FireWire Current Limiter and Low-Drop

ORing Switch Controller

10

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Detailed Description

The MAX5943 performs hot-swapping, power-supply

ORing, and current limiting for FireWire power-supply

applications. The MAX5943 incorporates two MOSFET

drivers (GATE1 and GATE2) to control two external

n-channel power MOSFETs to perform low-voltage-drop

power-supply ORing (GATE1) and hot swapping and

current limiting (GATE2) from the input power supply to

the load. A sense resistor provides accurate current-

limiting/circuit-breaker function. GATE1 and GATE2

provide true load disconnect to prevent current flowing

from either direction between IN and OUT.

The MAX5943 remains in low-current shutdown mode

shutdown mode disables the MAX5943, resulting in

less than 10µA supply current. Shutdown places all

logic inputs in a high-impedance state allowing the

inputs to be connected to IN without drawing additional

current from the supply.

turns on, sourcing 45µA current from GATE2 (current

regulation) to enhance Q2 slowly. For the MAX5943A, if

greater than the programmed current-limit threshold,

the MAX5943A regulates the GATE2 voltage to limit the

GATE2 rises to approximately 5.5V above OUT. Since

the MAX5943B–MAX5943E do not regulate the load

current, a capacitor can be added from GATE2 to GND

to limit inrush current during startup (see the

Applications Information section).

SENSE

SENSE GATE1

6.5V

1.24V

GATE1

GATE2

OUT

MAX5943A–MAX5943E

POWER

SOURCE

(FAST CURRENT-

LIMIT

THRESHOLD)

CIRCUIT-BREAKER

(CURRENT-LIMIT)

THRESHOLD

OR

COMPARATOR

THRESHOLD

GND

LATCH

TIM

X128

FAULT

+

-

+

-

+

-

+

-

+

-

0.4V

SHUTDOWN

MODE

ON COMPARATOR

( ) MAX5943A ONLY.

UVLO COMPARATOR

+

-

FAULT

MANAGEMENT

LATCH OR

AUTORETRY

AUTORETRY

TIMEOUT

PERIOD

FAULT

TIMEOUT

GATE1

DRIVE

CP1

CP2

GATE

CHARGE

PUMPS

OUT

GATE2

GATE2

DRIVE

ONQ1

OR_ADJ

ILIM

ON

Q1

Q2

Figure 1. MAX5943 Functional Diagram