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19-1766; Rev 2; 5/03
Multichannel Remote/Local Temperature Sensors
________________General Description
The MAX1668/MAX1805/MAX1989 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 low-cost, easily mounted 2N3904 NPN types--that replace conventional thermistors or thermocouples. Remote accuracy is 3C 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 (SMBusTM) 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 1C, 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.
____________________________Features
o Multichannel 4 Remote, 1 Local (MAX1668/MAX1989) 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 2C (+60C to +100C, Local) 3C (-40C to +125C, Local) 3C (+60C to +100C, Remote) o 3A (typ) Standby Supply Current o 700A (max) Supply Current o Small, 16-Pin QSOP/TSSOP Packages
MAX1668/MAX1805/MAX1989
_______________Ordering Information ________________________Applications
Desktop and Notebook Computers LAN Servers Industrial Controls Central-Office Telecom Equipment Test and Measurement Multichip Modules
PART MAX1668MEE MAX1805MEE MAX1989MEE MAX1989MUE TEMP RANGE -55C to +125C -55C to +125C -55C to +125C -55C to +125C PIN-PACKAGE 16 QSOP 16 QSOP 16 QSOP 16 TSSOP
Pin Configuration
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 16 GND 15 STBY 14 SMBCLK
Typical Operating Circuit
0.1F 3V TO 5.5V 200 VCC STBY 10k EACH
MAX1668 MAX1805 MAX1989
MAX1668 MAX1805 MAX1989
13 SMBDATA 12 ALERT 11 ADD0 10 ADD1 9 VCC
DXP1 2200pF
SMBCLK SMBDATA ALERT
CLOCK DATA INTERRUPT TO C
*
DXN1
DXP4 2200pF
*
DXN4 ADD0 ADD1 GND
QSOP/TSSOP
( ) ARE FOR MAX1805.
* DIODE-CONNECTED TRANSISTOR
Patents Pending 1
SMBus is a trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products
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Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
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 = +70C) QSOP (derate 8.30mW/C above +70C) ....................667mW TSSOP (derate 9.40mW/C above +70C) ..................755mW Operating Temperature Range .........................-55C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +125C, unless otherwise noted.) PARAMETER ADC AND POWER SUPPLY Temperature Resolution (Note 1) Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2, 3) Temperature Error, Local Diode (Notes 1, 2) Supply Voltage Range Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On Reset (POR) Threshold POR Threshold Hysteresis Logic inputs forced to VCC or GND SMBus static Hardware or software standby, SMBCLK at 10kHz VCC, falling edge 1.3 VCC input, disables A/D conversion, rising edge Monotonicity guaranteed TA = +60C to +100C TA = 0C to +125C TR = +60C to +100C TR = -55C to +125C Including long-term drift TA = +60C to +100C TA = 0C to +85C 8 -2 -3 -3 -5 -2.5 -3.5 3.0 2.60 2.8 50 1.8 50 3 5 400 260 70 7 320 100 10 200 50 0.7 ADD0, ADD1; momentary upon power-on reset 160 V A 10 A 12 700 380 130 13 A A ms 2.3 +2 +3 +3 +5 +2.5 +3.5 5.5 2.95 Bits C C C V V mV V mV CONDITIONS MIN TYP MAX UNITS
Standby Supply Current
Average Operating Supply Current Conversion Time
Average measured over 4s; logic inputs forced VCC or GND From stop bit to conversion complete (all channels) High level (POR state) Low level (POR state) Configuration byte = X0XXXX10, high level Configuration byte = X0XXXX01, high level
Remote-Diode Source Current
DXP_ forced to 1.5V
DXN_ Source Voltage Address Pin Bias Current
2
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Multichannel Remote/Local Temperature Sensors
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA = 0C to +125C, unless otherwise noted.) PARAMETER SMBus INTERFACE Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current ALERT Output High Leakage Current Logic Input Current SMBus Input Capacitance SMBus Clock Frequency SMBCLK Clock Low Time SMBCLK Clock High Time SMBus Start-Condition Setup Time SMBus Repeated Start-Condition Setup Time SMBus Start-Condition Hold Time SMBus Stop-Condition Setup Time SMBus Data Valid to SMBCLK Rising-Edge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time tSU:STA, 90% to 90% points tHD:STA, 10% of SMBDATA to 90% of SMBCLK tSU:STO, 90% of SMBCLK to 10% of SMBDATA tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK tHD:DAT, slave receive (Note 5) Master clocking in data STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V ALERT, SMBDATA forced to 0.4V ALERT forced to 5.5V Logic inputs forced to VCC or GND SMBCLK, SMBDATA (Note 4) tLOW, 10% to 10% points tHIGH, 90% to 90% points DC 4.7 4 4.7 250 4 4 250 0 1 -1 5 100 6 1 +1 2.2 0.8 V V mA A A pF kHz s s s ns s s ns ns s CONDITIONS MIN TYP MAX UNITS
