LTC4301L Hot Swappable 2-Wire Bus Buffer with Low Voltage Level Translation DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®4301L hot swappable, 2-wire bus buffer allows I/O card insertion into a live backplane without corruption of the data and clock busses. In addition, the LTC4301L SDAIN and SCLIN pins are compatible with systems with pull-up voltages as low as 1V. Control circuitry prevents the backplane from being connected to the card until a stop bit or a bus idle is present. When the connection is made, the LTC4301L provides bidirectional buffering, keeping the backplane and card capacitances isolated. Level Translates 1V Signals to Standard 3.3V and 5V Logic Rails Allows Bus Pull-Up Voltages as Low as 1V on SDAIN and SCLIN Bidirectional Buffer* for SDA and SCL Lines Increases Fanout Prevents SDA and SCL Corruption During Live Board Insertion and Removal from Backplane Isolates Input SDA and SCL Line from Output 10kV Human Body Model ESD Protection Supports Clock Stretching, Arbitration and Synchronization High Impedance SDA, SCL Pins for VCC = 0V CS Gates Connection from Input to Output Compatible with I2CTM, I2C Fast Mode and SMBus Standards (Up to 400kHz Operation) Small 8-Pin MSOP and DFN (3mm × 3mm) Packages When driven low, the CS input pin allows the part to connect after a stop bit or bus idle occurs. Driving CS high breaks the connection between SCLIN and SCLOUT and between SDAIN and SDAOUT. A logic high on READY indicates that the backplane and card sides are connected together. The LTC4301L is offered in 8-pin DFN (3mm × 3mm) and MSOP packages. U APPLICATIO S ■ ■ ■ Hot Board Insertion Servers Capacitance Buffer/Bus Extender Desktop Computers U ■ , LTC and LT are registered trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V. *Patent Pending TYPICAL APPLICATIO Input-Output Connection 1.2V 3.3V 0.01µF 2k VCC SDA 2k 10k VCC SDAIN µP SDAOUT 10k SDA LTC4301L SCL SCLIN SCLOUT SCL INPUT SIDE 55pF OUTPUT SIDE 20pF 0.5V/DIV CS GND READY GND 4301l TA01a 1µs/DIV 4301 TA01b 4301lf 1 LTC4301L U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) VCC to GND ................................................. –0.3V to 7V SDAIN, SCLIN, SDAOUT, SCLOUT, CS ........ –0.3V to 7V READY ........................................................ –0.3V to 6V Operating Temperature Range LTC4301LC ............................................. 0°C to 70°C LTC4301LI .......................................... – 40°C to 85°C Storage Temperature Range MSOP ............................................... – 65°C to 150°C DFN .................................................. – 65°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C W U U PACKAGE/ORDER INFORMATION ORDER PART NUMBER TOP VIEW CS 1 8 VCC SCLOUT 2 7 SDAOUT 6 SDAIN 5 READY SCLIN 3 9 GND 4 DD8 PACKAGE 8-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 9) IS GND PCB CONNECTION OPTIONAL LTC4301LCDD8 LTC4301LIDD8 DD8 PART MARKING ORDER PART NUMBER TOP VIEW CS SCLOUT SCLIN GND LBHS 8 7 6 5 1 2 3 4 LTC4301LCMS8 LTC4301LIMS8 VCC SDAOUT SDAIN READY MS8 PART MARKING MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 200°C/W LTBHQ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 2.7V to 5.5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 5.5 V 4.5 300 6.2 mA µA Power Supply VCC Positive Supply Voltage ICC Supply Current ● 2.7 VCC = 5.5V, VSDAIN = VSCLIN = 0V VCC = 5.5V, CS = 5.5V ● SDAOUT, SCLOUT Floating ● 0.85 1.05 1.25 V ● 60 95 175 µs 0.4 V 2 V ±0.1 ±1 µA 0.6 1.8 0.75 2.0 V V Start-Up Circuitry VPRE Precharge Voltage tIDLE Bus Idle Time RDYVOL READY