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EDA Skillpack

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eda-engineering / skills / eda-addressable-rgb-leds / SKILL.md
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John Lauer eda-addressable-rgb-leds: decoupling history (V1.3 said no capacitor; current sheets ask for 100 nF) 9988a3e 2d ago

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 component page and its verification log; the adom/587-1024-147f page (Dialight); and the design decisions of 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 (for example the V6 sheet's Typical Application Circuit, p.5: "C1 is the filter capacitor of the LED's VDD pin, C1 = 100nF"). The original WS2812B-2020 went back and forth: V1.0 (2018) shows 100 nF, while V1.3 (2019) added that "there is no need for any electronic components including capacitors on the periphery". Design to the current sheet and fit the capacitor. 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 and multilayer current review.