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19-5260 ; Rev 0; 8/10
TION KIT EVALUA BLE ILA AVA
1C Accurate 8-Channel Temperature Sensor
General Description
The MAX6581 precision multichannel temperature sensor monitors its own temperature and the temperatures of up to seven external diode-connected transistors. All temperature channels have programmable alert and overtemperature thresholds. When the measured temperature of a channel crosses the respective threshold, a status bit is set in one of the status registers. Two open-drain alarm outputs (ALERT and OVERT) assert corresponding to these bits in the status register(s). Resistance cancellation is available for all channels and compensates for high series resistance in circuit-board traces and thermal diodes. The 2-wire serial interface accepts SMBusTM protocols (write byte, read byte, send byte, and receive byte) for reading the temperature data and programming the alarm thresholds. The MAX6581 is specified for an operating temperature range of -40NC to +125NC and is available in a 24-pin, 4mm x 4mm thin QFN package with an exposed pad. One Local Temperature
S 11-Bit, 0.125NC Resolution S High Accuracy of 1NC (max) from +60NC to
Features
S Eight Channels to Measure Seven Remote and
MAX6581
+100NC (Remote Channels)
S -64NC to +150NC Remote Temperature Range S Programmable Undertemperature/
Overtemperature Alerts
S SMBus/I2C-Compatible Interface S Two Open-Drain Alarm Outputs (ALERT and
OVERT)
S Resistance Cancellation on All Remote Channels
Applications
Desktop Computers Notebook Computers Workstations Servers Data Communications
Ordering Information/Selector Guide
PART MAX6581TG9A+ MAX6581TG9C+** MAX6581TG9E+** MAX6581TG98+** SLAVE ADDRESS 0X9A 0X9C 0X9E 0X98 PIN-PACKAGE 24 TQFN-EP* 24 TQFN-EP* 24 TQFN-EP* 24 TQFN-EP* OPERATING TEMPERATURE RANGE -40NC to +125NC -40NC to +125NC -40NC to +125NC -40NC to +125NC MEASURED TEMPERATURE RANGE -64NC to +150NC -64NC to +150NC -64NC to +150NC -64NC to +150NC
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. **Future product--contact factory for availability. Note: These devices operate over the -40NC to +125NC operating temperature range.
Typical Application Circuit appears at end of data sheet.
SMBus is a trademark of Intel Corp.
_______________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1C Accurate 8-Channel Temperature Sensor MAX6581
ABSOLUTE MAXIMUM RATINGS
(All Voltages Referenced to GND) VCC, SMBCLK, SMBDATA, ALERT, OVERT, STBY to GND..........................................-0.3V to +4V DXP_ to GND............................................ -0.3V to (VCC + 0.3V) DXN_ to GND ........................................... -0.3V to (VCC + 0.3V) SMBDATA, ALERT, OVERT Current .................. -1mA to +50mA DXN_ Current .................................................................... Q1mA Continuous Power Dissipation (TA = +70NC) 24-Pin Thin QFN (derate 27.8mW/NC above +70NC) .. 2222mW Package Junction-to-Ambient Thermal Resistance (BJA) (Note 1) ............................................................36.0NC/W Package Junction-to-Case Thermal Resistance (BJC) (Note 1) ..............................................................3.0NC/W ESD Protection (all pins, Human Body Model) ...................Q2kV Operating Temperature Range ........................ -40NC to +125NC Junction Temperature .....................................................+150NC Storage Temperature Range .......................... -65NC to +150NC Lead Temperature (soldering, 10s) ...............................+300NC Soldering Temperature (reflow) ......................................+260NC
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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 = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2) PARAMETER Supply Voltage Standby Supply Current Operating Current Temperature Resolution TA = +30NC to +85NC, TRJ = +60NC to +100NC VCC = 3.3V TA, TRJ = -40NC to +125NC TA = +30NC to +85NC, TRJ = 100NC to +150NC TA = +30NC to +85NC VCC = 3.3V TA = -40NC to +125NC TA = 0NC to +150NC TA = +30NC to +85NC, TRJ = +60NC to +100NC VCC = 3.3V TA, TRJ = -40NC to +125NC TA = +30NC to +85NC, TRJ = 100NC to +125NC TA = +30NC to +85NC VCC = 3.3V TA = -40NC to +125NC TA = 0NC to +150NC -0.85 -1.2 -2.5 -1 -2 -3 -1 -2 -2.75 -1.5 -2.5 -3.5 Q0.2 SYMBOL VCC ISS ICC1 ICC2 SMBus static During conversion, RC off During conversion, RC on CONDITIONS MIN 3.0 4 500 550 11 0.125 +0.85 +1.2 +2.5 +1 +2 +3 +1 +2 +2.75 +1.5 +2.5 +3.5 NC/V NC NC NC NC TYP MAX 3.6 15 600 650 UNITS V FA FA Bits NC
3-Sigma Temperature Accuracy (Remote Channels 1-7)
3-Sigma Temperature Accuracy (Local)
6-Sigma Temperature Accuracy (Remote Channels 1-7)
6-Sigma Temperature Accuracy (Local) Supply Sensitivity of Temperature Accuracy
2
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1C Accurate 8-Channel Temperature Sensor
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2) PARAMETER Conversion Time per Channel SYMBOL tCONV CONDITIONS Resistance cancellation mode off Resistance cancellation mode on or beta compensation on High level Low level Remote-Diode Source Current IRJ High level Low level DXP_ and DXN_ Leakage Current Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On-Reset (POR) Threshold POR Threshold Hysteresis ALERT and OVERT Output Low Voltage Input Leakage Current SMBus INTERFACE, STBY Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Output Low Voltage Input Capacitance Serial-Clock Frequency Bus Free Time Between STOP and START Condition START Condition Setup Time Repeat START Condition Setup Time START Condition Hold Time STOP Condition Setup Time Clock Low Period Clock High Period Data-In Hold Time Data-In Setup Time tSU:STA tHD:STA tSU:STO tLOW tHIGH tHD:DAT tSU:DAT (Note 5) VOL CIN fSMBCLK tBUF (Note 4) fSMBCLK = 400kHz fSMBCLK = 400kHz 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 400kHz 10% of SMBDATA to 90% of SMBCLK, fSMBCLK = 400kHz 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 400kHz 10% to 10%, fSMBCLK = 400kHz 90% to 90% 1.6 0.6 50 0.6 0.6 1 0.6 0 100 0.9 ISINK = 6mA 5 400 VOL ILEAK VIL VIH VCC = 3.6V VCC = 3.0V 2.2 -1 +1 0.1 ISINK = 1mA ISINK = 6mA -1 0.01 0.3 +1 0.8 V FA V V FA V pF kHz Fs Fs ns Fs Fs Fs Fs us ns VCC falling edge 1.3 UVLO Resistance cancellation mode off Resistance cancellation mode on or beta compensation on MIN 95 190 80 8 160 16 TYP 125 250 100 10 200 20 MAX 156 312 120 12 240 24 100 2.25 2.80 90 2.0 90 2.2 2.95 nA V mV V mV FA ms UNITS
MAX6581
Standby mode Falling edge of VCC disables ADC
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 3)
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3
1C Accurate 8-Channel Temperature Sensor MAX6581
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2) PARAMETER Receive SMBCLK/SMBDATA Rise Time Receive SMBCLK/SMBDATA Fall Time Data-Out Hold Time Pulse Width of Spike Suppressed SMBus Timeout Note Note Note Note 2: 3: 4: 5: SYMBOL tR tF tDH tSP tTIMEOUT SMBDATA low period for interface reset 50 0 25 37 50 45 CONDITIONS MIN TYP MAX 300 300 UNITS ns ns ns ns ms
All parameters are tested at TA = +85NC. Specifications over temperature are guaranteed by design. Timing specifications are guaranteed by design. The serial interface resets when SMBCLK is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK's falling edge.
