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MAX1989MUE+T

hot MAX1989MUE+T

MAX1989MUE+T

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Part Number MAX1989MUE+T
Manufacturer Maxim Integrated
Description SENSOR TEMPERATURE SMBUS 16TSSOP
Datasheet MAX1989MUE+T Datasheet
Package 16-TSSOP (0.173", 4.40mm Width)
In Stock 8022 piece(s)
Unit Price $ 5.2265 *
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MAX1989MUE+T Specifications

ManufacturerMaxim Integrated
CategorySensors, Transducers - Temperature Sensors, Transducers
Datasheet MAX1989MUE+T Datasheet
Package16-TSSOP (0.173", 4.40mm Width)
Series-
Sensor TypeDigital, Local/Remote
Sensing Temperature - Local-55°C ~ 125°C
Sensing Temperature - Remote-55°C ~ 125°C
Output TypeSMBus
Voltage - Supply4.5 V ~ 5.5 V
Resolution7 b
FeaturesOutput Switch, Standby Mode
Accuracy - Highest (Lowest)��2.5°C (��3.5°C)
Test Condition60°C ~ 100°C (0°C ~ 85°C)
Operating Temperature-55°C ~ 125°C
Mounting TypeSurface Mount
Package / Case16-TSSOP (0.173", 4.40mm Width)
Supplier Device Package16-TSSOP

MAX1989MUE+T Datasheet

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________________General Description The MAX1668/MAX1805/MAX1989 are precise multi- channel digital thermometers that report the tempera- ture of all remote sensors and their own packages. The remote sensors are diode-connected transistors—typi- cally low-cost, easily mounted 2N3904 NPN types—that replace conventional thermistors or thermocouples. Remote accuracy is ±3°C for multiple transistor manu- facturers, with no calibration needed. The remote chan- nels can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. The 2-wire serial interface accepts standard system management bus (SMBus™) write byte, read byte, send byte, and receive byte commands to program the alarm thresholds and to read temperature data. The data for- mat is 7 bits plus sign, with each bit corresponding to 1°C, in two’s-complement format. The MAX1668/MAX1805/MAX1989 are available in small, 16-pin QSOP surface-mount packages. The MAX1989 is also available in a 16-pin TSSOP. ________________________Applications ____________________________Features  Multichannel 4 Remote, 1 Local (MAX1668/MAX1989) 2 Remote, 1 Local (MAX1805)  No Calibration Required  SMBus 2-Wire Serial Interface  Programmable Under/Overtemperature Alarms  Supports SMBus Alert Response  Accuracy ±2°C (+60°C to +100°C, Local) ±3°C (-40°C to +125°C, Local) ±3°C (+60°C to +100°C, Remote)  3µA (typ) Standby Supply Current  700µA (max) Supply Current  Small, 16-Pin QSOP/TSSOP Packages M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors ________________________________________________________________ Maxim Integrated Products 1 SMBCLK ADD0 ADD1 VCC STBY GND ALERT SMBDATA DXP1 DXP4 DXN4 INTERRUPT TO µC 3V TO 5.5V 200Ω 0.1µF CLOCK 10kΩ EACH DATA DXN1 2200pF 2200pF * DIODE-CONNECTED TRANSISTOR * * MAX1668 MAX1805 MAX1989 Pin Configuration 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 DXP1 GND STBY SMBCLK SMBDATA ALERT ADD0 ADD1 VCC TOP VIEW MAX1668 MAX1805 MAX1989 QSOP/TSSOP DXN1 DXP2 (N.C.) DXN3 DXN2 (N.C.) DXP3 (N.C.) DXP4 ( ) ARE FOR MAX1805. (N.C.) DXN4 Typical Operating Circuit 19-1766; Rev 2; 5/03 PART MAX1668MEE -55°C to +125°C TEMP RANGE PIN-PACKAGE 16 QSOP _______________Ordering Information SMBus is a trademark of Intel Corp. †Pg MAX1805MEE -55°C to +125°C 16 QSOP Desktop and Notebook Computers LAN Servers Industrial Controls Central-Office Telecom Equipment Test and Measurement Multichip Modules MAX1989MEE -55°C to +125°C 16 QSOP For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX1989MUE -55°C to +125°C 16 TSSOP

