LTC1694CS5#TRMPBF

LTC1694 SMBus/I2C Accelerator* U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO 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 Low Profile (1mm) SOT-23 (ThinSOTTM) Package U APPLICATIO S ■ ■ ■ ■ ■ ■ Notebook and Palmtop Computers Portable Instruments Battery Chargers Industrial Control Application TV/Video Products ACPI SMBus Interface The LT C®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 275µA 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. ThinSOT is a trademark of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V. *U.S. Patent No. 6,650,174 U TYPICAL APPLICATIO Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up VCC 5V SMBus1 VCC C1 0.1µF LTC1694 GND SMBus2 LTC1694 SCL SMBus SDA 1V/DIV CLK IN DATA IN CLK IN DATA IN CLK OUT DATA OUT CLK OUT DATA OUT DEVICE 1 DEVICE N 1694 TA01 RPULL-UP = 15.8k VCC = 5V CLD = 200pF fSMBus = 100kHz 1µs/DIV 1694 TA02 1694fa 1 LTC1694 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) ................................................. 7V SMBus1, SMBus2 Inputs ............ – 0.3V to (VCC + 0.3V) Operating Ambient Temperature Range LTC1694C ............................................... 0°C to 70°C LTC1694I ............................................ – 40°C to 85°C Junction Temperature ........................................... 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW 5 SMBus1 VCC 1 LTC1694CS5 LTC1694IS5 GND 2 NC 3 4 SMBus2 S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC TSOT-23 LTEE LTA8 TJMAX = 125°C, θJA = 256°C/ W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 2.7V to 6V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX VCC Supply Voltage Range ICC Supply Current SMBus1 = SMBus2 = Open ● 6 V 20 60 100 µA IPULL-UP Pull-Up Current SMBus1 = SMBus2 = 0V ● 125 275 350 µA Boosted Pull-Up Current Positive Transition on SMBus ( Figure 1) Slew Rate = 0.5V/µs, SMBus > VTHRES ● 1.0 2.2 VTHRES Input Threshold Voltage Slew Rate = 0.5V/µs (Figure 1) ● 0.4 0.65 0.9 V SRTHRES tr Slew Rate Detector Threshold SMBus > VTHRES ● 0.2 0.5 V/µs SMBus Rise Time Standard Mode I2C Bus Rise Time Bus Capacitance = 200pF (Note 2) Bus Capacitance = 400pF (Note 3) ● ● 0.32 0.30 1.0 1.0 µs µs fMAX SMBus Maximum Operating Frequency (Note 4) ● 100 kHz 2.7 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 125µA, a minimum boosted pull-up current of 1mA and a maximum input threshold voltage of 0.9V: Rise Time = [(0.9V – 0.65V)/125µA + (2.25V – 0.9V)/1mA] • 200pF = 0.67µs UNITS mA 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 = 0.6µs Note 4: This parameter is guaranteed by design and not tested. 1694fa 2 LTC1694 U W TYPICAL PERFOR A CE CHARACTERISTICS 3.50 325 3.25 VCC = 6V 275 VCC = 5V 250 VCC = 2.7V 225 200 175 150 125 100 –50 –25 50 0 75 25 TEMPERATURE (°C) 100 3.5 3.00 2.75 VCC = 6V 2.50 2.25 VCC = 5V 2.00 VCC = 2.7V 1.75 1.50 1.25 1.00 –50 125 BOOSTED PULL-UP CURRENT (mA) 350 300 Boosted Pull-Up Current vs SMBus Voltage Boosted Pull-Up Current BOOSTED PULL-UP CURRENT (mA) PULL-UP CURRENT (µA) Pull-Up Current at SMBus = 0V –25 50 0 75 25 TEMPERATURE (°C) 100 0.75 VCC = 6V 0.65 VCC = 2.7V 0.55 0.50 0.45 0.40 –50 –25 50 0 75 25 TEMPERATURE (°C) 1.0 VCC = 2.7V 0.5 0 100 125 4 3 5 2 SMBus VOLTAGE (V) 1 6 7 LT1694 G03 Standby Mode Supply Current 100 0.45 90 0.40 SUPPLY CURRENT (µA) SLEW RATE DETECTOR THRESHOLD (V/µs) INPUT THRESHOLD VOLTAGE (V) 0.80 VCC = 5V 1.5 0 125 0.50 0.60 2.0 Slew Rate Detector Threshold Input Threshold Voltage 0.90 0.85 VCC = 6V 2.5 1694 G02 1694 G01 0.70 VCC = 5V 3.0 0.35 0.30 0.25 0.20 VCC = 6V 0.15 0.10 VCC = 5V VCC = 2.7V –25 50 0 75 25 TEMPERATURE (°C) 1694 G04 70 VCC = 6V 60 50 VCC = 5V VCC = 2.7V 40 30 0.05 0 –50 80 100 125 20 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) 1694 G05 1694 G06 U U U PI FU CTIO S VCC (Pin 1): Power Supply Input. VCC can range from 2.7V to 6V and requires a 0.1µF bypass capacitor to GND. SMBus2 (Pin 4): Active Pull-Up for SMBus. SMBus1 (Pin 5): Active Pull-Up for SMBus. GND (Pin 2): Ground. NC (Pin 3): No Connection. 1694fa 3 LTC1694 W BLOCK DIAGRA VCC CHANNEL ONE 1 100µA 175µA SLEW RATE DETECTOR 1.925mA CONTROL LOGIC SMBus1 + 5 VOLTAGE COMP GND 2 – STANDBY 0.65V VREF CHANNEL TWO (DUPLICATE OF CHANNEL ONE) SMBus2 4 1694 BD TEST CIRCUITS VCC 5V 1 C1 0.1µF BOOSTED PULL-UP 2.2mA (TYP) 5 VCC SMBus1 LTC1694 2 IPULL-UP = 4 GND VR 1kΩ SMBus2 275µA (TYP) 0µA HP5082-2080 – LT1360 TEST RAMP VOLTAGE BSS284 VCC TEST RAMP VOLTAGE + 0.5V/µs VR 1k VTHRES –10V 1694 f01a 0V 1694 F01b Figure 1 1694fa 4 LTC1694 U W U U APPLICATIO S I FOR ATIO SMBus Overview Maximum RS Considerations 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. 