QuickCarrier Developer’s Guide
7
Chapter 2 – Design Considerations
USB Power Considerations
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Use a high speed USB cable that is as short as possible. It is recommended that you use a 12 inch cable.
Some computers with high speed USB connectors run additional cables to the mother board. The
additional length can then cause enumeration issues.
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If possible, connect directly to the USB connector on the motherboard.
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Use USB 3.0 ports if available because these ports are typically rated for more current.
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The peak current measurements—which you can find in the power draw section for your model—show
that transmit spikes can happen. Although the bulk caps on the MT100UCC handle these spikes in most
cases, review your power design with the spikes in mind.
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Your device may not power up on all Host PCs or host USB devices due to the higher current
requirements of the cellular radio. Check your particular USB host port or PC motherboard's electrical
specs for details on max current capabilities of the particular USB port you are trying to use.
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Depending on your design, you may be able to use a dual USB cable to share the current between two
low power USB ports or create a custom USB cable that provides external power.
Noise Suppression Design Considerations
Adhere to engineering noise-suppression practices when designing a printed circuit board (PCB) containing
the QuickCarrier USB modem. Noise suppression is essential to the proper operation and performance of
the modem and surrounding equipment.
Any OEM board design that contains the QuickCarrier should consider both on-board and off-board
generated noise that can affect digital signal processing. Both on-board and off-board generated noise that
is coupled on-board can affect interface signal levels and quality. Noise in frequency ranges that affect
modem performance is of particular concern.
On-board generated electromagnetic interference (EMI) noise that can be radiated or conducted off-board
is equally important. This type of noise can affect the operation of surrounding equipment. Most local
government agencies have stringent certification requirements that must be met for use in specific
environments.
Proper PC board layout (component placement, signal routing, trace thickness and geometry, etc.)
component selection (composition, value, and tolerance), interface connections, and shielding are required
for the board design to achieve desired modem performance and to attain EMI certification.
Other aspects of proper noise-suppression engineering practices are beyond the scope of this developer’s
guide. The developer should consult noise suppression techniques described other sources, such as
technical publications, electronics and electrical engineering text books, and component supplier
application notes.
Mounting Hardware
Use #4 or M2/M3 hardware to mount the QuickCarrier modem to the board.
