LTC4310IMS-1#TRPBF Datasheet LTC4310CDD-1#PBF, LTC4310CMS-2#PBF, LTC4310CMS-1#PBF | P13-P15

LTC4310-1/LTC4310-2

431012fa

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 I

C 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 I

C 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 V

= 3.3V curve in Figure 2,

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

C bus connects to another LTC4310-1 and four slave

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

Referring to the V

= 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.

applicaTions inForMaTion

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

EPF8119S

0.01µF

3.3V

4.3k

3.3k

. . .

SLAVE SLAVE#1

SCL1 SCL2

0.01µF

431012 F07

TXP

TXN

RXP

RXN

SDA

SCL

READY

GND GND

RXP

RXN

TXP

TXN

READY

LTC4310-2

SDA

SCL

µP SLAVE#4

10k

IS0LATED

10/100Base-TX

ETHERNET

TRANSFORMER

BUS

= 40pF

BUS

= 80pF

LTC4310-1/LTC4310-2

431012fa

applicaTions inForMaTion

TYPICAL APPLICATIONS

Figure 8 shows the LTC4310-1 providing I

C communica-

tions between an I

C bus referenced to system ground and

an I

C bus using –5V for its ground reference. Ceramic

coupling capacitors, C1-C5, are used to bridge the isolation

barrier. This circuit is recommended for ground isolation

voltages less than 100V and is limited by the voltage rating

of C1-C5. Higher voltage ceramic capacitors may be used

to achieve higher isolation voltages. Because the LTC4310

uses a pseudo-differential transmit scheme, capacitor C5

must be connected between ground and –5V to provide a

return path for the transmitted current.

Figure 9 shows the LTC4310-1 in an application circuit

using its zero current shutdown mode. A microprocessor

only activates the left LTC4310-1 when it needs to com-

municate with the isolated I

C bus. Because the LTC4310-1

contains a STOP bit and bus idle detection circuitry, there

is no danger of connecting in the middle of a message

when the microprocessor asynchronously reenables the

LTC4310-1.

Figure 8. Low Voltage I

C Isolation Between a Ground Referenced Bus and a –5V Referenced Bus

3.3V

BUS

= 30pFC

BUS

= 100pF

5.1k

10k

431012 F08

0.01µF

–5V

10k

GND

RXP

RXN

TXP

TXN

LTC4310-1

READY

SDA

SCL

10k

0.01µF

GND

TXP

TXN

RXP

RXN

LTC4310-1

READY

SDA

SCL

C1 TO C5 = 47pF, 100V

Figure 9. The LTC4310-1 in a Zero Current Shutdown Application

3.3k

10k

431012 F09

0.01µF

–5V

5.1k

GND

RXP

RXN

TXP

TXN

LTC4310-1

READY

SDA

SCL

10k

0.01µF

GND

TXP

TXN

RXP

RXN

LTC4310-1

READY

SDA

SCL

. . .

SLAVE#1

µP

SLAVE#N

OFF

C1 TO C5 = 47pF, 100V

BUS

= 150pFC

BUS

= 200pF

LTC4310-1/LTC4310-2

431012fa

applicaTions inForMaTion

Figure 10. The LTC4310-1 in an I

C Hot-Swapping Application

BACKPLANE

CONNECTOR

BACKPLANE

CARD

CONNECTOR

10k

I/O PERIPHERAL CARD

431012 F10

0.01µF

6.8k

10k

100k

GND

RXP

RXN

TXP

TXN

LTC4310-1

READY

SDA

SCL

READY

SDA

SCL

READY2

EN2

SDA2

3.3V

SCL2

6.8k

0.01µF

GND

TXP

TXN

RXP

RXN

LTC4310-1

READY

SDA

SCL

C1 TO C5 = 47pF, 100V

BUS

= 50pFC

BUS

= 400pF

Figure 10 shows the LTC4310-1 in a two-wire bus Hot Swap

application. Using a staggered connector, make EN the

shortest length pin to ensure that the transients associated

with hot swapping have settled before the LTC4310-1 can

be enabled. After connection is complete, a master on the

backplane may drive EN high to bring the LTC4310-1 out

of shutdown mode and into normal operation. Due to its

STOP bit and bus idle detection circuitry, the LTC4310-1’s

driver circuitry is not activated until transactions on both

buses are complete.

LTC4310 Compatibility with Other LTC Bus Buffers

The LTC4310 cannot be used on the same I

C bus with the

LTC4300A-1, LTC4303 or LTC4307. During rising edges,

the rise time accelerators of these buffers turn on before

the LTC4310 disables its rise rate regulation circuitry,

resulting in nonmonotonic bus edges.

The LTC4310-1 is compatible with the LTC4301 and

LTC4301L. It is also compatible with the LTC4302, LTC4304,

LTC4305 and LTC4306, provided that the rise time accelera-

tors of these buffers are permanently disabled. All of the

previously mentioned buffers are incompatible with the

LTC4310-2 because the compensation networks of these

buffers cause the bus to rise more slowly than (0.35 •

)/300ns, therefore the LTC4310-2 would not be able

to control the bus rise rate.

LTC4310-1 Compatibility with LTC4310-2

In a typical application such as shown in Figure 1, an

LTC4310-1 can be used on one bus and an LTC4310-2 can

be used on the other, provided that the bus pull-up resis-

tors connected to the LTC4310-1 meet the requirements

of Figure 2, and the bus pull-up resistors connected to the

LTC4310-2 meet the requirements of Figure 3. However,

the bus switching frequency is limited by the rise rate

regulation circuitry of the LTC4310-1. In addition, signiﬁcant

skew is introduced on the rising edges due to the large

difference in the controlled rise rates of the two buses. For

this reason, it is recommended to use two LTC4310-1’s

in SMBus and standard mode I

C applications and to use

two LTC4310-2’s in fast mode I

C applications.

The LTC4310-1 cannot be used on the same physical I

bus with the LTC4310-2, because the LTC4310-1’s rise

rate regulation circuitry controls the bus rise rate to (0.35

• V

)/900ns, therefore the LTC4310-2 would not be able

to control the bus rise rate.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

LTC4310IMS-1#TRPBF

Mfr. #:

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Manufacturer:

Analog Devices Inc.

Description:

Digital Isolators I2C Isolater, 100kHz Max Bus Frequency

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