EMCT03 1°C Triple SMBus Temperature Sensor Datasheet General Description Features The EMCT03 is a System Management Bus (SMBus) temperature sensor that is capable of monitoring three temperature zones. The three temperature zones consist of two external and one internal temperature diode. The internal 11 bit sigma-delta ADC architecture with digital filtering attributes to superb linearity and immunity to interference and noise. An extended temperature format may be selected for compatibility with a broad range of CPUs. Selectable conversion rates and standby mode support low-power operation. ■ Low Power; 3.0V to 3.6V Supply — Programmable conversion rate — < 1mA at 16 Conversions per Second — < 3uA in Standby Mode ■ ■ SMBus 2.0 Compliant interface Two External Temperature Monitors: — — — — ■ Range -64°C to +191°C 0.125°C resolution ±1°C Accuracy 40°C to 80°C Diode Fault Reporting Internal Temperature Monitor — Range 0°C to +85°C — 0.125°C resolution — ±3°C Accuracy 0°C to 85°C ■ ■ Programmable Conversion Rate MSOP-8 3x3mm Package; Green, Lead-Free Package also available. Simplified Block Diagram EMCT03 Switching Current Configuration Register Analog Mux DN1 DP2 11-bit Sigma Delta ADC Remote Temp Register 2 Digital Mux and Byte Interlock DN2 Local Temp Diode Local Temp Register SMCLK Status Register SMSC EMCT03 DATASHEET SMBus Interface Remote Temp Register 1 DP1 SMDATA Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet ORDER NUMBER(S): EMCT03-ACZB for 8-pin MSOP package EMCT03-ACZB-TR for 8-pin MSOP package (Tape and Reel) EMCT03-ACZL for 8-pin MSOP package (Green Lead-Free) EMCT03-ACZL-TR for 8-pin MSOP package (Green Lead-Free, Tape and Reel) Evaluation Board Available upon request. 80 Arkay Drive Hauppauge, NY 11788 (631) 435-6000 FAX (631) 273-3123 Copyright © SMSC 2005. All rights reserved. Circuit diagrams and other information relating to SMSC products are included as a means of illustrating typical applications. Consequently, complete information sufficient for construction purposes is not necessarily given. Although the information has been checked and is believed to be accurate, no responsibility is assumed for inaccuracies. SMSC reserves the right to make changes to specifications and product descriptions at any time without notice. Contact your local SMSC sales office to obtain the latest specifications before placing your product order. The provision of this information does not convey to the purchaser of the described semiconductor devices any licenses under any patent rights or other intellectual property rights of SMSC or others. All sales are expressly conditional on your agreement to the terms and conditions of the most recently dated version of SMSC's standard Terms of Sale Agreement dated before the date of your order (the "Terms of Sale Agreement"). The product may contain design defects or errors known as anomalies which may cause the product's functions to deviate from published specifications. Anomaly sheets are available upon request. SMSC products are not designed, intended, authorized or warranted for use in any life support or other application where product failure could cause or contribute to personal injury or severe property damage. Any and all such uses without prior written approval of an Officer of SMSC and further testing and/or modification will be fully at the risk of the customer. Copies of this document or other SMSC literature, as well as the Terms of Sale Agreement, may be obtained by visiting SMSC’s website at http://www.smsc.com. SMSC is a registered trademark of Standard Microsystems Corporation (“SMSC”). Product names and company names are the trademarks of their respective holders. SMSC DISCLAIMS AND EXCLUDES ANY AND ALL WARRANTIES, INCLUDING WITHOUT LIMITATION ANY AND ALL IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE, AND AGAINST INFRINGEMENT AND THE LIKE, AND ANY AND ALL WARRANTIES ARISING FROM ANY COURSE OF DEALING