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MAX1668/MAX1805† 19-1766; Rev 0; 8/00 Multichannel Remote/Local Temperature Sensor ________________General Description The MAX1668/MAX1805 are precise multichannel digital thermometers that report the temperature of all remote sensors and their own packages. The remote sensors are diode-connected transistors—typically lowcost, easily mounted 2N3904 NPN types—that replace conventional thermistors or thermocouples. Remote accuracy is ±3°C for multiple transistor manufacturers, with no calibration needed. The remote channels 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 format is 7 bits plus sign, with each bit corresponding to 1°C, in two’s-complement format. The MAX1668/MAX1805 are available in small, 16-pin QSOP surface-mount packages. ________________________Applications Desktop and Notebook Computers Central Office Telecom Equipment LAN Servers Test and Measurement Industrial Controls Multichip Modules ____________________________Features o Multichannel 4 Remote, 1 Local (MAX1668) 2 Remote, 1 Local (MAX1805) o No Calibration Required o SMBus 2-Wire Serial Interface o Programmable Under/Overtemperature Alarms o Supports SMBus Alert Response o 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) o 3µA (typ) Standby Supply Current o 700µA (max) Supply Current o Small, 16-Pin QSOP Package _______________Ordering Information PART MAX1668MEE MAX1805MEE TEMP. RANGE -55°C to +125°C -55°C to +125°C PIN-PACKAGE 16 QSOP 16 QSOP Pin Configurations Typical Operating Circuit TOP VIEW DXP1 1 DXN1 2 DXP2 3 DXN2 4 (N.C.) DXP3 5 (N.C.) DXN3 6 (N.C.) DXP4 7 (N.C.) DXN4 8 ( ) ARE FOR MAX1805. MAX1668 MAX1805 QSOP 16 GND 15 STBY 14 SMBCLK 13 SMBDATA 12 ALERT 11 ADD0 10 ADD1 9 VCC 0.1µF 3V TO 5.5V 200Ω 2200pF * 2200pF * VCC STBY MAX1668 MAX1805 DXP1 SMBCLK DXN1 SMBDATA ALERT DXP4 DXN4 ADD0 ADD1 GND 10k EACH CLOCK DATA INTERRUPT TO µC * DIODE-CONNECTED TRANSISTOR SMBus is a trademark of Intel Corp. †Patents Pending ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor ABSOLUTE MAXIMUM RATINGS 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 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 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. ELECTRICAL CHARACTERISTICS (VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0°C to +125°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP ADC AND POWER SUPPLY Temperature Resolution (Note 1) Monotonicity guaranteed 8 Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2 and 3) Temperature Error, Local Diode (Notes 1 and 2) Supply-Voltage Range TA = +60°C to +100°C TA = 0°C to +125°C TR = +60°C to +100°C TR = -55°C to +125°C Including long-term drift -2 -3 -3 -5 TA = +60°C to +100°C -2.5 TA = 0°C to +85°C -3.5 3.0 Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis VCC input, disables A/D conversion, rising edge 2.60 2.8 50 Power-On Reset Threshold (POR) POR Threshold Hysteresis VCC, falling edge 1.3 1.8 50 Logic inputs SMBus static 3 Standby Supply Current forced to VCC or GND Hardware or software standby, SMB- CLK at 10kHz 5 Average Operating Supply Current Average measured over 4s; logic inputs forced VCC or GND 400 Conversion Time From stop bit to conversion complete (all channels) 260 320 High level (POR state) 70 100 Low level (POR state) 7 10 Remote-Diode Source Current DXP_ forced to 1.5V Configuration byte = X0XXXX10, high level 200 Configuration byte = X0XXXX01, high level 50 DXN_ Source Voltage 0.7 Address Pin Bias Current ADD0, ADD1; momentary upon power-on reset 160 MAX UNITS Bits 2 °C 3 3 °C 5 2.5 °C 3.5 5.5 V 2.95 V mV 2.3 V mV 10 µA 12 700 µA 380 ms 130 13 µA V µA 2 _______________________________________________________________________________________ MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor ELECTRICAL CHARACTERISTICS (continued) (VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0°C to +125°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP SMBus INTERFACE Logic Input High Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V 2.2 Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V 6 ALERT Output High Leakage Current ALERT forced to 5.5V Logic Input Current SMBus Input Capacitance Logic inputs forced to VCC or GND SMBCLK, SMBDATA -1 5 SMBus Clock Frequency (Note 4) DC SMBCLK Clock Low Time tLOW, 10% to 10% points 4.7 SMBCLK Clock High Time