Typical Operating Characteristics
(VCC = +3.3V, VSTBY = VCC, TA = +25NC, unless otherwise noted.)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6581 toc01
AVERAGE OPERATING SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6581 toc02
REMOTE-DIODE TEMPERATURE ERROR vs. REMODE-DIODE TEMPERATURE
10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 REMOTE-DIODE TEMPERATURE ERROR (C)
MAX6581 toc03
AVERAGE OPERATING SUPPLY CURRENT (A)
5.0 4.5 STANDBY SUPPLY CURRENT (A) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 3.0 3.1 3.2 3.3 3.4 3.5 HARDWARE OR SOFTWARE STANDBY SUPPLY CURRENT
400 395 390 385 380 375 370 365 360 3.0 3.1 3.2 3.3 3.4 3.5 RESISTANCE CANCELLATION OFF
3.6
3.6
-10
10
30
50
70
90
110
130
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
REMOTE-DIODE TEMPERATURE (C)
4
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1C Accurate 8-Channel Temperature Sensor
Typical Operating Characteristics (continued)
(VCC = +3.3V, VSTBY = VCC, TA = +25NC, unless otherwise noted.)
LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE
MAX6581 toc04
MAX6581
REMOTE-DIODE TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
REMOTE-DIODE TEMPERATURE ERROR (C) 4 3 2 1 0 -1 -2 -3 -4 -5 0.001 0.01 0.1 1 10 100mVP-P TRJ = +85C
MAX6581 toc05
5 4 LOCAL TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 -5
5
-10 0 10 20 30 40 50 60 70 80 90 100 DIE TEMPERATURE (C)
POWER-SUPPLY NOISE FREQUENCY (MHz)
LOCAL TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6581 toc06
REMOTE-DIODE TEMPERATURE ERROR vs. CAPACITANCE
REMOTE-DIODE TEMPERATURE ERROR (C) 4 3 2 1 0 -1 -2 -3 -4 -5 1 10 CAPACITANCE (nF) 100 100mVP-P TRJ = +85C
MAX6581 toc07
5 4 LOCAL TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 -5 0.001 0.01 0.1
100mVP-P
5
1
10
POWER-SUPPLY NOISE FREQUENCY (MHz)
REMOTE-DIODE TEMPERATURE ERROR vs. RESISTANCE
REMOTE-DIODE TEMPERATURE ERROR (C) 45 40 35 30 25 20 15 10 5 0 -5 0 10 20 30 40 50 60 70 80 90 100 RESISTANCE (I) RESISTANCE CANCELLATION ON RESISTANCE CANCELLATION OFF TRJ = +85C
MAX6581 toc08
50
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1C Accurate 8-Channel Temperature Sensor MAX6581
Pin Configuration
OVERT ALERT DXP7 13 12 11 10 DXN7 DXP6 DXN6 DXN5 DXP5 DXN4 9 *EP 8 7 1 DXP2 2 DXN2 3 DXP3 4 DXN3 5 DXP4 6 N.C. STBY 14 VCC I.C. 15
TOP VIEW
18 SMBDATA 19 SMBCLK 20 GND 21 N.C. 22 DXP1 23 DXN1 24
17
16
MAX6581
*EP = EXPOSED PAD, CONNECT TO GND
Pin Description
PIN NAME FUNCTION Combined Current Source and ADC Positive Input for Channel 2 Remote Diode. Connect DXP2 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP2 unconnected or connect to DXN2 if a remote diode is not used. Connect a 100pF capacitor between DXP2 and DXN2 for noise filtering. Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diodeconnected transistor to DXN2. If the channel 2 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN2. Leave DXN2 unconnected or connect to DXP2 if a remote diode is not used. Connect a 100pF capacitor between DXP2 and DXN2 for noise filtering. Combined Current Source and ADC Positive Input for Channel 3 Remote Diode. Connect DXP3 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP3 unconnected or connect to DXN3 if a remote diode is not used. Connect a 100pF capacitor between DXP3 and DXN3 for noise filtering. Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 3 remote-diodeconnected transistor to DXN3. If the channel 3 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN3. Leave DXN3 unconnected or connect to DXP3 if a remote diode is not used. Connect a 100pF capacitor between DXP3 and DXN3 for noise filtering. Combined Current Source and ADC Positive Input for Channel 4 Remote Diode. Connect DXP4 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP4 unconnected or connect to DXN4 if a remote diode is not used. Connect a 100pF capacitor between DXP4 and DXN4 for noise filtering. No Connection. Connect to other N.C. or leave unconnected.