OR USAGE OF TRADE. IN NO EVENT SHALL SMSC BE LIABLE FOR ANY DIRECT, INCIDENTAL, INDIRECT, SPECIAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES; OR FOR LOST DATA, PROFITS, SAVINGS OR REVENUES OF ANY KIND; REGARDLESS OF THE FORM OF ACTION, WHETHER BASED ON CONTRACT; TORT; NEGLIGENCE OF SMSC OR OTHERS; STRICT LIABILITY; BREACH OF WARRANTY; OR OTHERWISE; WHETHER OR NOT ANY REMEDY OF BUYER IS HELD TO HAVE FAILED OF ITS ESSENTIAL PURPOSE, AND WHETHER OR NOT SMSC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Revision 2.3 (04-19-05) 2 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet Chapter 1 Pin Configuration DP1 1 DN1 2 DP2 3 DN2 4 EMCT03 TOP VIEW 8 SMCLK 7 SMDATA 6 VDD 5 GND Figure 1.1 EMCT03 Pin Configuration Table 1.1 Pin Description PIN PIN NO. DESCRIPTION DP1 1 Positive Analog Input for External Temperature Diode 1 DN1 2 Negative Analog Input for External Temperature Diode 1 DP2 3 Positive Analog Input for External Temperature Diode 2 DN2 4 Negative Analog Input for External Temperature Diode 2 GND 5 Ground VDD 6 Supply Voltage SMDATA 7 System Management Bus Data Input/Output, open drain output SMCLK 8 System Management Bus Clock Input Table 1.2 Absolute Maximum Ratings DESCRIPTION Supply Voltage VDD Voltage on any other pin Operating Temperature Range Storage Temperature Range ESD Rating, All Pins Human Body Model SMSC EMCT03 3 DATASHEET RATING UNIT -0.3 to 5.0 V -0.3 to VDD+0.3 V 0 to 85 °C -55 to 150 °C 2000 V Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet Chapter 2 Electrical Characteristics VDD=3.3V±10%, AmbientTemp=0°C to 85°C, except as noted below. CHARACTERISTIC MIN TYP MAX UNIT 3.0 3.3 3.6 V 3 1.75 1 700 500 3 mA mA mA µA µA µA DC Power Supply Voltage VDD Current Consumption from VDD: 16 sets of conversions per second 8 sets of conversions per second 4 full sets of conversions per second 2 full sets of conversions per second 1 full set of conversions per second Power Down POR Threshold 2.5 V Internal Temperature Monitor Temperature Accuracy Ambient Temp 0°C to 85°C ±1 Temperature Resolution ±3 °C °C 0.125 Two External Temperature Monitors Temperature Accuracy Remote Diode 40°C to 80°C, Ambient Temp 15°C to 70°C Remote Diode 0°C to 125°C Temperature Resolution Current Source Low Level High Level ±1 ±3 °C °C 0.125 °C 10 170 µA µA 60 ms ADC Conversion Time for all three sensors Wake-up from STOP mode (During one shot command or transition to RUN mode) 1 Resolution 11 ms bit Differential Non Linearity ±1 LSB Integral Non Linearity ±1 LSB Revision 2.3 (04-19-05) 4 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet TLOW THIGH THD:STA TR SMCLK THD:STA TSU:STO TF THD:DAT TSU:DAT TSU:STA SMDATA TBUF P S S S - Start Condition P - Stop Condition P Figure 2.1 System Management Bus Timing Diagram VDD=3.3V±10%, Temp=0°C to 85°C, unless otherwise noted. CHARACTERISTIC MIN TYP MAX UNIT 400 kHz 50 ns System Management Bus Timing Operating Frequency, FSMB 10 Spike Suppression Bus free time Start to Stop, TBUF 1.3 µs Hold time Start THD:STA 0.6 µs Setup time Start TSU:STA 0.6 µs Setup time Stop TSU:STO 0.6 µs Data hold time THD:DAT 0.3 Data setup time TSU:DAT 100 ns Clock Low period TLOW 1.3 µs Clock High Period THIGH 0.6 µs 0.9 µs Clock/Data Fall Time, TF 300 ns Clock/Data Rise Time, TR 300 ns Input High Current 10 µA Input Low Current -10 µA Input Capacitance 10 pF Low Input Level 0.8 V System Management Bus SMCLK, SMDATA High Input Level 2.0 Hysteresis 500 Low Output Level @ 4mA SMSC EMCT03 V mV 0.4 5 DATASHEET V Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet Chapter 3 Product Description The EMCT03 is an SMBus sensor that is capable of monitoring three temperature zones. The part may be used as a companion to one of SMSC’s broad line of SIO host circuits, or other devices capable of performing the SMBus host function. EMCT03 Host (SMSC SIO) DP1 DN1 SMBus Interface SMBus DP2 DN2 Internal Diode Figure 3.1 System Overview In cooperation with