Tinyswitch PCB Layout
How to know it’s a good layout?

Three check points

Step 1

• Switch loop: Try to find the power device
• MOSFET
• Diode
• Reduce the switch loop circle area in the layout; Keep switching loops as small as possible
• Can’t put any signal components inside or around the switch loop

Step 2

• Power and signal loop: Try to find the power path
• MOSFET
• Diode

• Mostly is related with switch loop ,B+ and B-; Kelvin connection
• Power path is needed to be separated with signal path; Switching loops need totally separated with signal loops

Step 3

• Small Signal components as close as possible the device’s pin

Switch loop of Standard schematic for Tiny switch
Normal we will separate to 4 switch loops in a standard circuit

Main loop

Primary snubber circuit loop

Primary bias winding loop

Secondary power winding loop

• Snubber should be noted too

1.Main Mosfet switch loop

B+(Buck cap or decoupling cap) → Main transformer → Drain pin of Tiny → Source pin of Tiny → B-(Buck cap or decoupling cap)

Switching loops as small as possible

Power path

• The Green line, MOSFET currents flow into Bulk cap directly; the Signal loops need to pass through Source pin, can’t connect with high current path between Source pin to Bulk cap(Green line)
• The purple line, it’s the Signal ground. High current will flow in Bulk cap(Green line), purple path has no switch current

2. Primary snubber loop

Switch loop

• B+ of Main transformer → Clamp diode → TVS or RC → B+

Switching loops as small as possible

3. Primary bias winding loop

Switch loop

• Bias winding high side → Rectifier Diode → Capacitor → Bias winding low side

Switching loops as small as possible

Power path

• The Green line, bias winding currents flow into Bulk cap directly; the Aux Ground need totally separated with signal loops and don’t pass through Tny’s Source pins when it back to Bulk cap Ground

4. Secondary power winding loop

Switch loop

• Output winding high side → Rectifier Diode → Capacitor → Output winding low side

Switching loops as small as possible

5. Signal loop

Signal loop need to be Separated with Power path

• Yellow & purple line is clean ground. Signal components connect to source pin directly without through power path (Green line is non-clean; power current flow into bulk cap)

Signal loop need to be Separated with Switch loop

• Signal components and trace can’t be closed switch loop, especially Drain pin (trace) or snubber circuit (Because high dv/dt)

Kelvin connection

What's Kelvin connection?
A Kelvin connection is a means of making precision electrical potential contact with a current carrying component or reference point in such a way that eliminates or greatly reduces the effect of contact resistance.

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