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M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors 2 _______________________________________________________________________________________ ABSOLUTE MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS (VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0°C to +125°C, unless otherwise noted.) Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. VCC to GND..............................................................-0.3V to +6V DXP_, ADD_, STBY to GND........................-0.3V to (VCC + 0.3V) DXN_ to GND ........................................................-0.3V to +0.8V SMBCLK, SMBDATA, ALERT to GND......................-0.3V to +6V SMBDATA, ALERT Current .................................-1mA to +50mA DXN_ Current......................................................................±1mA Continuous Power Dissipation (TA = +70°C) QSOP (derate 8.30mW/°C above +70°C)....................667mW TSSOP (derate 9.40mW/°C above +70°C) ..................755mW Operating Temperature Range .........................-55°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C DXP_ forced to 1.5VRemote-Diode Source Current Low level (POR state) Configuration byte = X0XXXX10, high level Configuration byte = X0XXXX01, high level High level (POR state) 7 10 13 200 50 DXN_ Source Voltage 0.7 V Hardware or software standby, SMBCLK at 10kHz SMBus static TA = 0°C to +85°C TA = +60°C to +100°C Average measured over 4s; logic inputs forced VCC or GND Temperature Error, Local Diode (Notes 1, 2) -3.5 +3.5 °C -2.5 +2.5 Including long-term drift Temperature Error, Remote Diode (Notes 2, 3) -5 +5 °C -3 +3 TR = -55°C to +125°C TR = +60°C to +100°C PARAMETER MIN TYP MAX UNITS Undervoltage Lockout Hysteresis 50 mV Undervoltage Lockout Threshold 2.60 2.8 2.95 V Supply Voltage Range 3.0 5.5 V Initial Temperature Error, Local Diode (Note 2) -3 +3 °C Power-On Reset (POR) Threshold 1.3 1.8 2.3 V POR Threshold Hysteresis 50 mV 3 10 Standby Supply Current 5 12 µA Temperature Resolution (Note 1) 8 Bits -2 +2 Average Operating Supply Current 400 700 µA Conversion Time 260 320 380 ms 70 100 130 µA Address Pin Bias Current 160 µA CONDITIONS VCC input, disables A/D conversion, rising edge TA = 0°C to +125°C VCC, falling edge From stop bit to conversion complete (all channels) Logic inputs forced to VCC or GND ADD0, ADD1; momentary upon power-on reset Monotonicity guaranteed TA = +60°C to +100°C ADC AND POWER SUPPLY

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M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors _______________________________________________________________________________________ 3 ELECTRICAL CHARACTERISTICS (continued) (VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0°C to +125°C, unless otherwise noted.) STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V tHIGH, 90% to 90% points tLOW, 10% to 10% points (Note 4) SMBCLK, SMBDATA Logic inputs forced to VCC or GND ALERT forced to 5.5V STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V ALERT, SMBDATA forced to 0.4V CONDITIONS µs4SMBCLK Clock High Time µs4.7SMBCLK Clock Low Time kHzDC 100SMBus Clock Frequency pF5SMBus Input Capacitance µA-1 +1Logic Input Current µA1 ALERT Output High Leakage Current V2.2Logic Input High Voltage V0.8Logic Input Low Voltage mA6Logic Output Low Sink Current UNITSMIN TYP MAXPARAMETER tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK tSU:STO, 90% of SMBCLK to 10% of SMBDATA tHD:STA, 10% of SMBDATA to 90% of SMBCLK tSU:STA, 90% to 90% points ns250 SMBus Data Valid to SMBCLK Rising-Edge Time µs4SMBus Stop-Condition Setup Time µs4SMBus Start-Condition Hold Time ns250 SMBus Repeated Start-Condition Setup Time µs4.7SMBus Start-Condition Setup Time nsSMBus Data-Hold Time Master clocking in data µs1 SMBCLK Falling Edge to SMBus Data-Valid Time SMBus INTERFACE ELECTRICAL CHARACTERISTICS (VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55°C to +125°C, unless otherwise noted.) (Note 6) CONDITIONS Monotonicity guaranteed TA = +60°C to +100°C Bits8Temperature Resolution -2 +2 TR = +60°C to +100°C TA = -55°C to +125°C °C -3 +3 Initial Temperature Error, Local Diode (Note 2) V4.5 5.5Supply-Voltage Range From stop bit to conversion complete (both channels) ms260 380Conversion Time -3 +3 TR = -55°C to +125°C °C UNITSMIN TYP MAX -5 +5 PARAMETER Temperature Error, Remote Diode (Notes 2, 3) ADC AND POWER SUPPLY tHD:DAT, slave receive (Note 5) 0