1
DXP2
2
DXN2
3
DXP3
4
DXN3
5
DXP4
6, 22
N.C.
6
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1C Accurate 8-Channel Temperature Sensor
Pin Description (continued)
PIN NAME FUNCTION Cathode Input for Channel 4 Remote Diode. Connect the cathode of the channel 4 remote-diodeconnected transistor to DXN4. If the channel 4 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN4. Leave DXN4 unconnected or connect to DXP4 if a remote diode is not used. Connect a 100pF capacitor between DXP4 and DXN4 for noise filtering. Combined Current Source and ADC Positive Input for Channel 5 Remote Diode. Connect DXP5 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP5 unconnected or connect to DXN5 if a remote diode is not used. Connect a 100pF capacitor between DXP5 and DXN5 for noise filtering. Cathode Input for Channel 5 Remote Diode. Connect the cathode of the channel 5 remote-diodeconnected transistor to DXN5. If the channel 5 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN5. Leave DXN5 unconnected or connect to DXP5 if a remote diode is not used. Connect a 100pF capacitor between DXP5 and DXN5 for noise filtering. Cathode Input for Channel 6 Remote Diode. Connect the cathode of the channel 6 remote-diodeconnected transistor to DXN6. If the channel 6 remote transistor is a pnp to DXN6. Leave DXN6 unconnected or connect to DXP6 if a remote diode is not used. Connect a 100pF capacitor between DXP6 and DXN6 for noise filtering. Combined Current Source and ADC Positive Input for Channel 6 Remote Diode. Connect DXP6 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP6 unconnected or connect to DXN6 if a remote diode is not used. Connect a 100pF capacitor between DXP6 and DXN6 for noise filtering. Cathode Input for Channel 7 Remote Diode. Connect the cathode of the channel 7 remote-diodeconnected transistor to DXN7. If the channel 7 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN7. Leave DXN7 unconnected or connect to DXP7 if a remote diode is not used. Connect a 100pF capacitor between DXP7 and DXN7 for noise filtering. Combined Current Source and ADC Positive Input for Channel 7 Remote Diode. Connect DXP7 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP7 unconnected or connect to DXN7 if a remote diode is not used. Place a 100pF capacitor between DXP7 and DXN7 for noise filtering. Active-Low Standby Input. Drive STBY logic-low to place the MAX6581 in standby mode, or logichigh for normal mode. Temperature and threshold data are retained in standby mode. Internally Connected. I.C. is internally connected to VCC. Connect I.C. to VCC or leave unconnected. Overtemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature of any remote channel exceeds the programmed threshold limit. Supply Voltage Input. Bypass to GND with a 0.1FF capacitor. SMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature of any channel crosses a programmed ALERT high or low threshold. SMBus Serial-Data Input/Output. Connect SMBDATA to a pullup resistor. SMBus Serial-Clock Input. Connect SMBCLK to a pullup resistor.
MAX6581
7
DXN4
8
DXP5
9
DXN5
10
DXN6
11
DXP6
12
DXN7
13
DXP7
14 15 16 17 18 19 20
STBY I.C. OVERT VCC ALERT SMBDATA SMBCLK
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1C Accurate 8-Channel Temperature Sensor MAX6581
Pin Description (continued)
PIN 21 NAME GND Ground Combined Current Source and ADC Positive Input for Channel 1 Remote Diode. Connect DXP1 to the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP1 unconnected or connect to DXN1 if a remote diode is not used. Connect a 100pF capacitor between DXP1 and DXN1 for noise filtering. Cathode Input for Channel 1 Remote Diode. Connect the cathode of the channel 1 remote-diodeconnected transistor to DXN7. If the channel 1 remote transistor is a substrate pnp (e.g., on a CPU die), connect the base of the pnp to DXN1. Leave DXN1 unconnected or connect to DXP1 if a remote diode is not used. Connect a 100pF capacitor between DXP1 and DXN1 for noise filtering. Exposed Pad. Connect EP to GND. FUNCTION
23
DXP1
24
DXN1
--
EP
Detailed Description
The MAX6581 is a precision multichannel temperature monitor that features one local and seven remote temperature-sensing channels with a programmable alert threshold for each temperature channel and a programmable overtemperature threshold for channels 1-7 (see Figure 1). Communication with the MAX6581 is achieved through the SMBus serial interface and a dedicated alert pin (ALERT). The alarm outputs, (OVERT and ALERT) assert if the software-programmed temperature thresholds are exceeded. ALERT also asserts if the measured temperature falls below the ALERT low limits. ALERT typically serves as an interrupt, while OVERT can be connected to a fan, system shutdown, or other thermalmanagement circuitry. The MAX6581 starts the conversion sequence by measuring the temperature on channel 1, followed by 2, local channel, 3-7. The conversion result for each active channel is stored in the corresponding temperature data register. No conversion is performed on any channel that does not have a diode. Enter software-standby mode by setting the STOP bit to 1 in the Configuration 1 register. Enter hardwarestandby by pulling STBY low. Software-standby mode disables the ADC and reduces the supply current to approximately 4FA. During either software or hardware standby, data is retained in memory. During hardware standby, the SMBus interface is inactive. During software
standby, the SMBus interface is active and listening for commands. The timeout is enabled if a START condition is recognized on SMBus. Activity on the SMBus causes the supply current to increase. If a standby command is received while a conversion is in progress, the conversion cycle is interrupted, and the temperature registers are not updated. The previous data is not changed and remains available. The MAX6581 operates at different operating-current levels depending on how many external channels are in use and how many of those are in resistance cancellation (RC) mode. The average operating current is:
I AV = NN + 1 2 x NR I CC1 + x I CC2 NN + 2 x NR + 1 NN + 2 x NR + 1
Operating-Current Calculation
ADC Conversion Sequence
where: NN = the number of remote channels that are operating in normal mode. NR = the number of remote channels that are in RC mode. IAV = the average operating power-supply current over a complete series of conversions. ICC1 = the average operating power-supply current during a conversion in normal mode. ICC2 = the average operating power-supply current during a conversion in RC mode.
