LTC1694CS5#TR Linear Technology, LTC1694CS5#TR Datasheet - Page 5

• Manufacturer Part Number: LTC1694CS5#TR
• Description: IC ACCEL SMBUS DUAL TSOT23-5
• Manufacturer: Linear Technology

Specifications of LTC1694CS5#TR

• Applications: Data Transport
• Interface: SMBus (2-Wire/I²C)
• Voltage - Supply: 2.7 V ~ 6 V
• Package / Case: TSOT-23-5, TSOT-5, TSOP-5
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
SMBus Overview
SMBus communication protocol employs open-drain
drivers with resistive or current source pull-ups. This
protocol allows multiple devices to drive and monitor the
bus without bus contention. The simplicity of resistive or
fixed current source pull-ups is offset by the slow rise
times they afford when bus capacitance is high. Rise
times can be improved by using lower pull-up resistor
values or higher fixed current source values, but the
additional current increases the low state bus voltage,
decreasing noise margins. Slow rise times can seriously
impact data reliability, enforcing a maximum practical
bus speed well below the established SMBus maximum
transmission rate.
Theory of Operation
The LTC1694 overcomes these limitations by using bilevel
hysteretic current sources as pull-ups. During positive
SMBus line transitions, the pull-up current sources typi-
cally provide 2.2mA to quickly slew any parasitic bus
capacitance. Therefore, rise time is dramatically improved,
especially with maximum SMBus loading conditions.
The LTC1694 has separate but identical circuitry for each
SMBus output pin. The circuitry consists of a positive edge
slew rate detector and a voltage comparator.
The LTC1694 nominally sources only 275 A of pull-up
current to maintain good V
boosted pull-up current is only turned on if the voltage on
the SMBus line voltage is greater than the 0.65V compara-
tor threshold voltage and the positive slew rate of the
SMBus line is greater than the 0.2V/ s threshold of the
slew rate detector. The boosted pull-up current remains on
until the voltage on the SMBus line is within 0.5V of V
and/or the slew rate drops below 0.2V/ s.
Auto Detect Standby Mode
The LTC1694 enters standby mode if the voltage on both
the SCL and SDA lines is high (idle state). In standby mode,
the pull-up currents drop to 100 A, thereby lowering the
system power consumption.
U
U
OL
noise margin. The 2.2mA
W
U
CC
Maximum R
For ESD protection of the SMBus lines, a series resistor R
(Figure 2) is sometimes added to the open-drain driver of
the bus agents. This is especially common in SMBus-
controlled smart batteries. The maximum value of R
limited by the low state noise margin and timing require-
ments of the SMBus specification. The maximum value for
R
sources are used.
In general, an R
protection while meeting both the low state noise margin
and fall time requirement. If a larger value of R
take care to ensure that the low state noise margin and
timing requirement of the SMBus specification is not
violated. Also, the fall time of an SMBus line will also be
increased by using a high value series resistor.
Low State Noise Margin
An acceptable V
low pull-up current (350 A maximum) of the LTC1694.
The maximum value of R
state noise margin (NM
V
OL(MAX)
S
R
is 700
S MAX
:
S
if resistive pull-ups or fixed value current
Considerations
V
The maximum V
tion is 0.4V
I
OL
OL MAX
S
PU
of 100 to 200 is sufficient for ESD
noise margin is easily achieved with the
LL-UP
DATA
DATA
OUT
IN
L
S
Figure 2
):
MAX
is calculated from a desired low
NM
L
R
R
OL
S
ON
1694 F02
of the SMBus specifica-
R
ON MAX
SDA
LTC1694
S
is required,
1694fa
5
S
(1)
is
S