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LTC4411

4411f

BLOCK DIAGRA

Figure 2. Detailed Block Diagram

–

OVERTEMP

UVLO

OUTMAX

µA

VREF

OFF

SHDB

STAT

OUT

CTL

GND

4411 F03

VGATE

Figure 3. LTC4411 vs Schottky Diode

Forward Conduction Characteristics

OPERATIO

The LTC4411 operation is described with the aid of

Figure 3. Forward regulation for the LTC4411 has three

operation modes depending on the magnitude of the load

current. For small load currents, the LTC4411 will provide

a constant voltage drop; this operating mode is referred to

as “constant VON” regulation. As the current exceeds IFWD

the voltage drop will increase linearly with the current with

a slope of 1/RON; this operating mode is referred to as

“constant RON” regulation. As the current increases fur-

ther, exceeding IMAX, the forward voltage drop will in-

crease rapidly; this operating mode is referred to as

“constant ION” regulation. The characteristics for the

following parameters: RFWD, RON, VFWD, IFWD, and IMAX

are specified with the aid of Figure 3.

Operation begins when the power source at IN rises above

the UVLO voltage of 2.4V (typ) and the CTL (control) pin

is low. If only the voltage at the IN pin is present, the power

source to LTC4411 (VDD) will be supplied from the IN pin.

The amplifier (A) will deliver a voltage proportional to the

difference between VIN and VOUT to the gate (VGATE) of the

internal P-channel MOSFET (P1), driving this gate voltage

below VIN. This will turn on P1. As P1 conducts, VOUT will

be pulled up towards VIN. The LTC4411 will then control

VGATE to maintain a low forward voltage drop. The system

is now in forward regulation and the load at OUT will be

powered from the supply at IN. As the load current varies,

VGATE will be controlled to maintain a low forward voltage

drop. If the load current exceeds P1’s ability to deliver the

current, as VGATE approaches GND, the P1 will behave as

a fixed resistor, with resistance RON, whereby the forward

voltage will increase with increased load current. As ILOAD

increases further (ILOAD > IMAX) the LTC4411 will regulate

the load current as described below. During the forward

regulation mode of operation the STAT pin will be an open

circuit.

VFWD

IOC

IMAX

IFWD

FORWARD VOLTAGE (V)

3.0

2.5

2.0

1.5

1.0

0.5

0.25

0.5

0.75

1.0

4411 F04

TA = 40°C

SLOPE

1/RON

SLOPE

1/RFWD

SCHOTTKY

DIODE

LTC4411

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