Low-Power Standby Mode
8
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1C Accurate 8-Channel Temperature Sensor MAX6581
VCC
DXP1
MAX6581
DXN1 DXP2 IRJ
ALARM ALU
OVERT ALERT
DXN2 DXP3
DXN3 DXP4 +
REGISTER BANK
INPUT BUFFER DXN4 DXP5 -
COUNT COUNTER
COMMAND BYTE REMOTE TEMPERATURES LOCAL TEMPERATURES ALERT THRESHOLD OVERT THRESHOLD ALERT RESPONSE ADDRESS
REF DXN5 DXP6
SMBus INTERFACE DXN6
STBY
DXP7
DXN7
LOCAL TRANSISTOR
SMBCLK
SMBDATA
Figure 1. Internal Block Diagram
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1C Accurate 8-Channel Temperature Sensor MAX6581
From a software perspective, the MAX6581 appears as a series of 8-bit registers that contain temperaturemeasurement data, alarm threshold values, and control bits. A standard SMBus-compatible, 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. The same SMBus slave address also provides access to all functions. The MAX6581 employs four standard SMBus protocols: write byte, read byte, send byte, and receive byte (Figure 2). 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. Figure
SMBus Digital Interface
3 is the SMBus write timing diagram and Figure 4 is the SMBus read timing diagram. The remote-diode-measurement channels provide 11 bits of data (1 LSB = 0.125NC). The eight most significant bits (MSBs) can be read from the local temperature and remote temperature registers. The remaining 3 bits for remote can be read from the extended temperature register. If extended resolution is desired, the extended-resolution register should be read first. This prevents the MSBs from being overwritten by new conversion results until they have been read. If the MSBs have not been read within a SMBus timeout period (nominally 37ms), normal updating continues. Table 1 shows the main temperature register (high-byte) data format and Table 2 shows the extended-resolution register (lowbyte) data format.
WRITE-BYTE FORMAT
S ADDRESS 7 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP-SELECT LINE OF A 3-WIRE INTERFACE WR ACK COMMAND 8 BITS ACK DATA 8 BITS DATA BYTE: DATA GOES INTO THE REGISTER SET BY THE COMMAND BYTE (TO SET THRESHOLDS, CONFIGURATION MASKS, AND SAMPLING RATE) COMMAND 8 BITS COMMAND BYTE: SELECTS WHICH REGISTER YOU ARE REDING FROM ACK S ADDRESS 7 BITS SLAVE ADDRESS: REPEATED DUE TO CHANGE IN DATAFLOW DIRECTION RD ACK DATA 8 BITS DATA BYTE: READS FROM THE REGISTER SET BY THE COMMAND BYTE /// P ACK P 1
READ-BYTE FORMAT
S ADDRESS 7 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP SELECT LINE WR ACK
SEND-BYTE FORMAT
S ADDRESS 7 BITS WR ACK COMMAND 8 BITS COMMAND BYTE: SENDS COMMAND WITH NO DATA, USUALLY USED FOR ONE-SHOT COMMAND S = START CONDITION P = STOP CONDITION SHADED = SLAVE TRANSMISSION /// = NOT ACKNOWLEDGED ACK P
RECEIVE-BYTE FORMAT
S ADDRESS 7 BITS RD ACK DATA 8 BITS DATA BYTE: READS DATA FROM THE REGISTER COMMANDED BY THE LAST READ-BYTE OR WRITE-BYTE TRANSMISSION; ALSO USED FOR SMBus ALERT RESPONSE RETURN ADDRESS /// P
Figure 2. SMBus Protocols
10
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1C Accurate 8-Channel Temperature Sensor MAX6581
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
tSU:DAT 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 DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
tSU:STO
tBUF
Figure 3. SMBus Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
SMBCLK
SMBDATA tSU:STA tHD:STA tSU:DAT tHD:DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER tSU:STO tBUF I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION
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
Figure 4. Read-Timing Diagram
Table 1. Main Temperature Register (High-Byte) Data Format
TEMPERATURE (NC) Diode fault (open or short) > +191 +191 +150 +127 +25 0 -39 -64 < -64 DIGITAL OUTPUT NORMAL FORMAT 1111 1111 1111 1111 1111 1111 1101 0110 1011 1111 0101 1001 0100 0000 0001 1001 0000 0000 0000 0000 EXTENDED FORMAT 1111 1111 1111 1111 1111 1111 1100 1100 1011 1111 1001 1001 0100 0000 0101 1001 0000 0000 0000 0000
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1C Accurate 8-Channel Temperature Sensor MAX6581
Table 2. Extended-Resolution Temperature Register (Low-Byte) Data Format
TEMPERATURE (NC) 0 +0.125 +0.250 +0.375 +0.500 +0.625 +0.750 +0.875 X = Don't care. DIGITAL OUTPUT 000X XXXX 001X XXXX 010X XXXX 011X XXXX 100X XXXX 101X XXXX 110X XXXX 111X XXXX
Table 3. Command Byte Register Bit Assignment
REGISTER Remote 1 Remote 2 Remote 3 Remote 4 Remote 5 Remote 6 Local Remote 7 Remote 1 Extended Bits* Manufacturer ID Revision ID Remote 1 ALERT High Limit Remote 2 ALERT High Limit Remote 3 ALERT High Limit Remote 4 ALERT High Limit Remote 5 ALERT High Limit Remote 6 ALERT High Limit Local ALERT High Limit Remote 7 ALERT High Limit Local OVERT High Limit 12 ADDRESS (HEX) 01 02 03 04 05 06 07 08 09 0A 0F 11 12 13 14 15 16 17 18 20 POR VALUE (HEX) 00 00 00 00 00 00 00 00 00 4D 00 7F 7F 64 64 64 64 5A 64 50 READ/ WRITE R R R R R R R R R R R R/W R/W R/W R/W R/W R/W R/W R/W R/W DESCRIPTION Read channel 1 remote temperature Read channel 2 remote temperature Read channel 3 remote temperature Read channel 4 remote temperature Read channel 5 remote temperature Read channel 6 remote temperature Read local temperature Read channel 7 remote temperature Read channel 1 remote-diode extended temperature Read manufacturer ID Read revision ID Read/write channel 1 remote-diode alert high-temperature threshold limit Read/write channel 2 remote-diode alert high-temperature threshold limit Read/write channel 3 remote-diode alert high-temperature threshold limit Read/write channel 4 remote-diode alert high-temperature threshold limit Read/write channel 5 remote-diode alert high-temperature threshold limit Read/write channel 6 remote-diode alert high-temperature threshold limit Read/write local-diode alert high-temperature threshold limit Read/write channel 7 remote-diode alert high-temperature threshold limit Read/write channel local-diode overtemperature threshold limit
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1C Accurate 8-Channel Temperature Sensor
Table 3. Command Byte Register Bit Assignment (continued)
