Adafruit ISO1540 Bidirectional I2C Isolator
Created by Kattni Rembor
Last updated on 2021-02-09 02:41:10 PM EST
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Guide Contents
Guide Contents
Overview
Pinouts
Power Pins:
I2C Logic pins:
Downloads
Files
Schematic
Fab Print
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 2 of 8
Overview
Sometimes you'll find yourself with an I2C bus controller on one side, and an I2C bus device on the other
and you gotta keep em (electrically) separated (https://adafru.it/QsD). Maybe because one is Earth-
grounded, maybe because you've got some funky power monitoring setup, maybe you want to reduce
noise.
Whatever it is, you can use the Adafruit ISO1540 Bidirectional I2C Isolator to add full electrical isolation
between two sides of an I2C bus. The chip we use, the TI ISO1540 is fully bi-directional, supports up to 1
MHz clock rates, supports clock-stretching, works with 3 to 5V DC power or logic (separate on either side
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 3 of 8
of course), with 2500 V-RMS isolation
Usage is easy - you get power/ground/clock/data breakout pads for each side as well as a matching
STEMMA QT connector. Unlike our other QT boards, the two sides are obviously electrically isolated,
which means each half must be powered! Check that the green LED is lit on both sides. Now send data
over I2C and you're good to go. We have 10K pullups on each side, from the I2C pins to the matching
VCC for that side.
For more details about chip specifications, check out the TI product page. (https://adafru.it/QsE)
To get you going fast, we spun up a custom made PCB in the STEMMA QT form
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 4 of 8
factor (https://adafru.it/LBQ), making it easy to interface with. The STEMMA QT
connectors (https://adafru.it/JqB) on either side are compatible with the SparkFun
Qwiic (https://adafru.it/Fpw) I2C connectors. This allows you to make solderless connections between
your development board and the ISO1540 or to chain it with a wide range of other sensors and
accessories using a compatible cable (https://adafru.it/JnB). QT Cable is not included , but we have a
variety in the shop (https://adafru.it/JnB).
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 5 of 8
Pinouts
There are TWO SETS of power and data lines that are ELECTRICALLY ISOLATED! Each set is on one
half of the isolation barrier.
Power Pins:
VCC - this is the power pin for each side of the isolator. Each side must be powered, provide
(separated) 3 to 5 VDC on
both
sides!
GND - this is the ground pin for each side of the isolator. Each side must be powered, connect the
reference ground on either side.
I2C Logic pins:
SCL - the I2C clock pin, connect to your I2C clock line on either side. There is a 10K pullup to the
side's VCC
SDA - the I2C data pin, connect to your I2C data line on either side. There is a 10K pullup to the
side's VCC
STEMMA QT (https://adafru.it/Ft4) - These connectors allow you to connectors to dev boards
with STEMMA QT connectors or to other things with various associated
accessories (https://adafru.it/Ft6)
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 6 of 8
Downloads
Files
ISO1540 Datasheet (https://adafru.it/Qta)
Fritzing object in the Adafruit Fritzing Library (https://adafru.it/Qtb)
EagleCAD PCB files on GitHub (https://adafru.it/Qtc)
Schematic
Fab Print
© Adafruit Industries https://learn.adafruit.com/adafruit-iso1540-bidirectional-i2c-isolator Page 7 of 8
© Adafruit Industries Last Updated: 2021-02-09 02:41:10 PM EST Page 8 of 8
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