LTC1694
SMBus/I
2
C Accelerator*
FEATURES
s
s
DESCRIPTIO
s
s
s
s
Improves SMBus Rise Time Transition
Ensures Data Integrity with Multiple Devices
on the SMBus
Improves Low State Noise Margin
Auto Detect Low Power Standby Mode
Wide Supply Voltage Range: 2.7V to 6V
Low Profile (1mm) SOT-23 (ThinSOT
TM
) Package
APPLICATIO S
s
s
s
s
s
s
Notebook and Palmtop Computers
Portable Instruments
Battery Chargers
Industrial Control Application
TV/Video Products
ACPI SMBus Interface
The LT C
®
1694 is a dual SMBus active pull-up designed to
enhance data transmission speed and reliability under all
specified SMBus loading conditions. The LTC1694 is also
compatible with the Philips I
2
C
TM
Bus.
The LTC1694 allows multiple device connections or a
longer, more capacitive interconnect, without compro-
mising slew rates or bus performance, by using two
bilevel hysteretic current source pull-ups.
During positive bus transitions, the LTC1694 current
sources provide 2.2mA to quickly slew the SMBus line.
During negative transitions or steady DC levels, the cur-
rent sources decrease to 275µA to improve negative slew
rate and improve low state noise margins. An auto detect
standby mode reduces supply current if both SCL and
SDA are high.
The LTC1694 is available in a 5-pin SOT-23 package,
requiring virtually the same space as two surface mount
resistors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
I
2
C is a trademark of Philips Electronics N.V.
*U.S. Patent No. 6,650,174
TYPICAL APPLICATIO
V
CC
5V
V
CC
C1
0.1µF
SMBus1
LTC1694
GND
SCL
SMBus
SDA
SMBus2
Comparison of SMBus Waveforms for
the LTC1694 vs Resistor Pull-Up
LTC1694
1V/DIV
DATA
IN
DATA
OUT
CLK
IN
CLK
OUT
DEVICE N
1694 TA01
CLK
IN
CLK
OUT
DEVICE 1
DATA
IN
DATA
OUT
V
CC
= 5V
C
LD
= 200pF
f
SMBus
= 100kHz
U
R
PULL-UP
= 15.8k
1µs/DIV
1694 TA02
U
U
1694fa
1
LTC1694
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
CC
1
GND 2
NC 3
4 SMBus2
5 SMBus1
Supply Voltage (V
CC
) ................................................. 7V
SMBus1, SMBus2 Inputs ............ – 0.3V to (V
CC
+ 0.3V)
Operating Ambient Temperature Range
LTC1694C ............................................... 0°C to 70°C
LTC1694I ............................................ – 40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1694CS5
LTC1694IS5
S5 PART MARKING
LTEE
LTA8
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 256°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications that apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
CC
= 2.7V to 6V unless otherwise noted.
SYMBOL
V
CC
I
CC
I
PULL-UP
PARAMETER
Supply Voltage Range
Supply Current
Pull-Up Current
Boosted Pull-Up Current
V
THRES
SR
THRES
t
r
f
MAX
Input Threshold Voltage
Slew Rate Detector Threshold
SMBus Rise Time
Standard Mode I
2
C Bus Rise Time
SMBus Maximum Operating Frequency
SMBus1 = SMBus2 = Open
SMBus1 = SMBus2 = 0V
Positive Transition on SMBus ( Figure 1)
Slew Rate = 0.5V/µs, SMBus > V
THRES
Slew Rate = 0.5V/µs (Figure 1)
SMBus > V
THRES
Bus Capacitance = 200pF (Note 2)
Bus Capacitance = 400pF (Note 3)
(Note 4)
q
q
q
q
q
q
q
q
CONDITIONS
MIN
2.7
20
125
1.0
0.4
TYP
60
275
2.2
0.65
0.2
0.32
0.30
MAX
6
100
350
UNITS
V
µA
µA
mA
0.9
0.5
1.0
1.0
100
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The rise time of an SMBus line is calculated from (V
IL(MAX)
–
0.15V) to (V
IH(MIN)
+ 0.15V) or 0.65V to 2.25V. This parameter is
guaranteed by design and not tested. With a minimum pull-up current of
125µA, a minimum boosted pull-up current of 1mA and a maximum input
threshold voltage of 0.9V:
Rise Time = [(0.9V – 0.65V)/125µA + (2.25V – 0.9V)/1mA] • 200pF
= 0.67µs
Note 3:
The rise time of an I
2
C bus line is calculated from V
IL(MAX)
to
V
IH(MIN)
or 1.5V to 3V (with V
CC
= 5V). This parameter is guaranteed by
design and not tested. With a minimum boosted pull-up current of 1mA:
Rise Time = (3V – 1.5V) • 400pF/1mA = 0.6µs
Note 4:
This parameter is guaranteed by design and not tested.
