LTC1694
SMBus/I2C Accelerator
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FEATURES
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DESCRIPTIO
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
Tiny 5-Pin SOT-23 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 I2CTM Bus.
The LTC1694 allows multiple device connections or a
longer, more capacitive interconnect, without compromising 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 current 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.
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APPLICATIO S
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Notebook and Palmtop Computers
Portable Instruments
Battery Chargers
Industrial Control Application
TV/Video Products
ACPI SMBus Interface
, LTC and LT are registered trademarks of Linear Technology Corporation.
I2C is a trademark of Philips Electronics N.V.
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TYPICAL APPLICATIO
VCC
5V
Comparison of SMBus Waveforms for
the LTC1694 vs Resistor Pull-Up
1
5
SMBus1
VCC
C1
0.1µF
LTC1694
2
4
GND
SMBus2
LTC1694
SCL
SMBus
SDA
1V/DIV
CLK
IN
DATA
IN
CLK
IN
DATA
IN
CLK
OUT
DATA
OUT
CLK
OUT
DATA
OUT
DEVICE 1
DEVICE N
1694 TA01
RPULL-UP
= 15.8k
VCC = 5V
CLD = 200pF
fSMBus = 100kHz
1µs/DIV
1694 TA02
LTC1694: Patent Pending
1
LTC1694
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltage (VCC) ................................................. 7V
SMBus1, SMBus2 Inputs ............ – 0.3V to (VCC + 0.3V)
Operating Ambient Temperature Range ....... 0°C to 70°C
Junction Temperature ........................................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................. 300°C
ORDER PART
NUMBER
TOP VIEW
5 SMBus1
VCC 1
LTC1694CS5
GND 2
NC 3
4 SMBus2
S5 PART MARKING
S5 PACKAGE
5-LEAD PLASTIC SOT-23
LTEE
TJMAX = 125°C, θJA = 256°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
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
VCC
Supply Voltage Range
ICC
Supply Current
SMBus1 = SMBus2 = Open
●
IPULL-UP
Pull-Up Current
SMBus1 = SMBus2 = 0V
Boosted Pull-Up Current
VTHRES
Input Threshold Voltage
SRTHRES
tr
fMAX
TYP
MAX
6
V
20
60
100
µA
●
125
275
350
µA
Positive Transition on SMBus ( Figure 1)
Slew Rate = 0.5V/µs, SMBus > VTHRES
●
1.0
2.2
Slew Rate = 0.5V/µs (Figure 1)
●
0.4
0.65
0.9
V
Slew Rate Detector Threshold
SMBus > VTHRES
●
0.2
0.5
V/µs
SMBus Rise Time
Standard Mode I2C Bus Rise Time
Bus Capacitance = 200pF (Note 2)
Bus Capacitance = 400pF (Note 3)
●
●
0.32
0.30
1.0
1.0
µs
µs
SMBus Maximum Operating Frequency
(Note 4)
●
100
kHz
2.7
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 (VIL(MAX) –
0.15V) to (VIH(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
2
MIN
UNITS
mA
Note 3: The rise time of an I2C bus line is calculated from VIL(MAX) to
VIH(MIN) or 1.5V to 3V (with VCC = 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.
LTC1694
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TYPICAL PERFOR A CE CHARACTERISTICS
3.50
325
3.25
VCC = 6V
275
VCC = 5V
250
VCC = 2.7V
225
200
175
150
125
100
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
3.5
3.00
2.75
VCC = 6V
2.50
2.25
VCC = 5V
2.00
VCC = 2.7V
1.75
1.50
1.25
1.00
–50
125
BOOSTED PULL-UP CURRENT (mA)
350
300
Boosted Pull-Up Current vs
SMBus Voltage
Boosted Pull-Up Current
BOOSTED PULL-UP CURRENT (mA)
PULL-UP CURRENT (µA)
Pull-Up Current at SMBus = 0V
–25
50
0
75
25
TEMPERATURE (°C)
100
0.75
VCC = 6V
0.65
VCC = 2.7V
0.55
0.50
0.45
0.40
–50
–25
50
0
75
25
TEMPERATURE (°C)
1.0
VCC = 2.7V
0.5
0
100
125
4
3
5
2
SMBus VOLTAGE (V)
1
6
7
LT1694 G03
Standby Mode Supply Current
100
0.45
90
0.40
SUPPLY CURRENT (µA)
SLEW RATE DETECTOR THRESHOLD (V/µs)
INPUT THRESHOLD VOLTAGE (V)
0.80
VCC = 5V
1.5
0
125
0.50
0.60
2.0
Slew Rate Detector Threshold
Input Threshold Voltage
0.90
0.85
VCC = 6V
2.5
1694 G02
1694 G01
0.70 VCC = 5V
3.0
0.35
0.30
0.25
0.20
VCC = 6V
0.15
0.10
VCC = 5V
VCC = 2.7V
–25
50
0
75
25
TEMPERATURE (°C)
1694 G04
70
VCC = 6V
60
50
VCC = 5V
VCC = 2.7V
40
30
0.05
0
–50
80
100
125
20
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1694 G05
1694 G06
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PI FU CTIO S
VCC (Pin 1): Power Supply Input. VCC can range from 2.7V
to 6V and requires a 0.1µF bypass capacitor to GND.
SMBus2 (Pin 4): Active pull-up for SMBus.
SMBus1 (Pin 5): Active pull-up for SMBus.
GND (Pin 2): Ground.
NC (Pin 3): No Connection.
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LTC1694
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BLOCK DIAGRA
VCC
CHANNEL ONE
1
100µA
175µA
SLEW RATE
DETECTOR
1.925mA
CONTROL
LOGIC
SMBus1
+
5
VOLTAGE
COMP
GND
2
–
STANDBY
0.65V
VREF
CHANNEL TWO
(DUPLICATE OF CHANNEL ONE)
SMBus2
4
1694 BD
TEST CIRCUITS
VCC
5V
1
C1
0.1µF
BOOSTED PULL-UP
2.2mA (TYP)
5
VCC
SMBus1
LTC1694
2
IPULL-UP =
4
GND
VR
1kΩ
SMBus2
275µA
(TYP)
0µA
HP5082-2080
–
LT1360
TEST RAMP VOLTAGE
BSS284
VCC
TEST RAMP
VOLTAGE
+
0.5V/µs
VR
1k
VTHRES
–10V
1694 f01a
0V
Figure 1
4
1694 F01b
LTC1694
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APPLICATIO S I FOR ATIO
SMBus Overview
Maximum RS Considerations
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.
For ESD protection of the SMBus lines, a series resistor RS
(Figure 2) is sometimes added to the open-drain driver of
the bus agents. This is especially common in SMBuscontrolled smart batteries. The maximum value of RS is
limited by the low state noise margin and timing requirements of the SMBus specification. The maximum value for
RS is 700Ω if resistive pull-ups or fixed value current
sources are used.
Theory of Operation
In general, an RS 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 RS 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.
The LTC1694 overcomes these limitations by using bilevel
hysteretic current sources as pull-ups. During positive
SMBus line transitions, the pull-up current sources typically provide 2.2mA to quickly slew any parasitic bus
capacitance. Therefore, rise time is dramatically improved,
especially with maximum SMBus loading conditions.
SDA
RS
DATA
IN
DATA
OUT
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.
RON
1694 F02
The LTC1694 nominally sources only 275µA of pull-up
current to maintain good VOL 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 comparator 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 VCC
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.
Figure 2
Low State Noise Margin
An acceptable VOL noise margin is easily achieved with the
low pull-up current (350µA maximum) of the LTC1694.
The maximum value of RS is calculated from a desired low
state noise margin (NML):
V
− NML
RS(MAX ) = OL(MAX )
− RON(MAX )
IPULL-UP(MAX )
VOL(MAX):
(1)
The maximum VOL of the SMBus specification is 0.4V
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LTC1694
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APPLICATIO S I FOR ATIO
RON(MAX):
The maximum on resistance of the opendrain driver
IPULL-UP(MAX): The maximum LTC1694 low pull-up current is 350µA
Fall Time
Fall time is a function of the SMBus capacitance, RS, RON
and the pull-up current. Figure 3 shows the maximum
allowed (RS + RON) based on the Intel SMBus fall time
requirement of 300ns with a 50ns safety margin.
Rise time of an SMBus line is derived using equations 3,
4 and 5.
tr = t1 + t2
(3)
t1 = (VTHRES – VIL(MAX) + 0.15) •
CBUS/IPULL-UP
(4)
if VIL(MAX) – 0.15 > VTHRES, then t1 = 0µs.
t2 = (VIH(MIN) + 0.15 – VTHRES) • CBUS/IPULL-UP(B) (5)
IPULL-UP(B) is the LTC1694 boosted pull-up current (2.2mA
typ).
1.4
VCC = 5V
MAXIMUM VALUE OF RS + RON (kΩ)
SMBus Rise Time
1.2
0.8
For an SMBus system, VIL(MAX) = 0.8V and VIH(MIN) = 2.1V.
For the LTC1694, typically V THRES = 0.65V and
IPULL-UP = 275µA.
0.6
CBUS is the total capacitance of the SMBus line.
1.0
0.4
SMBus Fall Time
0.2
Fall time of an SMBus line is derived using equation 6.
0
0
100
200
400
300
BUS CAPACITANCE (pF)
tf = RT • CBUS • ln{[(0.9 • VCC) – (RL • IPULL-UP(LOW))]/
[VIL(MAX) – 0.15 – (RL • IPULL-UP(LOW))]}
(6)
500
1694 F03
where RL is the sum of RS and RON (see Figure 2).
Figure 3. Maximum Value of RS + RON as a Function of Bus
Capacitance for Meeting the SMBus tf(MAX) Requirement
The maximum value of RS, based on fall time requirements, can also be calculated by rearranging equation 6.
Given below are some equations that are useful for calculating rise and fall time and for selecting the value of RS.
Initial Slew Rate
(2)
CBUS is the total capacitance of the SMBus line.
IPULL-UP(MIN) is the LTC1694 minimum pull-up current
(125µA).
SR must be greater than SRTHRES, 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.
6
I2C Bus Rise and Fall Time
Rise time of an I2C line is derived using equation 7.
tr = (VIH(MIN) – VIL(MAX)) • CBUS/IPULL-UP(B)
(7)
Fall time of the I2C line can be derived using equation 8.
The initial slew rate, SR, of the Bus is determined by:
SR = IPULL-UP(MIN)/CBUS
Rise and fall time calculation for an I2C system is as
follows.
tf = RT • CBUS • ln{[VIH(MIN) – (RL • IPULL-UP)]/
[VIL(MAX) – (RL • IPULL-UP)]}
(8)
For an I2C system with fixed input levels, VIL(MAX) = 1.5V
and VIH(MIN) = 3V.
For an I2C system with VCC related input levels, VIL(MAX) =
0.3 • VCC and VIH(MIN) = 0.7 • VCC.
CBUS is the total capacitance of the I2C line.
LTC1694
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APPLICATIO S I FOR ATIO
ACK Data Setup Time
The data setup time requirement for ACK (acknowledge)
must be fulfilled if a high value of RS is used. An acknowledge 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 RS,
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PACKAGE DESCRIPTIO
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 RS, should pull the SDA low
earlier. Typically, a minimum setup time of 1.5µs is needed
for an SMBus device with an RS 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.
Dimensions in inches (millimeters) unless otherwise noted.
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 – 3.00
(0.110 – 0.118)
(NOTE 3)
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
0.35 – 0.55
(0.014 – 0.022)
1.90
(0.074)
REF
0.00 – 0.15
(0.00 – 0.006)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.95
(0.037)
REF
0.90 – 1.45
(0.035 – 0.057)
0.35 – 0.50
0.90 – 1.30
(0.014 – 0.020)
(0.035 – 0.051)
FIVE PLACES (NOTE 2)
S5 SOT-23 0599
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC1694
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APPLICATIO S I FOR ATIO
Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up
LTC1694
1V/DIV
LTC1694
1V/DIV
RPULL-UP
= 15.8k
VCC = 5V
CLD = 200pF
fSMBus = 100kHz
1µs/DIV
1694 TA03
RPULL-UP
= 10.5k
VCC = 3.3V
CLD = 200pF
fSMBus = 100kHz
1µs/DIV
1694 TA04
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Linear Technology Corporation
1694f LT/TP 0400 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 1998