tHIGH, 90% to 90% points 4 SMBus Start-Condition Setup Time 4.7 SMBus Repeated Start-Condition Setup Time tSU:STA, 90% to 90% points 250 SMBus Start-Condition Hold Time tHD:STA, 10% of SMBDATA to 90% of SMBCLK 4 SMBus Stop-Condition Setup Time tSU:STO, 90% of SMBCLK to 10% of SMBDATA 4 SMBus Data Valid to SMBCLK Rising-Edge Time tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK 250 SMBus Data-Hold Time tHD:DAT, slave receive (Note 5) 0 SMBCLK Falling Edge to SMBus Data-Valid Time Master clocking in data MAX UNITS V 0.8 V mA 1 µA 1 µA pF 100 kHz µs µs µs ns µs µs ns ns 1 µs ELECTRICAL CHARACTERISTICS (VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55°C to +125°C, unless otherwise noted.) (Note 6) PARAMETER CONDITIONS MIN TYP MAX ADC AND POWER SUPPLY Temperature Resolution Monotonicity guaranteed 8 Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2 and 3) Supply-Voltage Range TA = +60°C to +100°C TA = -55°C to +125°C TR = +60°C to +100°C TR = -55°C to +125°C -2 2 -3 3 -3 3 -5 5 4.5 5.5 Conversion Time From stop bit to conversion complete (both channels) 260 380 UNITS Bits °C °C V ms _______________________________________________________________________________________ 3 MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor ELECTRICAL CHARACTERISTICS (continued) (VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55°C to +125°C, unless otherwise noted.) (Note 6) PARAMETER CONDITIONS MIN TYP MAX SMBus INTERFACE UNITS Logic Input High Voltage STBY, SMBCLK, SMBDATA VCC = 4.5V to 5.5V 2.4 Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V 6 ALERT Output High Leakage Current ALERT forced to 5.5V V 0.8 V mA 1 µA Logic Input Current Logic inputs forced to VCC or GND -2 2 µA 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 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 +1/2°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 Remote Diode Selection 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 may 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. __________________________________________Typical Operating Characteristics (Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.) TEMPERATURE ERROR (°C) MAX1668/1805 toc01 TEMPERATURE ERROR (°C) MAX1668/1805 toc02 TEMPERATURE ERROR (°C) MAX1668/1805 toc03 TEMPERATURE ERROR vs. PC BOARD RESISTANCE 20 10 PATH = DXP_ TO GND 0 TEMPERATURE ERROR vs. TEMPERATURE 4 3 NPN (CMPT3904) 2 PNP (CMPT3906) 1 TEMPERATURE ERROR vs. SUPPLY NOISE FREQUENCY 24 WITH VCC 0.1µF CAPACITOR REMOVED 2200pF BETWEEN DXN_ AND DXP_ 20 250mVp-p 16 12 0 -10 PATH = DXP_ TO VCC (5V) -1 INTERNAL 8 100mVp-p 4 -20 1 10 100 LEAKAGE RESISTANCE (MΩ) -2 -50 -30 -10 10 30 50 70 90 110 TEMPERATURE (°C) 0 0.1 1 10 100 FREQUENCY (MHz) 4 _______________________________________________________________________________________ MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Typical Operating Characteristics (continued) (Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.) TEMPERATURE ERROR (°C) TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY 2.0 1.8 SQUARE WAVE AC-COUPLED INTO DXN 2200pF BETWEEN DXN_ AND DXP_ 1.6 1.4 100mVp-p 1.2 1.0 50mVp-p 0.8 0.6 0.4 0.2 0 0.1 1 10 100 1000 FREQUENCY (MHz) MAX1668/1805 toc04 TEMPERATURE ERROR (°C) TEMPERATURE ERROR vs. DXP_ TO DXN_ CAPACITANCE 4 2 0 -2 -4 -6 -8 -10 0 10 20 30 40 50 60 DXP_ TO DXN_ CAPACITANCE (nF) MAX16681805 toc05 SUPPLY CURRENT (µA) MAX1668/1805 toc06 STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY 60 STBY = GND 50 40 30 VCC = 5V 20 VCC = 3.3V 10 0 1 10 100 1000 SMBCLK FREQUENCY (kHz) MAX1668/1805 toc08 STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE 160 STBY = GND 140 ADD0 = ADD1 = GND 120 MAX1668/1805 toc07 RESPONSE TO THERMAL SHOCK 125 100 TEMPERATURE (°C) SUPPLY CURRENT (µA) 100 75 80 60 50 40 20 0 0 ADD0 = ADD1 = HIGH-Z 1 2 3 4 5 SUPPLY VOLTAGE (V) 25 16 QSOP IMMERSED IN +115°C FLUORINERT BATH 0 -2 0 2 4 6 8 TIME (s) _______________________________________________________________________________________ 5 MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Pin Description PIN MAX1668 MAX1805 NAME FUNCTION — 5–8 N.C. No Connection. Not internally connected. May be used for PC board trace routing. 9 1, 3, 5, 7 2, 4, 6, 8 10 11 16 12 13 14 15 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. Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave 1, 3 DXP_ DXP floating; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. 2, 4 DXN_ Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above ground. SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. 10 ADD1 Excess capacitance (>50pF) at the address pins when floating may cause address- recognition problems. 16 GND Ground 11 ADD0 SMBus Slave Address Select Pin 12 ALERT SMBus Alert (Interrupt) Output, Open Drain 13 SMBDATA SMBus Serial-Data Input/Output, Open Drain 14 SMBCLK SMBus Serial-Clock Input 15 STBY Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operate mode. _______________Detailed Description The MAX1668/MAX1805 are temperature sensors designed to work in conjunction with an external microcontroller (µC) or other intelligence in thermostatic, process-control, or monitoring applications. The µC is typically a power-management or keyboard controller, generating SMBus serial commands by “bit-banging” general-purpose input-output (GPIO) pins or via a dedicated SMBus interface block. These devices are essentially 8-bit serial analog-to-digital converters (ADCs) with sophisticated front ends. However, the MAX1668/MAX1805 also contain a switched current source, a multiplexer, an ADC, an SMBus interface, and associated control logic (Figure 1). In the MAX1668, 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 conversion 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, tie 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 analog-to-digital (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 causes about +1/2°C error per ohm. Likewise, 200µV of offset voltage forced on DXP_ to DXN causes about 1°C error. 6 _______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor Figure 1. MAX1668/MAX1805 Functional Diagram _______________________________________________________________________________________ 7 DXP4 DXN4 DXP3 DXN3 DXP2 DXN2 DXP1 DXN1 CURRENT SOURCES LOCAL MUX DIODE FAULT TEMPERATURE DATA REGISTERS HIGH LIMITS REGISTERS LOW LIMITS REGISTERS DIGITAL COMPARATORS DOTTED LINES ARE FOR MAX1668. MAX1668/MAX1805 STBY ADD ADD1 ADDRESS DECODER ADC CONTROL SMBus LOGIC SMBDATA SMBCLK COMMAND BYTE REGISTER STATUS BYTE REGISTERS 1 AND 2 CONFIGURATION BYTE REGISTER ALERT RESPONSE ADDRESS REGISTER ALERT MASK REGISTER R S Q ALERT MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor 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 performing 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-quality, diode-connected small-signal transistor. Accuracy has been experimentally verified for all of the devices listed in Table 1. The MAX1668/MAX1805 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; otherwise, 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 lowest expected temperature. Large power transistors don’t 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 manufacturer 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’s effective accuracy. The thermal time constant of the QSOP-16 package is about 140s in still air. For the MAX1668/MAX1805 junction temperature to settle to within +1°C after a sudden +100°C change requires about five time constants or 12 minutes. The use of smaller packages for remote sensors, such as SOT23s, improves the situation. 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 Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NUMBER Central Semiconductor (USA) Motorola (USA) National Semiconductor (USA) Rohm Semiconductor (Japan) Samsung (Korea) Siemens (Germany) Zetex (England) CMPT3904 MMBT3904 MMBT3904 SST3904 KST3904-TF SMBT3904 FMMT3904CT-ND Note: Transistors must be diode connected (base shorted to collector). 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 operation places constraints on high-frequency noise rejection; 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 introduces errors due to the rise time of the switched current source. Nearly all noise sources tested cause additional error measurements, typically by +1°C to +10°C, depending on the frequency and amplitude (see Typical Operating Characteristics). PC Board Layout 1) Place the MAX1668/MAX1805 as close as practical to the remote diode. In a noisy environment, such 8 _______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor MAX1668/MAX1805 as a computer motherboard, this distance can be 4 inches to 8 inches (typical) 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 highvoltage 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 possible 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 thermocouples are not a serious problem. A copper-solder 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 parasitic 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 aren’t absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) Copper can’t 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 signals does not help reduce EMI. PC Board Layout Checklist • Place the MAX1668/MAX1805 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. 