the host device, thermal management can be performed as outlined in Figure 3.1 above. Thermal management consists of the host reading the temperature data from the remote and internal temperature diodes of the EMCT03 and controlling the speed of one or multiple fans. Since the EMCT03 incorporates one internal and two external temperature diodes, three separate thermal zones can be monitored and controlled with this application. Also, measured temperature levels can quickly be compared to preset limits within the host device which in turn will take the appropriate action when values are found to be out of limit. The EMCT03 has two basic modes of operation: 3.1 ■ Run Mode: In this mode, the EMCT03 continuously converts temperature data and updates its registers. The conversion rate is configured by the lower bits in the configuration register as described in Table 3.11, "Configuration Register, Conversion Rate," on page 11. ■ Standby Mode: In this mode, the EMCT03 is powered down, drawing a maximum current of only 3uA. The SMBus is still operational and a one-shot command can be given which will force the circuit to complete one full set of temperature conversions. The EMCT03 will return to Standby Mode after the one shot conversion has finished. Temperature Monitors Thermal diode temperature measurements are based on the change in forward bias voltage of a diode when operated at two different currents: Vbe _ high − Vbe _ low = n KT I high ln q I low (1) where: K is Boltzmann’s constant T is Absolute Temperature in Kelvin q is Charge Electron n is Diode Ideality factor The change in forward bias voltage is now proportional to absolute temperature T. Revision 2.3 (04-19-05) 6 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet VDD Ihigh Internal or Remote Diode Ilow Ibias Bias Diode fs fs fs fs/2048 Delta Vbe Sample & Hold 1-bit Sigma Delta Modulator Digital Averaging Filter 11-bit Accurate Conversion Figure 3.2 Block Diagram of Temperature Measurement Circuit Figure 3.2 shows a detailed block diagram of the temperature measurement circuit. As shown, the EMCT03 incorporates switched capacitor technology that samples the external remote temperature diode voltage at two bias currents and holds the difference voltage. The sample frequency is 100kHz and the current levels Ihigh and Ilow are 170uA and 10uA respectively. The negative terminal for the remote temperature diode, DN, is internally biased with a forward diode voltage referenced to ground. The output of the switched capacitor sample and hold circuit interfaces to a single-bit sigma delta analog-to-digital converter. This ADC runs at 100kHz sample frequency and its output is digitally filtered and averaged over 2048 samples effectively generating 11 bit accuracy. The advantages of this architecture over Nyquist rate FLASH or SAR converters are superb linearity and inherent noise immunity. The linearity can be directly attributed to the sigma delta ADC single-bit comparator while the noise immunity is achieved by the digital averaging filter. The overall effective bandwidth of the system is fs/2048 which translates to a 50Hz bandwidth at 100kHz sample rate. Conversion time equals about 20ms per temperature monitor which equals 60ms total for three monitors when configured for maximum conversion rate (default). The 11 bit conversion can be displayed in either legacy format or in extended range format. In Legacy format, the temperature range covers –64ºC to 127ºC while in extended format, temperature readings span -64ºC to 191ºC. It should be noted that the latter range is really meant to cover thermal diodes with a non ideal curvature caused by factor n in equation (1) not being equal to exactly 1.000. In general, it is not recommended to run silicon based thermal diodes at temperatures above 150ºC. 3.2 System Management Bus Interface Protocol The EMCT03 communicates with a host controller, such as an SMSC SIO, through the