ADuM1250/ADuM1251

Rev. D | Page 10 of 12

APPLICATIONS INFORMATION

FUNCTIONAL DESCRIPTION

The ADuM1250/ADuM1251 interfaces on each side to a

into two unidirectional channels communicating in opposing

directions via a dedicated iCoupler isolation channel for each.

One channel (the bottom channel of each channel pair shown

on either causes the opposite pin to be pulled low enough to

least 50 mV less than the output low signal at the same pin. This

prevents an output logic low at Side 1 being transmitted back to

multiple ADuM1250/ADuM1251 devices connected to a bus by

their Side 2 pins can communicate with each other and with other

situations in which a component's logic levels do not necessarily

However, since the Side 1 pin has a modified output level/input

threshold, this side of the ADuM1250/ADuM1251 can only

ments. The Side 1 and Side 2 pins have open-collector outputs

whose high levels are set via pull-up resistors to their respective

supply voltages.

ENCODE

DECODE

DECODE

ENCODE

ENCODE

DECODE

DECODE

ENCODE

1

2

3

8

7

6

5

R2

R2

Figure 6. ADuM1250 Block Diagram

STARTUP

feature to prevent the signal channels from operating unless

certain criteria are met. This avoids the possibility of input logic

power-up/power-down.

The two criteria that must be met in order for the signal

channels to be enabled are as follows:

•

Both supplies must be at least 2.5 V.

•

At least 40 μs must elapse after both supplies exceed the

internal startup threshold of 2.0 V.

Until both of these criteria are met for both supplies, the

ADuM1250/ADuM1251 outputs are pulled high, ensuring a

startup that avoids any disturbances on the bus. Figure 7 and

Figure 8 illustrate the supply conditions for fast and slow input

supply slew rates.

MINIMUM RECOMMENDED

OPERATING SUPPLY, 3.0V

MINIMUM VALID SUPPLY, 2.5V

INTERNAL STARTUP

THRESHOLD, 2.0V

40µs

SUPPLY VALID

Figure 7. Start-Up Condition, Supply Slew Rate > 12.5 V/ms

40µs

SUPPLY VALID

MIN. RECOMMENDED

OPERATING SUPPLY, 3.0V

MIN. VALID SUPPLY, 2.5V

INTERNAL STARTUP

THRESHOLD, 2.0V

Figure 8. Start-Up Condition, Supply Slew Rate < 12.5 V/ms