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0 8 4 16 12 20 24 M A X 1 6 6 8 /1 8 0 5 t o c0 3 FREQUENCY (MHz) TE M P ER A TU R E ER R O R ( °C ) TEMPERATURE ERROR vs. SUPPLY NOISE FREQUENCY 100mVP-P 0.1 1 10 100 WITH VCC 0.1µF CAPACITOR REMOVED 2200pF BETWEEN DXN_ AND DXP_ 250mVP-P 20 -20 1 10 100 TEMPERATURE ERROR vs. PC BOARD RESISTANCE -10 M A X 1 6 6 8 /1 8 0 5 t o c0 1 LEAKAGE RESISTANCE (MΩ) TE M P ER A TU R E ER R O R ( °C ) 0 10 PATH = DXP_ TO GND PATH = DXP_ TO VCC (5V) -2 -1 0 1 2 3 4 -50 -10-30 10 30 50 70 90 110 TEMPERATURE ERROR vs. TEMPERATURE M A X 1 6 6 8 /1 8 0 5 t o c0 2 TEMPERATURE (°C) TE M P ER A TU R E ER R O R ( °C ) NPN (CMPT3904) PNP (CMPT3906) INTERNAL Typical Operating Characteristics (Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.) M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors 4 _______________________________________________________________________________________ ELECTRICAL CHARACTERISTICS (continued) (VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55°C to +125°C, unless otherwise noted.) (Note 6) Note 1: Guaranteed by design, but not production tested. Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1668/MAX1805/ MAX1989 device temperature is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization error plus the +0.5°C offset used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to +100°C temperature range. See Table 2. Note 3: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. See the Remote-Diode Selection section for remote-diode forward-voltage requirements. Note 4: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and can monopolize the bus. Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of SMBCLK’s falling edge tHD:DAT. Note 6: Specifications from -55°C to +125°C are guaranteed by design, not production tested. CONDITIONS UNITSMIN TYP MAXPARAMETER STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5VLogic Input High Voltage V2.4 ALERT forced to 5.5V µA1 ALERT Output High Leakage Current Logic inputs forced to VCC or GND µA-2 +2Logic Input Current ALERT, SMBDATA forced to 0.4V mA6Logic Output Low Sink Current STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V V0.8Logic Input Low Voltage SMBus INTERFACE