MAX1668/MAX1805/MAX1989
ELECTRICAL CHARACTERISTICS
(VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55C to +125C, unless otherwise noted.) (Note 6) PARAMETER ADC AND POWER SUPPLY Temperature Resolution Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2, 3) Supply-Voltage Range Conversion Time From stop bit to conversion complete (both channels) Monotonicity guaranteed TA = +60C to +100C TA = -55C to +125C TR = +60C to +100C TR = -55C to +125C 8 -2 -3 -3 -5 4.5 260 +2 +3 +3 +5 5.5 380 Bits C C V ms CONDITIONS MIN TYP MAX UNITS
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3
Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = -55C to +125C, unless otherwise noted.) (Note 6) PARAMETER SMBus INTERFACE Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current ALERT Output High Leakage Current Logic Input Current STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V ALERT, SMBDATA forced to 0.4V ALERT forced to 5.5V Logic inputs forced to VCC or GND -2 6 1 +2 2.4 0.8 V V mA A A CONDITIONS MIN TYP MAX UNITS
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 +66.7C, the ADC may report +66C, +67C, or +68C (due to the quantization error plus the +0.5C offset used for rounding up) and still be within the guaranteed 1C error limits for the +60C to +100C 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 -55C to +125C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25C, unless otherwise noted.)
TEMPERATURE ERROR vs. PC BOARD RESISTANCE
MAX1668/1805 toc01
TEMPERATURE ERROR vs. TEMPERATURE
MAX1668/1805 toc02
TEMPERATURE ERROR vs. SUPPLY NOISE FREQUENCY
WITH VCC 0.1F CAPACITOR REMOVED 2200pF BETWEEN DXN_ AND DXP_ 250mVP-P 16 12 8 4 0
MAX1668/1805 toc03
20
4 3 TEMPERATURE ERROR (C) NPN (CMPT3904) 2 1 0 -1 INTERNAL PNP (CMPT3906)
24 20 TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
10 PATH = DXP_ TO GND 0
-10
PATH = DXP_ TO VCC (5V)
100mVP-P
-20 1 10 LEAKAGE RESISTANCE (M) 100
-2 -50 -30 -10 10 30 50 70 90 110 TEMPERATURE (C)
0.1
1
10
100
FREQUENCY (MHz)
4
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Multichannel Remote/Local Temperature Sensors
Typical Operating Characteristics (continued)
(Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25C, unless otherwise noted.)
MAX1668/MAX1805/MAX1989
TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
MAX1668/1805 toc04
TEMPERATURE ERROR vs. DXP_ TO DXN_ CAPACITANCE
MAX16681805 toc05
STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY
STBY = GND 50 SUPPLY CURRENT (A) 40 30 20 VCC = 3.3V 10 0
MAX1668/1805 toc06
2.0 1.8 TEMPERATURE ERROR (C) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.1 1 10 FREQUENCY (MHz) 100 50mVP-P 100mVP-P SQUARE-WAVE AC-COUPLED INTO DXN 2200pF BETWEEN DXN_ AND DXP_
4 2 TEMPERATURE ERROR (C) 0 -2 -4 -6 -8 -10
60
VCC = 5V
1000
0
10
20
30
40
50
60
1
10
100
1000
DXP_ TO DXN_ CAPACITANCE (nF)
SMBCLK FREQUENCY (kHz)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1668/1805 toc07
RESPONSE TO THERMAL SHOCK
MAX1668/1805 toc08
160 STBY = GND 140 SUPPLY CURRENT (A) 120 100 80 60 40 ADD0 = ADD1 = HIGH-Z 20 0 0 1 2 3 4 5 SUPPLY VOLTAGE (V) ADD0 = ADD1 = GND
125
100 TEMPERATURE (C)
75
50
25 16 QSOP IMMERSED IN +115C FLUORINERT BATH 0 -2 0 2 TIME (s) 4 6 8
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5
Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
Pin Description
PIN MAX1668/ MAX1989 1, 3, 5, 7 FUNCTION MAX1805 NAME 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. Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above ground. Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1F capacitor. A 200 series resistor is recommended but not required for additional noise filtering. 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 addressrecognition problems. SMBus Slave Address Select Pin SMBus Alert (Interrupt) Output, Open Drain SMBus Serial-Data Input/Output, Open Drain SMBus Serial-Clock Input Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operate mode. Ground No Connection. Not internally connected. Can be used for PC board trace routing.
