Linear Technology LTC4359DCB Demoboard: 28V, 20A Ideal Diode and Switch with Reverse Input Protection DC1676A DC1676A 데이터 시트

제품 코드

DC1676A

LTC4359

4359fa

For more information

www.linear.com/LTC4359

OPERATION

The LTC4359 controls an external N-channel MOSFET to

form an ideal diode. The GATE amplifier (see Block Dia-

gram) senses across IN and OUT and drives the gate of the

MOSFET to regulate the forward voltage to 30mV. As the

load current increases, GATE is driven higher until a point

is reached where the MOSFET is fully on. Further increases

in load current result in a forward drop of R

DS(ON)

• I

LOAD

If the load current is reduced, the GATE amplifier drives

the MOSFET gate lower to maintain a 30mV drop. If the

input voltage is reduced to a point where a forward drop

of 30mV cannot be supported, the GATE amplifier drives

the MOSFET off.
In the event of a rapid drop in input voltage, such as an

input short-circuit fault or negative-going voltage spike,

reverse current temporarily flows through the MOSFET.

This current is provided by any load capacitance and by

other supplies or batteries that feed the output in diode-

OR applications.

The FPD COMP (Fast Pull-Down Comparator) quickly

responds to this condition by turning the MOSFET off in

300ns, thus minimizing the disturbance to the output bus.
The IN, SOURCE, GATE and SHDN pins are protected

against reverse inputs of up to –40V. The NEGATIVE COMP

detects negative input potentials at the SOURCE pin and

quickly pulls GATE to SOURCE, turning off the MOSFET

and isolating the load from the negative input.
When pulled low the SHDN pin turns off most of the

internal circuitry, reducing the quiescent current to 9µA

and holding the MOSFET off. The SHDN pin may be either

driven high or left open to enable the LTC4359. If left

open, an internal 2.6µA current source pulls SHDN high.

In applications where Q1 is replaced with back-to-back

MOSFETs, the SHDN pin serves as an on/off control for

the forward path, as well as enabling the diode function.

Blocking diodes are commonly placed in series with supply

inputs for the purpose of ORing redundant power sources

and protecting against supply reversal. The LTC4359

replaces diodes in these applications with a MOSFET to

reduce both the voltage drop and power loss associated

with a passive solution. The curve shown on page 1 illus-

trates the dramatic improvement in power loss achieved in

a practical application. This represents significant savings

in board area by greatly reducing power dissipation in the

pass device. At low input voltages, the improvement in

forward voltage loss is readily appreciated where head-

room is tight, as shown in Figure 2.
The LTC4359 operates from 4V to 80V and withstands

an absolute maximum range of –40V to 100V without

damage. In automotive applications the LTC4359 operates

through load dump, cold crank and two-battery jumps,

and it survives reverse battery connections while also

protecting the load.
A 12V/20A ideal diode application is shown in Figure 1.

Several external components are included in addition to

the MOSFET, Q1. Ideal diodes, like their nonideal coun-

APPLICATIONS INFORMATION

terparts, exhibit a behavior known as reverse recovery.

In combination with parasitic or intentionally introduced

inductances, reverse recovery spikes may be generated by

an ideal diode during commutation. D1, D2 and R1 protect

against these spikes which might otherwise exceed the

LTC4359’s –40V to 100V survival rating. C

OUT

also plays

a role in absorbing reverse recovery energy. Spikes and

protection schemes are discussed in detail in the Input

Short-Circuit Faults section.

Figure 1. 12V/20A Ideal Diode with Reverse Input Protection

4359 F01

LTC4359

SHDN

SOURCE

BSC028N06NS

OUT

47nF

GATE

SMAT70A

70V
D2

SMAJ24A

24V

12V

OUT

12V

20A

OUT