Contents
How to make a crystal PCB layout work?
Crystal, PCB Layout 1 Minimize distance between crystal and MCU 2 Match trace lengths for Osc_In and Osc_Out pins on MCU 3 Keep load capacitors close to the crystal 4 Place ground pour on bottom layer under the crystal 5 Create local power and ground for MCU/crystal More
What’s the best way to isolate a crystal?
Isolate the crystal from anything else. Use ground planes beneath the crystal. Avoid vias for signal lines. Here’s the layout of what I currently have for my crystal: The red represents the top PCB copper and blue is the bottom PCB layer (it’s a 2-layer design).
Where are the ground pins on a PCB?
Tie all the ground immediately associated with the micro together on the top layer. This includes the micro’s ground pins and the ground side of the crystal caps. Then connect this net to the main ground plane in only one place. This way the high frequency loop currents caused by the micro and the crystal stay on the local net.
Is the 32.768khz crystal oscillator required for RTC function?
This section describes specific layout and design considerations for the 32.768kHz crystal oscillator; this can be used to source the internal 32kHz clock domain, in lieu of the s ilicon oscillator or an external pin. The crystal implementation is required to support the RTC function within the CEC1702. 1.2.1 32.768KHZ CRYSTAL OSCILLATOR LAYOUT
Where do you place Vias on a PCB?
To the Grounding, I would suggest placing some vias close to the GND paths of the load capacitors rather than relying on the GND trace back to the MCU. I generally place a 0.2/0.4mm via near every signal component ground pad where possible and at least 3 0.4/0.8mm vias for power or transient prone components.
Are there benefits to using 16MHz matched length crystal lines?
At 16MHz matched length traces will not provide any benefit. They key however is to ensure that your GND return paths are short and that the crystal lines are isolated from clocking sensitive traces such as Uart RX or Reset lines, or any other functional traces to which coupled clocking could cause false interrupts or undesired functionality.
Do you need guard rings on PCB crystals?
Unless you have very high nearby dV/dt and poorly made crystals, there is no reason they need to have guard rings.
Which is better grounding or routing the crystal signal traces?
Your routing of the crystal signal traces is fine. Your grounding is bad. Fortunately, doing it better actually makes your PCB design easier. There will be significant high frequency content in the microcontroller return currents and the currents thru the crystal caps.
How many via’s should I place on my PCB?
I generally place a 0.2/0.4mm via near every signal component ground pad where possible and at least 3 0.4/0.8mm vias for power or transient prone components. The general rule for noise/high speed is to keep your ground impedance as low as possible.