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 700Ω if resistive pull-ups or fixed value current sources are used. Theory of Operation In general, an RS of 100Ω to 200Ω 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. 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. SDA RS DATA IN DATA OUT 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. RON 1694 F02 The LTC1694 nominally sources only 275µA 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/µs 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/µs. 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 100µA, thereby lowering the system power consumption. Figure 2 Low State Noise Margin An acceptable VOL noise margin is easily achieved with the low pull-up current (350µA 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 1694fa 5 LTC1694 U W U U 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 350µA 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. Rise time of an SMBus line is derived using equations 3, 4 and 5. tr = t1 + t2 (3) t1 = (VTHRES – VIL(MAX) + 0.15) • CBUS/IPULL-UP (4) if VIL(MAX) – 0.15 > VTHRES, then t1 = 0µs. t2 = (VIH(MIN) + 0.15 – VTHRES) • CBUS/IPULL-UP(B) (5) IPULL-UP(B) is the LTC1694 boosted pull-up current (2.2mA typ). 1.4 VCC = 5V MAXIMUM VALUE OF RS + RON (kΩ) SMBus Rise Time 1.2 0.8 For an SMBus system, VIL(MAX) = 0.8V and VIH(MIN) = 2.1V. For the LTC1694, typically V THRES = 0.65V and IPULL-UP = 275µA. 0.6 CBUS is the total capacitance of the SMBus line. 1.0 0.4 SMBus Fall Time 0.2 Fall time of an SMBus line is derived using equation 6. 0 0 100 200 400 300 BUS CAPACITANCE (pF) tf = RL • CBUS • ln{[(0.9 • VCC) – (RL • IPULL-UP(LOW))]/ [VIL(MAX) – 0.15 – (RL • IPULL-UP(LOW))]} (6) 500 1694 F03 where RL is the sum of RS and RON (see Figure 2). 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 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) (7) Fall time of the I2C line can be derived using equation 8. The initial slew rate, SR, of the Bus is determined by: SR = IPULL-UP(MIN)/CBUS Rise and fall time calculation for an I2C system is as follows. (2) CBUS is the total capacitance of the SMBus line. IPULL-UP(MIN) is the LTC1694 minimum pull-up current (125µA). SR must be greater than SRTHRES, the LTC1694 slew rate detector threshold (0.5V/µs max) in order to activate the 2.2mA boosted pull-up current. This limits the maximum SMBus capacitance. tf = RL • CBUS • ln{[VIH(MIN) – (RL • IPULL-UP)]/ [VIL(MAX) – (RL • IPULL-UP)]} (8) 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. 1694fa 6 LTC1694 U W U U APPLICATIO S I FOR ATIO ACK Data Setup Time a longer time is required for this SMBus slave device to pull SDA low before the rising edge of the ACK clock pulse. 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. 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 1.5µs is needed for an SMBus device with an RS of 700Ω and a bus capacitance of 200pF. 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, 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. U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 1.90 BSC S5 TSOT-23 0302 1694fa 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. 7 LTC1694 U W U U APPLICATIO S I FOR ATIO Comparison of SMBus Waveforms for the LTC1694 vs Resistor Pull-Up LTC1694 1V/DIV LTC1694 1V/DIV RPULL-UP = 15.8k VCC = 5V CLD = 200pF fSMBus = 100kHz 1µs/DIV 1694 TA03 RPULL-UP = 10.5k VCC = 3.3V CLD = 200pF fSMBus = 100kHz 1µs/DIV 1694 TA04 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1380/LTC1393 8-Channel/4-Channel Analog Multiplexer with SMBus Interface Low RON and Low Charge Injection LTC1427-50 10-Bit Current DAC with SMBus Interface 50µA Full-Scale Current 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 LTC1694-1 SMBus/I2C Accelerator Includes AC Pull-Up Current Only LTC1695 SMBus/I2C Fan-Speed Controller in SOT-23 0.75Ω PMOS Linear Regulator with 180mA Output Current, SMBus-Controlled 6-Bit DAC LTC1710 SMBus Dual High Side Switch Two 0.4Ω, 300mA N-Channel Switches LTC1759 Single Chip Smart Battery Charger Controller with SMBus Interface 94% Efficiency with Input Current Limiting, Up to 8A ICHG LT1786F SMBus-Controlled CCFL Switching Regulator 1.25A, 200kHz, Floating or Grounded Lamp Configurations LTC4300A-1/LTC4300A-2 Hot Swappable 2-Wire Bus Buffers Provides Capacitance Buffering, SDA and SCL Hot Swapping, Level Shifting 1694fa 8 Linear Technology Corporation LT/TP 0304 REV A 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com  LINEAR TECHNOLOGY CORPORATION 1998