LTC4310IMS-1 데이터 시트보기 (PDF) - Linear Technology

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LTC4310IMS-1

Hot-Swappable I2C Isolators

Linear Technology 

LTC4310-1/LTC4310-2

Applications Information

Once a STOP bit or bus idle occurs on both the local and

isolated buses, the LTC4310 reactivates its buffers and

rise time accelerators.

READY Digital Output

The READY pin provides a digital output flag that pulls

low to indicate that the LTC4310 is driving its SDA and

SCL pins with the logic state information it is receiving on

its RXP and RXN pins from the other LTC4310. READY is

driven by an N-channel MOSFET open-drain pull-down that

is capable of sinking 4mA while holding 0.4V maximum.

The pull-down turns off whenever the LTC4310 is not

driving its SDA and SCL pins—during start-up, thermal

shutdown, low current shutdown and after disconnection

due to a stuck bus or failure to receive a transmission

within 4.6ms. Connect a resistor to the bus pull-up supply

to provide the pull-up.

Design Example: High Voltage Isolation Using an

Inexpensive Ethernet Transformer

Figure 1 shows the LTC4310-1 providing I2C communi-

cations between two buses whose ground voltages can

differ up to 1500V. An EPF8119S Ethernet transformer is

used to bridge the isolation barrier. The left I2C bus con-

nects to the LTC4310-1 and two other devices, resulting

in a bus parasitic capacitance of 40pF in this example

set-up. Referring to the VCC = 3.3V curve in Figure 2,

7.5k pull-up resistors are chosen for R1 and R2. The right

I2C bus connects to another LTC4310-1 and four slave

devices, resulting in a bus parasitic capacitance of 80pF.

Referring to the VCC = 5V curve in Figure 2, 7.5k pull-up

resistors are also chosen for R5 and R6. Standard 5%

resistors are used.

Sudden changes in the ground differential across the

isolation barrier can be effectively resisted by tying the

center tap of the receive side of the transformer to the

local ground through a 0.01µF capacitor, as shown by

capacitors C2 and C3.

Figure 7 shows the same application as Figure 1, but with

each LTC4310-1 replaced by an LTC4310-2, so that the

bus can switch at frequencies up to 400kHz. To meet the

requirements shown in the curves of Figure 3, R1 and R2

are changed from 7.5k to 4.3k, and R5 and R6 are changed

from 7.5k to 3.3k.

3.3V

R1 R2

4.3k 4.3k

C1

0.01µF

READY

TXP

LTC4310-2

CBUS = 40pF

µP

SLAVE

VCC

EN

SDA TXN

SCL1

SCL

RXP

GND RXN

R3

10/100Base-TX

10k

ETHERNET

TRANSFORMER

1

16

R4

10k

READY

RXP

15

LTC4310-2

C3

0.01µF

VCC

EN

3

14

RXN SDA

6

11

TXP

SCL

C4

0.01µF

SCL2

7

C2

0.01µF

8

9

EPF8119S

TXN GND

431012 F07

Figure 7. The LTC4310-2 in a 400kHz Application

IS0LATED

5V

R5 R6

3.3k 3.3k

CBUS = 80pF

SLAVE#1 . . . SLAVE#4

431012fa

13

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