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LTC1694-1 SMBus/I2C Accelerator
FEATURES
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DESCRIPTIO
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Improves SMBus/I2CTM Rise Time Transition Ensures Data Integrity with Multiple Devices on the SMBus/I2C Improves Low State Noise Margin Wide Supply Voltage Range: 2.7V to 6V Tiny 5-Pin SOT-23 Package Parallel Multiple LTC1694-1 Devices for Increased Drive
APPLICATIO S
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Notebook and Palmtop Computers Portable Instruments Battery Chargers Industrial Control Application TV/Video Products ACPI SMBus Interface
The LTC(R)1694-1 is a dual SMBus active pull-up designed to enhance data transmission speed and reliability under all specified SMBus loading conditions. The LTC1694-1 is also compatible with the Philips I2C Bus. The LTC1694-1 allows multiple device connections or a longer, more capacitive interconnect, without compromising slew rates or bus performance, by supplying a high pull-up current of 2.2mA to slew the SMBus or I2C lines during positive bus transitions During negative transitions or steady DC levels, the LTC1694-1 sources zero current. External resistors, one on each bus line, trigger the LTC1694-1 during positive bus transitions and set the pull-down current level. These resistors determine the slew rate during negative bus transitions and the logic low DC level. The LTC1694-1 is available in a 5-pin SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V.
TYPICAL APPLICATIO
VCC 5V C1 0.1F
1 VCC 2 GND SMBus2 SMBus1 LTC1694-1
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VCC 5V
Comparison of SMBus Waveforms for the LTC1694-1 vs Resistor Pull-Up
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RP1
RP2
SCL SMBus SDA
LTC1694-1 1V/DIV
CLK IN CLK OUT DEVICE 1
DATA IN DATA OUT
CLK IN CLK OUT DEVICE N
DATA IN DATA OUT
VCC = 5V CLD = 200pF fSMBus = 100kHz 1s/DIV
1694-1 TA02
1694-1 TA01
LTC1694-1: Patent Pending
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RPULL-UP = 15.8k
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LTC1694-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW VCC 1 GND 2 NC 3 4 SMBus2 5 SMBus1
Supply Voltage (VCC) ................................................. 7V SMBus1, SMBus2 Inputs ............ - 0.3V to (VCC + 0.3V) Operating Ambient Temperature Range ....... 0C to 70C Junction Temperature ........................................... 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec.)................. 300C
ORDER PART NUMBER LTC1694-1CS5 S5 PART MARKING LTHE
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 256C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VCC ICC IPULL-UP VTHRES SRTHRES tr fMAX PARAMETER Supply Voltage Range Supply Current Pull-Up Current Input Threshold Voltage Slew Rate Detector Threshold SMBus Rise Time Standard Mode I2C Bus Rise Time SMBus Maximum Operating Frequency
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.7V to 6V, unless otherwise noted.
CONDITIONS SMBus1 = SMBus2 = VCC Positive Transition on SMBus ( Figure 1) Slew Rate = 0.5V/s, SMBus > VTHRES Slew Rate = 0.5V/s (Figure 1) SMBus > VTHRES Bus Capacitance = 200pF (Note 2) Bus Capacitance = 400pF (Note 3) (Note 4)
q q q q q q q
MIN 2.7 15 1.0 0.4
TYP 45 2.2 0.65 0.2 0.32 0.30
MAX 6 80
UNITS V A mA
0.9 0.5 1.0 1.0 100
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The rise time of an SMBus line is calculated from (VIL(MAX) - 0.15V) to (VIH(MIN) + 0.15V) or 0.65V to 2.25V. This parameter is guaranteed by design and not tested. With a minimum initial slew rate of 0.5V/s, a minimum pull-up current of 1mA and a maximum input threshold voltage of 0.9V: Rise Time = [(0.9V - 0.65V)/0.5V/s] + [(2.25V - 0.9V) * 200pF/1mA] = 0.77s
Note 3: The rise time of an I2C bus line is calculated from VIL(MAX) to VIH(MIN) or 1.5V to 3V (with VCC = 5V). This parameter is guaranteed by design and not tested. With a minimum boosted pull-up current of 1mA: Rise Time = (3V - 1.5V) * 400pF/1mA = 0.6s Note 4: This parameter is guaranteed by design and not tested.
