LTC4311ISC6#PBF Linear Technology, LTC4311ISC6#PBF Datasheet - Page 8

• Manufacturer Part Number: LTC4311ISC6#PBF
• Manufacturer: Linear Technology

Specifications of LTC4311ISC6#PBF

• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
LTC4311
For an I
and V
levels, V
C
SMBus Rise and Fall Time
Rise time of a SMBus line is derived using equations 5,
6 and 7.
t
rate measurement point, until the bus reaches V
accelerators fi re. The time from when the accelerators fi re
until the bus reaches the upper slew rate measure point is
given by t
If (V
Fall time of an SMBus line is derived using equation 8:
For an SMBus system, V
C
8
1
BUS
BUS
is the time from when the bus crosses the lower slew
t
ln
ln
t
t
t
r
1
2
f
ILMAX
⎧
⎨
⎩
⎧
⎪ ⎪
⎨
⎪
⎪
⎩
is the total capacitance of the I
is the total bus capacitance of the SMBus line.
IHMIN
= t
= –R
= R
= –R
V
V
V
2
IHMIN
ILMAX
ILMAX
1
IHMIN
C system with fi xed input levels, V
T
+ t
2
– 0.15V) > V
. Equations for t
P
• C
P
= 3V. For I
V
2
• C
• C
V
V
THR
+ 0.15V – V
BUS
– 0.15V
= 0.3V
CC
CC
+ 0.15V
BUS
BUS
– V
•
•
• ln
CC
CC
2
THR
C systems with V
• (R
• (R
and V
⎧
⎨
⎩
– R
ILMAX
V
CC
, then t
1
ILMAX
P
P
P
and t
+ R
– R
•I
+ R
IHMIN
V
= 0.8V and V
PULLUP AC
THR
P
L
L
– 0.15V – V
1
2
) – R
•I
) – R
= 0
are given here:
= 0.7V
2
PULLUPAC
– V
C line.
L
L
CC
⎫
⎪ ⎪
⎬
⎪
⎪
⎭
CC
CC
ILMAX
related input
IHMIN
.
CC
THR
⎫
⎬
⎭
⎫
⎬
⎭
and the
= 2.1V.
= 1.5V
(8)
(7)
(5)
(6)
A general procedure for selecting R
lows:
1. R
2. The value of R
3. For I
I
Given the following conditions and requirements:
If an R
200Ω, then R
to fi nd the required R
2
C Design Example
requirement. Generally, an R
high voltage spikes and ESD protection. R
determined by the size of the open-drain driver, a large
driver will have a lower R
minimum slew rate requirements. The V
the smallest resistance value that can be used in a
system, and the minimum slew requirement will bound
the resistance on the upper end. Generally the largest
value of resistance that meets the minimum slew rate
with some margin will be selected.
times are met under most loading conditions, due to
the strong accelerator current. The pull-down drivers
are typically low impedance, and therefore fall times
are not generally an issue. Rise and fall time
requirements must be verifi ed using equations 3 and
4 (for an I
system). The value chosen for R
both the rise and fall time specifi cations are met
simultaneously.
C
R
R
V
V
V
t
r
L
ILMAX
CC
OL
BUS
P
P
= 0.3µs MAXIMUM,t
S
is fi rst selected based on the I/O protection
=
= 2.175k
= 3.3V NOMINAL
= 0.4V MAXIMUM
2
of 100Ω is used and the max R
C systems incorporating the LTC4311, the rise
= 600pF
300Ω•(3.3V – 0.4V)
= 0.99V,V
2
C system) or equations 5 to 8 (for an SMBus
L
= 200Ω + 100Ω = 300Ω. Use equation 1
0.4V
P
is determined based on the V
IHMIN
P
to meet V
f
= 2.31V
= 0.3µs MAXIMUM
ON
.
S
of 100Ω is suffi cient for
OL
.
P
P
must ensure that
and R
ON
OL
of the driver is
will determine
L
is as fol-
OL
ON
(10)
4311fa
and
(9)
is