10mils 10mils GND DXP_ DXN_ GND 10mils MINIMUM 10mils Figure 2. Recommended DXP_/DXN_ PC Traces • Use guard traces flanking DXP_ and DXN_ and connecting to GND. • Place the noise filter and the 0.1µF VCC bypass capacitors close to the MAX1668/MAX1805. • Add a 200Ω resistor in series with VCC for best noise filtering (see Typical Operating Circuit). Twisted-Pair and Shielded Cables For remote-sensor distances longer than 8 inches, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6 feet to 12 feet (typical) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100 feet 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 sensor distances (see Typical Operating Characteristics). For very long cable runs, the cable’s parasitic capacitance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy; 1Ω series resistance introduces about +1/2°C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the supply-current drain to less than 12µA. Enter standby mode by forcing the STBY pin low or via 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 may be connected to the system SUSTAT# suspend-state signal. The STBY pin low state overrides any software conversion command. If a hardware or software standby command _______________________________________________________________________________________ 9 Multichannel Remote/Local Temperature Sensor MAX1668/MAX1805 is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into either temperature reading register. The previous data is not changed and remains available. In standby mode, supply current drops to about 3µA. At very low supply voltages (under the power-on-reset threshold), the supply current is higher due to the address pin bias currents. It can be as high as 100µA, depending on ADD0 and ADD1 settings. SMBus Digital Interface From a software perspective, the MAX1668/MAX1805 appear as a set of byte-wide registers that contain temperature data, alarm threshold values, or control bits. A standard SMBus 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. Each A/D channel within the devices responds to the same SMBus slave address for normal reads and writes. The MAX1668/MAX1805 employ four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte (Figure 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data register was previously selected by a Read Byte instruction. Use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master. The temperature data format is 7 bits plus sign in two’s-complement form for each channel, with each data bit representing 1°C (Table 2), transmitted MSB first. Measurements are offset by +1/2°C to minimize internal rounding errors; for example, +99.6°C is reported as +100°C. Alarm Threshold Registers Ten (six for MAX1805) registers store alarm threshold data, with high-temperature (THIGH) and low-temperature (TLOW) registers for each A/D channel. If either measured temperature equals or exceeds the corresponding alarm threshold value, an ALERT interrupt is asserted. The power-on-reset (POR) state of all THIGH registers is full scale (0111 1111, or +127°C). The POR state of all TLOW registers is 1100 1001 or -55°C. Write Byte Format S ADDRESS WR ACK COMMAND ACK DATA ACK P 7 bits 8 bits 8 bits 1 Slave Address: equivalent to chip-select line of a 3-wire interface Command Byte: selects which register you are writing to Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) Read Byte Format S ADDRESS WR ACK COMMAND ACK S ADDRESS RD ACK DATA /// P 7 bits 8 bits 7 bits 8 bits Slave Address: equivalent to chip-select line Command Byte: selects which register you are reading from Slave Address: repeated due to change in dataflow direction Data Byte: reads from the register set by the command byte Send Byte Format Receive