1, 3
DXP_
2, 4, 6, 8 9 10 11 12 13 14 15 16
2, 4 9 10 11 12 13 14 15 16 5-8
DXN_ VCC ADD1 ADD0 ALERT SMBDATA SMBCLK STBY GND N.C.
--
_______________Detailed Description
The MAX1668/MAX1805/MAX1989 are temperature sensors designed to work in conjunction with an external microcontroller (C) or other intelligence in thermostatic, process-control, or monitoring applications. The C is typically a power-management or keyboard controller, generating SMBus serial commands by "bitbanging" general-purpose input-output (GPIO) pins or through 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/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 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, 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 causes about +0.5C error per ohm. Likewise, 200V of offset voltage forced on DXP_ to DXN_ causes about 1C error.
6
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STBY
ADD ADD1
DXP4 DXN4 ADDRESS DECODER MUX CURRENT SOURCES SMBDATA SMBus SMBCLK ADC DIODE FAULT LOCAL CONTROL LOGIC
DXP3 DXN3
DXP2 DXN2
DXP1 DXN1
COMMAND BYTE REGISTER TEMPERATURE DATA REGISTERS
Figure 1. MAX1668/MAX1805/MAX1989 Functional Diagram
STATUS BYTE REGISTERS 1 AND 2 HIGH LIMITS REGISTERS CONFIGURATION BYTE REGISTER LOW LIMITS REGISTERS ALERT RESPONSE ADDRESS REGISTER ALERT R ALERT MASK REGISTER S Q DIGITAL COMPARATORS NOTE: DOTTED LINES ARE FOR MAX1668 AND MAX1989.
MAX1668/MAX1805/MAX1989
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Multichannel Remote/Local Temperature Sensors
7
Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
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.
Table 1. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Motorola (USA) National Semiconductor (USA) Rohm Semiconductor (Japan) Samsung (Korea) Siemens (Germany) Zetex (England) MODEL NO. CMPT3904 MMBT3904 MMBT3904 SST3904 KST3904-TF SMBT3904 FMMT3904CT-ND
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/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; otherwise, the A/D input voltage range can be violated. The forward voltage must be greater than 0.25V at 10A; check to ensure this is true at the highest expected temperature. The forward voltage must be less than 0.95V at 100A; check to ensure this is true at the lowest expected temperature. Large power transistors do not work at all. Also, ensure that the base resistance is less than 100. 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).
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 400A plus 0.4V x 1mA. Package theta J-A is about 150C/W, so with VCC = 5V and no copper PC board heat sinking, the resulting temperature rise is: dT = 2.4mW x 150C/W = 0.36C 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 +1C to +10C, depending on the frequency and amplitude (see the Typical Operating Characteristics).
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 +1C after a sudden +100C 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
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
8
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Multichannel Remote/Local Temperature Sensors
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 +30C 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 20M leakage path from DXP_ to ground causes about +1C 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 3V/C, and it takes about 200V of voltage error at DXP_ to DXN_ to cause a +1C 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 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 signals does not help reduce EMI.
10mils
MAX1668/MAX1805/MAX1989
GND 10mils DXP_ MINIMUM 10mils DXN_ 10mils GND
Figure 2. Recommended DXP_/DXN_ PC Traces
* Place the noise filter and the 0.1F V CC bypass capacitors close to the MAX1668/MAX1805/ MAX1989. * Add a 200 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 particularly noisy environments, a twisted pair is recommended. Its practical length is 6ft to 12ft (typ) 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 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-sensor distances (see the 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; 1 series resistance introduces about +0.5C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply-current drain to less than 12A. 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 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 is received while a conversion is in progress, the conver9
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 connecting to GND.
