LTC2913 datasheet(17/22 Pages) AD

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LTC4368

Rev. B

For more information www.analog.com

APPLICATIONS INFORMATION

FAULT Status

The FAULT high voltage open drain output is driven low

if SHDN is asserted low, if VIN is outside the desired UV/

OV voltage window, if there is an overcurrent fault, or if

VIN has not risen above VIN(UVLO). Figures 5, 6, 8, 9, 10

and 16 show the FAULT output timing.

Ideal Diode Alternative

Figure 17 shows two LTC4368-2 connected in parallel.

With both devices turned on, the output will be the higher

of V1 or V2. Unlike ideal diode controllers, the LTC4368

always fully enhances the MOSFETs, even at light loads.

Note, however, that if the voltage difference between V1

and V2 is less than 3mV, the reverse overcurrent com-

parators will not detect a fault and up to 150mA can flow

from the higher to the lower supply. Similarly, disconnect-

ing the higher supply may not generate sufficient reverse

current to turn off the MOSFETs. A subsequent reconnec-

tion may result in an inrush current that temporarily trips

the circuit breakers.

By driving the SHDN pins separately, this potential back-

flow can be avoided. VOUT can then be selected from either

V1 or V2, irrespective of which supply voltage is higher or

lower. While in shutdown, the LTC4368-2 drives the GATE

pin just below the lower of VIN and VOUT, thus allowing

VOUT to be larger than VIN while in the off condition.

Single MOSFET Higher Power Application

When reverse VIN protection is not needed, only a single

external N-channel MOSFET is necessary. This provides

the user with a larger selection of MOSFETs (not just dual

packages), especially for higher power applications. Note

that care must be taken to stay within the SOA of the

external MOSFET. The RETRY pin of the LTC4368 can be

used to help keep the MOSFET within its SOA. The user

can ground the RETRY pin to latch off the MOSFET after a

forward current fault. For automatic retry after a forward

current fault, CRETRY must be large enough to maintain a

low on duty cycle for the MOSFET. See Figure 18.

VOUT

MOSFETs TURN OFF WHEN REVERSE CURRENT EXCEEDS –150mA

VOUT

LTC4368-2

SENSE

GATE

VIN

SHDN

–3mV

RSENSE

0.02

SEL V1

VOUT

LTC4368-2

SENSE

GATE

VIN

SHDN

–3mV

RSENSE

0.02

SEL V2

4368 F17

Figure 17. Alternative to Ideal Diode

OV = 18V

UV = 3.5V

VIN

12V

IOUT

–1A TO 16.67A

PSMN4R8-100BSE

453k

100µF

1330k

243k

59k

RETRY

4368 F18

VOUT

FAULT

LTC4368-2

SENSE

0.22µF

VIN

SHDN

GATE

GND

+50mV

–3mV

VOUT

3.5V TO 18V

0.003

2.2nF

INRUSH

CONTROL

22k

1200ms COOLDOWN

AFTER FORWARD

OC FAULT

Figure 18. Single MOSFET High Power Application

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