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0 20 40 60 80 100 120 140 160 0 1 2 3 4 5 STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE M A X 1 6 6 8 /1 8 0 5 t o c0 7 SUPPLY VOLTAGE (V) S U P P LY C U R R EN T (µ A ) STBY = GND ADD0 = ADD1 = HIGH-Z ADD0 = ADD1 = GND 0 25 75 50 100 125 -2 20 4 6 8 RESPONSE TO THERMAL SHOCK M A X 1 6 6 8 /1 8 0 5 t o c0 8 TIME (s) TE M P ER A TU R E (° C ) 16 QSOP IMMERSED IN +115°C FLUORINERT BATH M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors _______________________________________________________________________________________ 5 0.1 1 1000 TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY M A X 1 6 6 8 /1 8 0 5 t o c0 4 FREQUENCY (MHz) TE M P ER A TU R E ER R O R ( °C ) 10 100 0 0.6 0.4 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SQUARE-WAVE AC-COUPLED INTO DXN 2200pF BETWEEN DXN_ AND DXP_ 100mVP-P 50mVP-P Typical Operating Characteristics (continued) (Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.) TEMPERATURE ERROR vs. DXP_ TO DXN_ CAPACITANCE M A X 1 6 6 8 1 8 0 5 t o c0 5 DXP_ TO DXN_ CAPACITANCE (nF) TE M P ER A TU R E ER R O R ( °C ) -10 -6 -8 -2 -4 2 0 4 0 20 3010 40 50 60 STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY M A X 1 6 6 8 /1 8 0 5 t o c0 6 SMBCLK FREQUENCY (kHz) S U P P LY C U R R EN T (µ A ) 60 0 10 20 30 40 50 1 10 100 1000 STBY = GND VCC = 5V VCC = 3.3V

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M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors 6 _______________________________________________________________________________________ _______________Detailed Description The MAX1668/MAX1805/MAX1989 are temperature sensors designed to work in conjunction with an exter- nal microcontroller (µC) or other intelligence in thermo- static, process-control, or monitoring applications. The µC is typically a power-management or keyboard con- troller, generating SMBus serial commands by “bit- banging” general-purpose input-output (GPIO) pins or through a dedicated SMBus interface block. These devices are essentially 8-bit serial analog-to-digi- tal converters (ADCs) with sophisticated front ends. However, the MAX1668/MAX1805/MAX1989 also contain a switched current source, a multiplexer, an ADC, an SMBus interface, and associated control logic (Figure 1). In the MAX1668 and MAX1989, temperature data from the ADC is loaded into five data registers, where it is automatically compared with data previously stored in 10 over/undertemperature alarm registers. In the MAX1805, temperature data from the ADC is loaded into three data registers, where it is automatically compared with data previously stored in six over/undertemperature alarm registers. ADC and Multiplexer The ADC is an averaging type that integrates over a 64ms period (each channel, typical), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes, measures their forward voltages, and computes their temperatures. Each channel is automatically converted once the con- version process has started. If any one of the channels is not used, the device still performs measurements on these channels, and the user can ignore the results of the unused channel. If any remote-diode channel is unused, connect DXP_ to DXN_ rather than leaving the pins open. The DXN_ input is biased at 0.65V above ground by an internal diode to set up the A/D inputs for a differential measurement. The worst-case DXP_ to DXN_ differential input voltage range is 0.25V to 0.95V. Excess resistance in series with the remote diode caus- es about +0.5°C error per ohm. Likewise, 200µV of offset voltage forced on DXP_ to DXN_ causes about 1°C error. MAX1668/ MAX1989 FUNCTION 1, 3, 5, 7 DXP_ Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP floating; connect DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. PIN 12 ALERT SMBus Alert (Interrupt) Output, Open Drain 11 ADD0 SMBus Slave Address Select Pin 10 ADD1 SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance (>50pF) at the address pins when floating can cause address- recognition problems. 15 STBY Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operate mode. 14 SMBCLK SMBus Serial-Clock Input 13 SMBDATA SMBus Serial-Data Input/Output, Open Drain 1, 3 12 11 10 15 14 13 Pin Description NAMEMAX1805 2, 4, 6, 8 DXN_ Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode volt- age above ground. 2, 4 9 VCC Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recommended but not required for additional noise filtering. 9 16 GND Ground16 — N.C. No Connection. Not internally connected. Can be used for PC board trace routing.5–8

