MAXIM MAX6581TG9E+

19-5260 ; Rev 0; 8/10
TION KIT
EVALUA BLE
IL
AVA A
±1°C Accurate 8-Channel Temperature Sensor
Features
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).
S Eight Channels to Measure Seven Remote and
Resistance cancellation is available for all channels and
compensates for high series resistance in circuit-board
traces and thermal diodes.
S SMBus/I2C-Compatible Interface
One Local Temperature
S 11-Bit, 0.125NC Resolution
S High Accuracy of ±1NC (max) from +60NC to
+100NC (Remote Channels)
S -64NC to +150NC Remote Temperature Range
S Programmable Undertemperature/
Overtemperature Alerts
S Two Open-Drain Alarm Outputs (ALERT and
OVERT)
The 2-wire serial interface accepts SMBus™ protocols
(write byte, read byte, send byte, and receive byte) for
reading the temperature data and programming the
alarm thresholds.
S Resistance Cancellation on All Remote Channels
Applications
Desktop Computers
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.
Notebook Computers
Workstations
Servers
Data Communications
Ordering Information/Selector Guide
PART
SLAVE ADDRESS
PIN-PACKAGE
OPERATING
TEMPERATURE RANGE
MEASURED
TEMPERATURE RANGE
MAX6581TG9A+
0X9A
24 TQFN-EP*
-40NC to +125NC
-64NC to +150NC
-64NC to +150NC
MAX6581TG9C+**
0X9C
24 TQFN-EP*
-40NC to +125NC
MAX6581TG9E+**
0X9E
24 TQFN-EP*
-40NC to +125NC
-64NC to +150NC
MAX6581TG98+**
0X98
24 TQFN-EP*
-40NC to +125NC
-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.
MAX6581
General Description
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
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
SYMBOL
Supply Voltage
VCC
Standby Supply Current
ISS
Operating Current
CONDITIONS
MIN
SMBus static
3-Sigma Temperature Accuracy
(Local)
6-Sigma Temperature Accuracy
(Remote Channels 1–7)
6-Sigma Temperature Accuracy
(Local)
Supply Sensitivity of
Temperature Accuracy
MAX
V
4
15
FA
ICC1
During conversion, RC off
500
600
During conversion, RC on
550
650
VCC = 3.3V
VCC = 3.3V
VCC = 3.3V
VCC = 3.3V
UNITS
3.6
ICC2
Temperature Resolution
3-Sigma Temperature Accuracy
(Remote Channels 1–7)
TYP
3.0
FA
11
Bits
0.125
NC
TA = +30NC to +85NC,
TRJ = +60NC to +100NC
-0.85
+0.85
TA, TRJ = -40NC to +125NC
-1.2
+1.2
TA = +30NC to +85NC,
TRJ = 100NC to +150NC
-2.5
+2.5
TA = +30NC to +85NC
-1
+1
TA = -40NC to +125NC
-2
+2
TA = 0NC to +150NC
-3
+3
TA = +30NC to +85NC,
TRJ = +60NC to +100NC
-1
+1
TA, TRJ = -40NC to +125NC
-2
+2
TA = +30NC to +85NC,
TRJ = 100NC to +125NC
-2.75
+2.75
TA = +30NC to +85NC
-1.5
+1.5
TA = -40NC to +125NC
-2.5
+2.5
TA = 0NC to +150NC
-3.5
+3.5
Q0.2
2 _______________________________________________________________________________________
NC
NC
NC
NC
NC/V
±1°C Accurate 8-Channel Temperature Sensor
(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
MIN
TYP
MAX
Resistance cancellation mode off
CONDITIONS
95
125
156
Resistance cancellation mode on or beta
compensation on
190
250
312
High level
Resistance cancellation
mode off
80
100
120
8
10
12
Resistance cancellation
mode on or beta
compensation on
160
200
240
16
20
24
Low level
Remote-Diode Source Current
IRJ
High level
Low level
DXP_ and DXN_ Leakage
Current
Undervoltage Lockout Threshold
Standby mode
UVLO
Falling edge of VCC disables ADC
100
2.25
Undervoltage Lockout Hysteresis
2.80
2.95
90
Power-On-Reset (POR)
Threshold
VCC falling edge
1.3
POR Threshold Hysteresis
2.0
UNITS
ms
FA
nA
V
mV
2.2
90
V
mV
ALERT and OVERT
Output Low Voltage
Input Leakage Current
VOL
ISINK = 1mA
0.01
ISINK = 6mA
0.3
-1
ILEAK
SMBus INTERFACE, STBY
Logic Input Low Voltage
VIL
VCC = 3.6V
Logic Input High Voltage
VIH
VCC = 3.0V
Input Leakage Current
Output Low Voltage