Byte Format S ADDRESS WR ACK COMMAND ACK P 7 bits 8 bits Command Byte: sends command with no data S = Start condition P = Stop condition Shaded = Slave transmission /// = Not acknowledged Figure 3. SMBus Protocols S ADDRESS RD ACK DATA /// P 7 bits 8 bits Data Byte: This command only works immediately following a Read Byte. Reads data from the register commanded by that last Read Byte; also used for SMBus Alert Response return address 10 ______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor MAX1668/MAX1805 Table 2. Data Format (Two’s Complement) TEMP. (°C) +130.00 +127.00 +126.50 +126.00 +25.25 +0.50 +0.25 +0.00 -0.25 -0.50 -0.75 -1.00 -25.00 -25.50 -54.75 -55.00 -65.00 -70.00 ROUNDED TEMP. (°C) +127 +127 +127 +126 +25 +1 +0 +0 +0 +0 -1 -1 -25 -25 -55 -55 -65 -65 DIGITAL OUTPUT DATA BITS SIGN MSB LSB 0 111 1111 0 111 1111 0 111 1111 0 111 1110 0 001 1001 0 000 0001 0 000 0000 0 000 0000 0 000 0000 0 000 0000 1 111 1111 1 111 1111 1 110 0111 1 110 0110 1 100 1001 1 100 1001 1 011 1111 1 011 1111 Diode Fault Alarm There is a continuity fault detector at DXP_ that detects whether the remote diode has an open-circuit condition. At the beginning of each conversion, the diode fault is checked, and the status byte is updated. This fault detector is a simple voltage detector; if DXP_ rises above VCC - 1V (typical) due to the diode current source, a fault is detected. Note that the diode fault isn’t checked until a conversion is initiated, so immediately after power-on reset, the status byte indicates no fault is present, even if the diode path is broken. If any remote channel is shorted (DXP_ to DXN_ or DXP_ to GND), the ADC reads 0000 0000 so as not to trip either the THIGH or TLOW alarms at their POR settings. In applications that are never subjected to 0°C in normal operation, a 0000 0000 result can be checked to indicate a fault condition in which DXP_ is accidentally short circuited. Similarly, if DXP_ is short circuited to VCC, the ADC reads +127°C for all remote and local channels, and the device alarms. ALERT Interrupts The ALERT interrupt output signal is latched and can only be cleared by reading the Alert Response address. Table 3. Read Format for Alert Response Address (0001100) BIT 7 (MSB) 6 5 4 3 2 1 0 (LSB) NAME ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 1 FUNCTION Provide the current MAX1668/MAX1805 slave address that was latched at POR (Table 8) Logic 1 Interrupts are generated in response to THIGH and TLOW comparisons and when a remote diode is disconnected (for continuity fault detection). The interrupt does not halt automatic conversions; new temperature data continues to be available over the SMBus interface after ALERT is asserted. The interrupt output pin is open drain so that devices can share a common interrupt line. The interrupt rate can never exceed the conversion rate. The interface responds to the SMBus Alert Response address, an interrupt pointer return-address feature (see Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. Alert Response Address The SMBus Alert Response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the Alert Response slave address (0001 100). Then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus (Table 3). The Alert Response can activate several different slave devices simultaneously, similar to the I2C General Call. If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until serviced (implies that the host interrupt input is level sensitive). Successful reading of the alert response address clears the interrupt latch. ______________________________________________________________________________________ 11 MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Command Byte Functions The 8-bit command byte register (Table 4) is the master index that points to the various other registers within the MAX1668/MAX1805. The register’s POR state is 0000 0000, so that a Receive Byte transmission (a protocol that lacks the command byte) that occurs immediately after POR returns the current local temperature data. Manufacturer and Device ID Codes Two ROM registers provide manufacturer and device ID codes. Reading the Manufacturer ID returns 4Dh, which is the ASCII code M (for Maxim). Reading the device ID will return 03h for MAX1668, and 05h for MAX1805. If Read Word 16-bit SMBus protocol is Table 4. Command Byte Bit