1
LTC1694
1694fa
SMBus/I
2
C Accelerator*
■
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
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.
■
Notebook and Palmtop Computers
■
Portable Instruments
■
Battery Chargers
■
Industrial Control Application
■
TV/Video Products
■
ACPI SMBus Interface
LTC1694
V
CC
GND
V
CC
5V
C1
0.1µF
SMBus1
SMBus2
SCL
SDA
DEVICE 1
CLK
IN
CLK
OUT
SMBus
DATA
IN
DATA
OUT
DEVICE N
1694 TA01
CLK
IN
CLK
OUT
DATA
IN
DATA
OUT
, 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
VCC = 5V 1µs/DIV
CLD = 200pF
fSMBus = 100kHz 1694 TA02
Comparison of SMBus Waveforms for
the LTC1694 vs Resistor Pull-Up
LTC1694
RPULL-UP
= 15.8k
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
1V/DIV
2
LTC1694
1694fa
ORDER PART
NUMBER
LTC1694CS5
LTC1694IS5
(Note 1)
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
V
CC
1
GND 2
NC 3
5 SMBus1
4 SMBus2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C, θ
JA
= 256°C/ W LTEE
LTA8
S5 PART MARKING
The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VCC = 2.7V to 6V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
Supply Voltage Range 2.7 6 V
I
CC
Supply Current SMBus1 = SMBus2 = Open ●20 60 100 µA
I
PULL-UP
Pull-Up Current SMBus1 = SMBus2 = 0V ●125 275 350 µA
Boosted Pull-Up Current Positive Transition on SMBus ( Figure 1) ●1.0 2.2 mA
Slew Rate = 0.5V/µs, SMBus > V
THRES
V
THRES
Input Threshold Voltage Slew Rate = 0.5V/µs (Figure 1) ●0.4 0.65 0.9 V
SR
THRES
Slew Rate Detector Threshold SMBus > V
THRES
●0.2 0.5 V/µs
t
r
SMBus Rise Time Bus Capacitance = 200pF (Note 2) ●0.32 1.0 µs
Standard Mode I
2
C Bus Rise Time Bus Capacitance = 400pF (Note 3) ●0.30 1.0 µs
f
MAX
SMBus Maximum Operating Frequency (Note 4) ●100 kHz
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.
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
ELECTRICAL CHARACTERISTICS
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LTC1694
1694fa
TEMPERATURE (°C)
–50
PULL-UP CURRENT (µA)
350
325
300
275
250
225
200
175
150
125
100 050 75
1694 G01
–25 25 100 125
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
TEMPERATURE (°C)
–50
BOOSTED PULL-UP CURRENT (mA)
3.50
3.25
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00 050 75
1694 G02
–25 25 100 125
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
Boosted Pull-Up Current vs
SMBus Voltage
TEMPERATURE (°C)
–50
INPUT THRESHOLD VOLTAGE (V)
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40 050 75
1694 G04
–25 25 100 125
V
CC
= 6V
V
CC
= 2.7V
V
CC
= 5V
TEMPERATURE (°C)
–50
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
0050 75
1694 G05
–25 25 100 125
V
CC
= 6V
V
CC
= 2.7V
V
CC
= 5V
Slew Rate Detector Threshold Standby Mode Supply Current
TEMPERATURE (°C)
–50
SUPPLY CURRENT (µA)
100
1694 G06
050
100
90
80
70
60
50
40
30
20 –25 25 75 125
V
CC
= 6V
V
CC
= 2.7V
V
CC
= 5V
Pull-Up Current at SMBus = 0V Boosted Pull-Up Current
SMBus VOLTAGE (V)
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
035
LT1694 G03
12 467
BOOSTED PULL-UP CURRENT (mA)
V
CC
= 6V
V
CC
= 5V
V
CC
= 2.7V
Input Threshold Voltage
TYPICAL PERFOR A CE CHARACTERISTICS
UW
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.
UU
U
PI FU CTIO S
4
LTC1694
1694fa
–
+
SLEW RATE
DETECTOR
CONTROL
LOGIC
0.65V
V
REF
VOLTAGE
COMP
1.925mA
STANDBY
CHANNEL ONE
CHANNEL TWO
(DUPLICATE OF CHANNEL ONE)
1694 BD
1
175µA100µA
V
CC
5
SMBus1
SMBus2
2
GND
4
BLOCK DIAGRA
W
Figure 1
LTC1694
V
CC
GND
V
CC
5V
C1
0.1µF
SMBus1
SMBus2
5
4
1
2
HP5082-2080
TEST RAMP VOLTAGE
BSS284
V
R
1k
–10V
1694 f01a
–
+
LT1360
BOOSTED PULL-UP
2.2mA (TYP)
275µA
(TYP)
TEST RAMP
VOLTAGE
0µA
VCC
1694 F01b
0.5V/µs
0V
VTHRES
IPULL-UP = VR
1kΩ
TEST CIRCUITS
5
LTC1694
1694fa
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.
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.
