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LTC1694 SMBus/I2C Accelerator
FEATURES
s s
DESCRIPTIO
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Improves SMBus Rise Time Transition Ensures Data Integrity with Multiple Devices on the SMBus Improves Low State Noise Margin Auto Detect Low Power Standby Mode Wide Supply Voltage Range: 2.7V to 6V Tiny 5-Pin SOT-23 Package
APPLICATIO S
s s s s s s
Notebook and Palmtop Computers Portable Instruments Battery Chargers Industrial Control Application TV/Video Products ACPI SMBus Interface
The LT C(R)1694 is a dual SMBus active pull-up designed to enhance data transmission speed and reliability under all specified SMBus loading conditions. The LTC1694 is also compatible with the Philips I2CTM Bus. The LTC1694 allows multiple device connections or a longer, more capacitive interconnect, without compromising slew rates or bus performance, by using two bilevel hysteretic current source pull-ups. During positive bus transitions, the LTC1694 current sources provide 2.2mA to quickly slew the SMBus line. During negative transitions or steady DC levels, the current sources decrease to 275A 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. The LTC1694 is available in a 5-pin SOT-23 package, requiring virtually the same space as two surface mount resistors.
, 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
Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up
1 VCC 2 GND SMBus2 SMBus1 LTC1694 4 5
LTC1694
SCL SMBus SDA
1V/DIV
DATA IN DATA OUT CLK IN CLK OUT DEVICE N
1694 TA01
CLK IN CLK OUT DEVICE 1
DATA IN DATA OUT
VCC = 5V CLD = 200pF fSMBus = 100kHz
LTC1694: Patent Pending
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RPULL-UP = 15.8k 1s/DIV
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LTC1694
ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
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 LTC1694C ............................................... 0C to 70C LTC1694I ............................................ - 40C to 85C Junction Temperature ........................................... 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1694CS5 LTC1694IS5 S5 PART MARKING LTEE LTA8
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 256C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.7V to 6V unless otherwise noted.
SYMBOL VCC ICC IPULL-UP PARAMETER Supply Voltage Range Supply Current Pull-Up Current Boosted Pull-Up Current VTHRES SRTHRES tr fMAX Input Threshold Voltage Slew Rate Detector Threshold SMBus Rise Time Standard Mode I2C Bus Rise Time SMBus Maximum Operating Frequency SMBus1 = SMBus2 = Open SMBus1 = SMBus2 = 0V 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 q
CONDITIONS
MIN 2.7 20 125 1.0 0.4
TYP 60 275 2.2 0.65 0.2 0.32 0.30
MAX 6 100 350
UNITS V A 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 pull-up current of 125A, a minimum boosted pull-up current of 1mA and a maximum input threshold voltage of 0.9V: Rise Time = [(0.9V - 0.65V)/125A + (2.25V - 0.9V)/1mA] * 200pF = 0.67s
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
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LTC1694 TYPICAL PERFOR A CE CHARACTERISTICS
Pull-Up Current at SMBus = 0V
350
BOOSTED PULL-UP CURRENT (mA)
BOOSTED PULL-UP CURRENT (mA)
325 300 VCC = 6V VCC = 5V VCC = 2.7V
PULL-UP CURRENT (A)
275 250 225 200 175 150 125 100 -50 -25
50 0 75 25 TEMPERATURE (C)
Input Threshold Voltage
0.90
SLEW RATE DETECTOR THRESHOLD (V/s)
0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05
0.85
INPUT THRESHOLD VOLTAGE (V)
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
SUPPLY CURRENT (A)
PI FU CTIO S
VCC (Pin 1): Power Supply Input. VCC can range from 2.7V to 6V and requires a 0.1F bypass capacitor to GND. 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.