Assignments for MAX1668/MAX1805 REGISTER RIT RET1 RET2 RET3** RET4** RS1 RS2 RC RIHL RILL REHL1 RELL1 REHL2 RELL2 REHL3** RELL3** REHL4** RELL4** WC WIHL WILL WEHI1 WELL1 WEHI2 WELL2 WEHI3** WELL3** WEHI4** WELL4** MFG ID DEV ID COMMAND 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 12h 13h 14h 15h 16h 17h 18h 19h 1Ah 1Bh 1Ch FEh FFh POR STATE 0000 0000* 0000 0000* 0000 0000* 0000 0000* 0000 0000* 0000 0000 0000 0000 0000 0000 0111 1111 1100 1001 0111 1111 1100 1001 0111 1111 1100 1001 0111 1111 1100 1001 0111 1111 1100 1001 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 0100 1101 0000 0011 (0000 0101) FUNCTION Read local temperature Read remote DX1 temp. Read remote DX2 temp. Read remote DX3 temp. Read remote DX4 temp. Read status byte #1 Read status byte #2 Read Configuration Byte Read local THIGH limit Read local TLOW limit Read remote DX1 THIGH limit Read remote DX1 TLOW limit Read remote DX2 THIGH limit Read remote DX2 TLOW limit Read remote DX3 THIGH limit Read remote DX3 TLOW limit Read remote DX4 THIGH limit Read remote DX4 TLOW limit Write configuration byte Write local THIGH limit Write local TLOW limit Write remote DX1 THIGH limit Write remote DX1 TLOW limit Write remote DX2 THIGH limit Write remote DX2 TLOW limit Write remote DX3 THIGH limit Write remote DX3 TLOW limit Write remote DX4 THIGH limit Write remote DX4 TLOW limit Read manufacture ID Read device ID (for MAX1805) *If the device is in hardware standby mode at POR, all temperature registers read 0°C. **Not available for MAX1805. 12 ______________________________________________________________________________________ MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor employed (rather than the 8-bit Read Byte), the least significant byte contains the data and the most significant byte contains 00h in both cases. Configuration Byte Functions The configuration byte register (Table 5) is used to mask (disable) interrupts and to put the device in software standby mode. Status Byte Functions The two status byte registers (Tables 6 and 7) indicate which (if any) temperature thresholds have been exceeded. The first byte also indicates whether the ADC is converting and whether there is an open circuit in a remote diode DXP_ to DXN_ path. After POR, the normal state of all the flag bits is zero, assuming none of the alarm conditions are present. The status byte is cleared by any successful read of the status byte, unless the fault persists. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit is cleared. When reading the status byte, you must check for internal bus collisions caused by asynchronous ADC timing, or else disable the ADC prior to reading the status byte (via the RUN/STOP bit in the configuration byte). To check for internal bus collisions, read the status byte. If the least significant 7 bits are ones, discard the data and read the status byte again. The status bits LHIGH, LLOW, RHIGH, and RLOW are refreshed on the SMBus clock edge immediately following the stop condition, so there is no danger of losing temperature-related status data as a result of an internal bus collision. The OPEN status bit (diode continuity fault) is only refreshed at the beginning of a conversion, so OPEN data is lost. The ALERT interrupt latch is independent of the status byte register, so no false alerts are generated by an internal bus collision. If the THIGH and TLOW limits are close together, it’s possible for both high-temp and low-temp status bits to be set, depending on the amount of time between status read operations (especially when converting at the fastest rate). In these circumstances, it’s best not to rely on the status bits to indicate reversals in long-term temperature changes and instead use a current temperature reading to establish the trend direction. Conversion Rate The MAX1668/MAX1805 are continuously measuring temperature on each channel. The typical conversion rate is approximately three conversions/s (for both devices). The resulting data is stored in the temperature data registers. Slave Addresses The MAX1668/MAX1805 appear to the SMBus as one device having a common address for all ADC channels. The device address can be set to one of nine different values by pin-strapping ADD0 and ADD1 so that more than one MAX1668/MAX1805 can reside on the same bus without address conflicts (Table 8). The address