VOL
CIN
+1
FA
0.8
V
+1
FA
2.2
V
-1
Input Capacitance
V
ISINK = 6mA
0.1
5
V
pF
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 3)
Serial-Clock Frequency
Bus Free Time Between STOP
and START Condition
fSMBCLK
tBUF
(Note 4)
400
kHz
fSMBCLK = 400kHz
1.6
Fs
START Condition Setup Time
fSMBCLK = 400kHz
0.6
Fs
Repeat START Condition Setup
Time
tSU:STA
90% of SMBCLK to 90% of SMBDATA,
fSMBCLK = 400kHz
50
ns
START Condition Hold Time
tHD:STA
10% of SMBDATA to 90% of SMBCLK,
fSMBCLK = 400kHz
0.6
Fs
STOP Condition Setup Time
tSU:STO
90% of SMBCLK to 90% of SMBDATA,
fSMBCLK = 400kHz
0.6
Fs
Clock Low Period
tLOW
10% to 10%, fSMBCLK = 400kHz
1
Fs
Clock High Period
tHIGH
90% to 90%
0.6
Fs
Data-In Hold Time
tHD:DAT
Data-In Setup Time
tSU:DAT
(Note 5)
100
0
0.9
us
ns
_______________________________________________________________________________________ 3
MAX6581
ELECTRICAL CHARACTERISTICS (continued)
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
SYMBOL
Receive SMBCLK/SMBDATA
Rise Time
Receive SMBCLK/SMBDATA Fall
Time
CONDITIONS
MIN
MAX
UNITS
tR
300
ns
tF
300
ns
Data-Out Hold Time
tDH
50
Pulse Width of Spike Suppressed
tSP
0
SMBus Timeout
Note
Note
Note
Note
tTIMEOUT
SMBDATA low period for interface reset
TYP
ns
25
37
50
ns
45
ms
2: All parameters are tested at TA = +85NC. Specifications over temperature are guaranteed by design.
3: Timing specifications are guaranteed by design.
4: The serial interface resets when SMBCLK is low for more than tTIMEOUT.
5: 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.)
3.5
3.0
2.5
2.0
1.5
1.0
HARDWARE OR SOFTWARE
STANDBY SUPPLY CURRENT
0.5
0
395
390
385
380
375
370
365
360
3.0
3.1
3.2
3.3
3.4
SUPPLY VOLTAGE (V)
3.5
3.6
3.0
3.1
3.2
3.3
3.4
SUPPLY VOLTAGE (V)
3.5
3.6
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
MAX6581 toc03
4.0
RESISTANCE
CANCELLATION OFF
REMOTE-DIODE TEMPERATURE ERROR
vs. REMODE-DIODE TEMPERATURE
REMOTE-DIODE TEMPERATURE ERROR (°C)
4.5
400
MAX6581 toc02
MAX6581 toc01
5.0
AVERAGE OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGE
AVERAGE OPERATING SUPPLY CURRENT (µA)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
STANDBY SUPPLY CURRENT (µA)
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
-10
10
30
50
70
90
110
REMOTE-DIODE TEMPERATURE (°C)
4 _______________________________________________________________________________________
130
±1°C Accurate 8-Channel Temperature Sensor
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
3
REMOTE-DIODE TEMPERATURE ERROR (°C)
4
2
1
0
-1
-2
-3
-4
-5
3
2
1
0
-1
-2
-3
-4
-5
0.001
-10 0 10 20 30 40 50 60 70 80 90 100
0.01
0.1
1
10
DIE TEMPERATURE (°C)
POWER-SUPPLY NOISE FREQUENCY (MHz)
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
REMOTE-DIODE TEMPERATURE ERROR
vs. CAPACITANCE
3
5
REMOTE-DIODE TEMPERATURE ERROR (°C)
100mVP-P
4
MAX6581 toc06
5
2
1
0
-1
-2
-3
-4
-5
0.001
100mVP-P
TRJ = +85°C
4
3
2
1
0
-1
-2
-3
-4
-5
0.01
0.1
1
10
10
1
POWER-SUPPLY NOISE FREQUENCY (MHz)
100
CAPACITANCE (nF)
50
MAX6581 toc08
REMOTE-DIODE TEMPERATURE ERROR
vs. RESISTANCE
REMOTE-DIODE TEMPERATURE ERROR (°C)
LOCAL TEMPERATURE ERROR (°C)
100mVP-P
TRJ = +85°C
4
MAX6581 toc07
LOCAL TEMPERATURE ERROR (°C)
5
MAX6581 toc04
5
MAX6581 toc05
REMOTE-DIODE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
TRJ = +85°C
45
40
35
30
RESISTANCE
CANCELLATION OFF
25
20
15
RESISTANCE
CANCELLATION ON
10
5
0
-5
0
10 20 30 40 50 60 70 80 90 100
RESISTANCE (I)
_______________________________________________________________________________________ 5
MAX6581
Typical Operating Characteristics (continued)
(VCC = +3.3V, VSTBY = VCC, TA = +25NC, unless otherwise noted.)
