Quick answer: According to World Semi's preliminary WS2801 datasheet, WS2801 is a three-channel RGB LED driver with separate clock and data inputs, a 3.3–5.5 V chip supply and a specified constant-current range of 5–30 mA per channel.
This guide covers the driver chip, its control signals and calculations for a proposed circuit. A chip specification does not establish the voltage, LED density or power rating of a finished strip. For broader selection questions, see our addressable LED strip guide.
Which WS2801 specifications matter?
Start with the electrical-characteristics table, especially when choosing current. According to World Semi's preliminary datasheet, the useful reference values are:
| Item | Datasheet value | Design implication |
|---|---|---|
| Chip supply, VCC | 3.3–5.5 V | Apply this range to the chip supply |
| Constant-current outputs | Three channels, 5–30 mA each | Set the channel current with feedback resistors |
| Input clock | 25 MHz maximum | Treat this as a chip limit, not a cable guarantee |
| Data per chip | 24 bits: red, green, blue | Allocate a complete RGB word to each driver |
| Output latch | Clock held low for more than 500 µs | Include a latch interval after transmission |
These values are from the single preliminary source linked above. Its current figures conflict: according to World Semi, the description and electrical table specify up to 30 mA, while the feature list says 5–150 mA and the constant-current absolute-maximum entry says 0–50 mA. Use the table's 30 mA figure for this discussion; the larger numbers do not establish a supported operating target.
How do the pins and data sequence work?
Send clock to CKI and serial data to SDI. According to World Semi, data enters on the rising clock edge, and the buffered CKO and SDO outputs support cascading to the next driver. These are signal names, not connector positions for a particular strip.
According to World Semi's data-format description, each chip accepts three 8-bit words in red, green, blue order, most significant bit first. After 24 rising edges it enters relay mode for the next chip. The arithmetic is 3 × 8 = 24 bits per driver, with 2^8 = 256 possible values per channel.
Use this signal-level checklist when preparing a controller:
- Identify the input end by CKI and SDI; identify the onward signals by CKO and SDO, following World Semi's interface description.
- Assemble complete RGB words in the order and bit direction specified by World Semi.
- End transmission with clock low for more than 500 µs, as required by World Semi's latch description.
The last step matters when debugging a strip that receives data but does not display the intended update. According to World Semi, that low-clock interval resets the internal state register and latches the shifted grayscale data (the datasheet's switching table notes the data is reloaded at the end of each PWM cycle).
How fast can a chain update?
Calculate transmission time from the total bit count, then add the latch interval. According to World Semi, the input clock ceiling is 25 MHz and each driver consumes 24 bits. The clock ceiling alone is not a complete frame-rate specification.
Worked example: an assumed chain
Assumed inputs: 100 drivers, clocked at 2 MHz, with a chosen 600 µs low-clock interval after the data. Use the source's 24 bits per driver and requirement for a low interval greater than 500 µs, according to World Semi.
- Total bits = driver count × bits per driver = 100 × 24 = 2,400 bits.
- Clock rate = 2 MHz = 2,000,000 bits/s for this calculation.
- Transmission time = bits ÷ clock rate = 2,400 ÷ 2,000,000 = 0.0012 s = 1.2 ms.
- Assumed latch interval = 600 µs = 0.6 ms.
- Total frame time = 1.2 + 0.6 = 1.8 ms = 0.0018 s.
- Ideal frame rate = 1 ÷ 0.0018 ≈ 556 frames/s, excluding controller overhead.
This is arithmetic for the assumed chain, not a measured refresh result. It is also distinct from PWM: according to World Semi, the internal PWM free-runs at about 2.5 kHz, and the highest grayscale value corresponds to a duty ratio of 255/256.
How do you set the LED current?
In constant-current mode, select each channel's feedback resistor from the desired current. According to World Semi, the typical feedback reference is 0.6 V and the relationship is I = 0.6 V ÷ R. The resistor sets channel current; the grayscale word controls its PWM duty.
Worked example: an assumed feedback resistor
Assumed input: a 30 Ω feedback resistor, using World Semi's typical reference voltage cited above.
- Current = reference voltage ÷ resistance.
- I = 0.6 ÷ 30 = 0.020 A.
- I = 0.020 × 1,000 = 20 mA.
According to World Semi, the voltage at each R/G/B OUT pin should be between 1 and 1.5 V for accurate constant-current operation while limiting chip dissipation. The feedback-resistor calculation alone therefore does not establish whether the whole circuit has suitable voltage headroom.
Constant-voltage mode uses a different resistor calculation. According to World Semi, the FB pin is grounded, POL is high or floating, and an external LED series resistor follows R = (VDD − VLED − VOUT) ÷ ILED; output saturation voltage is about 0.2–0.4 V.
Assumed inputs: 5 V supply, 3.0 V LED forward drop, 0.3 V output drop and 20 mA desired LED current.
- Current in amperes = 20 ÷ 1,000 = 0.020 A.
- Resistor voltage = 5 − 3.0 − 0.3 = 1.7 V.
- Required resistance = 1.7 ÷ 0.020 = 85 Ω.
This is a calculated resistance, not a specified standard component value. The site's resistor calculator uses the same voltage-drop-over-current principle, but this driver calculation must also subtract the output drop.
How should you estimate strip power?
Use the proposed circuit's current or the finished strip's rated power. Our LED strip calculator uses total watts = watts per metre × length, then current = watts ÷ voltage. Its generic strip presets do not establish WS2801 power consumption.
Assumed inputs: 100 RGB drivers, three channels per driver set to 20 mA, all channels treated as continuously on for an LED-load estimate, and a 5 V supply. This deliberately excludes chip operating current and controller power.
- Current per driver’s LEDs = 3 × 20 = 60 mA = 0.060 A.
- Total LED current = 100 × 0.060 = 6 A.
- LED-load supply power = voltage × current = 5 × 6 = 30 W.
Applying the calculator's planning figure of 20% headroom and its upward rounding to 10 W increments gives ceil(30 × 1.2 ÷ 10) × 10 = ceil(3.6) × 10 = 40 W. Add the excluded loads before making a final supply selection. If the supply involves mains wiring, use a qualified electrician.
FAQ
What voltage does WS2801 run on?
According to World Semi's electrical table, the chip supply range is 3.3–5.5 V. That is a chip-level rating, not a universal finished-strip input rating.
Can I run every channel at 150 mA?
The preliminary document does not establish that as a supported operating point. According to World Semi, its electrical table gives 5–30 mA per channel despite the conflicting 5–150 mA feature line.
Why is shifted data not appearing on the LEDs?
Check the clock-low interval first: according to World Semi, it must exceed 500 µs to latch the shifted data. Treat this as a troubleshooting check, not proof of the fault.
How long can the clock and data connection be?
According to World Semi, clock and data can travel up to 6 m at 2 MHz, with a recommended 50 Ω resistor at the data input or output port for impedance matching. That stated condition does not establish the same distance at the maximum clock speed.
Are WS2801 and WS2812 controllers interchangeable?
Choose a controller that explicitly supports the required device. For WS2801, World Semi specifies separate clock and data signals and 24-bit RGB words; this source does not establish WS2812 compatibility.
Jack Shi
Founder & editor, LEDaskJack Shi builds and writes LEDask, an independent LED-lighting tools project operated by clooms. He designs the calculators, checks their formulas and reference values against published engineering data, and writes the guides across the site.