APPLICATIO S I FOR ATIO
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SDA
R
S
R
ON
1694 F02
DATA
IN
DATA
OUT
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
):
RVNM
IR
S MAX OL MAX L
PU MAX ON MAX() ()
() ()
=−−
LL-UP
(1)
V
OL(MAX)
: The maximum V
OL
of the SMBus specifica-
tion is 0.4V
6
LTC1694
1694fa
R
ON(MAX)
: The maximum on resistance of the open-
drain driver
I
PULL-UP(MAX)
: The maximum LTC1694 low pull-up cur-
rent is 350µA
Fall Time
Fall time is a function of the SMBus capacitance, R
S
, R
ON
and the pull-up current. Figure 3 shows the maximum
allowed (R
S
+ R
ON
) based on the Intel SMBus fall time
requirement of 300ns with a 50ns safety margin.
BUS CAPACITANCE (pF)
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0300
1694 F03
100 200 400 500
MAXIMUM VALUE OF R
S
+ R
ON
(kΩ)
V
CC
= 5V
Figure 3. Maximum Value of RS + RON as a Function of Bus
Capacitance for Meeting the SMBus tf(MAX) Requirement
The maximum value of R
S
, based on fall time require-
ments, can also be calculated by rearranging equation 6.
Given below are some equations that are useful for calcu-
lating rise and fall time and for selecting the value of R
S
.
Initial Slew Rate
The initial slew rate, SR, of the Bus is determined by:
SR = I
PULL-UP(MIN)
/C
BUS
(2)
C
BUS
is the total capacitance of the SMBus line.
I
PULL-UP(MIN)
is the LTC1694 minimum pull-up current
(125µA).
SR must be greater than SR
THRES
, the LTC1694 slew rate
detector threshold (0.5V/µs max) in order to activate the
2.2mA boosted pull-up current. This limits the maximum
SMBus capacitance.
SMBus Rise Time
Rise time of an SMBus line is derived using equations 3,
4 and 5.
t
r
= t
1
+ t
2
(3)
t
1
= (V
THRES
– V
IL(MAX)
+ 0.15) •
C
BUS
/I
PULL-UP
(4)
if V
IL(MAX)
– 0.15 > V
THRES
, then t
1
= 0µs.
t
2
= (V
IH(MIN)
+ 0.15 – V
THRES
) • C
BUS
/I
PULL-UP(B)
(5)
I
PULL-UP(B)
is the LTC1694 boosted pull-up current (2.2mA
typ).
For an SMBus system, V
IL(MAX)
= 0.8V and V
IH(MIN)
= 2.1V.
For the LTC1694, typically V
THRES
= 0.65V and
I
PULL-UP
= 275µA.
C
BUS
is the total capacitance of the SMBus line.
SMBus Fall Time
Fall time of an SMBus line is derived using equation 6.
t
f
= R
L
• C
BUS
• ln{[(0.9 • V
CC
) – (R
L
• I
PULL-UP(LOW)
)]/
[V
IL(MAX)
– 0.15 – (R
L
• I
PULL-UP(LOW)
)]} (6)
where R
L
is the sum of R
S
and R
ON
(see Figure 2).
Rise and fall time calculation for an I
2
C system is as
follows.
I
2
C Bus Rise and Fall Time
Rise time of an I
2
C line is derived using equation 7.
t
r
= (V
IH(MIN)
– V
IL(MAX)
) • C
BUS
/I
PULL-UP(B)
(7)
Fall time of the I
2
C line can be derived using equation 8.
t
f
= R
L
• C
BUS
• ln{[V
IH(MIN)
– (R
L
• I
PULL-UP
)]/
[V
IL(MAX)
– (R
L
• I
PULL-UP
)]} (8)
For an I
2
C system with fixed input levels, V
IL(MAX)
= 1.5V
and V
IH(MIN)
= 3V.
For an I
2
C system with V
CC
related input levels, V
IL(MAX)
=
0.3 • V
CC
and V
IH(MIN)
= 0.7 • V
CC
.
C
BUS
is the total capacitance of the I
2
C line.
APPLICATIO S I FOR ATIO
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7
LTC1694
1694fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
ACK Data Setup Time
The data setup time requirement for ACK (acknowledge)
must be fulfilled if a high value of R
S
is used. An acknowl-
edge is accomplished by the SMBus host releasing the
SDA line (pulling high) at the end of the last bit sent and the
SMBus slave device pulling the SDA line low before the
rising edge of the ACK clock pulse.
The LTC1694 2.2mA boosted pull-up current is activated
when the SMBus host releases the SDA line, allowing the
voltage to rise above the LTC1694’s comparator threshold
of 0.65V. If an SMBus slave device has a high value of R
S
,
a longer time is required for this SMBus slave device to pull
SDA low before the rising edge of the ACK clock pulse.
To ensure sufficient data setup time for ACK, SMBus slave
devices, with high values of R
S
, should pull the SDA low
earlier. Typically, a minimum setup time of 1.5µs is needed
for an SMBus device with an R
S
of 700Ω and a bus
capacitance of 200pF.
An alternative is that the SMBus slave device can hold SCL
line low until the SDA line reaches a stable state. Then, SCL
can be released to generate the ACK clock pulse.
APPLICATIO S I FOR ATIO
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U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
S5 TSOT-23 0302
PIN ONE
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX 0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
8
LTC1694
1694fa
LT/TP 0304 REV A 1K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
VCC = 5V 1µs/DIV
CLD = 200pF
fSMBus = 100kHz 1694 TA03
VCC = 3.3V 1µs/DIV
CLD = 200pF
fSMBus = 100kHz 1694 TA04
Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up
RPULL-UP
= 15.8k
LTC1694 LTC1694
RPULL-UP
= 10.5k
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1V/DIV 1V/DIV
