19-1766; Rev 0; 8/00 Multichannel Remote/Local Temperature Sensor ____________________________Features 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. ♦ Multichannel 4 Remote, 1 Local (MAX1668) 2 Remote, 1 Local (MAX1805) The MAX1668/MAX1805 are available in small, 16-pin QSOP surface-mount packages. ♦ Small, 16-Pin QSOP Package ________________________Applications Desktop and Notebook Computers Central Office Telecom Equipment LAN Servers Test and Measurement Industrial Controls Multichip Modules ♦ 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 _______________Ordering Information PART MAX1668MEE MAX1805MEE Pin Configurations TEMP. RANGE -55°C to +125°C -55°C to +125°C PIN-PACKAGE 16 QSOP 16 QSOP Typical Operating Circuit 3V TO 5.5V 0.1µF 200Ω TOP VIEW DXP1 1 16 GND DXN1 2 15 STBY DXP2 3 14 SMBCLK DXN2 4 (N.C.) DXP3 5 MAX1668 MAX1805 VCC 10k EACH MAX1668 MAX1805 DXP1 2200pF 13 SMBDATA 12 ALERT (N.C.) DXN3 6 11 ADD0 (N.C.) DXP4 7 10 ADD1 (N.C.) DXN4 8 9 VCC STBY * SMBCLK SMBDATA CLOCK DATA DXN1 ALERT INTERRUPT TO µC DXP4 2200pF * DXN4 ADD0 ADD1 GND QSOP ( ) ARE FOR MAX1805. SMBus is a trademark of Intel Corp. * DIODE-CONNECTED TRANSISTOR †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† ________________General Description 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 MAX UNITS ADC AND POWER SUPPLY Temperature Resolution (Note 1) Monotonicity guaranteed 8 Initial Temperature Error, Local Diode (Note 2) TA = +60°C to +100°C -2 2 TA = 0°C to +125°C -3 3 TR = +60°C to +100°C -3 3 TR = -55°C to +125°C -5 5 TA = +60°C to +100°C -2.5 2.5 TA = 0°C to +85°C -3.5 3.5 Temperature Error, Remote Diode (Notes 2 and 3) Temperature Error, Local Diode (Notes 1 and 2) Including long-term drift Supply-Voltage Range Undervoltage Lockout Threshold 3.0 VCC input, disables A/D conversion, rising edge 2.60 Undervoltage Lockout Hysteresis Power-On Reset Threshold (POR) VCC, falling edge 1.3 Logic inputs forced to VCC or GND °C °C V V mV 2.3 V mV 3 10 Hardware or software standby, SMBCLK at 10kHz 5 12 400 700 µA ms Conversion Time From stop bit to conversion complete (all channels) DXP_ forced to 1.5V µA 260 320 380 High level (POR state) 70 100 130 Low level (POR state) 7 10 13 Configuration byte = X0XXXX10, high level 200 Configuration byte = X0XXXX01, high level 50 DXN_ Source Voltage 2 1.8 °C SMBus static Average measured over 4s; logic inputs forced VCC or GND Address Pin Bias Current 2.95 50 Average Operating Supply Current Remote-Diode Source Current 5.5 2.8 50 POR Threshold Hysteresis Standby Supply Current Bits ADD0, ADD1; momentary upon power-on reset µA 0.7 V 160 µA _______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor (VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0°C to +125°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS SMBus INTERFACE Logic Input High Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V ALERT Output High Leakage Current ALERT forced to 5.5V Logic Input Current Logic inputs forced to VCC or GND SMBus Input Capacitance SMBCLK, SMBDATA SMBus Clock Frequency (Note 4) DC SMBCLK Clock Low Time tLOW, 10% to 10% points 4.7 µs SMBCLK Clock High Time tHIGH, 90% to 90% points SMBus Start-Condition Setup Time 2.2 V 0.8 6 V mA -1 1 µA 1 µA 100 kHz 5 pF 4 µs 4.7 µs 250 ns SMBus Repeated Start-Condition Setup Time tSU:STA, 90% to 90% points SMBus Start-Condition Hold Time tHD:STA, 10% of SMBDATA to 90% of SMBCLK 4 µs SMBus Stop-Condition Setup Time tSU:STO, 90% of SMBCLK to 10% of SMBDATA 4 µs SMBus Data Valid to SMBCLK Rising-Edge Time tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK 250 ns SMBus Data-Hold Time tHD:DAT, slave receive (Note 5) 0 ns SMBCLK Falling Edge to SMBus Data-Valid Time Master clocking in data 1 µs MAX UNITS ELECTRICAL CHARACTERISTICS (VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55°C to +125°C, unless otherwise noted.) (Note 6) PARAMETER CONDITIONS MIN TYP ADC AND POWER SUPPLY Temperature Resolution Monotonicity guaranteed 8 Initial Temperature Error, Local Diode (Note 2) TA = +60°C to +100°C -2 2 TA = -55°C