SMBus. The SMBus is a two wire serial communication protocol between a computer host and its peripheral devices. Detailed timing diagrams can be found in the electrical characteristics of the SMBus. The EMCT03 is SMBus 2.0 compatible and supports Write Byte and Read Byte as valid protocols as shown below: SMSC EMCT03 7 DATASHEET Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet 3.2.1 Write Byte The write Byte is used to write one byte of data to the registers as shown in Table 3.1 below: Table 3.1 SMBus Write Byte Protocol Start Slave Address WR ACK Register Address ACK Register Data ACK STOP 1 7 1 1 8 1 8 1 1 3.2.2 Read Byte The Read Byte protocol is used to read one byte of data from the registers as shown in Table 3.2 below: Table 3.2 SMBus Read Byte Protocol Start Slave Address WR ACK Register Address ACK START Slave Address RD ACK Register Data NACK STOP 1 7 1 1 8 1 1 7 1 1 8 1 1 3.2.3 SMBus Address Attempting to communicate with the EMCT03 SMBus interface with an invalid slave address or invalid protocol, results in no response from the part and will not affect its register content. The EMCT03 supports stretching of the SMCLK signal by other devices on the SMBus but will not perform this operation itself. Table 3.3 SMBus Address CONDITION EMCT03 ADDRESS EMCT03 Default Address 3.3 1001100xb Register Allocation The following registers are accessible through the SMBus: Table 3.4 Register Table REGISTER READ ADDRESS REGISTER WRITE ADDRESS 00h N/A Legacy Format Internal Temperature High Byte 00h 23h N/A Legacy Format Internal Temperature Low Byte 00h 01h N/A Legacy Format Remote Temperature 1 High Byte 00h 10h N/A Legacy Format Remote Temperature 1 Low Byte 00h F8h N/A Legacy Format Remote Temperature 2 High Byte 00h F9h N/A Legacy Format Remote Temperature 2 Low Byte 00h Revision 2.3 (04-19-05) REGISTER NAME 8 DATASHEET DEFAULT VALUE SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet Table 3.4 Register Table (continued) REGISTER READ ADDRESS REGISTER WRITE ADDRESS FAh N/A Extended Format Remote Temperature 1 High Byte 00h FBh N/A Extended Format Remote Temperature 1 Low Byte 00h FCh N/A Extended Format Remote Temperature 2 High Byte 00h FDh N/A Extended Format Remote Temperature 2 Low Byte 00h 02h N/A Status register 00h 03h 09h Configuration register 47h N/A 0Fh One Shot Command -- FEh N/A Manufacturer Identifier 5Dh FFh N/A Silicon Revision Identifier 01h 11h, 16h, 4Ah, 60h, 61h, 62h, 79h, 7Ah 11h, 16h, 4Ah, 60h, 61h, 62h, 79h, 7Ah DEFAULT VALUE REGISTER NAME Reserved Registers for production test During Power on Reset (POR), the default values are stored in the registers. A POR is initiated when power is first applied to the part and the voltage on the VDD supply surpasses the POR level as specified in the electrical characteristics. Any reads to undefined registers will return 00h. Writes to any undefined registers will not have an effect. The EMCT03 uses an interlock mechanism that prevents changes in register content when fresh readings come in from the ADC during successive reads from a host. When the High Byte is read, the last conversion value is latched into the High Byte and Low Byte. Please note that the interlock mechanism is only effective when reading the High Byte first. 3.4 Temperature Monitor Registers As shown in Table 3.4, each temperature monitor has two byte wide data registers. The external monitors are equipped with both legacy and extended data format. The 11 bit data temperature is stored aligned to the left resulting in the High Byte to contain temperature in 1°C steps and the Low Byte to contain fractions of °C as outlined below: Table 3.5 High Byte Temperature Register REGISTER Temperature High Byte Registers 00h, 01h, F8h, FAh, FCh BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 SIGN 64 32 16 8 4 2 1 Table 3.6 Low Byte Temperature Register REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 Temperature Low Byte Registers 