LM3544

Quad Port USB Power Distribution Switch and

Over-Current Protection

General Description

The LM3544 is a quad high-side power switch that is an

excellent choice for use in Root, Self-Powered and

Bus-Powered USB (Universal Serial Bus) Hubs. Indepen-

dent port enables, flag signals to alert USB controllers of

error conditions, controlled start-up in hot-plug events, and

short circuit protection all satisfy USB requirements.

The LM3544 accepts input voltages between 2.7V and 5.5V.

The Enable logic inputs, available in active-high and

active-low versions, can be powered off any voltage in the

2.7V to 5.5V range. The LM3544 limits the continuous

current through a single port to 1.25A (max.) when it is

shorted to ground.

The low on-state resistance of the LM3544 switches ensures

the LM3544 will satisfy USB voltage drop requirements,

even when current through a switch reaches 500 mA. Thus,

High-Powered USB Functions, Low-Powered USB func-

tions, and Bus-Powered USB Hubs can all be powered off a

Root or Self-Powered USB Hub containing the LM3544.

Added features of the LM3544 include current foldback to

reduce power consumption in current overload conditions,

thermal shutdown to prevent device failure caused by

high-current overheating, and undervoltage lockout to keep

switches from operating if the input voltage is below

acceptable levels.

Features

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90m

Ω (typ.) High-Side MOSFET Switch

n

500mA Continuous Current per Port

n

7 ms Fault Flag Delay Filters Hot-Plug Events

n

Industry Standard Pin Order

n

Short Circuit Protection with Power-Saving Current

Foldback

n

Thermal Shutdown Protection

n

Undervoltage Lockout

n

Recognized by UL and Nemko CB

n

Input Voltage Range: 2.7V to 5.5V

n

5µA Maximum Standby Supply Current

n

16-Pin SOIC Package

n

Ambient Temperature Range: −40˚C to 85˚C

Applications

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USB Root, Self-Powered, and Bus-Powered Hubs

n

USB Devices such as Monitors and Printers

n

General Purpose High Side Switch Applications

10120832

10120833

Functional Diagram

10120801

March 2001

© 2001 National Semiconductor Corporation

DS101208

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