2
U
V
V/µs
µs
µs
kHz
1694fa
W
U
U
W W
W
LTC1694
TYPICAL PERFOR A CE CHARACTERISTICS
Pull-Up Current at SMBus = 0V
350
BOOSTED PULL-UP CURRENT (mA)
BOOSTED PULL-UP CURRENT (mA)
325
300
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
PULL-UP CURRENT (µA)
275
250
225
200
175
150
125
100
–50
–25
50
0
75
25
TEMPERATURE (°C)
Input Threshold Voltage
0.90
SLEW RATE DETECTOR THRESHOLD (V/µs)
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.85
INPUT THRESHOLD VOLTAGE (V)
0.80
0.75
0.70 V
CC
= 5V
0.65
0.60
0.55
0.50
0.45
0.40
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
V
CC
= 2.7V
V
CC
= 6V
SUPPLY CURRENT (µA)
PI FU CTIO S
V
CC
(Pin 1):
Power Supply Input. V
CC
can range from 2.7V
to 6V and requires a 0.1µF bypass capacitor to GND.
GND (Pin 2):
Ground.
NC (Pin 3):
No Connection.
SMBus2 (Pin 4):
Active Pull-Up for SMBus.
SMBus1 (Pin 5):
Active Pull-Up for SMBus.
U W
100
1694 G01
Boosted Pull-Up Current
3.50
3.25
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
V
CC
= 2.7V
V
CC
= 6V
V
CC
= 5V
3.0
2.5
2.0
1.5
1.0
3.5
Boosted Pull-Up Current vs
SMBus Voltage
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
0.5
0
0
1
4
3
5
2
SMBus VOLTAGE (V)
6
7
125
1694 G02
LT1694
G03
Slew Rate Detector Threshold
100
90
80
70
Standby Mode Supply Current
V
CC
= 6V
60
50
40
30
V
CC
= 5V
V
CC
= 2.7V
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
0
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
20
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1694 G05
1694 G06
1694 G04
U
U
U
1694fa
3
LTC1694
BLOCK DIAGRA
V
CC
1
SMBus1
5
GND
2
STANDBY
SMBus2
4
TEST CIRCUITS
V
CC
5V
C1
0.1µF
1
V
CC
2
GND
SMBus2
275µA
(TYP)
SMBus1
LTC1694
4
–
LT1360
TEST RAMP VOLTAGE
BSS284
+
V
R
1k
4
W
CHANNEL ONE
SLEW RATE
DETECTOR
100µA
175µA
1.925mA
CONTROL
LOGIC
+
–
VOLTAGE
COMP
0.65V
V
REF
CHANNEL TWO
(DUPLICATE OF CHANNEL ONE)
1694 BD
5
BOOSTED PULL-UP
2.2mA (TYP)
I
PULL-UP
=
V
R
1kΩ
HP5082-2080
V
CC
0µA
TEST RAMP
VOLTAGE
0.5V/µs
V
THRES
–10V
1694 f01a
0V
1694 F01b
Figure 1
1694fa
LTC1694
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 275µA of pull-up
current to maintain good V
OL
noise margin. The 2.2mA
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/µs 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
CC
and/or the slew rate drops below 0.2V/µs.
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 100µA, thereby lowering the
system power consumption.
U
Maximum R
S
Considerations
For ESD protection of the SMBus lines, a series resistor R
S
(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
S
is
limited by the low state noise margin and timing require-
ments of the SMBus specification. The maximum value for
R
S
is 700Ω if resistive pull-ups or fixed value current
sources are used.
In general, an R
S
of 100Ω to 200Ω is sufficient for ESD
protection while meeting both the low state noise margin
and fall time requirement. If a larger value of R
S
is required,
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.
SDA
R
S
DATA
IN
DATA
OUT
R
ON
1694 F02
W
U U
Figure 2
Low State Noise Margin
An acceptable V
OL
noise margin is easily achieved with the
low pull-up current (350µA maximum) of the LTC1694.
The maximum value of R
S
is calculated from a desired low
state noise margin (NM
L
):
V
−
NM
L
R
S
(
MAX
)
=
OL
(
MAX
)
−
R
ON
(
MAX
)
I
PULL-UP
(
MAX
)
V
OL(MAX)
:
(1)
The maximum V
OL
of the SMBus specifica-
tion is 0.4V
1694fa
5
京公网安备 11010802033920号
EEWORLD
