SDA2

SCL1

SCL2

GND2

GND1

VCC2

VCC1

SDA1

VREF

Figure 7-2. ISO1541 Block Diagram

7.3 Feature Description

The device enables a complete isolated I2C interface to be implemented within a small form factor having the

features listed in Table 7-1.

Table 7-1. Features List

PART NUMBER

CHANNEL DIRECTION

RATED ISOLATION(1)

MAXIMUM FREQUENCY

ISO1540

Bidirectional (SCL)

Bidirectional (SDA)

2500 VRMS

4242 VPK

1 MHz

ISO1541

Unidirectional (SCL)

Bidirectional (SDA)

(1)

See Section 6.7 for detailed Isolation specifications.

7.4 Isolator Functional Principle

To isolate a bidirectional signal path (SDA or SCL), the ISO1540 internally splits a bidirectional line into two

unidirectional signal lines, each of which is isolated through a single-channel digital isolator. Each channel output

is made open-drain to comply with the open-drain technology of I2C. Side 1 of the ISO1540 connects to a

low-capacitance I2C node, while side 2 is designed for connecting to a fully loaded I2C bus with up to 400 pF of

capacitance.

V

C-out

40 mV

50 mV

V

SDA1

V

OL1

V

IHT1

V

ILT1

R

PU1

C

node

V

CC1

SDA1

GND1

R

PU2

C

bus

V

CC2

SDA2

GND2

A

B

D

C

VREF

ISO1540

Figure 7-3. SDA Channel Design and Voltage Levels at SDA1

At first sight, the arrangement of the internal buffers suggests a closed signal loop that is prone to latch-up.

However, this loop is broken by implementing an output buffer (B) whose output low-level is raised by a diode

drop to approximately 0.75 V, and the input buffer (C) that consists of a comparator with defined hysteresis.

ISO1540, ISO1541

SLLSEB6F – JULY 2012 – REVISED DECEMBER 2022

www.ti.com

20

Submit Document Feedback

Copyright © 2022 Texas Instruments Incorporated

Product Folder Links: ISO1540 ISO1541