REGISTER Remote 1 OVERT High Limit Remote 2 OVERT High Limit Remote 3 OVERT High Limit Remote 4 OVERT High Limit Remote 5 OVERT High Limit Remote 6 OVERT High Limit Remote 7 OVERT High Limit ALERT Low Limits (all channels) Configuration ALERT Mask OVERT Mask ALERT High Status OVERT Status Diode Fault Status ALERT Low Status ALERT Low Disable Resistance Cancellation Transistor Ideality Ideality Select Offset Offset Select Remote 1 Extended Bits* Remote 2 Extended Bits Remote 3 Extended Bits Remote 4 Extended Bits Remote 5 Extended Bits Remote 6 Extended Bits Local Extended Bits *Duplicate entries. ADDRESS (HEX) 21 22 23 24 25 26 27 30 41 42 43 44 45 46 47 48 4A 4B 4C 4D 4E 51 52 53 54 55 56 57 POR VALUE (HEX) 6E 6E 6E 7F 5A 5A 5A 00 00 00 00 00 00 00 00 FF 00 00 00 00 00 00 00 00 00 00 00 00 READ/ WRITE R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R R R R/W R/W R/W R/W R/W R/W R R R R R R R DESCRIPTION
MAX6581
Read/write channel 1 remote-diode overtemperature threshold limit Read/write channel 2 remote-diode overtemperature threshold limit Read/write channel 3 remote-diode overtemperature threshold limit Read/write channel 4 remote-diode overtemperature threshold limit Read/write channel 5 remote-diode overtemperature threshold limit Read/write channel 6 remote-diode overtemperature threshold limit Read/write channel 7 remote-diode overtemperature threshold limit Read/write all channels alert low-temperature threshold limit Read/write configuration Read/write ALERT mask Read/write OVERT mask Read ALERT high status Read OVERT status Read diode fault status Read ALERT low status Read/write ALERT low disable Read/write resistance cancellation enable bits (1 = On, 0 = Off) Read/write ideality value for remote-sense transistor Read/write ideality value selection bits (1 = selected transistor ideality, 0 = 1.008) Read/write temperature offset value Read/write offset value selection bits (1 = value in Offset Select register, 0 = 0) Read channel 1 remote extended temperature Read channel 2 remote extended temperature Read channel 3 remote extended temperature Read channel 4 remote extended temperature Read channel 5 remote extended temperature Read channel 6 remote extended temperature Read local channel extended temperature
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13
1C Accurate 8-Channel Temperature Sensor MAX6581
If a channel's input DXP_ and DXN_ are left open or are shorted, the MAX6581 detects a diode fault. An open diode fault does not cause either ALERT or OVERT to assert. A bit in the status register for the corresponding channel is set to 1 and the temperature data for the channel is stored as all 1s (FFh). It takes approximately 4ms for the MAX6581 to detect a diode fault. Once a diode fault is detected, the MAX6581 goes to the next channel in the conversion sequence. There are 17 alarm threshold registers that store overtemperature and undertemperature ALERT and OVERT threshold values. Nine of these registers are dedicated to storing one local alert overtemperature threshold limit, seven remote alert overtemperature threshold limits, and one shared alert undertemperature temperature threshold limit (see the ALERT Interrupt Mode section). The remaining eight registers are dedicated to storing one local overtemperature threshold limit and seven remote channels to store overtemperature threshold limits (see the OVERT Overtemperature Alarms section). Access to these registers is provided through the SMBus interface. ALERT interrupts occur when the internal or external temperature reading exceeds a high-temperature limit (user programmable) or a low-temperature limit. The ALERT interrupt output signal can be cleared by reading the status register(s) associated with the fault(s) or by successfully responding to an alert response address transmission by the master. In both cases, the alert is cleared but is reasserted at the end of the next conversion if the fault condition still exists. The interrupt does not halt automatic conversions. The ALERT output is open-drain so that multiple devices can share a common interrupt line. All ALERT interrupts can be masked using the ALERT Mask register (42h). The POR state of these registers is shown in Table 3. The SMBus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex logic necessary to be a bus master. Upon receiving an interrupt signal, the host master can broadcast a receive-byte transmission to the alert response slave address (19h). Then, any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus. The alert response can activate several different slave devices simultaneously, similar to the I2C general call.
14
Diode Fault Detection
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 acknowledgment and continues to hold the ALERT line low until cleared (the conditions for clearing an alert vary depending on the type of slave device.) Successful completion of the alert response protocol clears the output latch. If the condition that caused the alert still exists, the MAX6581 reasserts the ALERT interrupt at the end of the next conversion. The MAX6581 has eight overtemperature registers that store alarm threshold data for the OVERT output. OVERT is asserted when a channel's measured temperature is greater than the value stored in the corresponding threshold register. OVERT remains asserted until the temperature drops below the programmed threshold minus 4NC hysteresis. An overtemperature output can be used to activate a cooling fan, send a warning, initiate clock throttling, or trigger a system shutdown to prevent component damage. See Table 3 for the POR state of the overtemperature threshold registers. The 8-bit Command Byte register (Table 3) is the master index that points to the various other registers within the MAX6581. This register's POR state is 0000 0000. The Configuration register (Table 4) has several functions. Bit 7 (MSB) is used to put the MAX6581 either in software-standby mode (STOP) or continuousconversion mode. Bit 6 resets all registers to their POR conditions and then clears itself. Bit 5 disables the SMBus timeout. Bit 1 sets the extended range of the remote temperature diodes. The remaining bits of the Configuration register are not used. The POR state of this register is 0000 0000 (00h). The ALERT Mask register functions are described in Table 5. Bits [7:0] are used to mask the ALERT interrupt output. Bit 6 masks the local alert interrupt and the remaining bits mask the remote alert interrupts. The power-up state of this register is 0000 0000 (00h). Table 6 describes the OVERT Mask register. Bit 6 and the remaining bits mask the OVERT interrupt output for all channels. The power-up state of this register is 0000 0000 (00h).