23h, 10h, F9h, FBh, FDh 0.500 0.250 0.125 0 0 0 0 0 SMSC EMCT03 9 DATASHEET Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet 3.5 Legacy Temperature Data Format Registers 00h, 23h, 01h, 10h, F8h, F9h: For registers displaying legacy temperature data format, the temperature range spans from –63.875ºC to +127.875ºC with 0,125ºC resolution. Temperatures outside this range are clipped to –63.875ºC and +127.875ºC. Data is stored in the registers in 2’s complement as shown in Table 3.7: Table 3.7 Legacy Temperature Data Format 3.6 TEMPERATURE (°C) 2’S COMPLEMENT HEX Diode Fault 1000 0000 0000 0000 8000 = -63.875 1100 0000 0010 0000 C020 -63 1100 0001 0000 0000 C100 -1 1111 1111 0000 0000 FF00 0 0000 0000 0000 0000 0000 +0.125 0000 0000 0010 0000 0020 +1 0000 0001 0000 0000 0100 +127 0111 1111 0000 0000 7F00 ≥ +127.875 0111 1111 1110 0000 7FE0 Extended Temperature Data Format Registers FAh, FBh, FCh, FDh For registers displaying extended temperature data format, a value of 64d is subtracted from the Legacy Format output. This effectively extends the range to cover higher external temperature measurements while still maintaining the 2’s complement format. Obviously, the host will have to compensate and add 64d to the read temperature data. This format spans from –63.875ºC to +191.875ºC with 0.125ºC resolution. Temperatures outside this range are limited to –63.875ºC and +191.875ºC. Table 3.8 shows example temperature readings and register content for this data format. Table 3.8 Extended Temperature Data Format ACTUAL TEMP. (°C) -64°C OFFSET (°C) Diode Fault 2’S COMPLEMENT OF -64°C OFFSET HEX 1000 0000 0000 0000 8000 = -63.875 -127.875 1000 0000 0010 0000 8020 -63 -127 1000 0001 0000 0000 8100 -1 -65 1011 1111 0000 0000 BF00 0 -64 1100 0000 0000 0000 C000 +0.125 -63.875 1100 0000 0010 0000 C020 +1 -63 1100 0001 0000 0000 C100 +63 -1 1111 1111 0000 0000 FF00 +64 0 0000 0000 0000 0000 0000 Revision 2.3 (04-19-05) 10 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet Table 3.8 Extended Temperature Data Format (continued) ACTUAL TEMP. (°C) -64°C OFFSET (°C) 2’S COMPLEMENT OF -64°C OFFSET HEX +65 1 0000 0001 0000 0000 0100 +191 127 0111 1111 0000 0000 7F00 = +191.875 127.875 0111 1111 1110 0000 7FE0 Table 3.7 and Table 3.8 show that temperature data is stored in 2’s complement in both Legacy and Extended Temperature Data Format. Both extended and legacy temperature formats are updated simultaneously after every conversion cycle. Code 8000h is reserved for diode fault signaling which occurs when open or short conditions are present between the external DP and DN pins. 3.7 Status Register Table 3.9 Status Register REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 DEF Status Busy - - - - - D2 D1 00h The Status register is a read only register and returns the operational status of the part. It indicates an external diode fault conditions through bit 0 and 1. When either D1 or D2 is set, a faulty diode connection is detected for external diode 1 or external diode 2 respectively. Also, when diode faults are detected, temperature readings for the faulty external diode will return 8000h. The EMCT03 detects both open and short conditions for the DP1/2 and DN1/2 pins. Bit 7 of the status register will be set when the internal ADC is busy converting data. 3.8 Configuration Register Table 3.10 Configuration Register REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 DEF Configuration - nRun/Stop - - - CR2 CR1 CR0 47h Bits 0 through bit 2 of the configuration register set the ADC conversion rate of the part: Table 3.11 Configuration Register, Conversion Rate CR2, CR1, CR0 SMSC EMCT03 CONVERSION RATE 000 Reserved 001 Reserved 010 Reserved 011 1 Conversions per second 100 2 Conversions per second 101 4 Conversions per second 110 8 Conversions per second 111 16 Conversions per second 11 DATASHEET Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet A conversion for all 3 temperature