UW
100
1694 G01
Boosted Pull-Up Current
3.50 3.25 3.00 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
3.0 2.5 2.0 1.5 1.0 3.5
Boosted Pull-Up Current vs SMBus Voltage
VCC = 6V
VCC = 5V
VCC = 2.7V 0.5 0 0 1 4 3 5 2 SMBus VOLTAGE (V) 6 7
125
1694 G02
LT1694 G03
Slew Rate Detector Threshold
100 90 80 70
Standby Mode Supply Current
VCC = 6V 60 50 40 30 VCC = 5V VCC = 2.7V
VCC = 6V VCC = 5V VCC = 2.7V
0 -50
-25
50 0 75 25 TEMPERATURE (C)
100
125
20 -50 -25
0
25
50
75
100
125
TEMPERATURE (C)
1694 G05
1694 G06
1694 G04
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LTC1694
BLOCK DIAGRA
VCC 1
SMBus1 5 GND 2 STANDBY
SMBus2 4
TEST CIRCUITS
VCC 5V C1 0.1F 1 VCC 2 GND SMBus2
275A (TYP)
SMBus1 LTC1694 4
-
LT1360 TEST RAMP VOLTAGE BSS284
+
VR 1k
4
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CHANNEL ONE SLEW RATE DETECTOR 100A 175A 1.925mA CONTROL LOGIC
+ -
VOLTAGE COMP
0.65V VREF
CHANNEL TWO (DUPLICATE OF CHANNEL ONE)
1694 BD
5
BOOSTED PULL-UP 2.2mA (TYP) IPULL-UP = VR 1k
HP5082-2080
VCC
0A
TEST RAMP VOLTAGE 0.5V/s VTHRES
-10V
1694 f01a
0V
1694 F01b
Figure 1
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LTC1694
APPLICATIO S I FOR ATIO
SMBus Overview
SMBus communication protocol employs open-drain drivers 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 they afford 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 overcomes these limitations by using bilevel hysteretic current sources as pull-ups. During positive SMBus line transitions, the pull-up current sources typically provide 2.2mA to quickly slew any parasitic bus capacitance. Therefore, rise time is dramatically improved, especially with maximum SMBus loading conditions. The LTC1694 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 LTC1694 nominally sources only 275A of pull-up current to maintain good VOL noise margin. The 2.2mA boosted 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 boosted 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. Auto Detect Standby Mode The LTC1694 enters standby mode if the voltage on both the SCL and SDA lines is high (idle state). In standby mode, the pull-up currents drop to 100A, thereby lowering the system power consumption.
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Maximum RS Considerations For ESD protection of the SMBus lines, a series resistor RS (Figure 2) is sometimes added to the open-drain driver of the bus agents. This is especially common in SMBuscontrolled smart batteries. The maximum value of RS is limited by the low state noise margin and timing requirements of the SMBus specification. The maximum value for RS is 700 if resistive pull-ups or fixed value current sources are used. In general, an RS of 100 to 200 is sufficient for ESD protection while meeting both the low state noise margin and fall time requirement. If a larger value of RS is required, take care to ensure that the low state noise margin and timing requirement of the SMBus specification is not violated. Also, the fall time of an SMBus line will also be increased by using a high value series resistor.
SDA RS DATA IN DATA OUT RON
1694 F02
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Figure 2
Low State Noise Margin An acceptable VOL noise margin is easily achieved with the low pull-up current (350A maximum) of the LTC1694. The maximum value of RS is calculated from a desired low state noise margin (NML): V - NML RS(MAX ) = OL(MAX ) - RON(MAX ) IPULL-UP(MAX ) VOL(MAX): (1)
The maximum VOL of the SMBus specification is 0.4V
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LTC1694
APPLICATIO S I FOR ATIO
RON(MAX):
The maximum on resistance of the opendrain driver
IPULL-UP(MAX): The maximum LTC1694 low pull-up current is 350A Fall Time Fall time is a function of the SMBus capacitance, RS, RON and the pull-up current. Figure 3 shows the maximum allowed (RS + RON) based on the Intel SMBus fall time requirement of 300ns with a 50ns safety margin.
