Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsInterface ICsInterface IC - accelerators I²C 100 kHz TSOT 23 5

LTC1694

1694fa

SMBus/I

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

) 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

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

GND

0.1µF

SMBus1

SMBus2

SCL

SDA

DEVICE 1

CLK

OUT

SMBus

DATA

OUT

DEVICE N

1694 TA01

CLK

OUT

DATA

OUT

, LTC and LT are registered trademarks of Linear Technology Corporation.

ThinSOT is a trademark of Linear Technology Corporation.

C is a trademark of Philips Electronics N.V.

*U.S. Patent No. 6,650,174

= 5V 1µs/DIV

= 200pF

SMBus

= 100kHz 1694 TA02

Comparison of SMBus Waveforms for

the LTC1694 vs Resistor Pull-Up

LTC1694

PULL-UP

= 15.8k

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

1V/DIV

Summary of content (8 pages)

PAGE 1
LTC1694 SMBus/I2C Accelerator* U FEATURES ■ ■ ■ ■ ■ ■ 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.
PAGE 2
LTC1694 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) ................................................. 7V SMBus1, SMBus2 Inputs ............ – 0.3V to (VCC + 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 .................
PAGE 3
LTC1694 U W 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.
PAGE 4
LTC1694 W 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.
PAGE 5
LTC1694 U W U U 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.
PAGE 6
LTC1694 U W U U 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.
PAGE 7
LTC1694 U W U U APPLICATIO S I FOR ATIO ACK Data Setup Time a longer time is required for this SMBus slave device to pull SDA low before the rising edge of the ACK clock pulse. 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.
PAGE 8
LTC1694 U W U U 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.