LM3544

www.ti.com

SNVS062C – AUGUST 2000 – REVISED MAY 2013

Figure 27. Using the LM3544 in USB Bus-Powered Functions

WAKE-ON-USB AND REMOTE WAKE-UP APPLICATIONS

The LM3544 can be used in desktop and notebook PC based root hubs to switch the power connection of USB

devices between the main power source, used when the device is active, and a reduced power auxiliary supply.

The auxiliary supply, used when the device is in suspend mode, can dramatically decrease the power

consumption of a computer that contains devices that spend extended periods of time in suspend mode. This

application also works especially well with devices configured for remote wake-up capabilities (i.e.: using a

keystroke on a mouse or keyboard to awaken a suspended PC). A schematic showing an example of how the

LM3544 can be configured to switch the power connection of a device between two separate sources is shown in

Figure 28, below.

In the example, the logic signals EN and SRC control the power supply connections. If the EN signal is low, all

four LM3544 switches will be open and neither supply will be connected to the bus. If EN and SRC are both high,

switch 1 and switch 3 close, connecting the main power supply to the two bus power outputs. When EN is high

and SRC is low, the auxiliary supply is connected to the power outputs through switches 2 and 4.

In order to allow the power-switching circuit to smoothly transition from one supply to another, delay networks

must be placed before the enable pins. These delay networks account for the turn-on delay of the LM3544

switches by slowing the fall time of the enable signals. Rise times of these signals are not affected by the delay

networks. Glitch free transition is assured as long as both supplies remain within operating specifications for a

minimum of 5 ms after the logic signal SRC is toggled.

Copyright © 2000–2013, Texas Instruments Incorporated

Submit Documentation Feedback

15

Product Folder Links: LM3544