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M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors _______________________________________________________________________________________ 7 Figure 1. MAX1668/MAX1805/MAX1989 Functional Diagram D XP 4 D XP 3 D XP 2 D XP 1 D XN 4 D XN 3 D XN 2 D XN 1 LO C AL C U RR EN T SO U RC ES M U X D IO D E FA U LT AD C C O N TR O L LO G IC SM Bu s AD D RE SS D EC O D ER ST BY A D D A D D 1 SM BD AT A SM BC LK AL ER T Q R S D IG IT AL C O M PA RA TO RS AL ER T RE SP O N SE C O N FI G U RA TI O N B YT E AD D RE SS R EG IS TE R RE G IS TE R ST AT U S BY TE R EG IS TE RS 1 AN D 2 C O M M AN D B YT E RE G IS TE R TE M PE RA TU RE D AT A RE G IS TE RS H IG H L IM IT S RE G IS TE RS LO W L IM IT S RE G IS TE RS AL ER T M AS K RE G IS TE R N O TE : D O TT ED L IN ES A RE F O R M AX 16 68 A N D M AX 19 89 .

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A/D Conversion Sequence If a start command is written (or generated automatically in the free-running autoconvert mode), all channels are converted, and the results of all measurements are available after the end of conversion. A BUSY status bit in the status byte shows that the device is actually per- forming a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available. Remote-Diode Selection Temperature accuracy depends on having a good-qual- ity, diode-connected small-signal transistor. Accuracy has been experimentally verified for all of the devices listed in Table 1. The MAX1668/MAX1805/MAX1989 can also directly measure the die temperature of CPUs and other ICs having on-board temperature-sensing diodes. The transistor must be a small-signal type, either NPN or PNP, with a relatively high forward voltage; other- wise, the A/D input voltage range can be violated. The forward voltage must be greater than 0.25V at 10µA; check to ensure this is true at the highest expected temperature. The forward voltage must be less than 0.95V at 100µA; check to ensure this is true at the low- est expected temperature. Large power transistors do not work at all. Also, ensure that the base resistance is less than 100Ω. Tight specifications for forward-current gain (+50 to +150, for example) indicate that the manu- facturer has good process controls and that the devices have consistent VBE characteristics. For heat-sink mounting, the 500-32BT02-000 thermal sensor from Fenwal Electronics is a good choice. This device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (Fenwal Inc., Milford, MA, 508-478-6000). Thermal Mass and Self-Heating Thermal mass can seriously degrade the MAX1668/ MAX1805/MAX1989s’ effective accuracy. The thermal time constant of the 16-pin QSOP package is about 140s in still air. For the MAX1668/MAX1805/MAX1989 junction temperature to settle to within +1°C after a sudden +100°C change requires about five time con- stants or 12 minutes. The use of smaller packages for remote sensors, such as SOT23s, improves the situa- tion. Take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. Self-heating does not significantly affect measurement accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode, the worst-case error occurs when sinking maximum current at the ALERT output. For example, with ALERT sinking 1mA, the typical power dissipation is VCC x 400µA plus 0.4V x 1mA. Package theta J-A is about 150°C/W, so with VCC = 5V and no copper PC board heat sinking, the resulting temperature rise is: dT = 2.4mW x 150°C/W = 0.36°C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors. ADC Noise Filtering The ADC is an integrating type with inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower opera- tion places constraints on high-frequency noise rejec- tion; therefore, careful PC board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. High-frequency EMI is best filtered at DXP_ and DXN_ with an external 2200pF capacitor. This value can be increased to about 3300pF (max), including cable capacitance. Higher capacitance than 3300pF intro- duces errors due to the rise time of the switched cur- rent source. Nearly all noise sources tested cause additional error measurements, typically by +1°C to +10°C, depending on the frequency and amplitude (see the Typical Operating Characteristics). PC Board Layout 1) Place the MAX1668/MAX1805/MAX1989 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors 8 _______________________________________________________________________________________ CMPT3904Central Semiconductor (USA) MMBT3904Motorola (USA) MMBT3904 SST3904Rohm Semiconductor (Japan) KST3904-TFSamsung (Korea) FMMT3904CT-NDZetex (England) MANUFACTURER MODEL NO. SMBT3904Siemens (Germany) Table 1. Remote-Sensor Transistor Manufacturers Note: Transistors must be diode connected (base shorted to collector). National Semiconductor (USA)