readings takes about 60ms. Therefore, the maximum conversion rate, equals 16 conversions per second. Bits 6 set of the Configuration Register sets the power mode of the part: Table 3.12 Configuration Registers Data Format NRUN/STOP 0 1 DESCRIPTION Run Mode Standby Mode In Run Mode, the EMCT03 will operate at the preset conversion rate. In Standby Mode, the part is powered down to minimize current consumption. The SMBus is fully operational in either mode. In Standby Mode, a WRITE command to the One Shot register will trigger a one time conversion of the 3 temperature monitors. After the part finishes the conversion, it will go back to Standby Mode. The host can now read the updated temperature information. Revision 2.3 (04-19-05) 12 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet Chapter 4 Application Information This chapter provides information on maintaining accuracy when using diodes as remote sensors with SMSC Environmental Monitoring and Control devices. It is assumed that the users have some familiarity with hardware design and transistor characteristics. SMSC supplies a family Environmental Monitoring and Control (EMC) devices that are capable of accurately measuring temperatures. Most devices include an internal temperature sensor along with the ability to measure one or more external sensors. The characteristics of an appropriate diode for use as the external sensor are listed in this chapter. Recommendations for the printed circuit board layout are provided to help reduce error caused by electical noise or trace resistance. 4.1 Maintaining Accuracy 4.1.1 Physical Factors Temperature measurement is performed by measuring the change in forward bias voltage of a diode when two different currents are forced through the junction. The circuit board itself can impact the ability to accurately measure these small changes in voltage. For example, an excessive amount of series resistance can introduce error in the measurement. 4.1.1.1 Layout Apply the following guidelines when designing the printed circuit board: 1. Route the remote diode traces on the top layer. 2. Place a ground guard signal on both sides of the differential pair. This guard band should be connected to the ground plane at least every 0.25 inches. 3. Place a ground plane on the layer immediately below the diode traces. 4. Keep the diode traces as short as possible. 5. Keep the diode traces parallel, and the length of the two traces identical within 0.3 inches. 6. Use a trace width of 0.01 inches with a 0.01 inch guard band on each side. 7. Keep the diode traces away from sources of high frequency noise such as power supply filtering or high speed digital signals. 8. When the diode traces must cross high speed digital signals, make them cross at a 90 degree angle. 9. Avoid joints of copper to solder that can introduce thermocouple effects. These recommendations are illustrated in Figure 4.1 Routing the Diode Traces on page 14. SMSC EMCT03 13 DATASHEET Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet .01 GAP MIN. .01 WIDE MIN. .01 WIDE MIN. .01 GAP MIN. DP or DN GND PLANE .01 GAP MIN. DP or DN COPPER TRACE COPPER TRACE GND PLANE BOARD MATERIAL COPPER PLANE (TO SHIELD FROM NOISE) RECOMMEND VIA STICTCHING AT .25 INCH INTERVALS. Figure 4.1 Routing the Diode Traces 4.1.1.2 Bypass Capacitors Accurate temperature measurements require a clean, stable power supply. Locate a 0.1µF capacitor as close as possible to the power pin with a good ground. A low ESR capacitor (such as a 10µF ceramic) should be placed across the power source. Add additional power supply filtering in systems that have a noisy power supply. A capacitor may be placed across the DP/DN pair at the remote sensor in noisy environments. Do not exceed a value of 100 pF if this capacitor is installed. 