u-blox LEA-5 Series Hardware Manual page 24

Is the voltage VDDUSB within the specified range?

 Compare the peak current consumption of your u-blox 5 module with the specification of the power
supply.
GPS receivers require a stable power supply, avoid ripple on VCC (<50mVpp)

 For low power applications using Power Save and backup modes, ensure that the power supply or low ESR
capacitors at the module input can deliver the required current/charge for switching from backup mode to
normal operation. In certain situations charging the internal capacitors in the core domain can result in a
significant instantaneous current draw.
Backup Battery
 For achieving a minimal Time To First Fix (TTFF), connect a backup battery to V_BCKP after power down.
Antenna
 The total noise figure should be well below 3dB.
If a patch antenna is the preferred antenna, choose a patch of at least 15x15mm. For smaller antennas an

LNA with a noise figure <2dB Is recommended, this can increase sensitivity up to 2dB. To optimize TTFF
make use of u-blox‖ free A-GPS services AssistNow Online and AssistNow Offline.
 Make sure the antenna is not placed close to noisy parts of the circuitry. (e.g. micro-controller, display, etc.)
For active antennas add a 10R resistor in front of V_ANT

antenna supervisor circuitry.
 To optimize performance in environments with out-band jamming sources, use an additional SAW filter.
For more information dealing with interference issues see the GPS Antenna Application Note [6].
Schematic
 If required, does your schematic allow using different module variants?
Don‖t drive RESET_N high!

i
 Plan use of 2nd nterface (Testpoints on serial port, DDC or USB) for firmware updates or as a service
connector.
Layout optimizations (Section 2.5)
 Is the GPS module placed according to the recommendation in Section 2.5.2?
 Has the Grounding concept been followed (see Section 2.5.3)?
 Has the micro strip been kept as short as possible?
 Add a ground plane underneath the GPS module to reduce interference.
 For improved shielding, add as many vias as possible around the micro strip, around the serial
communication lines, underneath the GPS module etc.
 Have ESD protection measures been included (see Section 2.7)?
Calculation of the micro strip (Section 2.5.4)
 The micro strip must be 50 Ohms and be routed in a section of the PCB where minimal interference from
noise sources can be expected.
 In case of a multi-layer PCB, use the thickness of the dielectric between the signal and the 1st
l
(typically the 2nd ayer) for the micro strip calculation.
 If the distance between the micro strip and the adjacent GND area (on the same layer) does not exceed 5
times the track width of the micro strip, use the "Coplanar Waveguide" model in AppCad to calculate the
micro strip and not the "micro strip" model.
7 Only available with LEA-5-H, LEA-5S, LEA-5A, LEA-5T and TIM-5H
GPS.G5-MS5-09027-A2
LEA-5, NEO-5, TIM-5H - Hardware Integration Manual
7
input for short circuit protection or use the
Released
G
ND layer
Design-in
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