u-blox LEXI-R422, System Integration Manual

Page: 81 / 108

LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 81 of 108
C1-Public
2.8 Reserved pins (RSVD)
LEXI-R422 modules have pins reserved for future use, marked as RSVD , which can all be left
unconnected on the application board, except for the RSVD pin number 99 (also identified as J5),
which is recommended to be externally accessible by connecting it to a dedicated Test-Point.
LEXI-R422
RSVD
Test-Point
J5
RSVD
Figure 62: Application circuit for RSVD pins
☞
It is highly recommended to provide accessible test point directly connected to the RSVD #99 (J5)
pin for diagnostic purposes (see Figure 62 ).
☞
It is also highly recommended to provide access to the V_INT , PWR_CTRL , USB_5V0 , USB_3V3 ,
USB_D+ , USB_D- pins for FW update and/or for diagnostic purposes, making available accessible
dedicated Test-Points directly connected to each of these pins, or making available a dedicated
connector / circuit (see
Figure 56 ).
2.9 Module placement
An optimized placement allows a minimum RF line’s length and closer path from DC source for VCC .
Make sure that the module, analog parts and RF circuits are clearly separated from any possible
source of radiated energy. In particular, digital circuits can radiate digital frequency harmonics, which
can produce electro-magnetic interference that affects the module, analog parts and RF circuits
performance. Implement suitable countermeasures to avoid any possible electro-magnetic
compatibility issue.
Make sure that the module is placed in order to keep the antenna as far as possible from VCC supply
line and related parts (refer to
Figure 27 ), from high speed digital lines (as USB) and from any possible
noise source.
Provide enough clearance between the module and any external part: clearance of at least 0.4 mm per
side is recommended to let suitable mounting of the parts.
☞
The heat dissipation during continuous transmission at maximum power can significantly raise
the temperature of the application base-board below the LEXI-R422 modules: avoid placing
temperature sensitive devices close to the module.