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Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
sion 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 3A. 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 100A, depending on ADD0 and ADD1 settings. tion. 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 1C (Table 2), transmitted MSB first. Measurements are offset by +0.5C to minimize internal rounding errors; for example, +99.6C is reported as +100C.
SMBus Digital Interface
From a software perspective, the MAX1668/MAX1805/ MAX1989 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/MAX1989 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 instrucWrite Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line of a 3-wire interface Read Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line WR ACK COMMAND 8 bits Command Byte: selects which register you are reading from ACK S ADDRESS 7 bits RD WR ACK COMMAND 8 bits Command Byte: selects which register you are writing to ACK
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 of the MAX1668 and MAX1805 is full scale (0111 1111, or +127C). The POR state of the channel 1 THIGH register of the MAX1989 is 0110 1110 or +110C, while all other channels are at +127C. The POR state of all TLOW registers is 1100 1001 or -55C.
DATA 8 bits
ACK
P 1
Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate)
ACK
DATA 8 bits
///
P
Slave Address: repeated due to change in dataflow direction Receive Byte Format
Data Byte: reads from the register set by the command byte
Send Byte Format S ADDRESS 7 bits WR ACK COMMAND 8 bits Command Byte: sends command with no data ACK P
S
ADDRESS 7 bits
RD
ACK
DATA 8 bits
///
P
S = Start condition P = Stop condition
Shaded = Slave transmission /// = Not acknowledged
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 ______________________________________________________________________________________
Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
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 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 MSB 111 111 111 111 001 000 000 000 000 000 111 111 110 110 100 100 011 011 LSB 1111 1111 1111 1110 1001 0000 0000 0000 0000 0000 1111 1111 0111 0110 1001 1001 1111 1111
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 Logic 1 Provide the current MAX1668/MAX1805/MAX1989 slave address that was latched at POR (Table 8) FUNCTION
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 (typ) due to the diode current source, a fault is detected. Note that the diode fault is not 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 0C 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 +127C for all remote and local channels, and the device alarms.
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
ALERT Interrupts
The ALERT interrupt output signal is latched and can only be cleared by reading the alert response address.
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Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
level sensitive). Successful reading of the alert response address clears the interrupt latch.
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/MAX1989. 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.
Table 4. Command Byte Bit Assignments for MAX1668/MAX1805/MAX1989
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 (0110 1110) 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) [0000 1011] FUNCTION Read local temperature Read remote DX1 temperature Read remote DX2 temperature Read remote DX3 temperature Read remote DX4 temperature Read status byte 1 Read status byte 2 Read Configuration Byte Read local THIGH limit Read local TLOW limit Read remote DX1 THIGH limit (MAX1989) 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) [for MAX1989]
*If the device is in hardware standby mode at POR, all temperature registers read 0C. **Not available for MAX1805. 12 ______________________________________________________________________________________
Multichannel Remote/Local Temperature Sensors
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 returns 03h for MAX1668, 05h for MAX1805, and 0Bh for MAX1989. If the read word 16-bit SMBus protocol is 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. on the status bits to indicate reversals in long-term temperature changes and instead use a current temperature reading to establish the trend direction.
MAX1668/MAX1805/MAX1989
Conversion Rate
The MAX1668/MAX1805/MAX1989 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/MAX1989 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/ MAX1989 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/MAX1989 also respond to the SMBus alert response slave address (see the Alert Response Address section).
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 (through 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
POR and Undervoltage Lockout
The MAX1668/MAX1805/MAX1989 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 (typ, see the Electrical Characteristics table). When power is first applied and V CC rises above 1.85V (typ), 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 typ). * Interrupt latch is cleared. * Address select pins are sampled. * ADC begins converting.
Power-Up Defaults
* 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.
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Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
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 standby 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
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Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
A tLOW B tHIGH C D E F G H I J K
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
tSU:DAT 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
tSU:STO I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION
tBUF
Figure 4. SMBus Read Timing Diagram
A B C D E F G H I J K L M
tLOW
tHIGH
SMBCLK
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
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. ______________________________________________________________________________________ 15
Multichannel Remote/Local Temperature Sensors MAX1668/MAX1805/MAX1989
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
QSOP.EPS
16
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Multichannel Remote/Local Temperature Sensors
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
TSSOP4.40mm.EPS
MAX1668/MAX1805/MAX1989
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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