Datasheet

LTC4313-1/LTC4313-2/
LTC4313-3
13
4313123f
applicaTions inForMaTion
Telecommunications Systems
The LTC4313 has several features that make it an excellent
choice for use in telecommunication systems such as ATCA.
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
the 690pF maximum specification. The 0.33 • V
CC
turn-off
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
on the shelf managers and the I
2
C slave devices on the
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
V
CC
3.3V
SCLOUTSCLIN
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
I
2
C
DEVICE
3.3V
3.3V
SCLOUT
V
CC
SCLIN
R3
10k
R4
10k
LTC4313-3
SCLOUT
V
CC
SCLIN
FRU #N
LTC4313-3
I
2
C
DEVICE
3.3V
3.3V
SCLOUT
V
CC
SCLIN
R6
10k
R5
10k
LTC4313-3
SCLOUT
V
CC
SCLIN
• • •