LM3544M-H National Semiconductor, LM3544M-H Datasheet - Page 12

• Manufacturer Part Number: LM3544M-H
• Description: Quad Port USB Power Distribution Switch and Over-Current Protection
• Manufacturer: National Semiconductor

www.national.com
Typical Applications
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 8 , 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.
FIGURE 8. Using the LM3544 in a Wake-on-USB Application
(Continued)
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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.
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