figure 9 shows some examples. ORing at the load is

usually the safest method since it protects against shorts

in interconnects.

The LT4351 tighter forward voltage tolerance makes it

easier to balance current between similar supplies using

the droop method. The droop method uses the supply

voltage and series resistance in the power path to provide

load sharing. In this case, size the MOSFET’s RDS(ON) low

to allow for regulation.

ORing Disparate Supplies

The LT4351 provides an easy solution for connecting

together different types of power sources. Again because

of the low forward drop, the efficiency of the system is

improved and the voltage transition between supplies is

more accurate. In addition, the undervoltage and overvolt-

age features of the LT4351 provide options for enabling

and disabling the supplies that are not available from a

common diode. Figure 10 shows some examples of con-

necting disparate supplies.

Figure 9. Redundant Backplane Supplies

Figure 10

LT4351

BOARD

LT4351

LOAD

SOURCE 1

BACKPLANE

SOURCE 2

LT4351

BOARD

LT4351

LOAD

4351 F09

SOURCE 1

BACKPLANE

SOURCE 2

LT4351

Isolated System Supply

from Wall Adapter

Isolated Battery Backup

Three Source ORing Provides Protection

Against Out of Range Supplies

WALL

ADAPTER

SYSTEM

SUPPLY

LOAD

LT4351

BATTERY

WALL

ADAPTER

LOAD

LT4351

BATTERY

LT4351

WALL

ADAPTER

LOAD

4351 F10

SYSTEM

SUPPLY

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