ADUM1250(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
ADUM1250 Datasheet PDF : 12 Pages
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ADuM1250/ADuM1251
APPLICATION NOTES
FUNCTIONAL DESCRIPTION
The ADuM1250/ADuM1251 interfaces on each side to a
bidirectional I2C signal. Internally, the I2C interface is split 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
in Figure 6) senses the voltage state of the Side 1 I2C pin and
transmits its state to its respective Side 2 I2C pin.
Both the Side 1 and the Side 2 I2C pins are designed to interface
to an I2C bus operating in the 3.0 V to 5.5 V range. A logic low
on either causes the opposite pin to be pulled low enough to
comply with the logic low threshold requirements of other I2C
devices on the bus. Avoidance of I2C bus contention is ensured
by an input low threshold at SDA1 or SCL1 guaranteed to be at
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
Side 2 and pulling down the I2C bus.
Since the Side 2 logic levels/thresholds are standard I2C values,
multiple ADuM1250/ADuM1251 devices connected to a bus by
their Side 2 pins can communicate with each other and with
other devices having I2C compatibility1.
However, since the Side 1 pin has a modified output level/input
threshold, this side of the ADuM1250/ADuM1251 can only
communicate with devices conforming to the I2C standard. In
other words, Side 2 of the ADuM1250/ADuM1251 is I2C-
compliant while Side 1 is only I2C-compatible.
The output logic low levels are independent of the VDD1 and
VDD2 voltages. The input logic low threshold at Side 1 is also
independent of VDD1. However, the input logic low threshold at
Side 2 is designed to be at 0.3 VDD2, consistent with I2C
requirements. 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.
VDD1 1
SDA1 2
SCL1 3
GND1 4
DECODE
ENCODE
DECODE
ENCODE
ENCODE
DECODE
ENCODE
DECODE
VDD2
8
SDA2
7
SCL2
6
GND2
5
R2 R2
CL CL
Figure 6. ADuM1250 Block Diagram
1 Here a distinction is made between I2C compatibility and I2C compliance. I2C
compatibility refers to situations in which a component's logic levels do not
necessarily meet the requirements of the I2C specification but still allow the
component to communication with an I2C-compliant device. I2C compliance
refers to situations in which a component's logic levels meet the
requirements of the I2C specification.
STARTUP
Both the VDD1 and VDD2 supplies have an under voltage lockout
feature to prevent the signal channels from operating unless
certain criteria are met. This avoids the possibility of input logic
low signals from pulling down the I2C bus inadvertently during
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 exceeded 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
SUPPLY VALID
40µs
Figure 7. Start-Up Condition, Supply Slew Rate >12.5 V/ms
MIN. RECOMMENDED
OPERATING SUPPLY, 3.0V
MIN. VALID SUPPLY, 2.5V
INTERNAL STARTUP
THRESHOLD, 2.0V
SUPPLY VALID
40µs
Figure 8. Start-Up Condition, Supply Slew Rate <12.5 V/ms
Rev. 0 | Page 10 of 12
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