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V V/s s s kHz
LTC1694-1 TYPICAL PERFORMANCE CHARACTERISTICS
Pull-Up Current
3.50 3.25 3.00
PULL-UP CURRENT (mA)
Pull-Up Current vs SMBus Voltage
3.5 0.90 0.85 3.0
INPUT THRESHOLD VOLTAGE (V)
PULL-UP CURRENT (mA)
2.5 2.0 1.5 1.0
VCC = 6V
VCC = 5V
VCC = 2.7V 0.5 0 0 1 4 3 5 2 SMBus VOLTAGE (V) 6 7
Slew Rate Detector Threshold
0.50
SLEW RATE DETECTOR THRESHOLD (V/s)
0.45 0.40
SUPPLY CURRENT (A)
0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 -50 -25 50 0 75 25 TEMPERATURE (C) 100 125 VCC = 5V VCC = 6V VCC = 2.7V
UW
2.75 2.50 2.25 2.00 1.75 1.50 1.25 1.00 -50 -25 50 0 75 25 TEMPERATURE (C) 100 125 VCC = 2.7V VCC = 6V VCC = 5V
1694-1 G01
Input Threshold Voltage
0.80 0.75 0.70 VCC = 5V 0.65 0.60 0.55 0.50 0.45 0.40 -50 -25 50 0 75 25 TEMPERATURE (C) 100 125 VCC = 2.7V VCC = 6V
LT1694 G02
1694 G03
Standby Mode Supply Current
80 70 60 50 VCC = 6V 40 30 20 10 -50 -25 VCC = 5V VCC = 2.7V
0
25
50
75
100
125
TEMPERATURE (C)
1694 G04
1694-1 G05
3
LTC1694-1
PIN FUNCTIONS
VCC (Pin 1): Power Supply Input. VCC can range from 2.7V to 6V and requires a 0.1F bypass capacitor to GND. Supply current is typically 45A when the SMBus or I2C lines are inactive (SCL and SDA are a logic high level). GND (Pin 2): Ground. NC (Pin 3): No Connection. SMBus2 (Pin 4): Active pull-up for SMBus. SMBus1 (Pin 5): Active pull-up for SMBus.
BLOCK DIAGRAM
TEST CIRCUITS
VCC 5V VCC C1 0.1F SMBus1 4 GND SMBus2 VCC 5V 200A 5 LTC1694-1
200A (TYP) 0A PULL-UP = 2.2mA (TYP) IPULL-UP = VR 1k
-
LT(R)1360 TEST RAMP VOLTAGE BSS284
+
VR 1k -10V
1694-1 F01a
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VCC 1 2.2mA SLEW RATE DETECTOR CONTROL LOGIC SMBus1 5 GND 2 CHANNEL ONE
+ -
VOLTAGE COMP
0.65V VREF SMBus2 4 CHANNEL TWO (DUPLICATE OF CHANNEL ONE)
1694-1 BD
HP5082-2080
TEST RAMP VOLTAGE 0.5V/s VTHRES 0V
VCC
1694-1 F01b
Figure 1
LTC1694-1
APPLICATIONS INFORMATION
SMBus Overview SMBus communication protocol employs open-drain drives 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 resulting when bus capacitance is high. Rise times can be improved by using lower pull-up resistor values or higher fixed current source values, but the additional current increases the low state bus voltage, decreasing noise margins. Slow rise times can seriously impact data reliability, enforcing a maximum practical bus speed well below the established SMBus maximum transmission rate. Theory of Operation The LTC1694-1 overcomes these limitations by providing a 2.2mA pull-up current only during positive bus transitions to quickly slew any bus capacitance. Therefore, rise time is dramatically improved, especially with maximum SMBus loading conditions. The LTC1694-1 has separate but identical circuitry for each SMBus output pin. The circuitry consists of a positive edge slew rate detector and a voltage comparator. The 2.2mA pull-up current is only turned on if the voltage on the SMBus line voltage is greater than the 0.65V comparator threshold voltage and the positive slew rate of the SMBus line is greater than the 0.2V/s threshold of the slew rate detector. The pull-up current remains on until the voltage on the SMBus line is within 0.5V of VCC and/or the slew rate drops below 0.2V/s. Selecting the Values of RS and RP An external pull-up resistor RP is required in each SMBus line to supply a steady state pull-up current if the SMBus is at logic zero. This pull-up current is used for slewing the SMBus line during the initial portion of the positive transition in order to activate the LTC1694-1 2.2mA pull-up current. Using an external RP to supply the steady state pull-up current permits the user the freedom to adjust rise time versus fall time as well as defining the low state logic level (VOL).
