Tag
pcb layout
10 articles.
- How much current melts a PCB trace
Onderdonk's equation, where it stops being true, how it compares against IPC's continuous rating, and why a resettable fuse can be slower than the copper.
- Guard rings: stopping PCB leakage into high-impedance nodes
Gigaohm trace-to-trace resistance still leaks nanoamps at 5 V. Compute when board leakage beats V_OS and bias current, and lay out a driven guard to remove it.
- How many thermal vias, and when more stop helping
One 12-mil via is 261 °C/W, sixteen under the pad are 16 °C/W, and the fortieth buys almost nothing. Size the array, the pad and the copper from TI's data.
- Buck converter PCB layout: find the hot loop first
The two switch-state current loops differ by one small loop carrying chopped current. Its area sets the EMI, and the input capacitor's placement sets its area.
- How to choose and place a TVS diode for ESD protection
Why a 5 V TVS hands the pin 10 V mid-strike, which datasheet numbers predict it, and the placement rules that stop loop inductance adding 40 V per nanohenry.
- Should you split analog and digital ground planes?
One continuous ground plane with partitioned placement beats a split: where return current really flows, where AGND and DGND tie, and when a moat is right.
- Reflections you can see: when a trace becomes a transmission line
The rule is not length, it is rise time. TI's rule is four times the one-way delay: below it a trace is a wire, above it each unterminated end is a mirror.
- The via is the decoupling: 40 dB from layout alone
Würth built one board with the same ferrite and the same two 100 nF capacitors in every channel, and changed only the layout. The worst channel is 40 dB down.
- θJA is a property of the test board, not of your board
The thermal resistance on the datasheet was measured on a JEDEC board that is not yours. What the number actually contains, and the five terms you control.
- Why the crystal won't start
A Pierce oscillator fails in a few ways: too little gain for the crystal's ESR, too much drive, wrong load capacitance, or stray capacitance. Each has a test.