UART Optoisolator Selection

Question

Problem: UART Optoisolator Selection. Solve this hands-on electronics task on EWskills.

Accepted Answer

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

5. Filtered DigiKey Link

➡ View Matching Parts — Logic Output, 1-Ch, ≥3000Vrms, ≥1MHz, SOIC-8

66. UART Optoisolator Selection