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PDF LTC4307 Data sheet ( Hoja de datos )
| Número de pieza | LTC4307 | |
| Descripción | Low Offset Hot Swappable 2-Wire Bus Buffer | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC4307
Low Offset Hot Swappable
2-Wire Bus Buffer with Stuck
Bus Recovery
FEATURES
■ Bidirectional Buffer with Stuck Bus Recovery
■ 60mV Buffer Offset Independent of Load
■ 30ms Stuck Bus Timeout
■ Compatible with Non-Compliant VOL I2C Devices
■ Prevents SDA and SCL Corruption During Live
Board Insertion and Removal from Backplane
■ ±5kV Human Body Model ESD Protection
■ Isolates Input SDA and SCL Line from Output
■ Compatible with I2CTM, I2C Fast Mode and SMBus
■ READY Open-Drain Output
■ 1V Precharge on All SDA and SCL Lines
■ High Impedance SDA, SCL Pins for VCC = 0V
■ Small 8-Lead (3mm × 3mm) DFN and 8-Lead MSOP
Packages
U
APPLICATIO S
■ Live Board Insertion
■ Servers
■ Capacitance Buffer/Bus Extender
■ RAID Systems
■ ATCA
DESCRIPTIO
The LTC®4307 hot swappable, 2-wire bus buffer allows
I/O card insertion into a live backplane without corrup-
tion of the data and clock busses. The LTC4307 provides
bidirectional buffering, keeping the backplane and card
capacitances isolated. Low offset and high VOL tolerance
allows multiple devices to be cascaded on the clock and
data busses. If SDAOUT or SCLOUT are low for 30ms, the
LTC4307 will automatically break the bus connection. At
this time the LTC4307 automatically generates up to 16
clock pulses on SCLOUT in an attempt to free the bus. A
connection will resume if the stuck bus is cleared.
During insertion, the SDA and SCL lines are pre-charged
to 1V to minimize bus disturbances. When driven high,
the ENABLE input allows the LTC4307 to connect after a
stop bit or bus idle. Driving ENABLE low breaks the con-
nection between SDAIN and SDAOUT, SCLIN and SCLOUT.
READY is an open-drain output which indicates that the
backplane and card sides are connected.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 7032051, 6356140, 6650174
TYPICAL APPLICATIO
3.3V
0.01μF
MICRO-
CONTROLLER
10k 10k
VCC
ENABLE
LTC4307
SCLIN SCLOUT
2.7k 2.7k
VCC
ENABLE
100k
LTC4307
SCLIN SCLOUT
10k 10k
0.01μF
CARD_SCL
SDAIN SDAOUT
3.3V
10k
READY
GND
SDAIN SDAOUT
3.3V
10k
READY
GND
4307 TA01a
CARD_SDA
BACKPLANE CARD
CONNECTOR CONNECTOR
CARD
Rising Edge from Asserted Low
1000
800
600
LOW
OFFSET
400
SDAOUT
SDAIN
200
0
0 100 200 300 400 500 600
100ns/DIV
4307 TA01b
4307f
1
1 page  
LTC4307
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C, VCC = 3.3V, unless otherwise indicated.
ICC vs Temperature
8.3
VCC = 5.5V
8.0
7.7
7.4
VCC = 3.3V
7.1
6.8
VCC = 2.3V
6.5
6.2
5.9
–50 –25
0
25 50 75
TEMPERATURE (°C)
100
4307 G01
IPULLUPAC vs Temperature
20
16
VCC = 5.5V
12
VCC = 3.3V
8
4
0
–50 –25 0 25 50
TEMPERATURE (°C)
75 100
4307 G02
ISD vs Temperature
950
VCC = 5.5V
900
850
800 VCC = 3.3V
750
VCC = 2.3V
700
–50 –25
0
25 50
TEMPERATURE (°C)
75 100
4307 G02
Input-Output High to Low
Propagation Delay vs Temperature
100
80 VCC = 2.3V
VCC = 5.5V
VCC = 3.3V
60
Input-Output High to Low
Propagation Delay vs COUT
130
CIN = 50pF
120 RPULLUPIN = RPULLUPOUT = 10k
110
VCC = 5.5V
100
40
20
CIN = COUT = 50pF
RPULLUPIN = RPULLUPOUT = 10k
0
–50 –25 0 25 50
TEMPERATURE (°C)
75 100
4307 G04
90
VCC = 3.3V
80
70
60
0
200 400 600 800 1000
COUT (pF)
4307 G07
Connection Circuitry VOUT – VIN
(VOS)
85
Bus Stuck Low Timeout vs VCC
34
75 32
65 30
55 28
45
1 2 3 4 5 6 7 8 9 10
RPULLUP (kΩ)
4307 G05
26
2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
4307 G06
4307f
5
5 Page 
LTC4307
APPLICATIONS INFORMATION
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 I2C 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 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
end of the system may violate the allowed VOL specification
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.
BACKPLANE
VCC
SDA
SCL
ENA1
READY
R1 R2 R3
10k 10k 10k
BACKPLANE
CARD
CONNECTOR CONNECTORS
I/O PERIPHERAL CARD 1
SDAIN
C1
0.01μF
R5 R6
10k 10k
VCC
SDAOUT
CARD1_SDA
SCLIN LTC4307 SCLOUT
ENABLE
CARD1_SCL
READY
R4
10k
GND
ENAn
•
•
•
I/O PERIPHERAL CARD N
SDAIN
C2
0.01μF
R8 R9
10k 10k
VCC
SDAOUT
CARDn_SDA
SCLIN LTC4307 SCLOUT
ENABLE
CARDn_SCL
READY
R7
10k
GND
4307 F05
Figure 5. The LTC4307 in an Application Where All the Pins Have the Same Length
4307f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC4307.PDF ] | |
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