4.1.1.3 Manufacturing Circuit board assembly processes may leave a residue on the board. This residue can result in unexpected leakage currents that may introduce errors if the circuit board is not clean. For example, processes that use water-soluble soldering fluxes have been known to cause problems if the board is not kept clean. 4.1.1.4 Thermal Considerations Keep the sensor in good thermal contact with the component to be measured. The temperature of the leads of a discrete diode will greatly impact the temperature of the diode junction. Make use of the printed circuit board to disperse any self-heating that may occur. 4.1.1.5 Remote Sensors Connected by Cables When connecting remote diodes with a cable (instead of traces on the PCB) use shielded twisted pair cable. The shield should be attached to ground near the EMCT03, and should be left unconnected at the sensor end. Belden 8451 cable is a good choice for this application. 4.1.2 Sensor Characteristics The characteristics of the diode junction used for temperature sensing will affect the accuracy of the measurement. 4.1.2.1 Selecting a Sensor A diode connected small signal transistor is recommended. Silicon diodes are not a good choice for remote sensors. Small signal transistors such as the 2N3904 or the 2N3906 are recommended. Desired characteristics for the sensor include the following: 1. Constant value of hFE in the range of 7.5 to 130 microamps. Variation in hFE from one device to another or one manufacturer to another cancels out of the temperature equations. Revision 2.3 (04-19-05) 14 DATASHEET SMSC EMCT03 1°C Triple SMBus Temperature Sensor Datasheet 2. The lowest emitter and base resistance values will also be helpful as a matter of series input resistance 4.1.2.2 Compensating for Ideality of the diode The remote diode may have an ideality factor based on the manufacturing process. Inaccuracy in the temperature measurement resulting from this ideality factor may be eliminated by calibrating the remote diode with the temperature sensor. The EMCT03 is trimmed to an ideality factor of 1.008. 4.1.2.3 Circuit Connections The more negative terminal for the remote temperature diode, DN, is internally biased with a forward diode voltage. Terminal DN is not referenced to ground. Remote temperature diodes can be constructed as shown in Figure 4.2 Remote Temperature Diode Examples on page 15. To DP To DP To DP To DN To DN To DN Local Ground Typical Remote Parasitic Substrate Transistor e.g. CPU substrate PNP Typical Remote Discrete PNP Transistor e.g 2N3906 Typical Remote Discrete NPN Transistor e.g. 2N3904 Figure 4.2 Remote Temperature Diode Examples Environmental Monitoring and Control (EMC) devices supplied by SMSC are designed to make accurate temperature measurements. Careful design of the printed circuit board and proper selection of the remote sensing diode will help to maintain the accuracy. SMSC EMCT03 15 DATASHEET Revision 2.3 (04-19-05) 1°C Triple SMBus Temperature Sensor Datasheet Chapter 5 Package Outline Figure 5.1 8-Pin MSOP Package Outline - 3x3mm Body 0.65mm Pitch Table 5.1 8-Pin MSOP Package Parameters MIN NOMINAL MAX REMARKS A 0.80 ~ 1.10 Overall Package Height A1 0.05 ~ 0.15 Standoff A2 0.75 0.85 0.95 Body Thickness D 2.80 3.00 3.20 X Body Size E 4.65 4.90 5.15 Y Span E1 2.80 ~ 3.20 Y body Size H 0.08 ~ 0.23 Lead Foot Thickness L 0.40 ~ 0.80 Lead Foot Length L1 0.95 REF e Lead Length 0.65 BSC Lead Pitch θ 0o W 0.22 ~ 0.38 Lead Width ccc ~ ~ 0.10 Coplanarity ~ 8o Lead Foot Angle Notes: 1. Controlling Unit: millimeters. 2. Tolerance on the true position of the leads is ± 0.065 mm maximum. 3. Package body dimensions D and E1 do not include mold protrusion or flash. Dimensions D and E1 to be determined at datum plane H. Maximum mold protrusion or flash is 0.15mm (0.006 inches) per end, and 0.15mm (0.006 inches) per side. 4. Dimension for foot length L measured at the gauge plane 0.25 mm above the seating plane. 5. Details of pin 1 identifier are optional but must be located within the zone indicated. Revision 2.3 (04-19-05) 16 DATASHEET SMSC EMCT03