interface to sensors and actuators. The ISO1541 device provides the required isolation between different ground

potentials of the system controller, remote sensor, and actuator circuitry to prevent ground loop currents that

otherwise may falsify the acquired data.

The entire circuit operates from a single 3.3-V supply. A low-power push-pull converter, SN6501, drives a

center-tapped transformer with an output that is rectified and linearly regulated to provide a stable 5-V supply for

the data converter.

VCC1

VCC2

GND1

GND2

8

7

4

5

4

XOUT

XIN

5

6

2

MSP430

G2132

1

2

3

DVss

DVcc

0.1 μF

0.1 μF

0.1 μF

6

SDA

SCL

9

8

10 μF

VS

0.1 μF

MBR0520L

MBR0520L

1:2.2

0.1 μF

3

1

D2

SN6501

D1

Vcc

4,5

2

GND

3.3V

IN

ON

GND

OUT

1

5

2

3

LP2981-50

10 μF

10 μF

SDA2

SDA1

SCL1

SCL2

1.5 kΩ

1.5 kΩ

1. kΩ

5

1. kΩ

5

0.1 μF

8

VDD

GND

AIN0

2

1

9

10

SDA

SCL

4

ADDR

ADS 1115

AIN3

RDY

3

4 Analog

Inputs

7

V

IN

GND

V

OUT

2

6

4

REF5040

1 μF

22 μF

4

VDD

V

A

OUT

V

D

OUT

V

H

REF

V

L

REF

11

10

SDA

SCL

1

DAC8574

8

GND

6

12

3

A2

15

IOV

DD

5

4 Analog

Outputs

A3

16

A0

13

9

14

LDAC

A1

0.1 μF

5VISO

5VISO

5VISO

5VISO

ISO-BARRIER

1 Ω

Copyright © 2016, Texas Instruments Incorporated

ISO1541

Figure 8-4. Isolated I2C Data Acquisition System

8.2.1 Design Requirements

The recommended power supply voltages (VCC1 and VCC2) must be from 3 V to 5.5 V. A recommended

decoupling capacitor with a value of 0.1 µF is required between both the VCC1 and GND1 pins, and the VCC2

and GND2 pins to support of power supply voltages transient and to ensure reliable operation at all data rates.

8.2.2 Detailed Design Procedure

The power-supply capacitor with a value of 0.1-µF must be placed as close to the power supply pins as possible.

The recommended placement of the capacitors must be 2-mm maximum from input and output power supply

pins (VCC1 and VCC2).

The maximum load permissible on the input lines, SDA1 and SCL1, is ≤ 40 pF and on the output lines, SDA2

and SCL2, is ≤ 400 pF.

The minimum pullup resistors on the input lines, SDA1 and SCL1 to VCC1 must be selected in such a way that

input current drawn is ≤ 3.5 mA. The minimum pullup resistors on the input lines, SDA2 and SCL2, to VCC2

must be selected in such a way that output current drawn is ≤ 35 mA. The maximum pullup resistors on the input

ISO1540, ISO1541

SLLSEB6F – JULY 2012 – REVISED DECEMBER 2022

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