ADuM1250/ADuM1251

Data Sheet

Rev. F | Page 10 of 12

APPLICATIONS INFORMATION

FUNCTIONAL DESCRIPTION

The ADuM1250/ADuM1251 interface 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 pin 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

which the logic levels of a component do not necessarily meet the

refers to situations in which the logic levels of a component meet

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

input threshold, this side of the ADuM1250/ADuM1251 can

dard. In other words, Side 2 of the ADuM1250/ADuM1251 is

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 feature prevents input logic low

power-up/power-down.

For the signal channels to be enabled, the following two criteria

must be met:



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 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 START-UP

THRESHOLD, 2.0V

40µs

SUPPLY VALID

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

40µs

SUPPLY VALID

MINIMUM RECOMMENDED

OPERATING SUPPLY, 3.0V

MINIMUM VALID SUPPLY, 2.5V

INTERNAL START-UP

THRESHOLD, 2.0V

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

TYPICAL APPLICATION DIAGRAM

Figure 9 shows a typical application circuit including the pull-up

resistors required for both Side 1 and Side 2 buses. Bypass capaci-

in Figure 9 is required for latch-up immunity if the ambient

temperature can be between 105°C and 125°C.

ADuM1250

1

2

3

4

8

7

6

5

OPTIONAL

200Ω