Datasheet

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LTC4311

4311fa

4311 TA01b

LTC4311

1V/DIV

= 5V

= 200pF

= 100kHz

1μs/DIV

PULL-UP

= 15.8k

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Low Voltage I

C/SMBus

Accelerator

The LTC

4311 is a dual I

C active pull-up designed to

enhance data transmission speed and reliability for bus

loading conditions well beyond the 400pF I

C speciﬁ cation

limit. The LTC4311 operates at supply voltages from 1.6V

to 5.5V and is also compatible with SMBus.

The LTC4311 allows multiple device connections or a lon-

ger, more capacitive interconnect, without compromising

slew rates or bus performance, by using two slew limited

pull-up currents.

During positive bus transitions, the LTC4311 provides slew

limited pull-up currents to quickly slew the I

C or SMBus

lines to the bus pull-up voltage. During negative transitions

or steady DC levels, the currents are disabled 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. When disabled, the LTC4311

goes into low (<5μA) current shutdown.

The LTC4311 is available in the 2mm × 2mm × 0.75mm

DFN, and SC70 packages.

Comparison of I

C Waveforms for

the LTC4311 vs Resistor Pull-Up

■

Improves I

C Bus Rise Time Transition

■

Ensures Data Integrity with Multiple Devices on the

C Bus.

■

Wide Supply Voltage Range: 1.6V to 5.5V

■

Improves Low State Noise Margin

■

Up to 400kHz Operation

■

Auto Detect Low Power Standby Mode

■

Low (<5μA) Supply Current Shutdown

■

Does Not Load Bus When Disabled or Powered Down

■

Strong Slew Limited Pull-up Current

■

±8kV Human Body Model ESD Ruggedness

■

2mm × 2mm DFN and SC70 Packages

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Battery Chargers

■

Industrial Controls

■

TV/Video Products

■

ACPI SMBus Interface

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

other trademarks are the property of their respective owners. Protected by U.S. Patents

includin

6356140 and 6650174.

LTC4311

ENABLE

GND

2.5V

0.01μF

BUS1

BUS2

DEVICE 1

CLK

OUT

2.5V

DATA

OUT

DEVICE N

4311 TA01a

CLK

10k

CLK

OUT

DATA

OUT

10k

SCL

SDA

Summary of content (12 pages)

PAGE 1
LTC4311 Low Voltage I2C/SMBus Accelerator FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Improves I2C Bus Rise Time Transition Ensures Data Integrity with Multiple Devices on the I2C Bus. Wide Supply Voltage Range: 1.6V to 5.
PAGE 2
LTC4311 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) VCC to GND .................................................... – 0.3 to 6V BUS1, BUS2, ENABLE Inputs ......................... – 0.3 to 6V Operating Temperature LTC4311C ................................................ 0°C to 70°C LTC4311I..............................................– 40°C to 85°C Storage Temperature Range (DFN) ........– 65°C to 125°C Storage Temperature Range (SC70).......– 65°C to 125°C Lead Temperature (Soldering 10, sec) SC70 .........
PAGE 3
LTC4311 ELECTRICAL CHARACTERISTICS • The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = 3.3V, unless otherwise noted. SYMBOL PARAMETER VCC Positive Supply Voltage ICC Supply Current CONDITIONS MIN ● TYP MAX 1.6 UNITS 5.5 V VCC = 5.5V, ENABLE = 5.5V, VBUS1 = VBUS2 = 0V ● 200 300 μA ICC_STANDBY Supply Current, Standby Mode VCC = 5.5V, ENABLE = 5.5V, VBUS1 = VBUS2 = 5.
PAGE 4
LTC4311 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, unless otherwise indicated) Boost Pull-Up Current vs Bus Capacitance Boost Pull-Up Current vs Temperature 60 RP = 4.7kΩ CBUS = 1nF 35 30 VCC = 5.5V 25 20 15 10 5 VCC = 3.3V VCC = 2.5V 40 30 VCC = 3.3V 20 VCC = 2.5V 10 VCC = 1.8V 60 40 20 TEMPERATURE (°C) 0 80 0 100 0 VCC = 1.8V VCC = 5.5V VCC = 2.5V 250 VCC = 3.3V VCC = 3.
PAGE 5
LTC4311 PIN FUNCTIONS BUS1: Active Pull-up for Bus. Connect to either clock line or data line for 2-wire bus. EXPOSED PAD (DFN Package Only): Exposed Pad may be left open or connected to device ground. BUS2: Active Pull-up for Bus. Connect to either clock line or data line for 2-wire bus. GND: Device Ground. Connect this pin to a ground plane for best results. ENABLE: Device Enable Input. This is a 1V nominal digital threshold input pin. For normal operation drive ENABLE to a voltage greater than 1.5V.
PAGE 6
LTC4311 OPERATION I2C and SMBus Overview The I2C communication protocol employs open-drain pull-down drivers with resistive or current source pullups. 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 resulting when bus capacitance is high.
PAGE 7
LTC4311 APPLICATIONS INFORMATION Selecting the values of RS and RP Low State Noise Margin The typical conﬁguration for the data bus for a 2-wire bus is shown in Figure 1. The parameters RP and RS should be chosen carefully. A description of the process for choosing the values of RP and RS follows. A low value of VOL, the low state logic level, is desired for good noise margin.
PAGE 8
LTC4311 APPLICATIONS INFORMATION For an I2C system with ﬁxed input levels, VILMAX = 1.5V and VIHMIN = 3V. For I2C systems with VCC related input levels, VILMAX = 0.3VCC and VIHMIN = 0.7VCC. CBUS is the total capacitance of the I2C line. SMBus Rise and Fall Time Rise time of a SMBus line is derived using equations 5, 6 and 7. tr = t 1 + t 2 (5) t1 is the time from when the bus crosses the lower slew rate measurement point, until the bus reaches VTHR and the accelerators ﬁre.
PAGE 9
LTC4311 APPLICATIONS INFORMATION This is the lowest resistor value that may be chosen and still meet VOL. Next calculate the largest value of RP that will satisfy SR, the minimum slew rate requirement. Using VOL = 0.4V and SR = 0.5V/μs calculate the value of RP with equation 2. 3.3V − 0.4V 600pF •0.5V / µs RP = 9.667k Given the following conditions and requirements for a low power SMBus system: VCC = 3.3V NOMINAL VOL = 0.
PAGE 10
LTC4311 APPLICATIONS INFORMATION t 2 = –13kΩ • 400pF • ⎧ 2.1V + 0.15V – 3.3V – 13kΩ • 2.5mA ⎫ In ⎨ ⎬ = 0.205µs 0.9V – 3.3V – 13kΩ • 2.5mA ⎩ ⎭ (20) tr = t1 + t 2 = 0.515µs + 0.205µs = 0.72µs (21) t f = 293Ω • 400pF • ⎧ 2.1V + 0.15V ⎫ • (13kΩ + 300Ω) – 300Ω ⎪ ⎪ 3.3V In ⎨ ⎬ 0.8V – 0.15V ⎪ • (13kΩ + 300Ω) – 300Ω ⎪ 3.3V ⎩ ⎭ = 0.156µs high) at the end of the last bit sent and the slave device pulling the SDA line low before the rising edge of the ACK clock pulse.
PAGE 11
LTC4311 PACKAGE DESCRIPTION DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 0.61 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.38 ± 0.05 4 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 ± 0.05 0.50 BSC 1.42 ±0.05 (2 SIDES) (DC6) DFN 1103 1 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.200 REF 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 12
LTC4311 TYPICAL APPLICATION Application Utilizing Low Current Shutdown VCC 2.5V VCC C1 0.01μF VCC 2.