LTC4352 datasheet(8/16 Pages) LINER

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LTC4352

4352f

High availability systems often employ parallel-connected

power supplies or battery feeds to achieve redundancy

and enhance system reliability. ORing diodes have been

a popular means of connecting these supplies at the

point of load. Diodes with storage capacitors also hold

up supply voltages when an input voltage sags or has a

brownout. The disadvantage of these approaches is the

diode’s signiﬁcant forward voltage drop and the resulting

power loss. Additionally, diodes provide no information

concerning the status of the sourcing supply. Separate

control must therefore be added to ensure that a supply

that is out of range is not allowed to affect the load.

The LTC4352 solves these problems by using an external

N-channel MOSFET as the pass element (see Figure 1). The

MOSFET is turned on when power is being passed, allowing

for a low voltage drop from the supply to the load. When

the input source voltage drops below the output common

supply voltage it turns off the MOSFET, thereby matching

the function and performance of an ideal diode.

Power Supply Conﬁguration

The LTC4352 can operate with supplies down to 0V. This

requires powering the VCC pin with an always present

external supply in the 2.9V to 6V range. If not always

present, a series 470Ω resistor or Schottky diode limits

device power dissipation and backfeeding of low VCC

supply when VIN is high. For a 2.9V to 4.7V VCC supply,

VIN should be lower than VCC. A 0.1μF bypass capacitor

should also be connected between the VCC and GND pins,

close to the device. Figure 2 illustrates this.

If VIN operates above 2.9V then the external supply at

VCC is not needed. The 0.1μF capacitor is still required

for bypassing.

APPLICATIONS INFORMATION

Figure 1. 12V Ideal Diode with Status and Fault Indicators

VCC

REV

LTC4352

STATUS

FAULT

0.1μF

2.7k

D1: GREEN LED LN1351C

D2: RED LED LN1261CAL

MOSFET

FAULT

2.7k

TO LOAD

12V

Si7336ADP

0.1μF

4352 F01

CPO

VIN

SOURCE

GATE

GND

OUT

Figure 2. Power Supply Conﬁgurations

VCC

LTC4352

TO LOAD

0V TO VCC

VIN

GATE

OUT

0.1μF

2.9V TO 4.7V

GND

VCC

LTC4352

TO LOAD

0V TO 18V

4352 F02

VIN

GATE

OUT

GND

VCC

LTC4352

TO LOAD

2.9V TO 18V

VIN

GATE

OUT

0.1μF

GND

0.1μF

4.7V TO 6V

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