Schematics

This page contains all basics rules that must be checked during schematics phase.

Power Supply

• Power pins are connected to the right voltage
• Analog power pins are connected to a quiet power rail with a PI filter (Capacitor, Ferrite, Capacitor)
• One 100nF bypass capacitor per digital Power pin
• One 100nF bypass capacitor for two analog power pins if they are next to each other.
• Power sequence at power on and power off follow chip specification

I/O Pins

• I/O pins are connected to a supported voltage level
• I/O pins might use sample at reset configuration. Check that the right configuration is applied, resistor has the right value and it is connected to supported voltage
• Pin direction is clearly identified on schematics
• Pin direction is supported by the chosen I/O pin
• Check that if a special hardware fonction is required, it is available (blink, SATA activity, …)

Clock

• Show clock frequencies on schematics
• Check that clock frequency is right
• In case of a crystal, check capacitor load value
• In case of a crystal, check resistive load value

Differential pairs

• For each differential pair, polarity and impedance are indicated (single ended and common)

IC

• All IC with a reset pin must reset at every power on or product wake up. If this is not possible, CPU shall be able to control reset using a GPIO.
• Chips ID shall be identified in Hardware specification document
• Chips address on bus shall be identified on Schematics and Hardware specification

Power

• Bulk capacitors : 22uF every square inch per power plane
• Decoupling capacitors : 1x100nF per power ball
• DC/DC minimal efficiency shall be 85%

Misc

• Chips ID or address shall be visible on schematics (I²C, JTAG, PCIE …)
• Important nets must have a clear name (Differentials pairs, power rails, CPU signals, Memories)
• Double footprints shall have correct reference (R57, R57A, R57B, etc…)
• Run DRC tools to check if there are unconnected nets
• Generate a BOM and check that it is ok (footprints, component value, tolerance, voltage)
• Check that “NC” (not connected) parts are really not connected.
• Collect all datasheets, erratas and make sure you have the latest version
• Check for all available tools from chip manufacturer