Output Low Voltage VTHRCS Connection Sense Threshold ICS CS Input Current CS from 0V to VCC VTHR SDAIN, SCLIN Logic Input Threshold Voltage SDAOUT, SCLOUT Logic Input Threshold Voltage Rising Edge Rising Edge VHYS SDAIN, SCLIN Logic Input Threshold Hysteresis SDAOUT, SCLOUT Logic Input Threshold Hysteresis (Note 3) (Note 3) tPLH IPULLUP = 3mA ● 0.8 0.45 1.55 1.4 85 50 mV mV CS Delay On-Off READY Delay Off-On 10 10 ns ns tPHL CS Delay Off-On READY Delay On-Off 95 10 µs ns IOFF Ready Off Leakage Current ±0.1 µA 4301lf 2 LTC4301L ELECTRICAL CHARACTERISTICS The ● indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 2.7V to 5.5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0 100 175 mV Input-Output Connection VOS Input-Output Offset Voltage 10k to VCC on SDA, SCL, VCC = 3.3V, SDA or SCL = 0.2V (Note 2) CIN Digital Input Capacitance SDAIN, SDAOUT, SCLIN, SCLOUT (Note 3) 10 pF ILEAK Input Leakage Current SDA, SCL Pins ±5 µA VOL Output Low Voltage, Input = 0V SDA, SCL Pins, ISINK = 3mA, VCC = 2.7V SDA, SCL Pins, ISINK = 1mA, VCC = 2.7V 0.4 0.2 V V ● ● 0 0 Timing Characteristics fI2C,MAX I2C Maximum Operating Frequency (Note 3) tBUF Bus Free Time Between Stop and Start Condition (Note 3) 1.3 µs tHD,STA Hold Time After (Repeated) Start Condition (Note 3) 100 ns tSU,STA Repeated Start Condition Set-Up Time (Note 3) 0 ns tSU,STO Stop Condition Set-Up Time (Note 3) 0 ns tHD,DATI Data Hold Time Input (Note 3) 0 ns tSU,DAT Data Set-Up Time (Note 3) 100 ns Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The connection circuitry always regulates its output to a higher voltage than its input. The magnitude of this offset voltage as a function of 400 600 kHz the pull-up resistor and VCC voltage is shown in the Typical Performance Characteristics section. Note 3: Determined by design, not tested in production. 4301lf 3 LTC4301L U W TYPICAL PERFOR A CE CHARACTERISTICS Input – Output High to Low Propagation Delay vs Temperature ICC vs Temperature 4.9 100 4.8 300 VCC = 5.5V 250 80 4.6 TIME (ns) VCC = 3.3V 4.3 VCC = 2.7V 4.2 4.1 60 40 20 4.0 3.9 –80 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 VOUT – VIN (mV) VCC = 3.3V 4.5 4.4 TA = 25°C VIN = 0V VCC = 2.7V 4.7 ICC (mA) Connection Circuitry VOUT – VIN 0 –50 VCC = 5.5V 200 150 VCC = 5V 100 VCC = 3.3V CIN = COUT = 100pF RPULLUPIN = RPULLUPOUT = 10k –25 0 25 50 TEMPERATURE (°C) 4301 G01 50 75 100 4301 G02 0 0 10,000 20,000 30,000 RPULLUP (Ω) 40,000 4301 G03 U U U PI FU CTIO S CS (Pin 1): The connection sense pin is a 1.4V threshold digital input pin. For normal operation CS is grounded. Driving CS above the 1.4V threshold isolates SDAIN from SDAOUT and SCLIN from SCLOUT and asserts READY low. READY (Pin 5): The READY pin is an open drain N-channel MOSFET output which pulls down when CS is high or when the start-up sequence described in the Operation section has not been completed. READY goes high when CS is low and a start-up is complete. SCLOUT (Pin 2): Serial Clock Output. Connect this pin to the SCL bus on the card. SDAIN (Pin 6): Serial Data Input. Connect this pin to the SDA bus on the backplane. SCLIN (Pin 3): Serial Clock Input. Connect this pin to SCL on the bus backplane. SDAOUT (Pin 7): Serial Data Output. Connect this pin to the SDA bus on the card. GND (Pin 4, 9): Ground. Connect this pin to a ground plane for best results. Exposed pad (DFN package) is ground. VCC (Pin 8): Main Input Supply. Place a bypass capacitor of at least 0.01µF close to VCC for best results. 4301lf 4 LTC4301L W BLOCK DIAGRA LTC4301L Supply Independent 2-Wire Bus Buffer PRECHARGE VCC 8 CONNECT PRECHARGE CONNECT 6 R1 200k SDAIN R2 200k SDAOUT 7 CONNECT 3 SCLOUT SCLIN LOGIC 2 PRECHARGE CONNECT 0.6V 1.8V 1 CONNECT CS 1.4V UVLO READY 5 95µs DELAY CONNECT GND 4 4301l BD 4301lf 5 LTC4301L U OPERATIO Start-Up Input-to-Output Offset Voltage When the LTC4301L first receives power on its VCC pin, either during power-up or live insertion, it starts in an undervoltage lockout (UVLO) state, ignoring any activity on the SDA or SCL pins until VCC rises above 2.5V. This is to ensure that the part does not try to function until it has enough voltage to do so. When a logic low voltage, VLOW1, is driven on any of the LTC4301L’s data or clock pins, the LTC4301L regulates the voltage on the other side of the device (call it VLOW2) at a slightly higher voltage, as directed by the following equation: During this time, the 1V precharge circuitry is active and forces 1V through 200k nominal resistors to the SDAOUT and SCLOUT pins. Precharging the SCLOUT and SDAOUT pins to 1V minimizes the worst-case voltage differential these pins will see at the moment of connection, therefore minimizing bus disturbances. where R is the bus pull-up resistance in ohms. For example, if a device is forcing SDAOUT to 10mV where VCC = 3.3V and the pull-up resistor R on SDAIN is 10k, then the voltage on SDAIN = 10mV + 75mV + (3.3/10000) • 70 = 108mV(typical). See the Typical Performance Characteristics section for curves showing the offset voltage as a function of VCC and R. Once the LTC4301L comes out of UVLO, it assumes that SDAIN and SCLIN have been inserted into a live system and that SDAOUT and SCLOUT are being powered up at the same time as itself. Therefore, it looks for either a stop bit or bus idle condition on the backplane side to indicate the completion of a data transaction. When either one occurs, the part also verifies that both the SDAOUT and SCLOUT voltages are high. When all of these conditions are met, the input-to-output connection circuitry is activated, joining the SDA and SCL busses on the I/O card with those on the backplane. VLOW2 = VLOW1 + 75mV + (VCC/R) • 70Ω (typical) Propagation Delays During a rising edge, the rise time on each side is determined by the bus pull-up resistor and the equivalent capacitance on the line. In Figure 1, VCC = 3.3V, SDAOUT and SCLOUT are pulled-up to 3.3V with 10k resistor (20pF on this side) and SDAIN and SCLIN are pulled-up to 1.2V with a 2k resistor (55pF on this side). Lower pull-up resistor values are used on the input side to allow the output side to be released sooner. Connection Circuitry Once the connection circuitry is activated, the functionality of the SDAIN and SDAOUT pins is identical. A low forced on either pin at any time results in both pin voltages being low. For proper operation, logic low input voltages should be no higher than 0.4V with respect to the ground pin voltage of the LTC4301L. SDAIN and SDAOUT enter a logic high state only when all devices on both SDAIN and SDAOUT release high. The same is true for SCLIN and SCLOUT. This important feature ensures that clock stretching, clock synchronization, arbitration and the acknowledge protocol always work, regardless of how the devices in the system are tied to the LTC4301L. Another key feature of the connection circuitry is that it provides bidirectional buffering, keeping the backplane and card capacitances isolated. Because of this isolation, the waveforms on the backplane busses look slightly different than the corresponding card bus waveforms as described here. INPUT SIDE 55pF OUTPUT SIDE 20pF 0.5V/DIV 1µs/DIV 4301 TA01b Figure 1. Input-Output Connection There is a finite high to low propagation delay through the connection circuitry for falling waveforms. Figure 2 shows the falling edge waveforms for the same pull-up resistors and equivalent capacitance conditions as used in Figure 1. An external N-channel MOSFET device pulls down the voltage on the side with 55pF capacitance; LTC4301L pulls down the voltage on the opposite side with a delay of 60ns. 4301lf 6 LTC4301L U OPERATIO This delay is always positive and is a function of supply voltage, temperature and the pull-up resistors and equivalent bus capacitances on both sides of the bus. The Typical Performance Characteristics section shows the high to low propagation delay as a function of temperature and voltage for 10k pull-up resistors pulled-up to VCC and 100pF equivalent capacitance on both sides of the part. Larger output capacitances translate to longer delays (up to 150ns). Users must quantify the difference in propaga- tion times for a rising edge versus a falling edge in their systems and adjust setup and hold times accordingly. Ready Digital Output This pin provides a digital flag which is low when either CS is high or the start-up sequence described earlier in this section has not been completed. READY goes high when CS is low and start-up is complete. The pin is driven by an open-drain pull-down capable of sinking 3mA while holding 0.4V on the pin. Connect a resistor of 10k to VCC to provide the pull-up. Connection Sense OUTPUT SIDE 20pF INPUT SIDE 55pF 0.5V/DIV 4301 F02 20ns/DIV Figure 2. Input-Output Connection High to Low Propagation Delay When the CS pin is driven above 1.4V with respect to the LTC4301L’s ground, the backplane side is disconnected from the card side and the READY pin is internally pulled low. When the pin voltage is low, the part waits for data transactions on both the backplane and card sides to be complete (as described in the Start-Up section) before reconnecting the two sides. At this time the internal pulldown on READY releases. U W U U APPLICATIO S I FOR ATIO Live Insertion and Capacitance Buffering Application Figure 3 illustrates applications of the LTC4301L with different bus pull-up and VCC voltages, demonstrating its ability to recognize and buffer bus data levels that are above or below its VCC supply. All of these applications take advantage of the LTC4301L’s Hot SwapTM controlling, capacitance buffering and precharge features. If the I/O cards were plugged directly into the backplane without the LTC4301L buffer, all of the backplane and card capacitances would add directly together, making rise- and falltime requirements difficult to meet. Placing an LTC4301L on the edge of each card, however, isolates the card capacitance from the backplane. For a given I/O card, the LTC4301L drives the capacitance of everything on the card and the backplane must drive only the capacitance of the LTC4301L, which is less than 10pF. In most applications the LTC4301L will be used with a staggered connector where VCC and GND will be long pins. SDA and SCL are medium length pins to ensure that the VCC and GND pins make contact first. This will allow the precharge circuitry to be activated on SDA and SCL before they make contact. CS is a short pin that is pulled up when not connected. This is to ensure that the connection between the backplane and the cards data and clock busses is not enabled until the transients associated with live insertion have settled. Figure 4 shows the LTC4301L in an application where all of the pins have the same length. In this case, an RC filter circuit on the I/O card with a product of 10ms provides a filter to prevent the LTC4301L from becoming activated until the transients associated with live insertion have settled. Connect the capacitor between VCC and CS, and the resistor from CS to GND. Hot Swap is a trademark of Linear Technology Corporation. 4301lf 7 LTC4301L U W U U APPLICATIO S I FOR ATIO STAGGERED CONNECTOR 5V 1.2V 2k 2k SDA SCL 0.01µF 10k 10k CS SDAIN SCLIN BACKPLANE CONNECTOR 10k VCC SDAOUT CARD_SDA LTC4301L SCLOUT CARD_SCL GND READY CARD STAGGERED CONNECTOR 3.3V 1.2V 2k 2k SDA SCL 0.01µF 10k 10k CS SDAIN SCLIN BACKPLANE CONNECTOR 10k VCC SDAOUT CARD_SDA LTC4301L SCLOUT CARD_SCL GND READY CARD 3V STAGGERED CONNECTOR 3.3V 1V 2k 2k SDA SCL 0.01µF 10k 10k CS SDAIN SCLIN 10k VCC SDAOUT CARD_SDA LTC4301L SCLOUT CARD_SCL GND READY 4301l F03 BACKPLANE CONNECTOR CARD Figure 3. Typical Supply Independent Applications 4301lf 8 LTC4301L U W U U APPLICATIO S I FOR ATIO 1.2V 3.3V 0.01µF 10k 2k LTC4301L STAGGERED CONNECTOR 2k 10k VCC BACK_SCL BACK_SDA SCLIN SCLOUT CARD_SCL SDAIN SDAOUT CARD_SDA 3.3V 10k FROM MICROPROCESSOR CS GND READY 4301l F05 BACKPLANE CONNECTOR CARD Figure 4. Inserting Multiple I/O Cards into a Live Backplane Using a Connector with All the Pins the Same Length 4301lf 9 LTC4301L U PACKAGE DESCRIPTIO 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) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD8) DFN 1203 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 ±0.05 0.00 – 0.05 4 0.25 ± 0.05 1 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON TOP AND BOTTOM OF PACKAGE 4301lf 10 LTC4301L U PACKAGE DESCRIPTIO MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.42 ± 0.038 (.0165 ± .0015) TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 1 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 0.65 (.0256) NOTE: BSC 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.127 ± 0.076 (.005 ± .003) MSOP (MS8) 0204 4301lf 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. 11 LTC4301L U TYPICAL APPLICATIO System with Active Connection Control 1.2V 3.3V 0.01µF 10k 10k VCC 2k LTC4301L STAGGERED CONNECTOR 2k BACK_SCL BACK_SDA SCLIN SCLOUT CARD_SCL SDAIN SDAOUT CARD_SDA 3.3V 10k FROM MICROPROCESSOR CS GND READY 4301l F05 BACKPLANE CONNECTOR CARD RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1380/LTC1393 Single-Ended 8-Channel/Differential 4-Channel Analog Mux with SMBus Interface Low RON: 35Ω Single-Ended/70Ω Differential, Expandable to 32 Single or 16 Differential Channels LTC1427-50 Micropower, 10-Bit Current Output DAC with SMBus Interface Precision 50µA ± 2.5% Tolerance Over Temperature, 4 Selectable SMBus Addresses, DAC Powers up at Zero or Midscale 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/LTC1694-1 SMBus Accelerator Improved SMBus/I2C Rise-Time, Ensures Data Integrity with Multiple SMBus/I2C Devices LT1786F SMBus Controlled CCFL Switching Regulator 1.25A, 200kHz, Floating or Grounded Lamp Configurations LTC1695 SMBus/I2C Fan Speed Controller in ThinSOTTM 0.75Ω PMOS 180mA Regulator, 6-Bit DAC LTC1840 Dual I2C Fan Speed Controller Two 100µA 8-Bit DACs, Two Tach Inputs, Four GPI0 LTC4300A-1/LTC4300A-2 Hot Swappable 2-Wire Bus Buffer Isolates Backplane and Card Capacitances LTC4301 Supply Independent Hot Swappable 2-Wire Bus Buffer Supply Independent LTC4302-1/LTC4302-2 Addressable 2-Wire Bus Buffer Address Expansion, GPIO, Software Controlled ThinSOT is a trademark of Linear Technology Corporation. 4301lf 12 Linear Technology Corporation LT/TP 0304 1K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003