Problem 10
Place and route a fixed 12 V to 5 V buck. The schematic is already correct.
- Keep the hot loop small and the switch-node copper small.
- Do not route feedback alongside the switch node just because that path is shorter.
Context
The schematic is already correct. The layout is the exercise. The switch node snaps every cycle. The hot loop is the switch, the catch diode, and the input capacitor. Feedback should measure the output, not the switching edge.
Components on this challenge
- Buck converter. A switching regulator that chops the input and filters it to a lower output.
- Input capacitor. Supplies the chopped current each cycle.
- Catch diode. Gives the inductor current a path when the switch is open.
Full brief
The schematic is already the converter. Keep the input capacitor, the switch, and the diode in a small loop, keep the switch-node copper small, and keep feedback off that node.
How PCBGrade measures this
The schematic is fixed: asynchronous buck, 12 V to 5 V at 1 A. You place and route it. You do not choose the regulator values, and there is no converter waveform. Board 40 × 30 mm, two layers. A via barrel is 1.565 mm. Zones are not allowed. CIN pin 1 is VIN and pin 2 is GND. COUT pin 1 is VOUT and pin 2 is GND. D1 pin 1 is the anode on GND and pin 2 is the cathode on SW. L1 pin 1 is the SW side. RT is the top feedback resistor (VOUT to FB) and RB is the bottom (FB to GND). U1 pins are VIN, GND, SW, FB. The hot loop is three routed lengths added together: CIN pin 1 to U1 VIN, U1 SW to D1 cathode, and D1 anode to CIN pin 2. That sum must be ≤ 35.0 mm. An open segment fails the rule; it is not treated as 0 mm. CIN pin 1 to U1 VIN ≤ 5.0 mm and CIN pin 2 to U1 GND ≤ 5.0 mm (12 points each). The loop sum is 16 points. U1 SW to D1 cathode ≤ 6.0 mm and U1 SW to L1 pin 1 ≤ 6.0 mm (10 points each). SW copper area ≤ 100.0 mm² (9 points): on each copper layer, the union of SW pad rectangles and trace rectangles, then added across layers. A trace rectangle is its length times its width with square ends, including a diagonal trace. It is not the axis-aligned bounding box. Overlap on one layer counts once. Pads are included. The feedback route is copper only, from COUT pin 1 to RT’s VOUT pin and from RT’s FB pin to U1 FB. The resistor body is not added. That length is ≤ 25.0 mm (8 points). Feedback copper must stay ≥ 2.5 mm edge to edge from SW copper, projected across layers (8 points). U1’s own FB and SW pads are already farther apart than 2.5 mm, so there is no courtyard exemption. DRC is 10 points (clearance 0.20 mm, copper at least 0.50 mm from the edge). Every net routed, with no shorts, is 5 points. An open net, a short, or SW copper over 100.0 mm² caps the score at 69. Trace width is not graded against the 1 A current.
- hot-loop geometry · 40 pts
- SW/feedback handling · 25 pts
- placement · 20 pts
- DRC · 15 pts
- Cap 69: An unrouted net or a short caps the score at 69.
- Cap 69: SW copper over 100 mm² caps the score at 69.
- Cap 69: Copper outside the outline cannot pass, and neither can a short between nets.
Reference
Training buck
VIN, GND, SW, and FB. FB and SW pads are more than 2.5 mm apart edge to edge.
- 1. VIN. Input
- 2. GND. Ground
- 3. SW. Switch node
- 4. FB. Feedback