LTC4331

18

Rev 0

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Table2. Link Speed

SPEED1

(Note 1)

SPEED2

(Note 1)

SPEED INDEX

I2C CLASS

EFFECTIVE I2C

LINK RATE

MAX CABLE

LENGTH (m) (Note 2)

SLEW RATE LIMITING

OPTION (Note 3)

L

L

8

Fm+

1MHz

30

No

Float

L

7

Fm

500kHz

60

No

H

L

6

Fm

250kHz

200

No

L

Float

5

Fm

125kHz

600

No

L

H

4

Sm

100kHz

1200

No

H

Float

3

Sm

63kHz

1200+

No

Float

Float

2

Sm

31kHz

1200+

No

Float

H

1

Sm

20kHz

1200+

Yes

H

H

0

Sm

12.5kHz

1200+

Yes

Note 1: For assignments to float, 0.5 • VL can also be applied to pin.

Note 2: Evaluated with Cat5E Ethernet cable in a lab environment. Actual maximum cable length depends on type of cable and application environment.

Note 3: Using SLO.

Propagation times across the link for the SYSTEM timing specifications are based on the SPEED1 and SPEED2 pins.

APPLICATIONS INFORMATION

all local slave device addresses must be greater (lower

priority) than the remote slave device address. This is

to allow proper slave address negotiation.

• Care must be taken when interrupting an I2C transaction

with a START or STOP. A START or STOP can only be

issued when the local side LTC4331 is in slave-receive

mode. Since internally the data is sampled on the rising

edge, the local I2C bus is considered slave driven after

the last rising edge of SCL in a master driven data cycle.

• The LTC4331 supports a faster local I2C clock rate

relative to the effective link rate. The device has a fixed

length internal buffer to hold a complete byte as it is

transferred across the link at the rate set by SPEED1

and SPEED2. During this time the local I2C bus stalls

preventing further I2C data from entering the buffer.

If however, a local master sends multiple consecu-

tive START/STOP commands faster than the effective

link rate, this buffer can overflow. The LTC4331 pro-

vides two status indicators for this event. First, if the

buffer is full, then RDY rises indicating that the local

I2C interface is not ready and further START, STOP, or

write data event can be lost. Second, a TX_BUFFER_

OVERFLOW FAULT event occurs if a local master

writes additional I2C events while RDY is high.

• A remote slave device will not see a SCL timeout con-

dition (bus reset) initiated by a local slave device if a

remote device is not the target of the local Master.

Link Speed

The link baud rate is set using the SPEED1 and SPEED2

pins as shown in Table 2. Column I2C Class shows the

timing mode set on the local and remote I2C interfaces.

The Effective I2C Link Rate shows the rate I2C data propa-

gates across the link. The local SCL frequency can exceed

this rate though increased clock-stretching times occur

as the Effective Link Rate decreases relative to the local

SCL frequency. The SPEED INDEX must be set to the same

value on each side of the link.

Table3. Speed Factors

SPEED INDEX

SPEED FACTOR (SF)

8

1×

7

2×

6

4×

5

8×

4

10×

3

16×

2

32×

1

50×

0

80×

Control Interface

The LTC4331 contains an addressable slave device pro-

viding a control interface for configuration and monitor-

ing. The internal slave is enabled by configuring pins A1

and A2 to assign the device a unique I2C address. When