LTC4307

11

4307f

The ENABLE pin is driven using a short pin. This is to

ensure that a connection is not enabled until the transients

associated with live insertion have settled.

Figure 5 shows the LTC4307 in an application where all

of the pins have the same length. In this application a

resistor is used to hold the ENABLE pin low during live

insertion, until the backplane control circuitry can enable

the device.

Repeater/Bus Extender Applications

Users who wish to connect two 2-wire systems separated

by a distance can do so by connecting two LTC4307s back-

for 400pF maximum bus capacitance, severely limiting

the length of the bus. The SMBus specification places no

restriction on bus capacitance, but the limited impedances

of devices connected to the bus require systems to remain

small if rise time and fall time specifications are to be met.

In this situation, the differential ground voltage between

the two systems may limit the allowed distance, because

a valid logic-low voltage with respect to the ground at one

with respect to the ground at the other end. In addition, the

connection circuitry offset voltages of the back-to-back

LTC4307s add together, directly contributing to the same

problem.

Figure 7 further illustrates a repeater application. This circuit

could be used in an AdvancedTCA system. In AdvancedTCA

applications, the bus pull-up resistance on the backplane

is quite small. Since there is no effect on the offset due

to the pull-up impedance, multiple LTC4307 buffers can

be used in a single system. This allows the user to divide

the line and device capacitances into more sections with

buffering and meet rise and fall times.

The LTC4307 disconnects when both bus I/Os are above

0.48V and rising. In systems with large ground bounce,

if many devices are cascaded, the 0.48V threshold can be

exceeded and the transients associated with the ground

bounce can appear to be a rising edge. Under this condition,

the LTC4307 with inputs above 0.48V may disconnect.

Figure 5. The LTC4307 in an Application Where All the Pins Have the Same Length

C1

0.01

μF

I/O PERIPHERAL CARD 1

CARD

CONNECTORS

BACKPLANE

CONNECTOR

BACKPLANE

R5

10k

R4

10k

SDAIN

SCLIN

ENABLE

READY

SDAOUT

SCLOUT

GND

LTC4307

R3

10k

R2

10k

R1

10k

ENAn

SDA

SCL

ENA1

READY

R6

10k

CARD1_SDA

CARD1_SCL

C2

0.01

μF

I/O PERIPHERAL CARD N

R8

10k

R7

10k

4307 F05

SDAIN

SCLIN

ENABLE

READY

SDAOUT

SCLOUT

GND

LTC4307

R9

10k

CARDn_SDA

CARDn_SCL

•

•

•

APPLICATIONS INFORMATION