LM3544MX-H National Semiconductor, LM3544MX-H Datasheet - Page 11

• Manufacturer Part Number: LM3544MX-H
• Manufacturer: National Semiconductor

Specifications of LM3544MX-H

• Short Circuit Current Limit: 2A
• Input Voltage Range: 2.7 to 5.5V
• Number Of Switches: Quad
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 16
• Package Type: SOIC N
• Lead Free Status / RoHS Status: Not Compliant

Typical Applications
ROOT AND SELF-POWERED USB HUBS
The LM3544 has been designed primarily for use in root and
self-powered USB hubs. In this application, the switches of
the LM3544 are used to connect the power source of the hub
to the power bus used by downstream devices and to protect
the hub from dangerously excessive loads and shorts to
ground. A high-power bus-powered function, low-power bus-
powered function, or a bus-powered hub can be driven
through a single port of the LM3544. A schematic of a circuit
that uses the LM3544 for power-supply switching in a typical
root or self-powered hub was shown earlier in this datasheet
in Figure 1.
Voltage drop requirements of USB power supplies require
the power outputs of the root and self-powered hubs to be no
less than 4.75V. For this reason, it is recommended that a 5V
power supply with a
this application. Combining a 3% supply with a low-
resistance PCB design and the low on-resistance of the
LM3544 power switches will ensure that the hub power
outputs meet the USB voltage drop specification even with a
500mA load, the maximum allowed in the USB standard.
BUS-POWERED USB HUBS
The LM3544 is capable of performing the power supply
switching functions required in Bus-Powered hubs. Use here
is very similar to the configuration used in root and self-
powered hubs. With bus-powered hubs, however, there is no
internal power supply to drive the input pins of the LM3544.
WAKE-ON-USB AND REMOTE WAKEUP
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
±
3% output voltage tolerance is used in
FIGURE 7. Using the LM3544 in USB Bus-Powered Functions
11
Instead, the input pins should be connected to the power bus
supplied by the upstream hub.
USB BUS-POWERED FUNCTIONS AND GENERAL
IN-RUSH CURRENT LIMITING APPLICATIONS
The LM3544 can be placed at the power-supply input of USB
bus-powered functions, or other similar devices, to protect
them from high in-rush currents. If the current being deliv-
ered to the device were to exceed the 2.0A over-current
threshold (typ.) of the LM3544, switches in violation would
open to protect the device from damage.
In addition to in-rush current limiting, the LM3544 can be
used in high-power bus-powered functions to keep current
levels of the function in compliance during power-up. The
USB specification requires the staged switching of power
when connecting high-power functions to the bus. When a
high-power function is initially connected to the bus, it must
not draw more than one unit supply (100mA). After a con-
nection is detected and enumerated, and if the upstream
device is capable of supplying the required power, the high-
power function may draw up to five unit loads (500mA). With
the proper control signals, the LM3544 can be used to
achieve this staged power connection. When the function is
connected to the bus, one or more of the LM3544 switches
can be closed to connect bus power only to circuitry needed
during the connection and enumeration process. If the func-
tion is to be powered fully, remaining switches on the
LM3544 can be closed to connect all blocks of the function to
the power bus. Figure 7 illustrates how the LM3544 can be
connected for use in bus powered functions.
auxiliary supply, used when the device is in suspend mode,
can dramatically decrease the power consumption of a com-
puter that contains devices that spend extended periods of
time in suspend mode. This application also works especially
well with devices configured for remote wakeup capabilities
(i.e.: using a keystroke on a mouse or keyboard to awaken a
suspended PC). A schematic showing an example of how
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