Adafruit
Adafruit ISO1540 Bidirectional I2C Isolator - STEMMA QT / Qwiic
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This compact breakout provides electrical isolation between two sides of an I2C bus, helping separate earth-grounded circuits, reduce noise, or protect sensi...
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This compact breakout provides electrical isolation between two sides of an I2C bus, helping separate earth-grounded circuits, reduce noise, or protect sensitive low-voltage monitoring equipment from faults cascading across the bus.
The ISO1540 is fully bidirectional, supports clock stretching, and works with I2C clock rates up to 1 MHz. Each side runs from its own 3V to 5.5V supply, so power and logic levels are independent across the isolation barrier.
STEMMA QT / Qwiic connectors on both sides make solderless wiring straightforward, while breakout pads provide access to power, ground, clock and data. Green LEDs on each half confirm that power is connected, and the package includes the breakout plus a header strip.
Important isolation note: the isolation figures and safety certifications apply to the TI ISO1540 chip only, not the assembled Adafruit breakout board. Do not use this board across a mains voltage boundary or where the isolation barrier is a safety barrier; the board is not certified for high voltage isolation.
Features:
- STEMMA QT / Qwiic Connectors: One on each isolated side for solderless wiring
- 10 kΩ Pull-ups: Built-in on both sides, connected to their respective VCC
- Power LEDs: Green LED on each side confirms power is connected
- Breakout Pads: Power, ground, clock and data broken out on each side
- Independent Supplies: Each side must be powered separately
Specifications:
- 2500 V-RMS Isolation: Galvanic isolation between chip sides
- Bidirectional I2C: Transparent data transfer in both directions with clock stretching support
- Up to 1 MHz I2C Clock: Standard, fast, and fast-mode plus compatible
- 3V – 5.5V Supply Range: Independent power and logic levels on each side
- Open-drain Outputs: 3.5 mA Side 1 and 35 mA Side 2 sink current capability
- ±50 kV/µs Transient Immunity: Typical
- −40°C to +125°C Operating Range: Chip rating; the PCB assembly and connectors are not rated to this range
- DIN VDE V 0884-11:2017-01 Isolation: 4242 V-PK isolation
- UL 1577 Isolation: 2500 V-RMS for 1 minute
- CSA Approval: Per IEC 60950-1 and IEC 62368-1 end equipment standards
- CQC Basic Insulation: Per GB4943.1-2011
- HBM ESD Protection: 4 kV on all pins, 8 kV on bus pins
Ideal for low-voltage I2C systems where ground loops, earth-referenced equipment, or noisy environments are a concern. Both sides must be powered independently, and STEMMA QT cables are not included.
Jargon buster
Plain-language definitions for the technical terms used above.
- breakout
- A breakout board carries a small or fine-pitched component and brings its connections out to standard, breadboard- and header-friendly pins. Describing a part as a breakout means it can be wired into a project without soldering directly to the component's tiny contacts.
- DIN
- As a pin label, DIN stands for 'data in', the input through which a device receives serial data from a controller, as found on SPI displays, LED drivers and other serial modules. DIN can also refer to the German standards body of that name, as in a round multi-pin DIN connector or DIN-rail mounting.
- ESD protection
- ESD protection helps protect electronics from damage caused by static electricity discharges. It is useful on development boards because cables, sensors and modules are often plugged and unplugged during prototyping.
- I2C
- I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.
- LED
- A light-emitting diode (LED) is a small electronic component that emits light when current flows through it in the correct direction. Because it only conducts one way, its polarity matters, and a through-hole LED must be soldered the correct way around to light up.
- open-drain
- A digital output style that can pull a signal line low but cannot drive it high by itself, so it needs a pull-up resistor or another circuit to make the high level. Open-drain outputs are often used for shared alert lines or buses because multiple devices can safely pull the same line low.
- PCB
- A printed circuit board (PCB) is a board, usually rigid, with etched copper tracks that connect electronic components together without loose wiring. Components are mounted on the board and signals route between them through the copper layout.
- Qwiic
- Qwiic is a plug-in connector system for I2C devices that uses small 4-pin cables, so you can connect compatible sensors without soldering. It matters because your controller or adapter also needs Qwiic, or you will need a cable or breakout to wire it up.
- RMS
- RMS is a way of describing the effective level of an AC signal, such as an audio output voltage. It helps compare audio output levels more meaningfully than a peak voltage number.
- STEMMA
- A plug-and-cable connection system used on some maker electronics boards to make wiring simpler. If a product uses STEMMA, you need the matching cable or connector type to plug it in without soldering.
- STEMMA QT
- A small plug-in connector system for I2C boards that lets you connect compatible sensors and controllers without soldering. It matters because it can make wiring faster and less error-prone, especially when adding several small modules to a project.
- VCC
- VCC is the positive power-supply connection on a chip or module. Connecting it to the correct supply voltage is needed for the part to power on and helps avoid damaging the electronics.
This design is not certified for high voltage isolation
See the TI page for isolation criteria. This design is not certified for high voltage isolation, more like if a 120v or less AC or DC voltage got on one side it wouldn't cascade to the other. If you need a specific isolation number above that, read the TI page on design criteria for their tolerances
Adafruit ISO1540 Bidirectional I2C Isolator Guide
User Guide · 1.4 MB · Click any page to view full size
ISO1540 Datasheet
Datasheet · 1.2 MB · Click any page to view full size
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