TransDimension Inc.
Interfacing TD242LP to Intel StrongArm SA1110 Processor
USB Signal Lines
To satisfy the impedance matching requirement, a 33 Ω resistor must be inserted between a USB
data line (DP2 or DM2) and its corresponding pin at the USB Type A connector.
If the port is not used, DM2 and DP2 pins should be left floating.
USB Host Power Distribution
In the reference design, VBus is supplied by an external power switch, the TPS2044, which is
controlled via the /PO pin. It supplies the power of 5V of up to 500mA and provides the over-
current protection required per the USB specification for standard USB host ports via the /OC
pin.
A sufficiently large capacitor (more than 120 µF) is applied to the VBus of port 2 per USB
specification. Ferrite beads are inserted in the VBus and ground circuits for EMI reduction.
3.2 TD242LP Port 1
This port can serve as either an OTG port or a standard downstream host port. Thus, it uses a
USB mini AB receptacle.
This port can be configured as a standard USB host port, a standard USB function port, or an
OTG port in this reference design. The only difference between the three in the reference design
is how VBUS for port is supplied. Refer to the USB Ports page of the schematics at the end of
this document. Install R2 for a standard USB host or function port. Install R1 for an OTG port.
The operational details are given in Section 6 of the TD242LP Technical Manual.
USB Signal Lines
To satisfy the impedance matching requirement, a 33 Ω resistor must be inserted between a USB
data line (DP1 or DM1) and its corresponding pin at the mini AB connector.
USB Host Power Distribution
In the reference design, VBUS is supplied by an external power switch, the TPS2044, which is
controlled via the /PO pin. As an A-Device, it supplies the power of 5V of up to 500mA and
provides the over-current protection required per the USB specification for standard USB host
ports via the /OC pin. As a B-Device, the TPS2044 is “VBus pulsed” using the /EXVBO and VBP
pins.
For systems that do not have a +5V supply available required for the TPS2044, please refer to the
TDI Charge Pump Application Note MU4032.
TransDimension, Inc.
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