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be 4in to 8in (typ) or more as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. 2) Do not route the DXP_ to DXN_ lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30°C error, even with good filtering. Otherwise, most noise sources are fairly benign. 3) Route the DXP_ and DXN_ traces in parallel and in close proximity to each other, away from any high- voltage traces such as +12VDC. Leakage currents from PC board contamination must be dealt with carefully, since a 20MΩ leakage path from DXP_ to ground causes about +1°C error. 4) Connect guard traces to GND on either side of the DXP_ to DXN_ traces (Figure 2). With guard traces in place, routing near high-voltage traces is no longer an issue. 5) Route through as few vias and crossunders as possi- ble to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the DXP_ and the DXN_ paths have matching thermocouples. In general, PC board-induced ther- mocouples are not a serious problem. A copper-sol- der thermocouple exhibits 3µV/°C, and it takes about 200µV of voltage error at DXP_ to DXN_ to cause a +1°C measurement error. So, most para- sitic thermocouple errors are swamped out. 7) Use wide traces. Narrow ones are more inductive and tend to pick up radiated noise. The 10mil widths and spacings recommended in Figure 2 are not absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) Copper cannot be used as an EMI shield, and only ferrous materials such as steel work well. Placing a copper ground plane between the DXP_ to DXN_ traces and traces carrying high-frequency noise sig- nals does not help reduce EMI. PC Board Layout Checklist • Place the MAX1668/MAX1805/MAX1989 as close as possible to the remote diodes. • Keep traces away from high voltages (+12V bus). • Keep traces away from fast data buses and CRTs. • Use recommended trace widths and spacings. • Place a ground plane under the traces. • Use guard traces flanking DXP_ and DXN_ and con- necting to GND. • Place the noise filter and the 0.1µF VCC bypass capacitors close to the MAX1668/MAX1805/ MAX1989. • Add a 200Ω resistor in series with VCC for best noise filtering (see the Typical Operating Circuit). Twisted-Pair and Shielded Cables For remote-sensor distances longer than 8in, or in partic- ularly noisy environments, a twisted pair is recommend- ed. Its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electronics lab- oratory. For longer distances, the best solution is a shielded twisted pair like that used for audio micro- phones. For example, Belden #8451 works well for dis- tances up to 100ft in a noisy environment. Connect the twisted pair to DXP_ and DXN_ and the shield to GND, and leave the shield’s remote end unterminated. Excess capacitance at DX_ _ limits practical remote-sen- sor distances (see the Typical Operating Characteristics). For very long cable runs, the cable’s parasitic capaci- tance often provides noise filtering, so the 2200pF capac- itor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy; 1Ω series resistance introduces about +0.5°C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the sup- ply-current drain to less than 12µA. Enter standby mode by forcing the STBY pin low or through the RUN/STOP bit in the configuration byte register. Hardware and software standby modes behave almost identically: all data is retained in memory, and the SMB interface is alive and listening for reads and writes. Activate hardware standby mode by forcing the STBY pin low. In a notebook computer, this line can be con- nected to the system SUSTAT# suspend-state signal. The STBY pin low state overrides any software conversion command. If a hardware or software standby command is received while a conversion is in progress, the conver- M A X 1 6 6 8 /M A X 1 8 0 5 /M A X 1 9 8 9 † Multichannel Remote/Local Temperature Sensors _______________________________________________________________________________________ 9 MINIMUM 10mils 10mils 10mils 10mils GND GND DXN_ DXP_ Figure 2. Recommended DXP_/DXN_ PC Traces

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