to +125°C -3 3 Temperature Error, Remote Diode (Notes 2 and 3) TR = +60°C to +100°C -3 3 TR = -55°C to +125°C -5 5 Supply-Voltage Range Conversion Time From stop bit to conversion complete (both channels) Bits °C °C 4.5 5.5 V 260 380 ms _______________________________________________________________________________________ 3 MAX1668/MAX1805 ELECTRICAL CHARACTERISTICS (continued) 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 UNITS SMBus INTERFACE Logic Input High Voltage STBY, SMBCLK, SMBDATA VCC = 4.5V to 5.5V Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V ALERT Output High Leakage Current ALERT forced to 5.5V Logic Input Current Logic inputs forced to VCC or GND 2.4 V 0.8 V 6 mA -2 1 µA 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.) 0 PATH = DXP_ TO VCC (5V) NPN (CMPT3904) 2 PNP (CMPT3906) 1 0 -1 -20 INTERNAL 10 LEAKAGE RESISTANCE (MΩ) 100 20 WITH VCC 0.1µF CAPACITOR REMOVED 2200pF BETWEEN DXN_ AND DXP_ 250mVp-p 16 12 8 100mVp-p 4 0 -2 1 4 3 24 TEMPERATURE ERROR (°C) PATH = DXP_ TO GND MAX1668/1805 toc02 10 4 TEMPERATURE ERROR (°C) MAX1668/1805 toc01 20 -10 TEMPERATURE ERROR vs. SUPPLY NOISE FREQUENCY TEMPERATURE ERROR vs. TEMPERATURE MAX1668/1805 toc03 TEMPERATURE ERROR vs. PC BOARD RESISTANCE TEMPERATURE ERROR (°C) MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor -50 -30 -10 10 30 50 70 TEMPERATURE (°C) 90 110 0.1 1 10 FREQUENCY (MHz) _______________________________________________________________________________________ 100 Multichannel Remote/Local Temperature Sensor 1.2 50mVp-p 1.0 0.8 0.6 0 -2 -4 -6 STBY = GND 50 40 30 20 10 -8 0 -10 0 0.1 1 10 100 VCC = 5V VCC = 3.3V 0.4 0.2 0 1000 10 20 30 40 50 1 60 10 100 1000 SMBCLK FREQUENCY (kHz) DXP_ TO DXN_ CAPACITANCE (nF) FREQUENCY (MHz) STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE RESPONSE TO THERMAL SHOCK STBY = GND ADD0 = ADD1 = GND 100 TEMPERATURE (°C) 120 100 80 60 40 MAX1668/1805 toc08 125 MAX1668/1805 toc07 160 140 MAX1668/1805 toc06 2 60 SUPPLY CURRENT (µA) 100mVp-p MAX16681805 toc05 1.6 1.4 4 TEMPERATURE ERROR (°C) SQUARE WAVE AC-COUPLED INTO DXN 2200pF BETWEEN DXN_ AND DXP_ SUPPLY CURRENT (µA) TEMPERATURE ERROR (°C) 1.8 MAX1668/1805 toc04 2.0 STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY TEMPERATURE ERROR vs. DXP_ TO DXN_ CAPACITANCE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY 75 50 25 ADD0 = ADD1 = HIGH-Z 16 QSOP IMMERSED IN +115°C FLUORINERT BATH 20 0 0 0 1 2 3 SUPPLY VOLTAGE (V) 4 5 -2 0 2 4 6 8 TIME (s) _______________________________________________________________________________________ 5 MAX1668/MAX1805 Typical Operating Characteristics (continued) (Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.) MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Pin Description PIN FUNCTION MAX1668 MAX1805 NAME — 5–8 N.C. No Connection. Not internally connected. May be used for PC board trace routing. 9 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. 1, 3, 5, 7 1, 3 DXP_ Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave 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, 6, 8 2, 4 DXN_ Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above ground. 10 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 may cause addressrecognition problems. 11 16 GND Ground 16 11 ADD0 SMBus Slave Address Select Pin 12 12 ALERT SMBus Alert (Interrupt) Output, Open Drain 13 13 SMBDATA SMBus Serial-Data Input/Output, Open Drain 14 14 SMBCLK SMBus Serial-Clock Input 15 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. 