66. UART Optoisolator Selection
1. Component Purpose
A standard transistor-output optocoupler is too slow for UART communication — its phototransistor output has turn-off times of 10–50µs, which distorts data at 115200 baud.
A logic output optoisolator has an integrated photodetector and output driver that produces clean, fast digital logic transitions. Data rates of 1MHz+ are typical, providing comfortable margin for 115200 baud UART.
Required: Open Collector · 1-Ch · ≥3000Vrms · ≥1MHz data rate · tpd ≤10µs · 3.3V supply · SOIC-8 · SMD
2. How to Find It on DigiKey
Go to DigiKey.com → Isolators → Optoisolators - Logic Output (Digital Isolators)
Apply these filters:
- Output Type → Open Collector
- Number of Channels → 1
- Voltage - Isolation → 3000Vrms or higher
- Data Rate → 1Mbps or higher
- Package / Case → 8-SOIC or 8-SMD
- Part Status → Active
Important: Logic output optoisolators need a supply voltage on the output side (unlike transistor-output types which are passive). Verify the Voltage - Supply range includes 3.3V (e.g., "2.7V ~ 5.5V" or "3V ~ 15V").
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Output Type | Open Collector | Logic-compatible digital output. |
| Channels | 1 | Single UART TX line. |
| Isolation | ≥3000Vrms | Industrial-grade isolation. |
| Data Rate | ≥1MHz | Margin for 115200 baud (≈115kHz). |
| Propagation Delay | ≤10µs | Clean signal edges at UART speed. |
| Supply Voltage | Includes 3.3V | Must work with MCU supply rail. |
| Package | 8-SOIC | Compact SMD. |
| Temp Range | −40°C to +85°C | Industrial conditions. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide