Datasheet LTC1694 Datasheet (Linear Technology)

FEATURES

■

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

U

APPLICATIO S

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Battery Chargers

■

Industrial Control Application

■

TV/Video Products

■

ACPI SMBus Interface

LTC1694

SMBus/I2C Accelerator

U

DESCRIPTIO

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.

TYPICAL APPLICATIO

V

CC

5V

1

C1

0.1µF

2

SCL

SMBus

SDA

CLK

IN

CLK

OUT

DEVICE 1

LTC1694: Patent Pending

V

CC

GND

DATA

DATA

OUT

LTC1694

IN

SMBus1

SMBus2

5

4

CLK

CLK

OUT

DEVICE N

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.

I2C is a trademark of Philips Electronics N.V.

U

Comparison of SMBus Waveforms for

the LTC1694 vs Resistor Pull-Up

LTC1694

1V/DIV

IN

DATA

DATA

OUT

IN

VCC = 5V 1µs/DIV

= 200pF

C

LD

= 100kHz 1694 TA02

f

1694 TA01

SMBus

R

PULL-UP

= 15.8k

1

LTC1694

VCC 1

GND 2

NC 3

5 SMBus1

4 SMBus2

TOP VIEW

S5 PACKAGE

5-LEAD PLASTIC SOT-23

PACKAGE/ORDER I FOR ATIO

UU

W

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Supply Voltage (VCC) ................................................. 7V

SMBus1, SMBus2 Inputs ............ –0.3V to (VCC + 0.3V)

Operating Ambient Temperature Range....... 0°C to 70°C

ORDER PART

NUMBER

LTC1694CS5

Junction Temperature........................................... 125°C

Storage Temperature Range ................. –65°C to 150°C

S5 PART MARKING

Lead Temperature (Soldering, 10 sec.).................300°C

T

= 125°C, θJA = 256°C/ W

JMAX

Consult factory for Industrial and Military grade parts.

LTEE

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 MIN TYP MAX UNITS

V

CC

I

CC

I

PULL-UP

V

THRES

SR

THRES

t

r

f

MAX

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

0.15V) to (V
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

Supply Voltage Range 2.7 6 V
Supply Current SMBus1 = SMBus2 = Open ● 20 60 100 µA
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

Input Threshold Voltage Slew Rate = 0.5V/µs (Figure 1) ● 0.4 0.65 0.9 V
Slew Rate Detector Threshold SMBus > V
SMBus Rise Time Bus Capacitance = 200pF (Note 2) ● 0.32 1.0 µs

Standard Mode I
SMBus Maximum Operating Frequency (Note 4) ● 100 kHz

+ 0.15V) or 0.65V to 2.25V. This parameter is

IH(MIN)

2

C Bus Rise Time Bus Capacitance = 400pF (Note 3) ● 0.30 1.0 µs

IL(MAX)

–

THRES

Note 3: The rise time of an I2C bus line is calculated from V
V

IH(MIN)

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.

THRES

● 0.2 0.5 V/µs

IL(MAX)

or 1.5V to 3V (with VCC = 5V). This parameter is guaranteed by

to

2

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Pull-Up Current at SMBus = 0V Boosted Pull-Up Current

350
325
300
275
250
225
200
175

PULL-UP CURRENT (µA)

150
125
100

–50

VCC = 6V

VCC = 5V

VCC = 2.7V

–25

0

50

25

TEMPERATURE (°C)

100

125

1694 G01

75

3.50

3.25

3.00

2.75

–50

VCC = 6V

VCC = 5V

VCC = 2.7V

0

–25

TEMPERATURE (°C)

50

25

2.50

2.25

2.00

1.75

1.50

BOOSTED PULL-UP CURRENT (mA)

1.25

1.00
75

100

1694 G02

125

LTC1694

Boosted Pull-Up Current vs
SMBus Voltage

3.5

3.0

2.5

2.0

1.5

1.0

0.5

BOOSTED PULL-UP CURRENT (mA)

0

0

VCC = 6V

12

SMBus VOLTAGE (V)

VCC = 5V

VCC = 2.7V

467

35

LT1694 G03

Input Threshold Voltage

0.90

0.85

0.80

0.75
VCC = 5V

0.70

0.65

0.60

0.55

0.50

INPUT THRESHOLD VOLTAGE (V)

0.45

0.40

–50

–25

VCC = 6V

VCC = 2.7V

0

25

TEMPERATURE (°C)

U

50

75

100

125

1694 G04

UU

Slew Rate Detector Threshold

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

SLEW RATE DETECTOR THRESHOLD (V/µs)

0.10

0.05
0

–50

VCC = 5V

0

–25

TEMPERATURE (°C)

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.

GND (Pin 2): Ground.

Standby Mode Supply Current

100

90

80

70

60

VCC = 6V

VCC = 2.7V

25

50

SUPPLY CURRENT (µA)

40

30

50

75

100

125

1694 G05

20

VCC = 5V

050

–25 25 75 125

–50

TEMPERATURE (°C)

SMBus2 (Pin 4): Active pull-up for SMBus.
SMBus1 (Pin 5): Active pull-up for SMBus.

VCC = 6V

VCC = 2.7V

100

1694 G06

NC (Pin 3): No Connection.

3

LTC1694

BLOCK DIAGRA

V

CC

1

SMBus1

5

GND

2

W

175µA100µA

STANDBY

1.925mA

0.65V
V

REF

CHANNEL ONE

SLEW RATE

DETECTOR

CONTROL

LOGIC

+

VOLTAGE

COMP

–

SMBus2

4

TEST CIRCUITS

V

CC

5V

1

V

C1

0.1µF

TEST RAMP VOLTAGE

CC

LTC1694

2

GND

SMBus1

SMBus2

–

LT1360

+

(DUPLICATE OF CHANNEL ONE)

5

4

HP5082-2080

BSS284

V

R

1k

–10V

1694 f01a

BOOSTED PULL-UP

2.2mA (TYP)

V

I

PULL-UP

TEST RAMP

VOLTAGE

R

=

1kΩ

275µA

(TYP)

V

THRES

0V

CHANNEL TWO

0.5V/µs

1694 BD

V

0µA

CC

1694 F01b

4

Figure 1

WUUU

APPLICATIO S I FOR ATIO

LTC1694

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 typi­cally 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 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 V

CC

and/or the slew rate drops below 0.2V/µs.

Maximum RS 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 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.

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.

SDA

R

S

DATA

IN

DATA

OUT

Figure 2

R

ON

1694 F02

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):

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.

R

S MAX

V

OL(MAX)

VNM

OL MAX L

=

I

PU MAX

−

()

()

LL-UP

R

−

ON MAX()

()

(1)

: The maximum VOL of the SMBus specifica-

tion is 0.4V

5

LTC1694

WUUU

APPLICATIO S I FOR ATIO

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, RS, R

ON

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.

1.4
VCC = 5V

1.2

(kΩ)

ON

1.0

+ R

S

0.8

0.6

0.4

0.2

MAXIMUM VALUE OF R

0

100 200 400 500

0

BUS CAPACITANCE (pF)

Figure 3. Maximum Value of RS + RON as a Function of Bus
Capacitance for Meeting the SMBus t

300

1694 F03

Requirement

f(MAX)

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

The initial slew rate, SR, of the Bus is determined by:

SR = I

PULL-UP(MIN)/CBUS

(2)

SMBus Rise Time

Rise time of an SMBus line is derived using equations 3,
4 and 5.

tr = t1 + t
t1 = (V

C

BUS/IPULL-UP

if V

IL(MAX)

t2 = (V

I

PULL-UP(B)

2

– V

THRES

– 0.15 > V

+ 0.15 – V

IH(MIN)

IL(MAX)

+ 0.15) •

, then t1 = 0µs.

THRES

THRES

) • C

BUS/IPULL-UP(B)

is the LTC1694 boosted pull-up current (2.2mA

(3)

(4)

(5)

typ).
For an SMBus system, V

For the LTC1694, typically V
I

PULL-UP

C

BUS

= 275µA.

is the total capacitance of the SMBus line.

IL(MAX)

= 0.8V and V

= 0.65V and

THRES

IH(MIN)

= 2.1V.