6 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. _______________________________________________________________________________________ DXP1 DXN1 DXP2 DXN2 DXP3 DXN3 DIODE FAULT MUX DOTTED LINES ARE FOR MAX1668. DIGITAL COMPARATORS LOW LIMITS REGISTERS HIGH LIMITS REGISTERS TEMPERATURE DATA REGISTERS LOCAL CURRENT SOURCES CONTROL LOGIC ALERT MASK REGISTER ALERT RESPONSE ADDRESS REGISTER CONFIGURATION BYTE REGISTER STATUS BYTE REGISTERS 1 AND 2 COMMAND BYTE REGISTER ADC S R SMBus ADDRESS DECODER ADD ADD1 Q ALERT SMBCLK SMBDATA MAX1668/MAX1805 DXP4 DXN4 STBY Multichannel Remote/Local Temperature Sensor Figure 1. MAX1668/MAX1805 Functional Diagram _______________________________________________________________________________________ 7 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 8 Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NUMBER Central Semiconductor (USA) CMPT3904 Motorola (USA) MMBT3904 National Semiconductor (USA) MMBT3904 Rohm Semiconductor (Japan) SST3904 Samsung (Korea) KST3904-TF Siemens (Germany) SMBT3904 Zetex (England) 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 _______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor 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. GND 10mils 10mils DXP_ MINIMUM 10mils DXN_ 10mils GND 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 V CC 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 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. MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor 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. 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. 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. SMBus Digital Interface Alarm Threshold Registers 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 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 7 bits ACK DATA 8 bits Slave Address: equivalent to chip-select line of a 3-wire interface ACK P 8 bits Command Byte: selects which register you are writing to 1 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 7 bits COMMAND ACK ACK Command Byte: selects which register you are reading from DATA WR ACK COMMAND ACK P 8 bits Command Byte: sends command with no data P 8 bits Slave Address: repeated due to change in dataflow direction Data Byte: reads from the register set by the command byte Shaded = Slave transmission /// = Not acknowledged S ADDRESS 7 bits RD ACK DATA /// P 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 Figure 3. SMBus Protocols 10 /// Receive Byte Format 7 bits S = Start condition P = Stop condition RD 7 bits Send Byte Format ADDRESS ADDRESS 8 bits Slave Address: equivalent to chip-select line S S ______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor TEMP. (°C) ROUNDED TEMP. (°C) DIGITAL OUTPUT DATA BITS SIGN MSB LSB +130.00 +127 0 111 1111 +127.00 +127 0 111 1111 +126.50 +127 0 111 1111 +126.00 +126 0 111 1110 +25.25 +25 0 001 1001 +0.50 +1 0 000 +0.25 +0 0 +0.00 +0 -0.25 Table 3. Read Format for Alert Response Address (0001100) BIT NAME 7 (MSB) ADD7 6 ADD6 5 ADD5 4 ADD4 3 ADD3 0001 2 ADD2 000 0000 1 ADD1 0 000 0000 +0 0 000 0000 0 (LSB) 1 -0.50 +0 0 000 0000 -0.75 -1 1 111 1111 -1.00 -1 1 111 1111 -25.00 -25 1 110 0111 -25.50 -25 1 110 0110 -54.75 -55 1 100 1001 -55.00 -55 1 100 1001 -65.00 -65 1 011 1111 -70.00 -65 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 V CC - 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 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. The ALERT interrupt output signal is latched and can only be cleared by reading the Alert Response address. ______________________________________________________________________________________ 11 MAX1668/MAX1805 Table 2. Data Format (Two’s Complement) MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Command Byte Functions Manufacturer and Device ID Codes 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. 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 COMMAND POR STATE RIT 00h 0000 0000* Read local temperature FUNCTION RET1 01h 0000 0000* Read remote DX1 temp. RET2 02h 0000 0000* Read remote DX2 temp. RET3** 03h 0000 0000* Read remote DX3 temp. RET4** 04h 0000 0000* Read remote DX4 temp. RS1 05h 0000 0000 Read status byte #1 RS2 06h 0000 0000 Read status byte #2 Read Configuration Byte RC 07h 0000 0000 RIHL 08h 0111 1111 Read local THIGH limit RILL 09h 1100 1001 Read local TLOW limit REHL1 0Ah 0111 1111 Read remote DX1 THIGH limit RELL1 0Bh 1100 1001 Read remote DX1 TLOW limit REHL2 0Ch 0111 1111 Read remote DX2 THIGH limit RELL2 0Dh 1100 1001 Read remote DX2 TLOW limit REHL3** 0Eh 