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-
to-back, as shown in Figure 6. The I
2
C specifi cation allows
for 400pF maximum bus capacitance, severely limiting
the length of the bus. The SMBus specifi cation 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 specifi cations 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
end of the system may violate the allowed V
OL
specifi cation
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
0.01μF
I/O PERIPHERAL CARD 1
CARD
CONNECTORS
BACKPLANE
CONNECTOR
BACKPLANE
R5
10k
R4
10k
SDAIN
SCLIN
ENABLE
READY
SDAOUT
SCLOUT
V
CC
GND
LTC4307
R3
10k
R2
10k
R1
10k
V
CC
ENAn
SDA
SCL
ENA1
READY
R6
10k
CARD1_SDA
CARD1_SCL
C2
0.01μF
I/O PERIPHERAL CARD N
R8
10k
R7
10k
4307 F05
SDAIN
SCLIN
ENABLE
READY
SDAOUT
SCLOUT
V
CC
GND
LTC4307
R9
10k
CARDn_SDA
CARDn_SCL
•
•
•
APPLICATIONS INFORMATION