Alarm Threshold Registers
OVERT Overtemperature Alarms
ALERT Interrupt Mode
Command Byte Register Functions
Configuration Register (41h)
ALERT Mask Register (42h)
ALERT Responses Address
OVERT Mask Register (43h)
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1C Accurate 8-Channel Temperature Sensor
Table 4. Configuration Register (41h)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME STOP POR TIMEOUT RESERVED RESERVED RESERVED EXTRANGE RESERVED POR VALUE 0 0 0 0 0 0 0 0 FUNCTION Standby-Mode Control Bit. If STOP is set to logic 1, the MAX6581 stops converting and enters standby mode. Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is selfclearing. Timeout Enable Bit. Set to logic 0 to enable SMBus timeout. Reserved. Must be set to 0. Reserved. Must be set to 0. Reserved. Must be set to 0. Extended-Range Enable Bit. Set bit 1 to logic 1 to set the temperature and limit data range to -64NC to +191NC. Set bit 1 to logic 0 to set the range to 0NC to +255NC. Reserved. Must be set to 0.
MAX6581
Table 5. ALERT Mask Register (42h)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Mask ALERT 7 Mask Local ALERT Mask ALERT 6 Mask ALERT 5 Mask ALERT 4 Mask ALERT 3 Mask ALERT 2 Mask ALERT 1 POR VALUE 0 0 0 0 0 0 0 0 FUNCTION Channel 7 Alert Mask. Set to logic 1 to mask channel 7 ALERT. Local Alert Mask. Set to logic 1 to mask local channel ALERT. Channel 6 Alert Mask. Set to logic 1 to mask channel 6 ALERT. Channel 5 Alert Mask. Set to logic 1 to mask channel 5 ALERT. Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT. Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT. Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT. Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.
Table 6. OVERT Mask Register (43h)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Mask OVERT 7 Mask Local OVERT Mask OVERT 6 Mask OVERT 5 Mask OVERT 4 Mask OVERT 3 Mask OVERT 2 Mask OVERT 1 POR VALUE 0 0 0 0 0 0 0 0 FUNCTION Channel 7 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 7 OVERT. Local Overt Mask. Set to logic 1 to mask local channel OVERT. Channel 6 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 6 OVERT. Channel 5 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 5 OVERT. Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4 OVERT. Channel 3 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 3 OVERT. Channel 2 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 2 OVERT. Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1 OVERT.
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15
1C Accurate 8-Channel Temperature Sensor MAX6581
There are four status registers (see Tables 7-10). The ALERT High Status register indicates whether a measured local or remote temperature has exceeded the associated threshold limit set in an ALERT High Limit register. The OVERT Status register indicates whether a measured temperature has exceeded the associated threshold limit set in an OVERT High Limit register. The Diode Fault Status register indicates whether there is a diode fault (open or short) in any of the remote-sensing channels. The ALERT Low Status register indicates whether the measured temperature has fallen below the threshold limit set in the ALERT Low Limits register for the local or remote-sensing diodes. Bits in the alert status registers are cleared by a successful read, but set again after the next conversion unless
Status Register Functions
the fault is corrected, either by a drop in the measured temperature or a change in the threshold temperature. The ALERT interrupt output follows the status flag bit. Once the ALERT output is asserted, it can be deasserted by either reading the ALERT High Status register or by successfully responding to an alert response address. In both cases, the alert is cleared even if the fault condition exists, but the ALERT output reasserts at the end of the next conversion. The bits indicating OVERT faults clear only when the measured temperature drops below the temperature threshold minus the hysteresis value (4NC), or when the trip temperature is set to a value at least 4NC above the current temperature.
Table 7. ALERT High Status Register (44h)
BIT NAME Remote ALERT High 7 Local ALERT High Remote ALERT High 6 Remote ALERT High 5 Remote ALERT High 4 Remote ALERT High 3 Remote ALERT High 2 Remote ALERT High 1 POR STATE 0 FUNCTION Channel 7 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 7 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 7 ALERT High Limit register. Local Channel High-Alert Bit. This bit is set to logic 1 when the local temperature exceeds the temperature threshold limit in the Local ALERT High Limit register. Channel 6 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 6 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 6 ALERT High Limit register. Channel 5 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 5 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 5 ALERT High Limit register. Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 4 ALERT High Limit register. Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 3 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 3 ALERT High Limit register. Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 2 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 2 ALERT High Limit register. Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the programmed temperature threshold limit in the Remote 1 ALERT High Limit register.
7 (MSB)
6
0
5
0
4
0
3
0
2
0
1
0
0
0
16
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1C Accurate 8-Channel Temperature Sensor
Table 8. OVERT Status Register (45h)
BIT NAME POR STATE 0 FUNCTION Channel 7 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 7 remote-diode temperature exceeds the temperature threshold limit in the Remote 7 OVERT High Limit register. Local Channel Overtemperature Status Bit. This bit is set to logic 1 when the local temperature exceeds the temperature threshold limit in the Local OVERT High Limit register. Channel 6 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 6 remote-diode temperature exceeds the temperature threshold limit in the Remote 6 OVERT High Limit register. Channel 5 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 5 remote-diode temperature exceeds the temperature threshold limit in the Remote 5 OVERT High Limit register. Channel 4 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the temperature threshold limit in the Remote 4 OVERT High Limit register. Channel 3 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 3 remote-diode temperature exceeds the temperature threshold limit in the Remote 3 OVERT High Limit register. Channel 2 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 2 remote-diode temperature exceeds the temperature threshold limit in the Remote 2 OVERT High Limit register. Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the temperature threshold limit in the Remote 1 OVERT High Limit register.
