Below is a list of the most common design review feedback items for EM35x customer design reviews.  Before you complete your EM35x-based design and submit design files for review by our support team, please review this list and refer to the documentation links below.

• The nRESET pin has an internal glitch filter and pull-up and should not have external filters or pull-up components attached, as they can negatively affect the overall stability of nRESET. For more information refer to the EM357 datasheet section 6.2.1.2. NRESET Pin.

• Verify the 24 MHz crystal case is not grounded in order to keep the crystal loop currents which are absorbed by the case from coupling into the EM35x reference ground.  These loop currents can be at frequencies which impact the IF and RF as noise. Note an exception is known for when the EM35x is referenced to a floating ground whereby custom PCB topology results in near field noise coupling onto the floating crystal case, such as from a switching power supply.  In this rare situation, the problem can be solved by grounding the crystal case.

• Confirm the 24 MHz crystal is compliant to the IEEE 802.15.4 specification for crystal frequency offset and symbol rate PPM.  When in doubt, request and review the crystal specification. For more details refer to following knowledge base article: http://community.silabs.com/t5/Wireless-Knowledge-Base/EM3xx-24-MHz-Crystal-Selection/ta-p/144602
• The 1V8 PCB power route should be connected serially from the source via to decoupling capacitor and then to target EM35xx pin for better noise suppression. Source vias which are placed between the decoupling capacitor and the target IC power pin results in reduced noise immunity for the power pin.
• 1.8V net routing should be star-routed to take advantage of the inductive impedance resulting from creating longer trace lengths to provide filtering to individual power pins without having to add external ferrite bead components at each IC power pin as they are more expensive. If star routing is not followed, then it results in reduced noise immunity and the chances of noise coupling to the power pins increases.
• Each decoupling capacitor ground pad should have its own separate via to the EM35x reference ground plane and not be attached to the top layer plane ground plane or share vias between two or more capacitors in order to reduce the potential for noise to couple into the EM35X power pin being decoupled. Refer to AN698 for more details: http://www.silabs.com/Support%20Documents/TechnicalDocs/AN698.pdf
• Crystal loading caps should share same ground via to make the crystal loop currents as short as possible and to prevent them from coupling onto the EM35x reference ground plane and/or nearby power and signal traces.
• The filtering capacitor for EM35x pins 5 (VDD_RF), 8 (VDD_IF) and the RF differential port DC bias pin(s) should be 8 pF to 10 pF because they have resonating frequency of 2.4 GHz.
• Verify the 24 MHz crystal tuning capacitor values.  Note the values may vary according to the crystal specification however they must be symmetrical. Verify crystal value as per the application note AN700, section 2.6. See the following link: http://www.silabs.com/Support%20Documents/TechnicalDocs/AN700.pdf.
• Create pastemask layer window openings within the ground slug pad area of Em35xx as they are necessary for properly creating the solder stencil used in the assembly process. Refer datasheet section 20 for more details. http://www.silabs.com/Support%20Documents/TechnicalDocs/EM35x.pdf

Please refer to the EM35x Reference Designs (http://www.silabs.com/products/wireless/zigbee/Pages/zigbee-reference-designs.aspx) for recommended design implementations.  Also, please refer to AN698 PCB Design with EM35x (http://www.silabs.com/Support%20Documents/TechnicalDocs/AN698.pdf) for detailed design recommendations.