LTC4313-1/LTC4313-2/

LTC4313-3

13

4313123f

applicaTions inForMaTion

Telecommunications Systems

The LTC4313 has several features that make it an excellent

choiceforuseintelecommunicationsystemssuchasATCA.

Referring to Figures 7 and 8, buffers are used on the edges

of the field replaceable units (FRU) and shelf managers to

shield devices on these cards from the large backplane

capacitance. The input capacitance of the LTC4313 is less

than the 10pF maximum specification for buffers used in

bussed ATCA applications. The LTC4313 buffers can drive

capacitances >1nF, which is greater than the maximum

backplane capacitance of 690pF in bussed ATCA systems.

The precharge feature, low input capacitance and high

impedance of the SDA and SCL pins of the LTC4313 when

it is unpowered, minimize disturbances to the bus when

cards are being hot swapped. In Figure 7, the RTA of the

LTC4313-2 on the shelf manager supplies sufficient pull-

up current, allowing the 1µs rise time requirement to be

met on the heavily loaded backplane for loads well beyond

voltage of the LTC4313’s buffers provides a large logic

low noise margin in these systems. In the bussed ATCA

application shown in Figure 7, the LTC4313s located on

the shelf managers #1 and #2 and on the FRUs, drive the

large backplane capacitance while the microcontrollers

FRUs drive the small input capacitance of the LTC4313-3.

Figure 7. LTC4313s Used in a Bussed ATCA Application. Only the Clock Path is Shown for Simplicity

LTC4313-2

µP

3.3V

SCLOUT

SCLIN

ENABLE

R1

10k

R2

2.7k

4313123 F07

BACKPLANE

IPMB-A

SCL

IPMB-B

SCL

SHELF MANAGER #1

SHELF MANAGER #2

IDENTICAL TO SHELF MANAGER #1

TO SHMC#2

TO SHMC#2

IPMB-B

IPMB-B DETAILS (NOT SHOWN) ARE IDENTICAL TO IPMB-A

FRU #1

LTC4313-3

DEVICE

3.3V

3.3V

SCLOUT

SCLIN

R3

10k

R4

10k

LTC4313-3

SCLOUT

SCLIN

FRU #N

LTC4313-3

DEVICE

3.3V

3.3V

SCLOUT

SCLIN

R6

10k

R5

10k

LTC4313-3

SCLOUT

SCLIN