EDA Skillpack

@@ -0,0 +1,114 @@+---+name: eda-addressable-rgb-leds+description: Use when choosing, placing, wiring or reviewing single-wire addressable RGB LEDs (WS2812B, WS2812B-2020, -V6, -V7, WS2812C, WS2812E, NeoPixel, SK6812-style, Dialight 587-1024-147F) in a schematic or PCB, including 3.3 V data drive, chain power budgets, substituting one 2020 part for another, and pin-1 orientation. Trigger words: WS2812, NeoPixel, addressable LED, RGB LED chain, LED strip, pixel LED, 2020 LED, DIN DOUT chain, level shift WS2812, LED power budget.+---+Parent skill: eda-engineering++# Addressable RGB LEDs: choose, wire and place them without a respin++Sources: Worldsemi datasheets for WS2812B-2020 (V1.0, 2018), WS2812B-2020-V6, WS2812B-2020-V7, WS2812C-2020-V6 and+WS2812E-2020 (world-semi.com, 2026 revisions); the [adom/ws2812b-2020](https://wiki.adom.inc/adom/ws2812b-2020) component+page and its verification log; the [adom/587-1024-147f](https://wiki.adom.inc/adom/587-1024-147f) page (Dialight); and+the design decisions of [adom/led-grid-wall](https://wiki.adom.inc/adom/led-grid-wall) (12,816 LEDs). Each number below is+from those sheets; re-read the sheet of the exact MPN you place, because Worldsemi revises figures between revisions.++## 1. The MPN is the part, the package name is not++"2020 addressable LED" names a 2.0 mm class, not a pinout. Two real cases:++| Part | Pin 1 | Pin 2 | Pin 3 | Pin 4 | Land pattern |+|---|---|---|---|---|---|+| Worldsemi WS2812B-2020, -V6, -V7, WS2812C-2020-V6, WS2812E-2020 | DO | GND | DI | VDD | 0.7 x 0.7 mm pads, centres (±0.915, ±0.55) |+| Dialight 587-1024-147F | DOUT | VDD | DIN | GND | 0.9 x 0.9 mm pads on 1.7 mm pitch |++The Dialight part swaps VDD and GND against the Worldsemi family and needs a different land pattern. Dropping it onto+a Worldsemi footprint reverses the supply on every pixel. Never substitute across makers by package name: compare the+pin table and the land pattern of both MPNs first, and change the footprint with the part. The five Worldsemi 2020+parts above do share one package drawing, pinout and land pattern, so they swap on the same footprint.++## 2. Pick the variant for the electrical job++| Worldsemi 2020 part | VDD | Data high (VIH min) | Per channel | Temperature (sheet) |+|---|---|---|---|---|+| WS2812B-2020 (V1.0 sheet) | 3.7 to 5.3 V | 0.7 x VDD | 16 mA (12 mA from V1.2) | -25 to 85 C |+| WS2812B-2020-V6 | 3.3 to 5.3 V | 0.55 x VDD | 12 mA | -40 to 85 C |+| WS2812B-2020-V7 | 3.3 to 5.3 V | 0.55 x VDD | 16 mA, about 2x V6 | -40 to 85 C |+| WS2812C-2020-V6 | 3.3 to 5.3 V | 0.55 x VDD | 5 mA, dim | -40 to 85 C |+| WS2812E-2020 | 3.7 to 5.3 V | 0.7 x VDD | 12 mA | -40 to 65 C |++All use the same 800 kbps single-wire protocol, 24 bits per pixel in G R B order, high bit first, and latch on a low+longer than 280 us.++## 3. Drive the data line from 3.3 V logic only where the sheet allows it++Compute VIH at the highest VDD the LEDs will see, not at nominal:++- 0.55 x VDD parts (V6, V7, C-V6): 2.75 V at 5.0 V and 2.92 V at 5.3 V. A 3.3 V CMOS output drives them directly,+  with about 0.4 V of margin at the top of the range.+- 0.7 x VDD parts (original WS2812B-2020, WS2812E-2020): 3.5 V at 5.0 V. A 3.3 V output does not meet it. Buffer the+  first DI through a 5 V-powered gate with TTL-level inputs (VIH about 2 V), for example SN74AHCT125 or a single-gate+  AHCT1G125, as the LED Grid Wall does.++Each pixel re-drives DO from its own VDD, so only the first DI of each chain needs this. Keep the buffer next to the+first pixel, not next to the MCU, when the first run is long. A small series resistor at the driver end to damp+ringing on a long first run is common practice; the Worldsemi 2020 sheets do not specify one, so treat it as a+judgment call and say so.