1.4 VCC = 5V
MAXIMUM VALUE OF RS + RON (k)
1.2 1.0 0.8 0.6 0.4 0.2 0 0 100 200 400 300 BUS CAPACITANCE (pF) 500
1694 F03
Figure 3. Maximum Value of RS + RON as a Function of Bus Capacitance for Meeting the SMBus tf(MAX) Requirement
The maximum value of RS, based on fall time requirements, can also be calculated by rearranging equation 6. Given below are some equations that are useful for calculating rise and fall time and for selecting the value of RS. Initial Slew Rate The initial slew rate, SR, of the Bus is determined by: SR = IPULL-UP(MIN)/CBUS CBUS is the total capacitance of the SMBus line. IPULL-UP(MIN) is the LTC1694 minimum pull-up current (125A). SR must be greater than SRTHRES, the LTC1694 slew rate detector threshold (0.5V/s max) in order to activate the 2.2mA boosted pull-up current. This limits the maximum SMBus capacitance. (2)
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SMBus Rise Time Rise time of an SMBus line is derived using equations 3, 4 and 5. tr = t1 + t2 t1 = (VTHRES - VIL(MAX) + 0.15) * CBUS/IPULL-UP if VIL(MAX) - 0.15 > VTHRES, then t1 = 0s. t2 = (VIH(MIN) + 0.15 - VTHRES) * CBUS/IPULL-UP(B) (5) IPULL-UP(B) is the LTC1694 boosted pull-up current (2.2mA typ). For an SMBus system, VIL(MAX) = 0.8V and VIH(MIN) = 2.1V. For the LTC1694, typically V THRES = 0.65V and IPULL-UP = 275A. CBUS is the total capacitance of the SMBus line. SMBus Fall Time Fall time of an SMBus line is derived using equation 6. tf = RT * CBUS * ln{[(0.9 * VCC) - (RL * IPULL-UP(LOW))]/ [VIL(MAX) - 0.15 - (RL * IPULL-UP(LOW))]} (6) where RL is the sum of RS and RON (see Figure 2). 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 7. tr = (VIH(MIN) - VIL(MAX)) * CBUS/IPULL-UP(B) tf = RT * CBUS * ln{[VIH(MIN) - (RL * IPULL-UP)]/ [VIL(MAX) - (RL * IPULL-UP)]} (7) Fall time of the I2C line can be derived using equation 8. (8) (3) (4) For an I2C system with fixed input levels, VIL(MAX) = 1.5V and VIH(MIN) = 3V. For an I2C system with VCC related input levels, VIL(MAX) = 0.3 * VCC and VIH(MIN) = 0.7 * VCC. CBUS is the total capacitance of the I2C line.
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LTC1694
APPLICATIO S I FOR ATIO
ACK Data Setup Time
The data setup time requirement for ACK (acknowledge) must be fulfilled if a high value of RS is used. 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 2.2mA boosted pull-up current is activated when the SMBus host releases the SDA line, allowing the voltage to rise above the LTC1694's comparator threshold of 0.65V. If an SMBus slave device has a high value of RS,
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
2.60 - 3.00 (0.102 - 0.118) 1.50 - 1.75 (0.059 - 0.069)
0.35 - 0.55 (0.014 - 0.022)
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)
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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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.
S5 Package 5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 - 3.00 (0.110 - 0.118) (NOTE 3) 1.90 (0.074) REF 0.00 - 0.15 (0.00 - 0.006) 0.95 (0.037) REF 0.90 - 1.45 (0.035 - 0.057) 0.09 - 0.20 (0.004 - 0.008) (NOTE 2) 0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) FIVE PLACES (NOTE 2) S5 SOT-23 0599
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LTC1694
APPLICATIO S I FOR ATIO
Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up
LTC1694 1V/DIV RPULL-UP = 15.8k 1V/DIV
VCC = 5V CLD = 200pF fSMBus = 100kHz
1s/DIV
1694 TA03
RELATED PARTS
PART NUMBER LTC1380/LTC1393 LTC1427-50 LTC1623 LTC1663 LTC1694-1 LTC1695 LTC1710 LTC1759 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/I2C Accelerator SMBus/I2C Fan-Speed Controller in SOT-23 SMBus Dual High Side Switch Single Chip Smart Battery Charger Controller with SMBus Interface 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 AC Pull-Up Current Only 0.75 PMOS Linear Regulator with 180mA Output Current, SMBus-Controlled 6-Bit DAC Two 0.4, 300mA N-Channel Switches 94% Efficiency with Input Current Limiting, Up to 8A ICHG 1.25A, 200kHz, Floating or Grounded Lamp Configurations
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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 RPULL-UP = 10.5k VCC = 3.3V CLD = 200pF fSMBus = 100kHz 1s/DIV
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(c) LINEAR TECHNOLOGY CORPORATION 1998

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