SMBus Fall Time

Fall time of an SMBus line is derived using equation 6.
tf = RT • C

[V

IL(MAX)

• ln{[(0.9 • VCC) – (RL • I

BUS

– 0.15 – (RL • I

PULL-UP(LOW)

PULL-UP(LOW)

)]/

)]} (6)
where RL is the sum of RS and RON (see Figure 2).
Rise and fall time calculation for an I2C system is as

follows.

I2C Bus Rise and Fall Time

Rise time of an I2C line is derived using equation 7.

tr = (V

IH(MIN)

– V

IL(MAX)

) • C

BUS/IPULL-UP(B)

(7)

Fall time of the I2C line can be derived using equation 8.

tf = RT • C
[V

IL(MAX)

• ln{[V

BUS

– (RL • I

IH(MIN)

PULL-UP

– (RL • I

PULL-UP

)]/

)]} (8)

C

is the total capacitance of the SMBus line.

BUS

I

PULL-UP(MIN)

is the LTC1694 minimum pull-up current

(125µA).
SR must be greater than SR

, the LTC1694 slew rate

THRES

detector threshold (0.5V/µs max) in order to activate the

2.2mA boosted pull-up current. This limits the maximum
SMBus capacitance.

6

For an I2C system with fixed input levels, V
and V

IH(MIN)

= 3V.

IL(MAX)

For an I2C system with VCC related input levels, V

0.3 • VCC and V
C

is the total capacitance of the I2C line.

BUS

IH(MIN)

= 0.7 • VCC.

= 1.5V

IL(MAX)

=

WUUU

APPLICATIO S I FOR ATIO

LTC1694

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,

U

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

S5 Package

5-Lead Plastic SOT-23

(LTC DWG # 05-08-1633)

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.

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

1.90

2.60 – 3.00

(0.102 – 0.118)

1.50 – 1.75

(0.059 – 0.069)

0.35 – 0.55

(0.014 – 0.022)

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)

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

(0.074)

REF

0.00 – 0.15

(0.00 – 0.006)

0.35 – 0.50

(0.014 – 0.020)

FIVE PLACES (NOTE 2)

0.95

(0.037)

REF

0.90 – 1.45

(0.035 – 0.057)

0.90 – 1.30

(0.035 – 0.051)

S5 SOT-23 0599

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.

7

LTC1694

WUUU

APPLICATIO S I FOR ATIO

Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up

1V/DIV

LTC1694

VCC = 5V 1µs/DIV
C

= 200pF

LD

= 100kHz 1694 TA03

f

SMBus

RELATED PARTS

R

PULL-UP

= 15.8k

1V/DIV

LTC1694

VCC = 3.3V 1µs/DIV

= 200pF

C

LD

= 100kHz 1694 TA04

f

SMBus

R

PULL-UP

= 10.5k

PART NUMBER DESCRIPTION COMMENTS

LTC1380/LTC1393 8-Channel/4-Channel Analog Multiplexer with SMBus Interface Low RON and Low Charge Injection
LTC1427-50 10-Bit Current DAC with SMBus Interface 50µA Full-Scale Current
LTC1623 Dual High Side Switch Controller with SMBus Interface 8 Selectable Addresses/16 Channel Capability
LTC1663 SMBus Interface 10-Bit Rail-to-Rail Micropower DAC DNL < 0.75LSB Max, 5-Lead SOT-23 Package
LTC1694-1 SMBus/I2C Accelerator Includes AC Pull-Up Current Only
LTC1695 SMBus/I2C Fan-Speed Controller in SOT-23 0.75Ω PMOS Linear Regulator with 180mA Output Current,

SMBus-Controlled 6-Bit DAC

LTC1710 SMBus Dual High Side Switch Two 0.4Ω, 300mA N-Channel Switches
LTC1759 Single Chip Smart Battery Charger Controller with SMBus Interface 94% Efficiency with Input Current Limiting, Up to 8A I

CHG

LT1786F SMBus-Controlled CCFL Switching Regulator 1.25A, 200kHz, Floating or Grounded Lamp Configurations

1694f LT/TP 0400 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1998

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com