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LTC4301IMS8#PBF

P1-P3P4-P6P7-P9P10-P12
7
LTC4301
4301fb
Live Insertion and Capacitance Buffering Application
Figures 3 illustrates applications of the LTC4301 with
different bus pull-up and V
CC
voltages, demonstrating its
ability to recognize and buffer bus data levels that are
above or below its V
CC
supply. All of these applications
take advantage of the LTC4301’s Hot Swap
TM
controlling,
capacitance buffering and precharge features. If the I/O
cards were plugged directly into the backplane without the
LTC4301 buffer, all of the backplane and card capaci-
tances would add directly together, making rise- and fall-
time requirements difficult to meet. Placing an LTC4301
APPLICATIO S I FOR ATIO
WUUU
on the edge of each card, however, isolates the card
capacitance from the backplane. For a given I/O card, the
LTC4301 drives the capacitance of everything on the card
and the backplane must drive only the capacitance of the
LTC4301, which is less than 10pF.
In most applications the LTC4301 will be used with a
staggered connector where V
CC
and GND will be long pins.
SDA and SCL are medium length pins to ensure that the
V
CC
and GND pins make contact first. This will allow the
precharge circuitry to be activated on SDA and SCL before
STAGGERED CONNECTOR
CS
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
10k 10k
LTC4301
CARD_SCL
CARD_SDA
0.01µF
10k
10k10k
BACKPLANE
CONNECTOR
5V
3.3V
SDA
SCL
STAGGERED CONNECTOR
CS
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
10k 10k
LTC4301
CARD_SCL
CARD_SDA
0.01µF
10k
10k10k
BACKPLANE
CONNECTOR
3.3V
5V
SDA
SCL
STAGGERED CONNECTOR
CS
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
4301 F03
10k
2.5V
10k
LTC4301
CARD_SCL
CARD_SDA
0.01µF
10k
10k10k
BACKPLANE
CONNECTOR
CARD
CARD
CARD
3.3V
5V
SDA
SCL
Figure 3. Typical Supply Independent Applications
Hot Swap is a trademark of Linear Technology Corporation.
8
LTC4301
4301fb
APPLICATIO S I FOR ATIO
WUUU
they make contact. CS is a short pin that is pulled up when
not connected. This is to ensure that the connection
between the backplane and the cards data and clock
busses is not enabled until the transients associated with
live insertion have settled.
Figure 4 shows the LTC4301 in a CompactPCI
TM
configu-
ration. The LTC4301 receives its V
CC
voltage from one of
the long “early power” pins. Because this power is not
switched, add a 5Ω to 10Ω resistor between V
CC
of the
LTC4301 and the connector V
CC
pin. Establishing early
power V
CC
ensures that the 1V precharge voltage is
present at SDAIN and SCLIN before they make contact.
The CS pin is driven by the CompactPCI’s BD_SEL# pin
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 LTC4301 in a PCI application where all
of the pins have the same length. In this case, an RC filter
circuit on the I/O card with a product of 10ms provides a
STAGGERED CONNECTOR
R13
10k
R12
10k
R14
10k
I/O PERIPHERAL CARD N
SDAIN
SCLIN
LTC4301
V
CC
GND
CARDN_SCL
CARDN_SDA
SDAOUT
SCLOUT
READY
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
CS
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
4301 F03
• • •
R9
10k
R8
10k
R10
10k
I/O PERIPHERAL CARD 2
LTC4301
CARD2_SCL
CARD2_SDA
STAGGERED CONNECTORSTAGGERED CONNECTOR
R5
10k
R4
10k
R6
10k
I/O PERIPHERAL CARD 1
LTC4301
CARD_SCL
CARD_SDA
R1
10k
V
CC
V
CC2
R2
10k
BACKPLANE
BACKPLANE
CONNECTOR
SDA
BD_SEL
SCL
0.01µF
R3
10k
5.1Ω
5.1Ω
5.1Ω
R7
10k
R11
10k
0.01µF
0.01µF
CS
CS
Figure 4. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4301 in a CompactPCI System
CompactPCI is a trademark of the PCI Industrial Computer Manufacturers Group.
9
LTC4301
4301fb
filter to prevent the LTC4301 from becoming activated
until the transients associated with live insertion have
settled. Connect the capacitor between V
CC
and CS, and
the resistor from CS to GND.
Repeater/Bus Extender Application
Users who wish to connect two 2-wire systems separated
by a distance can do so by connecting two LTC4301s
back-to-back as shown in Figure 6. The I
2
C specification
allows 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- and fall-time specifica-
tions are to be met. Using the LTC4301 allows the capaci-
tance to be isolated into smaller sections, enabling the
APPLICATIO S I FOR ATIO
WUUU
R3
100k
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
CS
SDAIN
SCLIN
V
CC
GND
SDAOUT
SCLOUT
READY
4301 F05
R9
10k
R8
10k
R10
10k
I/O PERIPHERAL CARD 2
LTC4301
CARD2_SCL
CARD2_SDA
R5
10k
R4
10k
I/O PERIPHERAL CARD 1
LTC4301
CARD_SCL
CARD_SDA
R1
10k
V
CC
V
CC2
R2
10k
BACKPLANE
BACKPLANE
CONNECTOR
SDA
SCL
0.01µF
0.1µF
0.01µF
R6
10k
•
•
•
R7
100k
CS
0.1µF
system to meet rise- and fall-time requirements. In this
situation, the differential ground voltage between the two
systems may limit the allowed distance, because valid
logic low voltage with respect to the ground at one end of
the system may violate the allowed V
OL
specification with
respect to the ground at the other end. In addition, the
connection circuitry offset voltages of the back-to-back
LTC4301s add together, directly contributing to the same
problem.
Systems with Supply Voltage Droop
In large 2-wire systems, the V
CC
voltages seen by devices
at various points in the system can differ by a few hundred
millivolts or more. This situation is well modelled by a series
resistor in the V
CC
line as shown in Figure 7. For proper
operation, make sure that the V
CC(LTC4301)
is ≥ 2.7V.
Figure 5. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4301 in a PCI System
P1-P3P4-P6P7-P9P10-P12

LTC4301IMS8#PBF

Mfr. #:
Buy LTC4301IMS8#PBF
Manufacturer:
Analog Devices Inc.
Description:
Interface - Signal Buffers, Repeaters Supply Independent I2C Bus Buffer
Lifecycle:
New from this manufacturer.
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