pin states are checked at POR only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-Z state detection. The MAX1668/MAX1805 also respond to the SMBus Alert Response slave address (see the Alert Response Address section). POR and Undervoltage Lockout The MAX1668/MAX1805 have a volatile memory. To prevent ambiguous power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls below 1.8V (typical, see Electrical Characteristics table). When power is first applied and VCC rises above 1.85V (typical), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC UVLO comparator, prevents the ADC from converting until there is sufficient headroom (VCC = 2.8V typical). Power-Up Defaults • Interrupt latch is cleared. • Address select pins are sampled. • ADC begins converting. • Command byte is set to 00h to facilitate quick remote Receive Byte queries. • THIGH and TLOW registers are set to max and min limits, respectively. ______________________________________________________________________________________ 13 MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Table 5. Configuration Byte Bit Assignments BIT 7 (MSB) 6 5 4 3 2 0 1 NAME MASKALL RUN/STOP MASK4* MASK3* MASK2 MASK1 IBIAS1 IBIAS0 POR 0 0 0 0 0 0 0 0 FUNCTION Masks all ALERT interrupts when high. Standby mode control bit. If high, the device immediately stops converting and enters stand-by mode. If low, the device converts. Masks remote DX4 interrupts when high. Masks remote DX3 interrupts when high. Masks remote DX2 interrupts when high. Masks remote DX1 interrupts when high. Medium/low-bias control bit. High = low bias, low = medium bias. IBIAS0 must be low. High-bias control bit. High bias on DXP_ when high. Overrides IBIAS1. *Not available for MAX1805. Table 6. Status Byte Bit 1 Assignments BIT 7 (MSB) 6 5 4 3 2 1 0 NAME BUSY LHIGH† LLOW† OPEN† ALARM† N/A N/A N/A FUNCTION A high indicates that the ADC is busy converting. A high indicates that the local high-temperature alarm has activated. A high indicates that the local low-temperature alarm has activated. A high indicates one of the remote-diode continuity (open-circuit) faults A high indicates one of the remote-diode channels has over/undertemperature alarm. N/A N/A N/A †These flags stay high until cleared by POR, or until the status byte register is read. Table 7. Status Byte 2 Bit Assignments BIT 7 (MSB) 6 5 4 3 2 1 0 NAME RLOW1 RHIGH1 RLOW2 RHIGH2 RLOW3* RHIGH3* RLOW4* RHIGH4* FUNCTION A high indicates that the DX1 low-temperature alarm has activated. A high indicates that the DX1 high-temperature alarm has activated. A high indicates that the DX2 low-temperature alarm has activated. A high indicates that the DX2 high-temperature alarm has activated. A high indicates that the DX3 low-temperature alarm has activated. A high indicates that the DX3 high-temperature alarm has activated. A high indicates that the DX4 low-temperature alarm has activated. A high indicates that the DX4 high-temperature alarm has activated. Note: All flags in this byte stay high until cleared by POR or until the status byte is read. *Not available for MAX1805. 14 ______________________________________________________________________________________ MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Table 8. Slave Address Decoding (ADD0 and ADD1) ADD0 GND GND GND High-Z High-Z High-Z VCC VCC VCC ADD1 GND High-Z VCC GND High-Z VCC GND High-Z VCC ADDRESS 0011 000 0011 001 0011 010 0101 001 0101 010 0101 011 1001 100 1001 101 1001 110 Note: High-Z means that the pin is left unconnected and floating. A B C D EF G tLOW tHIGH SMBCLK H I J K SMBDATA tSU:STA tHD:STA tSU:DAT A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE Figure 4. SMBus Read Timing Diagram E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER A B C D EF G tLOW tHIGH SMBCLK tSU:STO tBUF I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION H IJ K LM SMBDATA tSU:STA tHD:STA tSU:DAT tHD:DAT tSU:STO tBUF A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION Figure 5. SMBus Write Timing Diagram ______________________________________________________________________________________ 15 Multichannel Remote/Local Temperature Sensor ________________________________________________________Package Information MAX1668/MAX1805 QSOP.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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