Datasheet

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LTC4308

4308f

Low Voltage, Level Shifting

Hot Swappable 2-Wire Bus

Buffer with Stuck Bus Recovery

The LTC

4308 hot swappable, 2-wire bus buffer allows

I/O card insertion into a live backplane without corrup-

tion of the data and clock busses. The LTC4308 provides

bidirectional buffering, keeping the backplane and card

capacitances isolated. Negative offset from output to

input allows communication between output bus devices

with high V

and devices on the low voltage input side,

where bus supplies can be as low as 0.9V. If SDAOUT or

SCLOUT are low for 30ms, the LTC4308 will automati-

cally break the Input-Output connection. At this time the

LTC4308 automatically generates up to 16 clock pulses

on SCLOUT in an attempt to free the bus. A connection

will resume if the stuck bus is cleared.

During insertion, the SDAOUT and SCLOUT lines are pre-

charged to 1V to minimize bus disturbances. When driven

high, the ENABLE input allows the LTC4308 to connect after

a stop bit or bus idle condition. Driving ENABLE low breaks

the connection between SDAIN and SDAOUT, SCLIN and

SCLOUT. READY is an open-drain output which indicates

that the backplane and card sides are connected.

Live Board Insertion

Servers

Capacitance Buffer/Bus Extender

RAID Systems

ATCA

Optimized for Low Voltage Systems Down to 0.9V

Bidirectional Buffer with Stuck Bus Recovery

–200mV Offset In-Out/+300mV Offset Out-In

30ms Stuck Bus Timeout

Compatible with Non-Compliant V

C Devices

Prevents SDA and SCL Corruption During Live

Board Insertion and Removal from Backplane

±6kV Human Body Model (HBM) ESD Protection

Isolates Input SDA and SCL Lines from Output

Compatible with I

C™, I

C Fast Mode and SMBus

READY Open-Drain Output

1V Precharge on SDAOUT and SCLOUT Lines

Small 8-Lead (3mm × 3mm × 0.75mm) DFN and

8-Lead MSOP Packages

1.2V to 5V Level Shifting

The LTC4308 in a 1.2V

Microcontroller Application

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Hot Swap

is a trademark of Linear Technology Corporation. All other trademarks are the property of their

respective owners. Protected by U.S. Patents including 7032051, 6650174, 6356140.

1.2V

2.7k

LTC4308

SCLIN

SDAIN

SCLOUT

SDAOUT

CARD_SCL

READY

CARD_SDA

READY

GND

ENABLE

2.7k 2.7k

10k

4308 TA01a

2.7k

MICRO-

CONTROLLER

0.01μF

1μs/DIV

2V/DIV

CH1

0.5V/DIV

CH2

4308 TA01b

SDAOUT

SDAIN

Summary of content (16 pages)

PAGE 1
LTC4308 Low Voltage, Level Shifting Hot Swappable 2-Wire Bus Buffer with Stuck Bus Recovery DESCRIPTION FEATURES n n n n n n n n n n n n Optimized for Low Voltage Systems Down to 0.
PAGE 2
LTC4308 ABSOLUTE MAXIMUM RATINGS (Notes 1, 7) VCC to GND ................................................. – 0.3V to 6V SDAIN, SCLIN, SDAOUT, SCLOUT, READY, ENABLE .......................................... –0.3V to 6V Maximum Sink Current (SDAIN, SCLIN, SDAOUT, SCLOUT, READY) .............................................. 50mA Operating Temperature Range LTC4308C ................................................ 0°C to 70°C LTC4308I..............................................
PAGE 3
LTC4308 ELECTRICAL CHARACTERISTICS The l 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 tIDLE Bus Idle Time VTHR_EN ENABLE Threshold Voltage CONDITIONS ENABLE Rising Edge MIN TYP MAX UNITS l 55 95 175 μs l 0.45 0.6 0.
PAGE 4
LTC4308 ELECTRICAL CHARACTERISTICS The l 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 CONDITIONS MIN TYP MAX 25 30 35 400 600 UNITS Bus Stuck Low Timeout tTIMEOUT Bus Stuck Low Timer l SDAOUT = SCLOUT = 0V ms Timing Characteristics fI2C,MAX I2C Maximum Operating Frequency tBUF Bus Free Time Between Stop and Start Condition (Note 3) 1.
PAGE 5
LTC4308 TYPICAL PERFORMANCE CHARACTERISTICS ICC Enabled Current vs Temperature ISD Disabled Current vs Temperature 8.0 1000 7.5 950 VCC = 5.5V 7.0 6.5 ISD DISABLE CURRENT (μA) ICC ENABLED CURRENT (mA) TA = 25°C, VCC = 3.3V, unless otherwise indicated. VCC = 3.3V 6.0 VCC = 2.3V 5.5 5.0 4.5 900 850 800 750 700 650 4.
PAGE 6
LTC4308 PIN FUNCTIONS ENABLE (Pin 1): Connection Enable Input. This 0.6V nominal threshold input pin enables or disables the LTC4308. For normal operation, pull or connect ENABLE high. Driving ENABLE below the 0.45V threshold isolates SDAIN from SDAOUT, SCLIN from SCLOUT, asserts READY low, and prohibits automatic clock and stop bit generation during a fault condition. A rising edge on ENABLE after a fault has occurred forces a connection between SDAIN, SDAOUT and SCLIN, SCLOUT. Connect to VCC if unused.
PAGE 7
LTC4308 BLOCK DIAGRAM Low Voltage Level Shifting 2-Wire Bus Buffer with Stuck Bus Recovery 8mA CONNECT 6 VCC 8 IBOOSTSDA SDAIN SDAOUT 7 SLEW RATE DETECTOR 100k CONNECT PRECHARGE PC_CONNECT CONNECT 3 100k 8mA IBOOSTSCL SCLIN SCLOUT 2 SLEW RATE DETECTOR + CONNECT – 1.65V/1.6V 1.35V/1.3V 30ms TIMER + + 0.6V – IBOOSTSCL IBOOSTSDA + – 1.65V/1.6V 1.35V/1.3V LOGIC 0.6V – READY PC_CONNECT 1 ENABLE CONNECT 5 + 0.
PAGE 8
LTC4308 OPERATION Start-Up When the LTC4308 ﬁrst receives power on its VCC pin, either during power-up or live insertion, it starts in an under voltage lockout (UVLO) state, ignoring any activity on the SDA or SCL pins until VCC rises above 2V (typical). This ensures the LTC4308 does not try to function until enough supply voltage is present. During this time, the 1V precharge circuitry is actively forcing 1V through 100k nominal resistors to the SDAOUT and SCLOUT pins.
PAGE 9
LTC4308 OPERATION COUT = 50pF VPULLUP(OUT) = VCC = 3.3V 1V/DIV 1V/DIV COUT = 50pF VPULLUP(OUT) = VCC = 3.3V CIN = 150pF VPULLUP(IN) = 1.8V CIN = 150pF VPULLUP(IN) = 1.8V 200ns/DIV 200ns/DIV 4308 F02 Figure 2. Input-Output Rising Edge Waveforms Propagation Delays During a rising edge, the rise time on each side is inﬂuenced by rise time acceleration, bus pull-up resistor, and the equivalent capacitance on the line.
PAGE 10
LTC4308 OPERATION When powering up into a bus stuck low condition, the connection circuitry connecting the SDA and SCL pins are not activated. 30ms after UVLO, automatic clocking and stop bit generation takes place as described above. READY Digital Output This pin provides a digital ﬂag which is low when either ENABLE is low, the start-up sequence described earlier in this section has not been completed, or the LTC4308 has disconnected the input and output busses due to a bus stuck low condition.
PAGE 11
LTC4308 APPLICATIONS INFORMATION Resistor Pull-Up Value Selection To guarantee the SDAOUT and SCLOUT rise time accelerators are activated during a rising edge, the bus must rise on its own with a positive slew rate of at least 0.8V/μs. To achieve this, choose a maximum resistor value RPULLUP using the formula: (VBUS(MIN) − 0.8V)• 1250ns / V RPULLUP ≤ CBUS Where RPULLUP is the pull-up resistor value in kΩ, VBUS(MIN) is the minimum bus pull-up supply voltage and CBUS is the equivalent bus capacitance in pF.
PAGE 12
LTC4308 APPLICATIONS INFORMATION Systems with Supply Voltage Droop LTC4308 and LTC4301L Feature Comparison In large 2-wire systems, the VCC voltages seen by devices at various points in the system can differ by a few hundred millivolts or more. This situation is modeled by a series resistor in the VCC line, as shown in Figure 6. For proper operation, make sure that the VCC(LTC4308) is ≥ 2.3V.
PAGE 13
LTC4308 APPLICATIONS INFORMATION BACKPLANE CONNECTOR MIXED VOLTAGE BACKPLANE CARD CONNECTORS LOW VOLTAGE PERIPHERAL I/O CARD 1 3.3V 1V 1V R1 10k R2 10k C1 0.01μF R3 10k C2 0.01μF VCC SDAOUT SCLOUT LTC4308 READY ENABLE GND SDA SCL READY ENA1 R6 10k R4 2.7k R5 2.7k SDAIN SCLIN CARD1_SDA CARD1_SCL • • • LOW VOLTAGE PERIPHERAL I/O CARD N 1V C3 0.01μF C4 0.01μF R7 2.7k R8 2.7k VCC ENAn R9 10k SDAOUT SCLOUT LTC4308 READY ENABLE GND SDAIN SCLIN CARDn_SDA CARDn_SCL 4308 F03 Figure 4.
PAGE 14
LTC4308 TYPICAL APPLICATIONS VCC(LTC4308) V(BUS) RDROOP VCC C1 0.01μF R1 10k R2 10k R3 10k SDA1 SCL1 R4 10k VCC LTC4308 ENABLE SDAIN SDAOUT SCLIN SCLOUT R5 10k SDA2 SCL2 READY READY GND 4308 TA02 Figure 6. System with Voltage Droop 1.2V 5V 0.01μF 0.01μF 1.8k 1.8k VCC LTC4308 10k 10k ENABLE 200Ω* TEMPERATURE SENSOR SCLOUT SCLIN SDAOUT SDAIN SCL 200Ω* SDA 5V 10k READY GND *200Ω ARE ADDITIONAL ESD PROTECTION RESISTORS READY 4308 TA03 Figure 7.
PAGE 15
LTC4308 PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) R = 0.115 TYP 5 0.38 ± 0.10 8 0.675 ±0.05 3.5 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 1.65 ± 0.10 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) 4 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.00 – 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1 (DD8) DFN 1203 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1.
PAGE 16
LTC4308 TYPICAL APPLICATION The LTC4308 in a Level Shifting Application. 2.5V 1.8V 0.01μF 0.01μF 2.7k 2.7k 2.7k VCC 2.7k LTC4308 MICROCONTROLLER SCLIN SCLOUT SDAIN SDAOUT SCL SDA 3.