RS DATA IN DATA OUT RON
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For I/O stage protection from ESD and high voltage spikes on the SMBus, a series resistor RS (Figure 2) is sometimes added to the open-drain driver of the bus agents. This is especially common in SMBus-controlled smart batteries. Both the values of RP and RS must be chosen carefully to meet the low state noise margin and all timing requirements of the SMBus. A discussion of the electrical parameters affected by the values of RS and RP, as well as a general procedure for selecting the values of RS and RP follows.
VCC RP SMBus CBUS
1694-1 F02
Figure 2
Low State Noise Margin A low value of VOL, the low state logic level, is desired for good noise margin. VOL is calculated as follows: VOL = (RL * VCC)/(RL + RP) (1) RL is the series sum of RS and RON, the on-resistance of the open-drain driver. Increasing the value of RP decreases the value of VOL. Increasing RL increases the value of VOL. Initial Slew Rate The initial slew rate, SR, of the Bus is determined by: SR = (VCC - VOL)/(RP * CBUS) (2) SR must be greater than SRTHRES, the LTC1694-1 slew rate detector threshold (0.5/s max) in order to activate the 2.2mA pull-up current.
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LTC1694-1
APPLICATIONS INFORMATION
SMBus Rise Time Rise time of an SMBus line is derived using equations 3, 4 and 5. tr = t1 + t2 t1 = - RP * CBUS * ln[(VTHRES - VCC)/ (VILMAX - 0.15 - VCC)] if (VILMAX - 0.15) > VTHRES, then t1 = 0s. t2 = - RP * CBUS * ln{[VIHMIN + 0.15 - VCC - (RP * IPULL-UP)]/[VTHRES - VCC - (RP * IPULL-UP)]} (5) By ignoring the current through RP, a simplified version of equation 3 is obtained: t2 = (VIHMIN + 0.15 - VTHRES) * CBUS/IPULL-UP (6) For an SMBus system, VILMAX = 0.8V and VIHMIN = 2.1V. For the LTC1694-1, typically VTHRES = 0.65V and IPULL-UP = 2.2mA. CBUS is the total capacitance of the SMBus line. Increasing the value of RP increases the rise time. SMBus Fall Time Fall time of an SMBus line is derived using equation 7: tf = RT * CBUS * ln{[0.9 * (RP + RL) - RL]/ [(VILMAX - 0.15) * (RP + RL)/VCC - RL]} where RT is the parallel equivalent of RP and RL. The rise and fall time calculation for an I2C system is as follows. I2C Bus Rise and Fall Time Rise time of an I2C line is derived using equation 8. tr = - RP * CBUS * ln{[VIHMIN - VCC - (RP * IPULL-UP)]/ [VILMAX - VCC - (RP * IPULL-UP)]} (8) Fall time of an I2C line is derived using equation 9: tf = RT * CBUS * ln{[(VIHMIN/VCC) * (RP + RL) - RL]/ [(VILMAX/VCC) * (RP + RL) - RL]} (9) For an I2C system with fixed input levels, VILMAX = 1.5V and VIHMIN = 3V. (7) (3) (4) For an I2C system with VCC related input levels, VILMAX = 0.3VCC and VIHMIN = 0.7VCC. CBUS is the total capacitance of the I2C line. A general procedure for selecting RP and RL is as follows: 1. RL is first selected based on the I/O protection requirement. Generally, an RS of 100 is sufficient for high voltage spike and ESD protection. RON is determined by the size of the open-drain driver, a large driver will have a lower RON. 2. Next, the value of RP is determined based on the rise and fall time requirements using equations 3 to 7 (for an SMBus system) or 8 and 9 (for an I2C system). The value chosen for RP must ensure that both the rise and fall time specifications are met simultaneously. 3. After RP and RL are selected, use equations 1 and 2 to check if the VOL and SR requirements are fulfilled. If SR is too low, decrease the value of RP. If VOL is too high, increase the value of RP. SMBus Design Example Given the following conditions and requirements: VCC = 3.3V nom VOL = 0.4V max CBUS = 200pF max VILMAX = 0.8V, VIHMIN = 2.1V tr = 0.8s max, tf = 0.3s max If an RS of 500 is used and the max RON of the driver is 200, then RL = 500 + 200 = 700. Using the max VTHRES of 0.9V and a min IPULL-UP of 1mA. Using equation 6 to calculate the approximate value of t2: t2 = (2.1 + 0.15 - 0.9) * [(200 * 10-12)/(1 * 10-3)] = 0.27s t1 = 0.8 - 0.27 = 0.53s Using equation 4 to find the required RP to meet tr: RP = - t1/{CBUS * ln[(VTHRES - VCC)/ (VILMAX - 0.15 - VCC)]} = 27k RT = (RP * RL)/(RP + RL)
