ADuM1253

Ultra-Low-Power, I2C Isolator with

Unidirectional SCL, Extended VDD,

Idle-Bus Hot-Swap, and Low VOL

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Analog Devices | 21

125µs

FILTER

STOP DETECT

SDA

SCL

IDLE

STOP

200ns

GLITCH

FILTER

200ns

GLITCH

FILTER

SIDE1

HIGH

SIGNAL

S

R

Q

SIDE 1 OFF

RST

CON

PRECHARGE

SDA2

CON

SCL2

CON

0.45VDD2

RST

SDA2/SCL2

SIDE 1 BUS STUCK

0.38VDD2

VDD2

0.45VDD2

1/3 VDD2

PRECHARGE

1/3 VDD2

Figure 7. Bus Connection Logic

Bus Connection

The ADuM1253 connects the side 1 bus to the side 2 bus when both busses are idle or when side 1 is high and an I2C

stop condition has been detected on side 2. If a stuck bus condition is detected on side 1, then the ADuM1253 disconnects

the two busses to allow the external system to attempt a recovery.

Applications Information

Power-Supply Sequencing

The ADuM1253 does not require special power-supply sequencing. The logic levels are set independently on either side

by VDD1 and VDD2. Each supply can be present over the entire specified range regardless of the level or presence of the

other supply.

Power-Supply Decoupling

To reduce ripple and the chance of introducing data errors especially if large common-mode transients are expected in

the application, bypass VDD1 and VDD2 with 100nF and 1nF low-ESR ceramic capacitors to GND1 and GND2,

respectively. Place the bypass capacitors as close to the power-supply input pins as possible.

Thermal Considerations

Thermal performance is directly linked to printed circuit board (PCB) design and operating environment. Pay careful

attention to the PCB thermal design.

Thermal parameter values are specified in the Package Information section. θJA and θJB are mainly used to compare the

thermal performance of the package of the device with other semiconductor packages when all test conditions listed are

similar. ΨJB r ΨJT can be used to estimate the junction temperature when an accurate thermal measurement of the

board temperature is available. The temperature measurement must be near the device under test (DUT) or directly on

the package top surface, operating in the system environment.

θJA can be used for a first-order approximation to calculate the junction temperature in the system environment. The

power dissipation (PD), junction-to-ambient thermal impedance (θJA), and ambient temperature (TA) determine the

junction temperature (TJ) according to the expression:

TJ = TA + (PD x ������JA)