MAX6581
7 (MSB)
Remote OVERT 7
6
Local OVERT
0
5
Remote OVERT 6
0
4
Remote OVERT 5
0
3
Remote OVERT 4
0
2
Remote OVERT 3
0
1
Remote OVERT 2
0
0
Remote OVERT 1
0
Table 9. Diode Fault Status Register (46h)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME RESERVED Diode Fault 7 Diode Fault 6 Diode Fault 5 Diode Fault 4 Diode Fault 3 Diode Fault 2 Diode Fault 1 POR STATE 0 0 0 0 0 0 0 0 -- Channel 7 Remote-Diode Fault Bit. This bit is set to 1 when DXP7 and DXN7 are open circuit or when DXP7 is connected to VCC. Channel 6 Remote-Diode Fault Bit. This bit is set to 1 when DXP6 and DXN6 are open circuit or when DXP6 is connected to VCC. Channel 5 Remote-Diode Fault Bit. This bit is set to 1 when DXP5 and DXN5 are open circuit or when DXP5 is connected to VCC. Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4 are open circuit or when DXP4 is connected to VCC. Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3 are open circuit or when DXP3 is connected to VCC. Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2 are open circuit or when DXP2 is connected to VCC. Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1 are open circuit or when DXP1 is connected to VCC. 17 FUNCTION
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1C Accurate 8-Channel Temperature Sensor MAX6581
Table 10. ALERT Low Status Register
BIT NAME Remote ALERT Low 7 POR STATE 0 FUNCTION Channel 7 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 7 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 7 ALERT Low Limit register. Local Channel Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the local channel remote-diode temperature falls below the programmed temperature threshold limit in the Local ALERT Low Limit register. Channel 6 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 6 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 6 ALERT Low Limit register. Channel 5 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 5 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 5 ALERT Low Limit register. Channel 4 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 4 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 4 ALERT Low Limit register. Channel 3 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 3 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 3 ALERT Low Limit register. Channel 2 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 2 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 2 ALERT Low Limit register. Channel 1 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 1 remote-diode temperature falls below the programmed temperature threshold limit in the Remote 1 ALERT Low Limit register.
7 (MSB)
6
Local ALERT Low
0
5
Remote ALERT Low 6 Remote ALERT Low 5 Remote ALERT Low 4 Remote ALERT Low 3 Remote ALERT Low 2 Remote ALERT Low 1
0
4
0
3
0
2
0
1
0
0
0
The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote "diode" (actually a transistor). The default value for the MAX6581 is n = 1.008 (channels 1-7). A thermal diode on the substrate of an IC is normally a pnp with the base and emitter brought out and the collector (diode connection) grounded. DXP_ must be connected to the anode (emitter) and DXN_ must be connected to the cathode (base)
Effect of Ideality Factor
of this pnp. If a sense transistor with an ideality factor other than 1.008 is used, the output data is different from the data obtained with the optimum ideality factor. If necessary, a different ideality factor value can be chosen using the Transistor Ideality register (see Table 11). The Ideality Select register allows each channel to have the default ideality of 1.008 or the value programmed in the Transistor Ideality register.
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1C Accurate 8-Channel Temperature Sensor
Table 11. Transistor Ideality Register
REGISTER B7 X X X X X X X X X X X X X X X 0x4B X X X X X X X X X X X X X X X X X X = Don't care. B6 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X B5 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X B4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 B3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 B2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 B1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 B0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 IDEALITY FACTOR .999 1.000 1.001 1.002 1.003 1.004 1.005 1.006 1.007 1.008 1.009 1.010 1.011 1.012 1.013 1.014 1.015 1.016 1.017 1.018 1.019 1.020 1.021 1.022 1.023 1.024 1.025 1.026 1.027 1.028 1.029 1.030 HEX 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F 0x10 0x11 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F
MAX6581
19
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1C Accurate 8-Channel Temperature Sensor MAX6581
Some thermal diodes on high-power ICs have excessive series resistance that can cause temperature-measurement errors when used with conventional remotetemperature sensors. Channels 1-7 of the MAX6581 have a series-resistance cancellation feature (enabled by bits 7:0 of the Resistance Cancellation register) that eliminates the effect of diode series resistance and interconnection resistance. Set these bits to 1 if the series resistance is large enough to affect the accuracy of the channels. The series-resistance cancellation function increases the conversion time for the remote channels by 125ms (typ). This feature cancels the bulk resistance of the sensor and any other resistance in series (e.g., wire, contact resistance, etc.). The cancellation range is from 0I to 100I.
Series-Resistance Cancellation
Applications Information
The MAX6581 directly measures the die temperature of CPUs and other ICs that have on-chip temperature-sensing diodes (see the Typical Application Circuit), or it can measure the temperature of a discrete diode-connected transistor.
Remote-Diode Selection
When the remote-sensing diode is a discrete transistor, its collector and base must be connected together. Table 13 lists examples of discrete transistors that are appropriate for use with the MAX6581. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input-voltage range can be violated. The forward voltage at the highest expected temperature must be greater than 0.25V at 10FA, and at the lowest expected temperature the forward voltage must be less than 0.95V at 100FA. Large power transistors must not be used. Also, ensure that the base resistance is less than 100I. Tight specifications for forward-current gain (e.g., 50 < A < 150) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics. Manufacturers of discrete transistors do not normally specify or guarantee ideality factor. This normally is not a problem since good-quality discrete transistors tend to have ideality factors that fall within a relatively narrow range. Variations in remote temperature readings of less than Q2NC with a variety of discrete transistors have been observed. However, it is good design practice to verify good consistency of temperature readings with several discrete transistors from any supplier under consideration.
Discrete Remote Diodes
Table 12. Resistance Cancellation Register (4Ah)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME X RESISTANCE CANCELLATION 7 RESISTANCE CANCELLATION 6 RESISTANCE CANCELLATION 5 RESISTANCE CANCELLATION 4 RESISTANCE CANCELLATION 3 RESISTANCE CANCELLATION 2 RESISTANCE CANCELLATION 1 POR STATE 0 0 0 0 0 0 0 0 -- Channel 7 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 6 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 5 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 4 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 3 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 2 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. Channel 1 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable resistance cancellation. Set this bit to logic 0 to disable resistance cancellation. FUNCTION
X = Don't care.