0111 1111 Read remote DX3 THIGH limit RELL3** 0Fh 1100 1001 Read remote DX3 TLOW limit REHL4** 10h 0111 1111 Read remote DX4 THIGH limit RELL4** 11h 1100 1001 Read remote DX4 TLOW limit WC 12h N/A Write configuration byte WIHL 13h N/A Write local THIGH limit WILL 14h N/A Write local TLOW limit WEHI1 15h N/A Write remote DX1 THIGH limit WELL1 16h N/A Write remote DX1 TLOW limit Write remote DX2 THIGH limit WEHI2 17h N/A WELL2 18h N/A Write remote DX2 TLOW limit WEHI3** 19h N/A Write remote DX3 THIGH limit WELL3** 1Ah N/A Write remote DX3 TLOW limit WEHI4** 1Bh N/A Write remote DX4 THIGH limit WELL4** 1Ch N/A Write remote DX4 TLOW limit MFG ID FEh 0100 1101 DEV ID FFh 0000 0011 (0000 0101) 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 ______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor 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 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. MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor Table 5. Configuration Byte Bit Assignments BIT NAME POR FUNCTION 7 (MSB) MASKALL 0 Masks all ALERT interrupts when high. 6 RUN/STOP 0 Standby mode control bit. If high, the device immediately stops converting and enters stand-by mode. If low, the device converts. 5 MASK4* 0 Masks remote DX4 interrupts when high. 4 MASK3* 0 Masks remote DX3 interrupts when high. 3 MASK2 0 Masks remote DX2 interrupts when high. 2 MASK1 0 Masks remote DX1 interrupts when high. 0 IBIAS1 0 Medium/low-bias control bit. High = low bias, low = medium bias. IBIAS0 must be low. 1 IBIAS0 0 High-bias control bit. High bias on DXP_ when high. Overrides IBIAS1. *Not available for MAX1805. Table 6. Status Byte Bit 1 Assignments BIT NAME 7 (MSB) BUSY FUNCTION 6 LHIGH† 5 LLOW† A high indicates that the local low-temperature alarm has activated. 4 OPEN† A high indicates one of the remote-diode continuity (open-circuit) faults 3 ALARM† 2 N/A N/A 1 N/A N/A 0 N/A N/A A high indicates that the ADC is busy converting. A high indicates that the local high-temperature alarm has activated. A high indicates one of the remote-diode channels has over/undertemperature alarm. †These flags stay high until cleared by POR, or until the status byte register is read. Table 7. Status Byte 2 Bit Assignments BIT NAME 7 (MSB) RLOW1 A high indicates that the DX1 low-temperature alarm has activated. FUNCTION 6 RHIGH1 A high indicates that the DX1 high-temperature alarm has activated. 5 RLOW2 A high indicates that the DX2 low-temperature alarm has activated. 4 RHIGH2 A high indicates that the DX2 high-temperature alarm has activated. 3 RLOW3* A high indicates that the DX3 low-temperature alarm has activated. 2 RHIGH3* A high indicates that the DX3 high-temperature alarm has activated. 1 RLOW4* A high indicates that the DX4 low-temperature alarm has activated. 0 RHIGH4* 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 ______________________________________________________________________________________ Multichannel Remote/Local Temperature Sensor MAX1668/MAX1805 Table 8. Slave Address Decoding (ADD0 and ADD1) ADD0 ADD1 ADDRESS GND GND 0011 000 GND High-Z 0011 001 GND VCC 0011 010 High-Z GND 0101 001 High-Z High-Z 0101 010 High-Z VCC 0101 011 VCC GND 1001 100 VCC High-Z 1001 101 VCC VCC 1001 110 Note: High-Z means that the pin is left unconnected and floating. A B tLOW C D F E G H J I tHIGH K SMBCLK SMBDATA tSU:STA tHD:STA tSU:STO 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 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 tBUF I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION Figure 4. SMBus Read Timing Diagram A tLOW B tHIGH C D E F G H I J K L M SMBCLK SMBDATA tSU:STA tHD:STA 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 tSU:DAT tHD:DAT 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 tSU:STO tBUF 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 ________________________________________________________Package Information QSOP.EPS MAX1668/MAX1805 Multichannel Remote/Local Temperature Sensor 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.