LTC1694-1CS5#PBF Linear Technology, LTC1694-1CS5#PBF Datasheet - Page 6

• Manufacturer Part Number: LTC1694-1CS5#PBF
• Manufacturer: Linear Technology

Specifications of LTC1694-1CS5#PBF

• Operating Temperature (min): 0C
• Operating Temperature Classification: Commercial
• Operating Temperature (max): 70C
• Rad Hardened: No
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS
LTC1694-1
SMBus Rise Time
Rise time of an SMBus line is derived using equations 3,
4 and 5.
if (V
By ignoring the current through R
of equation 3 is obtained:
For an SMBus system, V
For the LTC1694-1, typically V
= 2.2mA.
C
Increasing the value of R
SMBus Fall Time
Fall time of an SMBus line is derived using equation 7:
where R
The rise and fall time calculation for an I
follows.
I
Rise time of an I
Fall time of an I
For an I
and V
6
2
BUS
C Bus Rise and Fall Time
t
t
(V
t
(R
t
t
[(V
t
[V
t
[(V
r
1
2
2
f
r
f
ILMAX
= t
= R
= – R
= R
ILMAX
ILMAX
= – R
= – R
P
= (V
is the total capacitance of the SMBus line.
ILMAX
ILMAX
IHMIN
• I
1
2
T
T
T
C system with fixed input levels, V
+ t
PULL-UP
IHMIN
• C
• C
P
is the parallel equivalent of R
P
P
– 0.15) > V
– 0.15 – V
– V
/V
2
• C
= 3V.
• C
• C
– 0.15) • (R
BUS
BUS
CC
CC
BUS
BUS
BUS
+ 0.15 – V
2
) • (R
2
C line is derived using equation 9:
)]/[V
• ln{[0.9 • (R
• ln{[(V
– (R
C line is derived using equation 8.
• ln{[V
• ln[(V
• ln{[V
U
P
THRES
CC
THRES
P
+ R
• I
)]
P
IHMIN
ILMAX
INFORMATION
P
IHMIN
IHMIN
THRES
THRES
+ R
PULL-UP
U
L
increases the rise time.
, then t
) – R
– V
L
/V
P
THRES
)/V
= 0.8V and V
– V
CC
+ 0.15 – V
) • C
+ R
CC
– V
L
CC
)]}
]}
) • (R
– (R
P
CC
1
L
CC
W
, a simplified version
BUS
) – R
= 0 s.
– R
= 0.65V and I
– (R
)/
P
P
P
/I
L
• I
]}
PULL-UP
L
and R
2
+ R
P
CC
]/
C system is as
PULL-UP
• I
IHMIN
ILMAX
L
–
PULL-UP
) – R
U
L
.
PULL-UP
= 2.1V.
)]} (5)
= 1.5V
L
]/
)]/
(3)
(4)
(6)
(7)
(8)
(9)
For an I
0.3V
C
A general procedure for selecting R
1. R
2. Next, the value of R
3. After R
If SR is too low, decrease the value of R
increase the value of R
SMBus Design Example
Given the following conditions and requirements:
If an R
is 200 , then R
V
Using equation 6 to calculate the approximate value of t
Using equation 4 to find the required R
BUS
THRES
ment. Generally, an R
voltage spike and ESD protection. R
the size of the open-drain driver, a large driver will have
a lower R
fall time requirements using equations 3 to 7 (for an
SMBus system) or 8 and 9 (for an I
value chosen for R
fall time specifications are met simultaneously.
check if the V
V
V
C
V
t
t
t
R
(V
R
r
2
1
CC
OL
BUS
ILMAX
L
P
T
CC
= 0.8 s max, t
= (2.1 + 0.15 – 0.9) • [(200 • 10
= 0.8 – 0.27 = 0.53 s
ILMAX
= 0.27 s
is the total capacitance of the I
is first selected based on the I/O protection require-
= (R
= – t
S
= 3.3V nom
= 0.4V max
and V
2
of 0.9V and a min I
= 200pF max
of 500 is used and the max R
C system with V
P
= 0.8V, V
1
P
– 0.15 – V
/{C
and R
• R
ON
IHMIN
BUS
.
L
L
)/(R
OL
L
= 500 + 200 = 700 . Using the max
• ln[(V
are selected, use equations 1 and 2 to
= 0.7V
and SR requirements are fulfilled.
f
IHMIN
P
= 0.3 s max
P
P
CC
+ R
is determined based on the rise and
must ensure that both the rise and
P
)]} = 27k
.
S
THRES
CC
= 2.1V
L
CC
)
of 100 is sufficient for high
PULL-UP
related input levels, V
.
– V
CC
P
of 1mA.
2
and R
)/
–12
C line.
ON
P
. If V
P
ON
2
is determined by
)/(1 • 10
C system). The
to meet t
L
of the driver
OL
is as follows:
is too high,
–3
ILMAX
r
:
)]
16941fa
2
=
: