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LTC4300A-1/LTC4300A-2 Hot Swappable 2-Wire Bus Buffers
FEATURES
s s
DESCRIPTIO
s s
s s s s s
s s
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 Lines from Output Compatible with I2CTM, I2C Fast Mode and SMBus Standards (Up to 400kHz Operation) Small MSOP 8-Pin Package Low ICC Chip Disable: <1A (LTC4300A-1) READY Open Drain Output (LTC4300A-1) 1V Precharge on all SDA and SCL Lines Supports Clock Stretching, Arbitration and Synchronization 5V to 3.3V Level Translation (LTC4300A-2) High Impedance SDA, SCL Pins for VCC = 0V
The LTC(R)4300A series hot swappable 2-wire bus buffers allow I/O card insertion into a live backplane without corruption of the data and clock busses. When the connection is made, the LTC4300A-1/LTC4300A-2 provide bidirectional buffering, keeping the backplane and card capacitances isolated. Rise-time accelerator circuitry* allows the use of weaker DC pull-up currents while still meeting rise-time requirements. During insertion, the SDA and SCL lines are precharged to 1V to minimize bus disturbances. The LTC4300A-1 incorporates a CMOS threshold digital ENABLE input pin, which forces the part into a low current mode when driven to ground and sets normal operation when driven to VCC. It also includes an open drain READY output pin, which indicates that the backplane and card sides are connected together. The LTC4300A-2 replaces the ENABLE pin with a dedicated supply voltage pin, VCC2, for the card side, providing level shifting between 3.3V and 5V systems. Both the backplane and card may be powered with supply voltages ranging from 2.7V to 5.5V, with no contraints on which supply voltage is higher. The LTC4300A-2 also replaces the READY pin with a digital CMOS input pin, ACC, which enables and disables the rise-time accelerator currents. The LTC4300A is available in a small 8-pin MSOP package.
APPLICATIO S
s s s s
Hot Board Insertion Servers Capacitance Buffer/Bus Extender Desktop Computer
, LTC and LT are registered trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N. V. *U.S. Patent No. 6,650,174
TYPICAL APPLICATIO
VCC 3.3V R1 10k SCLIN R2 10k 3 8
C1 0.01F
Input-Output Connection t PLH
R3 10k 2 R4 10k SCLOUT
OUTPUT SIDE 50pF INPUT SIDE 150pF
SDAIN
6
7
SDAOUT
1
LTC4300A-1 5 READY ENABLE GND 4
4300A-1/2 TA01
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4300A TA02
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LTC4300A-1/LTC4300A-2
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW ENABLE/VCC2* SCLOUT SCLIN GND 1 2 3 4 8 7 6 5 VCC SDAOUT SDAIN READY/ACC*
VCC to GND .................................................... - 0.3 to 7V VCC2 to GND (LTC4300A-2) ........................... - 0.3 to 7V SDAIN, SCLIN, SDAOUT, SCLOUT ................. - 0.3 to 7V READY, ENABLE (LTC4300A-1) .................... - 0.3 to 7V ACC (LTC4300A-2) ........................................ - 0.3 to 7V Operating Temperature Range LTC4300A-1C/LTC4300A-2C ................... 0C to 70C LTC4300A-1I/LTC4300A-2I ................ - 40C to 85C Storage Temperature Range ................. - 65C to 125C Lead Temperature (Soldering, 10 sec).................. 300C
LTC4300A-1CMS8 LTC4300A-1IMS8 LTC4300A-2CMS8 LTC4300A-2IMS8 MS8 PART MARKING LTABF LTABG LTACF LTACG
MS8 PACKAGE 8-LEAD PLASTIC MSOP *LTC4300A-2
TJMAX = 125C, JA = 200C/W
Consult LTC marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specfications are at TA = 25C. VCC = 2.7V to 5.5V, unless otherwise noted.
SYMBOL PARAMETER Power Supply VCC ICC ISD VCC2 IVCC1 IVCC2 Positive Supply Voltage Supply Current Supply Current in Shutdown Mode Card Side Supply Voltage VCC Supply Current VCC2 Supply Current VCC = 5.5V, VSDAIN = VSCLIN = 0V, LTC4300A-1 VENABLE = 0V, LTC4300A-1 LTC4300A-2 VSDAIN = VSCLIN = 0V, VCC1 = VCC2 = 5.5V, LTC4300A-2 VSDAOUT = VSCLOUT = 0V, VCC1 = VCC2 = 5.5V, LTC4300A-2 SDA, SCL Floating LTC4300A-1 LTC4300A-1, ENABLE Pin ENABLE from 0V to VCC, LTC4300A-1 LTC4300A-1 LTC4300A-1 LTC4300A-1 LTC4300A-1 LTC4300A-1 IPULLUP = 3mA, LTC4300A-1
q q q q q q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN 2.7
TYP
MAX 5.5
UNITS V mA A V mA mA
5.1 0.1 2.7 3 2.1
7 5.5 4.1 2.9
Start-Up Circuitry VPRE tIDLE VEN VDIS IEN tPHL tPLH IOFF VOL Precharge Voltage Bus Idle Time ENABLE Threshold Voltage Disable Threshold Voltage ENABLE Input Current ENABLE Delay, On-Off READY Delay, Off-On ENABLE Delay, Off-On READY Delay, On-Off READY OFF State Leakage Current READY Output Low Voltage 0.8 50 0.1 * VCC 1.0 95 0.5 * VCC 0.5 * VCC 0.1 10 10 95 10 0.1 0.4 1 1.2 150 0.9 * VCC V s V V A ns ns s ns A V
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LTC4300A-1/LTC4300A-2
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Rise-Time Accelerators IPULLUPAC Transient Boosted Pull-Up Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specfications are at TA = 25C. VCC = 2.7V to 5.5V, unless otherwise noted.
CONDITIONS Positive Transition on SDA,SCL, VCC = 2.7V, Slew Rate = 1.25V/s (Note 2), LTC4300A-2, ACC = 0.7 * VCC2, VCC2 = 2.7V LTC4300A-2 LTC4300A-2 LTC4300A-2 LTC4300A-2 10k to VCC on SDA, SCL, VCC = 3.3V (Note 3), LTC4300A-2, VCC2 = 3.3V, VIN = 0.2V Guaranteed by Design, Not Subject to Test Guaranteed by Design, Not Subject to Test SDA, SCL Pins, ISINK = 3mA, VCC = 2.7V, VCC2 = 2.7V, LTC4300A-2 SDA, SCL Pins = VCC = 5.5V, LTC4300A-2, VCC2 = 5.5V (Note 4) (Note 4) (Note 4) (Note 4) (Note 4) (Note 4) (Note 4) (Note 4) (Note 4) (Notes 4, 5) (Notes 4, 5) 0 1.3 0.6 0.6 0.6 300 100 1.3 0.6 20 + 0.1 * CB 20 + 0.1 * CB Note 4: Guaranteed by design, not subject to test. Note 5: CB = total capacitance of one bus line in pF. 300 300
q q
MIN 1
TYP 2
MAX
UNITS mA
VACCDIS VACCEN IVACC tPDOFF VOS fSCL, SDA CIN VOL ILEAK
Accelerator Disable Threshold Accelerator Enable Threshold ACC Input Current ACC Delay, On/Off Input-Output Offset Voltage Operating Frequency Digital Input Capacitance Output Low Voltage, Input = 0V Input Leakage Current
0.3 * VCC2
0.5 * VCC2 0.5 * VCC2 0.1 5 0.7 * VCC2 1
V V A ns 175 400 10 0.4 5 mV kHz pF V A
Input-Output Connection 0 0 0 100
Timing Characteristics fI2C tBUF thD,STA tsu,STA tsu,STO thD, DAT tsu, DAT tLOW tHIGH tf tr I2C Operating Frequency Bus Free Time Between Stop and Start Condition Hold Time After (Repeated) Start Condition Repeated Start Condition Setup Time Stop Condition Setup Time Data Hold Time Data Setup Time Clock Low Period Clock High Period Clock, Data Fall Time Clock, Data Rise Time 400 kHz s s s s ns ns s s ns ns
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired Note 2: IPULLUPAC varies with temperature and VCC voltage, as shown in the Typical Performance Characteristics section. Note 3: The connection circuitry always regulates its output to a higher voltage than its input. The magnitude of this offset voltage as a function of the pullup resistor and VCC voltage is shown in the Typical Performance Characteristics section.
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LTC4300A-1/LTC4300A-2 TYPICAL PERFOR A CE CHARACTERISTICS
ICC vs Temperature (LTC4300A-1)
5.3 5.2 5.1 5.0
t PHL (ns)
VCC = 5.5V 80
ICC (mA)
4.9 4.8 4.7 4.6 4.5 4.4 4.3 -40 25 TEMPERATURE (C) 85
4300-1/2 G01
VCC = 2.7V
IPULLUPAC vs Temperature
12 10 IPULLUPAC (mA) 8 6 4 2 VCC = 2.7V 0 -50 -25 0 25 50 TEMPERATURE (C) 75 100 0 VCC = 3V VCC = 5V
VOUT - VIN (mV)
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Input - Output tPHL vs Temperature (LTC4300A-1)
100 VCC = 2.7V
VCC = 3.3V 60
40
VCC = 5.5V
20
CIN = COUT = 100pF RPULLUPIN = RPULLUPOUT = 10k -25 0 25 50 TEMPERATURE (C) 75 100
0 -50
4300-1/2 G02
Connection Circuitry VOUT - VIN
300 250 200 150 VCC = 5V 100 VCC = 3.3V 50 TA = 25C VIN = 0V
0
10,000
20,000 30,000 RPULLUP ()
40,000
4300-1/2 G04
4300-1/2 G03
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LTC4300A-1/LTC4300A-2
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ENABLE/VCC2 (Pin 1): Chip Enable Pin/Card Supply Voltage. For the LTC4300A-1, this is a digital CMOS threshold input pin. Grounding this pin puts the part in a low current (<1A) mode. It also disables the rise-time accelerators, disables the bus precharge circuitry, drives READY low, isolates SDAIN from SDAOUT and isolates SCLIN from SCLOUT. Drive ENABLE all the way to VCC for normal operation. Connect ENABLE to VCC if this feature is not being used. For the LTC4300A-2, this is the supply voltage for the devices on the card I2C busses. Connect pull-up resistors from SDAOUT and SCLOUT to this pin. Place a bypass capacitor of at least 0.01F close to this pin for best results. SCLOUT (Pin 2): Serial Clock Output. Connect this pin to the SCL bus on the card. SCLIN (Pin 3): Serial Clock Input. Connect this pin to the SCL bus on the backplane. GND (Pin 4): Ground. Connect this pin to a ground plane for best results. READY/ACC (Pin 5): Connection Flag/Rise-Time Accelerator Control. For the LTC4300A-1, this is an open-drain NMOS output which pulls low when either ENABLE is low or the start-up sequence described in the Operation section has not been completed. READY goes high when ENABLE is high and start-up is complete. Connect a 10k resistor from this pin to VCC to provide the pull up. For the LTC4300A-2, this is a CMOS threshold digital input pin that enables and disables the rise-time accelerators on all four SDA and SCL pins. Drive ACC all the way to the VCC2 supply voltage to enable all four accelerators; drive ACC to ground to turn them off. SDAIN (Pin 6): Serial Data Input. Connect this pin to the SDA bus on the backplane. SDAOUT (Pin 7): Serial Data Output. Connect this pin to the SDA bus on the card. VCC (Pin 8): Main Input Power Supply from Backplane. This is the supply voltage for the devices on the backplane I2C busses. Connect pull-up resistors from SDAIN and SCLIN (and also from SDAOUT and SCLOUT for the LTC4300A-1) to this pin. Place a bypass capacitor of at least 0.01F close to this pin for best results.
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LTC4300A-1/LTC4300A-2
BLOCK DIAGRA
SDAIN 6
SCLIN 3
+ -
STOP BIT AND BUS IDLE 0.5A
+
0.55VCC/ 0.45VCC
-
95s DELAY, RISING ONLY
UVLO ENABLE 1
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(LTC4300A-1) 2-Wire Bus Buffer and Hot SwapTM Controller
2mA SLEW RATE DETECTOR BACKPLANE-TO-CARD CONNECTION CONNECT CONNECT ENABLE 100k RCH1 1V PRECHARGE 100k RCH2
2mA SLEW RATE DETECTOR 8 VCC 7 4 SDAOUT
CONNECT
100k RCH3
100k RCH4
2mA SLEW RATE DETECTOR BACKPLANE-TO-CARD CONNECTION CONNECT
2mA SLEW RATE DETECTOR
2 SCLOUT
CONNECT
+ -
VCC - 1V
+ -
20pF CONNECT RD QB S
5 READY
4 GND
0.5pF
4300A-1 BD
CONNECT
Hot Swap is a trademark of Linear Technology Corporation.
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LTC4300A-1/LTC4300A-2
BLOCK DIAGRA
VCC 8
ACC
SDAIN 6
ACC
SCLIN 3
+ -
STOP BIT AND BUS IDLE 0.5A
+
0.55VCC/ 0.45VCC
-
95s DELAY, RISING ONLY
UVLO
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(LTC4300A-2) 2-Wire Bus Buffer and Hot Swap Controller
2mA SLEW RATE DETECTOR BACKPLANE-TO-CARD CONNECTION CONNECT 100k RCH1 1V PRECHARGE 100k RCH2
2mA SLEW RATE DETECTOR 1 VCC2
7 4 SDAOUT
CONNECT 100k RCH3
CONNECT
100k RCH4
2mA SLEW RATE DETECTOR BACKPLANE-TO-CARD CONNECTION CONNECT
2mA SLEW RATE DETECTOR 5 ACC
2 SCLOUT
CONNECT
+ -
VCC2 - 1V
+ -
20pF CONNECT CONNECT RD QB S 4 GND 0.5pF
4300A-2 BD
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LTC4300A-1/LTC4300A-2
OPERATIO
Start-Up When the LTC4300A first receives power on its VCC pin, either during power-up or during live insertion, it starts in an undervoltage lockout (UVLO) state, ignoring any activity on the SDA and SCL pins until VCC rises above 2.5V. For the LTC4300A-2, the part also waits for VCC2 to rise above 2V. This ensures that the part does not try to function until it has enough voltage to do so. During this time, the 1V precharge circuitry is also active and forces 1V through 100k nominal resistors to the SDA and SCL pins. Because the I/O card is being plugged into a live backplane, the voltage on the backplane SDA and SCL busses may be anywhere between 0V and VCC. Precharging the SCL and SDA pins to 1V minimizes the worst-case voltage differential these pins will see at the moment of connection, therefore minimizing the amount of disturbance caused by the I/O card. Once the LTC4300A 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, and the rise time accelerators are enabled. 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 LTC4300A. 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 LTC4300A.
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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 to Output Offset Voltage When a logic low voltage, VLOW1, is driven on any of the LTC4300A's data or clock pins, the LTC4300A regulates the voltage on the other side of the chip (call it VLOW2) to a slightly higher voltage, as directed by the following equation: VLOW2 = VLOW1 + 75mV + (VCC/R) * 100 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) * 100 = 118mV. See the Typical Performance Characteristics section for curves showing the offset voltage as a function of VCC and R. Propagation Delays During a rising edge, the rise-time on each side is determined by the combined pull-up current of the LTC4300A boost current and the bus resistor and the equivalent capacitance on the line. If the pull-up currents are the same, a difference in rise-time occurs which is directly proportional to the difference in capacitance between the two sides. This effect is displayed in Figure 1 for VCC = 3.3V and a 10k pull-up resistor on each side (50pF on one side and 150pF on the other). Since the output side has less capacitance than the input, it rises faster and the effective tPLH is negative. There is a finite propagation delay, tPHL, through the connection circuitry for falling waveforms. Figure 2 shows the falling edge waveforms for the same VCC, pull-up resistors and equivalent capacitance conditions as used in Figure 1. An external NMOS device pulls down the voltage on the side with 150pF capacitance; the LTC4300A pulls down the voltage on the opposite side, with a delay of 55ns. This delay is always positive and is a function of
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LTC4300A-1/LTC4300A-2
OPERATIO
OUTPUT SIDE 50pF
Figure 1. Input-Output Connection t PLH
supply voltage, temperature and the pull-up resistors and equivalent bus capacitances on both sides of the bus. The Typical Performance Characteristics section shows tPHL as a function of temperature and voltage for 10k pull-up resistors and 100pF equivalent capacitance on both sides of the part. By comparison with Figure 2, the VCC = 3.3V curve shows that increasing the capacitance from 50pF to 100pF results in a tPHL increase from 55ns to 75ns. Larger output capacitances translate to longer delays (up to 150ns). Users must quantify the difference in propagation times for a rising edge versus a falling edge in their systems and adjust setup and hold times accordingly. Rise-Time Accelerators Once connection has been established, rise-time accelerator circuits on all four SDA and SCL pins are activated. These allow the user to choose weaker DC pull-up currents on the bus, reducing power consumption while still meeting system rise-time requirements. During positive bus transitions, the LTC4300A switches in 2mA (typical) of current to quickly slew the SDA and SCL lines once their DC voltages exceed 0.6V. Using a general rule of 20pF of capacitance for every device on the bus (10pF for the device and 10pF for interconnect), choose a pull-up current so that the bus will rise on its own at a rate of at least 1.25V/s to guarantee activation of the accelerators. For example, assume an SMBus system with VCC = 3V, a 10k pull-up resistor and equivalent bus capacitance of 200pF. The rise-time of an SMBus system is calculated from (VIL(MAX) - 0.15V) to (VIH(MIN) + 0.15V), or 0.65V to 2.25V. It takes an RC circuit 0.92 time constants to traverse this voltage for a 3V supply; in this case, 0.92 * (10k * 200pF) = 1.84s. Thus, the system exceeds the maximum allowed rise-time of 1s by 84%. However,
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INPUT SIDE 150pF INPUT SIDE 150pF OUTPUT SIDE 50pF
Figure 2. Input-Output Connection t PHL
using the rise-time accelerators, which are activated at a DC threshold of below 0.65V, the worst-case rise-time is: (2.25V - 0.65V) * 200pF/1mA = 320ns, which meets the 1s rise-time requirement. READY Digital Output (LTC4300A-1) This pin provides a digital flag which is low when either ENABLE is low or the start-up sequence described earlier in this section has not been completed. READY goes high when ENABLE is high 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. This feature is available for the LTC4300A-1 only. ENABLE Low Current Disable (LTC4300A-1) Grounding the ENABLE pin disconnects the backplane side from the card side, disables the rise-time accelerators, drives READY low, disables the bus precharge circuitry and puts the part in a near-zero current state. When the pin voltage is driven all the way to VCC, 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. This feature is available for the LTC4300A-1 only. ACC Boost Current Enable (LTC4300A-2) Users having lightly loaded systems may wish to disable the rise-time accelerators. Driving this pin to ground turns off the rise-time accelerators on all four SDA and SCL pins. Driving this pin to the VCC2 voltage enables normal operation of the rise-time accelerators, as described in the RiseTime Accelerators section above. This feature is available for the LTC4300A-2 only.
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LTC4300A-1/LTC4300A-2
APPLICATIO S I FOR ATIO
Resistor Pull-Up Value Selection
The system pull-up resistors must be strong enough to provide a positive slew rate of 1.25V/s on the SDA and SCL pins, in order to activate the boost pull-up currents during rising edges. Choose maximum resistor value R using the formula: R (VCC(MIN) - 0.6) (800,000) / C where R is the pull-up resistor value in ohms, VCC(MIN) is the minimum VCC voltage and C is the equivalent bus capacitance in picofarads (pF).
BACKPLANE CONNECTOR
BACKPLANE VCC R1 10k R2 10k
STAGGERED CONNECTOR
BD_SEL SDA SCL
STAGGERED CONNECTOR
STAGGERED CONNECTOR
Figure 3. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4300A-1 in a CompactPCI System
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In addition, regardless of the bus capacitance, always choose R 16k for VCC = 5.5V maximum, R 24k for VCC = 3.6V maximum. The start-up circuitry requires logic high voltages on SDAOUT and SCLOUT to connect the backplane to the card, and these pull-up values are needed to overcome the precharge voltage. Live Insertion and Capacitance Buffering Application Figures 3 through 6 illustrate the usage of the LTC4300A in applications that take advantage of both its hot swap controlling and capacitance buffering features. In all of
POWER SUPPLY HOT SWAP I/O PERIPHERAL CARD 1 R3 10k C1 0.01F R4 10k R5 10k R6 10k CARD_SDA CARD_SCL CARD ENABLE/DISABLE ENABLE SDAIN SCLIN VCC U1 LTC4300A-1 GND SDAOUT SCLOUT READY POWER SUPPLY HOT SWAP I/O PERIPHERAL CARD 2 R7 10k C3 0.01F R8 10k R9 10k R10 10k CARD2_SDA CARD2_SCL CARD ENABLE/DISABLE ENABLE SDAIN SCLIN VCC U2 LTC4300A-1 GND SDAOUT SCLOUT READY POWER SUPPLY HOT SWAP I/O PERIPHERAL CARD N R11 10k C5 0.01F R12 10k R13 10k R14 10k CARDN_SDA CARDN_SCL CARD ENABLE/DISABLE VCC U3 LTC4300A-1 GND
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SDAOUT SCLOUT READY
ENABLE SDAIN SCLIN
4300A-1/2 F03
LTC4300A-1/LTC4300A-2
APPLICATIO S I FOR ATIO
these applications, note that if the I/O cards were plugged directly into the backplane, all of the backplane and card capacitances would add directly together, making rise- and fall-time requirements difficult to meet. Placing a LTC4300A on the edge of each card, however, isolates the card capacitance from the backplane. For a given I/O card, the LTC4300A drives the capacitance of everything on the card and the backplane must drive only the capacitance of the LTC4300A, which is less than 10pF. Figure 3 shows the LTC4300A-1 in a CompactPCI configuration. Connect VCC and ENABLE to the output of one of the CompactPCI power supply Hot Swap circuits. Use a pull-up resistor to ENABLE for a card side enable/disable.
BACKPLANE VCC2 BD_SEL VCC SDA SCL R1 10k R2 10k BACKPLANE CONNECTOR
TM
STAGGERED CONNECTOR
STAGGERED CONNECTOR
STAGGERED CONNECTOR
Figure 4. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4300A-2 in a CompactPCI System
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VCC is monitored by a filtered UVLO circuit. With the V CC voltage powering up after all other pins have established connection, the UVLO circuit ensures that the backplane and card data and clock busses are not connected until the transients associated with live insertion have settled. Owing to their small capacitance, the SDAIN and SCLIN pins cause minimal disturbance on the backplane busses when they make contact with the connector. Figure 4 shows the LTC4300A-2 in a CompactPCI configuration. The LTC4300A-2 receives its VCC voltage from one of the long "early power" pins. Because this power is not switched, add a 5 to 10 resistor between the VCC pins
CompactPCI is a trademark of the PCI Industrial Computer Manufacturers Group.
POWER SUPPLY HOT SWAP 5.1 VCC SDAIN SCLIN C2 0.01F I/O PERIPHERAL CARD 1 C1 0.01F VCC2 U1 LTC4300A-2 GND SDAOUT SCLOUT ACC R4 10k R5 10k R6 10k CARD_SDA CARD_SCL POWER SUPPLY HOT SWAP 5.1 VCC SDAIN SCLIN C4 0.01F I/O PERIPHERAL CARD 2 C3 0.01F VCC2 U2 LTC4300A-2 GND SDAOUT SCLOUT ACC R8 10k R9 10k R10 10k CARD2_SDA CARD2_SCL POWER SUPPLY HOT SWAP 5.1 VCC SDAIN SCLIN C6 0.01F I/O PERIPHERAL CARD N C5 0.01F VCC2 U3 LTC4300A-2 GND SDAOUT SCLOUT ACC R12 10k R13 10k R14 10k CARDN_SDA CARDN_SCL
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4300A-1/2 F04
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LTC4300A-1/LTC4300A-2
APPLICATIO S I FOR ATIO
of the connector and the LTC4300A-2, as shown in the figure. In addition, make sure that the VCC bypassing on the backplane is large compared to the 0.01F bypass capacitor on the card. Establishing early power VCC ensures that the 1V precharge voltage is present at the SDAIN and SCLIN pins before they make contact. Connect VCC2 to the output of one of the CompactPCI power supply Hot Swap circuits. VCC2 is monitored by a filtered UVLO circuit. With the VCC2 voltage powering up after all other pins have established connection, the UVLO circuit ensures that the backplane and card data and clock busses are not connected until the transients associated with live insertion have settled. Figure 5 shows the LTC4300A-1 in a PCI application, where all of the pins have the same length. In this case, connect an RC series circuit on the I/O card between VCC and ENABLE. An RC product of 10ms provides a filter to prevent the LTC4300A-1 from becoming activated until the transients associated with live insertion have settled.
BACKPLANE CONNECTOR R3 100k ENABLE SDA SCL C2 0.1F SDAIN SCLIN VCC U1 LTC4300A-1 GND
BACKPLANE VCC R1 10k R2 10k
Figure 5. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4300A-1 in a PCI System
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Figure 6 shows the LTC4300A-2 in an application where the user has a custom connector with pins of three different lengths available. Making VCC2 the shortest pin ensures that all other pins are firmly connected before VCC2 receives any voltage. A filtered UVLO circuit on VCC2 ensures that the VCC2 pin is firmly connected before the LTC4300A-2 connects the backplane to the card. Repeater/Bus Extender Application Users who wish to connect two 2-wire systems separated by a distance can do so by connecting two LTC4300A-1s back-to-back, as shown in Figure 7. The I2C specification allows for 400pF maximum bus capacitance, severely limiting the length of the bus. The SMBus specification places no restriction on bus capacitance, but the limited impedances of devices connected to the bus require systems to remain small if rise- and fall-time specifications are to be met. The strong pull-up and pulldown impedances of the LTC4300A-1 are capable of
I/O PERIPHERAL CARD 1 C1 0.01F SDAOUT SCLOUT READY R4 10k R5 10k R6 10k CARD_SDA CARD_SCL I/O PERIPHERAL CARD 2 R7 100k ENABLE SDAIN SCLIN C4 0.1F VCC U2 LTC4300A-1 GND C3 0.01F SDAOUT SCLOUT READY R8 10k R9 10k R10 10k CARD2_SDA CARD2_SCL
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4300A-1/2 F05
sn4300a12 4300a12fs
LTC4300A-1/LTC4300A-2
APPLICATIO S I FOR ATIO
BACKPLANE VCC2 R1 10k VCC SDA SCL R2 10k BACKPLANE CONNECTOR STAGGERED CONNECTOR
STAGGERED CONNECTOR
Figure 6. Inserting Multiple I/O Cards into a Live Backplane Using the LTC4300A-2 with a Custom Connector
2-WIRE SYSTEM 1 VCC = 5V C1 0.01F R1 10k R4 10k R5 10k SDAOUT SCLOUT READY GND LONG DISTANCE BUS R2 R3 5.1k 5.1k R6 10k
LTC4300A-1 VCC ENABLE
SDA1 SCL1 TO OTHER SYSTEM 1 DEVICES
SDAIN SCLIN
Figure 7. Repeater/Bus Extender Application
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I/O PERIPHERAL CARD 1 C1 0.01F VCC SDAIN SCLIN C2 0.01F VCC2 U1 LTC4300A-2 GND SDAOUT SCLOUT ACC R4 10k R5 10k R6 10k CARD_SDA CARD_SCL I/O PERIPHERAL CARD 2 C3 0.01F VCC SDAIN SCLIN C4 0.01F VCC2 U2 LTC4300A-2 GND SDAOUT SCLOUT ACC R8 10k R9 10k R10 10k CARD2_SDA CARD2_SCL
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4300A-1/2 F06
2-WIRE SYSTEM 2 VCC C2 0.01F R7 10k ENABLE SDAIN SCLIN GND SDA1 SCL1 TO OTHER SYSTEM 2 DEVICES
4300A-1/2 F07
LTC4300A-1 VCC SDAOUT SCLOUT READY
R8 10k
sn4300a12 4300a12fs
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LTC4300A-1/LTC4300A-2
APPLICATIO S I FOR ATIO
meeting rise- and fall-time specifications for one nanofarad of capacitance, thus allowing much more interconnect distance. In this situation, the differential ground voltage between the two systems may limit the allowed distance, because a valid logic low voltage with respect to the ground at one end of the system may violate the allowed VOL specification with respect to the ground at the other end. In addition, the connection circuitry offset voltages of the back-to-back LTC4300A-1s add together, directly contributing to the same problem. Systems with Disparate Supply Voltages (LTC4300A-1) 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 well modelled by a series resistor in the VCC line, as shown in Figure 8. For proper operation of the LTC4300A-1, make sure that VCC(BUS) VCC(LTC4300A) - 0.5V.
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5V to 3.3V Level Translator and Power Supply Redundancy (LTC4300A-2) Systems requiring different supply voltages for the backplane side and the card side can use the LTC4300A-2, as shown in Figure 9. The pull-up resistors on the card side connect from SDAOUT to SCLOUT to VCC2, and those on the backplane side connect from SDAIN and SCLIN to VCC. The LTC4300A-2 functions for voltages ranging from 2.7V to 5.5V on both VCC and VCC2. There is no constraint on the voltage magnitudes of VCC and VCC2 with respect to each other. This application also provides power supply redundancy. If the VCC2 voltage falls below its UVLO threshold, the LTC4300A-2 disconnects the backplane from the card, so that the backplane can continue to function. If the VCC voltage falls below its UVLO threshold and the VCC2 voltage remains active, ground the ACC pin to ensure proper operation.
sn4300a12 4300a12fs
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LTC4300A-1/LTC4300A-2
PACKAGE DESCRIPTION
MS8 Package 8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
5.23 (.206) MIN
0.42 0.04 (.0165 .0015) TYP
RECOMMENDED SOLDER PAD LAYOUT DETAIL "A" 0 - 6 TYP 4.90 0.15 (1.93 .006) 3.00 0.102 (.118 .004) NOTE 4
0.254 (.010) GAUGE PLANE
0.18 (.077) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 0.13 0.076 (.005 .003)
MSOP (MS8) 0802
NOTE: 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
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.
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0.889 0.127 (.035 .005)
3.2 - 3.45 (.126 - .136)
0.65 (.0256) BSC
3.00 0.102 (.118 .004) (NOTE 3)
8
7 65
0.52 (.206) REF
0.53 0.015 (.021 .006) DETAIL "A"
1 1.10 (.043) MAX
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4 0.86 (.034) REF
0.65 (.0256) BSC
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LTC4300A-1/LTC4300A-2
TYPICAL APPLICATIO S
RDROP VCC (BUS) R1 10k R2 10k C2 0.01F ENABLE SDA SCL SDAIN SCLIN VCC U1 LTC4300A-1 GND SDAOUT SCLOUT READY
4300-1/2 F08
VCC 5V R1 10k SDA SCL R4 10k
RELATED PARTS
PART NUMBER LTC1380/LTC1393 LTC1427-50 LTC1623 LTC1663 LTC1694/LTC1694-1 LT1786F LTC1695 LTC1840 DESCRIPTION Single-Ended 8-Channel/Differential 4-Channel Analog Mux with SMBus Interface Micropower, 10-Bit Current Output DAC with SMBus Interface Dual High Side Switch Controller with SMBus Interface SMBus Interface 10-Bit Rail-to-Rail Micropower DAC SMBus Accelerator SMBus Controlled CCFL Switching Regulator SMBus/I2C Fan Speed Controller in ThinSOTTM Dual I2C Fan Speed Controller COMMENTS Low RON: 35 Single-Ended/70 Differential, Expandable to 32 Single or 16 Differential Channels Precision 50A 2.5% Tolerance Over Temperature, 4 Selectable SMBus Addresses, DAC Powers up at Zero or Midscale 8 Selectable Addresses/16-Channel Capability DNL < 0.75LSB Max, 5-Lead SOT-23 Package Improved SMBus/I2C Rise-Time, Ensures Data Integrity with Multiple SMBus/I2C Devices 1.25A, 200kHz, Floating or Grounded Lamp Configurations 0.75 PMOS 180mA Regulator, 6-Bit DAC Two 100A 8-Bit DACs, Two Tach Inputs, Four GPI0
ThinSOT is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
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VCC (LTC4300A) R3 10k R4 10k R5 10k SDA2 SCL2
Figure 8. System with Disparate VCC Voltages
C2 0.01F SDAIN SCLIN VCC VCC2
C1 0.01F SDAOUT SCLOUT ACC
CARD_VCC, 3.3V R3 10k R2 10k CARD_SDA CARD_SCL
4300-1/2 F09
U1 LTC4300A-2 GND
Figure 9. 5V to 3.3V Level Translator
sn4300a12 4300a12fs LT/TP 0203 2K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2001

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