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LTC1694-1
APPLICATIONS INFORMATION
Using equations 4 and 5 to check exact value of tr: tr = 0.535s + 0.254s = 0.79s Using equation 7 to check tf: tf = 0.222s which is less than 0.3s. Using equation 1 to check VOL: VOL = (3.3 * 700)/[700 + (27 * 103)] = 83mV which is less than 0.4V. And using equation 2 to check the initial slew rate: SR = 3.3/[(27 * 103) * (200 * 10 -12)] = 0.61V/s which is greater than 0.5V/s. Therefore, the value of RP chosen is 27k. ACK Data Setup Time Care must be taken in selecting the value of RS (in series with the pull-down driver) to ensure that the data setup time requirement for ACK (acknowledge) is fulfilled. 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. The LTC1694-1 2.2mA pull-up current is activated when the SMBus host releases the SDA line, allowing the voltage to rise above the LTC1694-1's comparator threshold of 0.65V. If an SMBus slave device has a high value of RS, a longer time is required for this SMBus slave device to pull SDA low before the rising edge of the ACK clock pulse. To ensure sufficient data setup time for ACK, SMBus slave devices with high values of RS, should pull the SDA low earlier. Typically, a minimum setup time of 1.5s is needed for an SMBus device with an RS of 700 and a bus capacitance of 200pF. An alternative is that the SMBus slave device can hold SCL line low until the SDA line reaches a stable state. Then, SCL can be released to generate the ACK clock pulse. Connecting Multiple LTC1694-1 in Parallel The LTC1694-1 is designed to guarantee a maximum SMBus rise time of 1s with a bus capacitance of 200pF. In some cases where the bus capacitance is higher than 200pF, multiple LTC1694-1s can be connected in parallel to provide a higher pull-up current to meet the rise time requirement. Figure 3 shows a typical application with two LTC1694-1s connected in parallel to supply a pull-up current of 4.4mA.
5 SMBus1 4 SMBus2 SCL SMBus SDA GND VCC LTC1694-1
CLK IN CLK OUT DEVICE 1
Figure 3. Paralleling Two LTC1694-1 to Provide 4.4mA of Pull-Up Current
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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VCC 5V 1 VCC C1 0.1F 2 GND SMBus2 SMBus1 4 LTC1694-1 RP1 RP2 5
DATA IN DATA OUT
CLK IN CLK OUT DEVICE N
DATA IN DATA OUT
1694-1 f03
7
LTC1694-1
APPLICATIONS INFORMATION
Comparison of SMBus Waveforms for the LTC1694-1 vs Resistor Pull-Up
LTC1694-1 1V/DIV
RPULL-UP = 15.8k
VCC = 5V CLD = 200pF fSMBus = 100kHz
1s/DIV
1694 TA03
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
2.60 - 3.00 (0.102 - 0.118) 1.50 - 1.75 (0.059 - 0.069) 0.00 - 0.15 (0.00 - 0.006) 0.90 - 1.45 (0.035 - 0.057) 2.80 - 3.00 (0.110 - 0.118) (NOTE 3)
0.35 - 0.55 (0.014 - 0.022)
0.09 - 0.20 (0.004 - 0.008) (NOTE 2)
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
RELATED PARTS
PART NUMBER LTC1380/LTC1393 LTC1427 LTC1623 LTC1663 LTC1694 LT1786F DESCRIPTION 8-Channel/4-Channel Analog Multiplexer with SMBus interface 10-Bit Current 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 COMMENTS Low RON and Low Charge Injection 50A Full-Scale Current 8 Selectable Addresses/16 Channel Capability DNL < 0.75LSB Max, 5-Lead SOT-23 Package Includes DC and AC Pull-Up Current 1.25A, 200kHz, Floating or Grounded Lamp Configurations
16941f LT/TP 1099 4K * PRINTED IN USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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LTC1694-1 1V/DIV RPULL-UP = 10.5k
VCC = 3.3V CLD = 200pF fSMBus = 100kHz
1s/DIV
1694 TA04
S5 Package 5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) FIVE PLACES (NOTE 2)
1.90 (0.074) REF
0.95 (0.037) REF
S5 SOT-23 0599
(c) LINEAR TECHNOLOGY CORPORATION 1999

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