LTC4300-2CMS8 Linear Technology, LTC4300-2CMS8 Datasheet - Page 10

• Manufacturer Part Number: LTC4300-2CMS8
• Description: IC HOT SWAP 2WIRE BUS BUFR MSOP8
• Manufacturer: Linear Technology
• Type: Hot-Swap Switchr

Specifications of LTC4300-2CMS8

• Applications: General Purpose, Buffer/Bus Extender
• Internal Switch(s): Yes
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: Q1354742

APPLICATIO S I FOR ATIO
LTC4300-1/LTC4300-2
Resistor Pull-Up Value Selection
The system pull-up resistors must be strong enough to
provide a positive slew rate of 1.25V/ s on the SDA and
SCL pins, in order to activate the boost pull-up currents
during rising edges. Choose maximum resistor value R
using the formula:
where R is the pull-up resistor value in ohms, V
the minimum V
capacitance in picofarads (pF).
In addition, regardless of the bus capacitance, always
choose R
V
high voltages on SDAOUT and SCLOUT to connect the
backplane to the card, and these pull-up values are needed
to overcome the precharge voltage. See the curves in
Figures 3 and 4 for guidance in resistor pull-up selection.
Minimum SDA and SCL Capacitance Requirements
The LTC4300 I/O connection circuitry requires a minimum
capacitance loading on the SDA and SCL pins in order to
function properly. The value of this capacitance is a
function of V
the bus capacitance on both the backplane and the card
data and clock busses, and refer to Figures 3 and 4 to
choose appropriate pull-up resistor values. Note from the
10
CC
R (V
= 3.6V maximum. The start-up circuitry requires logic
Figure 3. Bus Requirements for 3.3V Systems
CC(MIN)
30
25
20
15
10
5
0
16k for V
CC
0
and the bus pull-up resistance. Estimate
CC
– 0.6) (800,000) / C
RECOMMENDED
U
voltage and C is the equivalent bus
100
PULL-UP
CC
= 5.5V maximum, R
C
U
BUS
RISE-TIME > 300ns
200
(pF)
R
300
W
MAX
4300-1/2 F03
= 24k
400
U
CC(MIN)
24k for
is
figures that 5V systems must have at least 47pF capaci-
tance on their busses and 3.3V systems must have at least
22pF capacitance for proper operation of the LTC4300. For
applications with less capacitance, add a capacitor to
ground to ensure these minimum capacitance conditions.
Hot Swapping and Capacitance Buffering Application
Figures 5 through 8 illustrate the usage of the LTC4300 in
applications that take advantage of both its hot swapping
and capacitance buffering features. In all of these applica-
tions, note that if the I/O cards were plugged directly into
the backplane, all of the backplane and card capacitances
would add directly together, making rise- and fall-time
requirements difficult to meet. Placing a LTC4300 on the
edge of each card, however, isolates the card capacitance
from the backplane. For a given I/O card, the LTC4300 drives
the capacitance of everything on the card and the backplane
must drive only the capacitance of the LTC4300, which is
less than 10pF.
Figure 5 shows the LTC4300-1 in a CompactPCI
figuration. Connect V
CompactPCI power supply hot swap circuits and connect
ENABLE to the short “board enable” pin. V
by a filtered UVLO circuit. With the V
up after all other pins have established connection, the
UVLO circuit ensures that the backplane and card data and
clock busses are not connected until the transients asso-
CompactPCI is a trademark of the PCI Industrial Computer Manufacturers Group.
Figure 4. Bus Requirements for 5V Systems
20
15
10
5
0
0
0
100
CC
to the output of one of the
RECOMMENDED
C
BUS
PULL-UP
200
(pF)
CC
R
300
MAX
RISE-TIME
> 300ns
voltage powering
= 16k
4300-1/2 F04
CC
is monitored
400
sn430012 430012fs
TM
con-