LTC4359 查看數據表（PDF） - Linear Technology

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LTC4359

Ideal Diode Controller with Reverse Input Protection

Linear Technology 

LTC4359

Applications Information

is not needed. D1, a 70V TVS, protects IN and SOURCE in

the positive direction during load steps and overvoltage

conditions. OUT can be protected by an output capacitor,

COUT of at least 1.5µF, a TVS across the MOSFET or by

the MOSFET’s avalanche breakdown. Care must be taken

if the MOSFET’s avalanche breakdown is used to protect

the OUT pin. The MOSFET’s BVDSS must be sufficiently

lower than 100V, and the MOSFET’s avalanche energy rat-

ing must be ample enough to absorb the inductive energy.

If a TVS across the MOSFET or the MOSFET avalanche

is used to protect the OUT pin, COUT can be reduced to

47nF. COUT and R1 preserve the fast turn off time when

output parasitic inductance causes the IN and OUT volt-

ages to drop quickly.

Paralleling Supplies

Multiple LTC4359s can be used to combine the outputs of

two or more supplies for redundancy or for droop sharing,

as shown in Figure 5. For redundant supplies, the supply

with the highest output voltage sources most or all of the

load current. If this supply’s output is quickly shorted to

ground while delivering load current, the flow of current

temporarily reverses and flows backwards through the

LTC4359’s MOSFET. The LTC4359 senses this reverse

VINA = 12V

PSA

RTNA

Q1A

FDMS86101

D2A

SMAJ24CA

24V

IN SOURCE

GATE OUT

SHDN

LTC4359

VSS

12V

10A

BUS

COUTA

1.5µF

VINB = 12V

PSB

RTNB

R1A

1k

Q1B

FDMS86101

D2B

SMAJ24CA

24V

IN SOURCE

GATE OUT

SHDN

LTC4359

VSS

COUTB

1.5µF

R1B

1k

4359 F05

current and activates a fast pull-down to quickly turn off

the MOSFET.

If the other, initially lower, supply was not delivering any

load current at the time of the fault, the output falls until the

body diode of its ORing MOSFET conducts. Mean-while,

the LTC4359 charges the MOSFET gate with 10µA until

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

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

ORing MOSFET was already driven partially on. In this case,

the LTC4359 will simply drive the MOSFET gate harder in

an effort to maintain a drop of 30mV.

Droop sharing can be accomplished if both power supply

output voltages and output impedances are nearly equal.

The 30mV regulation technique ensures smooth load

sharing between outputs without oscillation. The degree

of sharing is a function of MOSFET RDS(ON), the output

impedance of the supplies and their initial output voltages.

Load Switching and Inrush Control

By adding a second MOSFET as shown in Figure 6, the

LTC4359 can be used to control power flow in the for-

ward direction while retaining ideal diode behavior in the

reverse direction. The body diodes of Q1 and Q2 prohibit

Q2

FQA140N10

Q1

FDMS86101

VIN

28V

D1

SMAJ58A

58V

R3

D2

C1

SMAJ24A 10nF

24V

R4

10k

10Ω

D4

DDZ9699T

12V

VOUT

28V

10A

CLOAD

IN

ON OFF SHDN

SOURCE GATE OUT

LTC4359

COUT

1.5µF

VSS

4359 F06

R1

1k

Figure 6. 28V Load Switch and Ideal

Diode with Reverse Input Protection

Figure 5. Redundant Power Supplies

4359f

10

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