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1C Accurate 8-Channel Temperature Sensor
Table 13. Remote Sensors Transistor Suppliers (for Channels 1-7)
SUPPLIER Central Semiconductor Corp. (USA) Fairchild Semiconductor (USA) Infineon (Germany) ON Semiconductor (USA) ROHM Semiconductor (USA) Samsung (Korea) Siemens (Germany) Zetex (England) CMPT3906 2N3906 MMBT3906 2N3906 SMBT3906 MMBT3906 2N3906 SST3906 KST3906-TF SMBT3906 FMMT3906CT-ND MODEL NO. PNP CMPT3904 2N3904 2N3904 -- 2N3904 SST3904 KST3904-TF SMBT3904 FMMT3904CT-ND NPN
MAX6581
Note: Discrete transistors must be diode connected (base shorted to collector).
If one or more of the remote-diode channels is not needed, disconnect the DXP_ and DXN_ inputs for that channel, or connect the DXP_ to the corresponding DXN_. The status register indicates a diode "fault" for this channel and the channel is ignored during the temperature-measurement sequence. It is also good practice to mask any unused channels immediately upon power-up by setting the appropriate bits in the ALERT Mask and OVERT Mask registers. This prevents unused channels from causing ALERT or OVERT to assert. When sensing local temperature, the MAX6581 measures the temperature of the PCB to which it is soldered. The leads provide a good thermal path between the PCB traces and the die. As with all IC temperature sensors, thermal conductivity between the die and the ambient air is poor by comparison, making air-temperature measurements impractical. Since the thermal mass of the PCB is far greater than that of the MAX6581, the device follows temperature changes on the PCB with little or no perceivable delay. When measuring the temperature of a CPU, or other IC with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. When measuring temperature with discrete remote transistors, the best thermal-response
Unused Diode Channels
times are obtained with transistors in small packages (i.e., SOT23 or SC70). 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. The integrating ADC has good noise rejection for lowfrequency signals, such as power-supply hum. In environments with significant high-frequency EMI, connect an external 100pF capacitor between DXP_ and DXN_. Larger capacitor values can be used for added filtering; however, it can introduce errors due to the rise time of the switched current source. High-frequency noise reduction is needed for high-accuracy remote measurements. Noise can be reduced with careful PCB layout as discussed in the PCB Layout section. The slave address for the MAX6581 is shown in Table 14.
ADC Noise Filtering
Thermal Mass and Self-Heating
Slave Address
Table 14. Slave Address
DEVICE ADDRESS A7 1 A6 0 A5 0 A4 1 A3 1 A2 0 A1 1 A0 R/W
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21
1C Accurate 8-Channel Temperature Sensor MAX6581
GND 5-10 mils 5-10 mils DXP_ MINIMUM 5-10 mils DXN_ 5-10 mils GND
traces away from any higher voltage traces, such as +12VDC. Leakage currents from PCB contamination must be dealt with carefully since a 20MI leakage path from DXP_ to ground causes approximately +1NC error. If high-voltage traces are unavoidable, connect guard traces to GND on either side of the DXP_-DXN_ traces (Figure 5). 4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 5) Use wide traces when possible (5-mil to 10-mil traces are typical). Be aware of the effect of trace resistance on temperature readings when using long, narrow traces. 6) When the power supply is noisy, add a resistor (up to 47I) in series with VCC. Use a twisted-pair cable to connect the remote sensor for remote-sensor distances longer than 8in or in very noisy environments. Twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. For longer distances, the best solution is a shielded twisted pair such as those used for audio microphones. For example, Belden #8451 works well for distances up to 100ft in a noisy environment. At the device, connect the twisted-pair cables to DXP_ and DXN_ and the shielded cable to GND. Leave the shielded cable unconnected at the remote sensor. For very long cable runs, the cable's parasitic capacitance often provides noise filtering; therefore the 100pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy. For every 1I of series resistance, the error is approximately +0.5NC.
Figure 5. Recommended DXP_-DXN_ PCB Traces. The two outer guard traces are recommended if high-voltage traces are near the DXN_ and DXP_ traces.
Follow the guidelines below to reduce the measurement error when measuring remote temperature: 1) Place the MAX6581 as close as possible to the remote diode. In noisy environments, such as a computer motherboard, this distance is typically 4in to 8in. This length can be increased if the worst-noise sources are avoided. Noise sources include displays, clock generators, memory buses, and PCI buses. 2) Do not route the DXP_-DXN_ lines next to the deflection coils of a CRT. Also, do not route the traces across fast digital signals, which can easily introduce +30NC error, even with good filtering. 3) Route the DXP_ and DXN_ traces in parallel and in close proximity to each other. Each parallel pair of traces should go to a remote diode. Route these
PCB Layout
Twisted-Pair and Shielded Cables
22
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1C Accurate 8-Channel Temperature Sensor
Typical Application Circuit
+3.3V
MAX6581
4.7kI 100pF
CPU 24 DXN1 1 DXP2 23 22 21 20
4.7kI 4.7kI
4.7kI TO P TO P
19 18
DXP1
N.C.
GND
SMBCLK SMBDATA
ALERT
TO P
100pF
2 3 DXN2 DXP3 OVERT 4 16 VCC 17
0.1F TO P
100pF
DXN3
MAX6581
I.C.
15
5
DXP4 STBY
14
6
N.C. DXP7 DXN4 7 DXNP5 8 DXN5 9 DXN6 10 DXP6 DXN7 11 12 13
100pF
100pF
FPGA
100pF
ASIC
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE OUTLINE NO. 21-0139 LAND PATTERN NO. 90-0022
24 TQFN-EP
T2444+4
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1C Accurate 8-Channel Temperature Sensor MAX6581
Revision History
REVISION NUMBER 0 REVISION DATE 8/10 Initial release DESCRIPTION PAGES CHANGED --
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.
24
(c)
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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