++## 4. Budget the power before you size anything++Full white draws all three channels: per pixel, 3 x the channel current plus the controller's quiescent current. Sum+the chain, then decide in this order:++1. Is full white ever allowed? If not, the firmware enforces a global cap and the hardware is sized to the cap, not the+   theoretical peak. The LED Grid Wall tile reads 27.8 A uncapped (1,760 pixels x 15.8 mA) and is built for a 20 A+   firmware cap; a cap that the hardware relies on is a stated requirement, not an assumption.+2. Carry the current in planes, not traces: the Grid Wall went to inner GND and V5 planes (4 GND layers at 20 A) so+   the far end of the field sees the same rail as the near end.+3. Feed power at several points on long chains. Green and blue dies need about 3.0 to 3.2 V forward and red about 2.0+   to 2.2 V, so sag down a chain dims green and blue first and the colour drifts warm; it also lowers VDD, which moves+   every pixel's VIH.++## 5. Decouple per the part's own sheet++Every current Worldsemi 2020 sheet asks for a 100 nF capacitor on VDD at each LED. Dialight's 587-1024-147F sheet+says no external capacitor is required. Follow the sheet of the MPN you place; do not carry one part's rule to the+other. Place the capacitor at the VDD and GND pads, on the same side, with its own short return.++## 6. Pin-1 orientation: check it as a chain, every time++A rotated LED is a scrapped board, and nothing electrical catches it before assembly. For the Worldsemi 2020 family:++| Link | What must agree |+|---|---|+| Footprint | pad 1 (DO) is the corner the silkscreen marks |+| 3D model | pin 1 on the same corner; pins 1 to 4 run counter-clockwise seen from the top, as the datasheet Top View |+| Underside | the polarity stripe sits beside pins 1/2 (Back View, PCB Solder Pad drawing, real-part photos) |+| Top side | the IC die sits toward the pin 2/3 edge (datasheet Top View, Worldsemi photo) |+| Assembly | the pick-and-place rotation puts pad 1 where the footprint does; check one placed part on the assembly preview |++The adom/ws2812b-2020 page records this chain in its verification log. Re-check it when you change the footprint, the+3D model, or the part's rotation in the PnP file.++## 7. Land pattern and handling notes that surprise people++- The WS2812B-2020 terminals are 0.78 mm long and the recommended pads 0.7 mm, so about 0.09 mm of each terminal sits+  off the copper. Every sheet draws it that way and none gives a reason. Use the datasheet pattern; do not grow the+  pads to cover the metal without a reason you can state.+- The original WS2812B-2020 sheet rates it MSL 6: solder right after opening the bag and bake before any second+  reflow. Check the rating on the sheet of the revision you buy.+- Distribution is uneven: Mouser does not distribute Worldsemi; LCSC carries WS2812B-2020 (C965555). Confirm stock for+  the exact MPN before committing a footprint, and if you must switch makers, go back to section 1.++## Execute and report++Deliver, for every addressable LED in the design:++1. The MPN and revision of the datasheet used, with its pin table copied next to the footprint's pad table.+2. A data-drive table: driver output high voltage, LED VIH at maximum VDD, margin, and the buffer if one is needed.+3. A power table: pixels per chain, worst-case current, the firmware cap if any, feed points and plane allocation.+4. The decoupling rule from the part's own sheet and where each capacitor sits.+5. The pin-1 chain from section 6, checked against the footprint, the 3D model and the assembly rotation.++Mark anything taken from common practice rather than the datasheet as such. For copper sizing and current review,+continue with [electrical routing](../eda-electrical-routing/SKILL.md) and+[multilayer current review](../eda-multilayer-current-review/SKILL.md).