±1°C Accurate 8-Channel Temperature Sensor
VCC
OVERT
I.C.
STBY
DXP7
TOP VIEW
ALERT
MAX6581
Pin Configuration
18
17
16
15
14
13
SMBDATA 19
12
DXN7
SMBCLK 20
11
DXP6
10
DXN6
9
DXN5
8
DXP5
7
DXN4
GND 21
MAX6581
N.C. 22
DXP1 23
*EP
1
2
3
4
5
6
DXP2
DXN2
DXP3
DXN3
DXP4
N.C.
DXN1 24
*EP = EXPOSED PAD, CONNECT TO GND
Pin Description
PIN
NAME
FUNCTION
DXP2
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.
DXN2
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.
DXP3
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.
DXN3
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.
5
DXP4
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.
6, 22
N.C.
No Connection. Connect to other N.C. or leave unconnected.
1
2
3
4
6 _______________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
PIN
NAME
FUNCTION
DXN4
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.
DXP5
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.
DXN5
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.
DXN6
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.
DXP6
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.
DXN7
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.
13
DXP7
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.
14
STBY
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.
15
I.C.
16
OVERT
17
VCC
18
ALERT
19
SMBDATA
20
SMBCLK
7
8
9
10
11
12
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.
_______________________________________________________________________________________ 7
MAX6581
Pin Description (continued)
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Pin Description (continued)
PIN
NAME
21
GND
Ground
DXP1
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.
24
DXN1
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.
—
EP
23
FUNCTION
Exposed Pad. Connect EP to GND.
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.
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.
Operating-Current Calculation
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 =
ADC Conversion Sequence
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.
Low-Power Standby Mode
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
NN + 1
2 × NR
I CC1 +
× I CC2
NN + 2 × NR + 1
NN + 2 × NR + 1
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.
8 _______________________________________________________________________________________
±1°C 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
COUNT
-
COUNTER
DXP5
COMMAND BYTE
REMOTE TEMPERATURES
LOCAL TEMPERATURES
ALERT THRESHOLD
REF
DXN5
OVERT THRESHOLD
DXP6
ALERT RESPONSE ADDRESS
SMBus INTERFACE
DXN6
STBY
DXP7
DXN7
LOCAL
TRANSISTOR
SMBCLK
SMBDATA
Figure 1. Internal Block Diagram
_______________________________________________________________________________________ 9
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
SMBus Digital Interface
3 is the SMBus write timing diagram and Figure 4 is the
SMBus read timing diagram.
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 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.
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
WRITE-BYTE FORMAT
S
ADDRESS
WR
ACK
COMMAND
7 BITS
ACK
DATA
8 BITS
ACK
P
8 BITS
SLAVE ADDRESS: EQUIVALENT
TO CHIP-SELECT LINE OF
A 3-WIRE INTERFACE
1
DATA BYTE: DATA GOES INTO THE REGISTER
SET BY THE COMMAND BYTE (TO SET
THRESHOLDS, CONFIGURATION MASKS, AND
SAMPLING RATE)
READ-BYTE FORMAT
S
ADDRESS
WR
ACK
7 BITS
COMMAND
ACK
S
SLAVE ADDRESS: EQUIVALENT
TO CHIP SELECT LINE
ADDRESS
ACK
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
REDING FROM
DATA
///
P
8 BITS
SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATAFLOW DIRECTION
DATA BYTE: READS FROM
THE REGISTER SET BY THE
COMMAND BYTE
RECEIVE-BYTE FORMAT
WR
ACK
7 BITS
COMMAND
ACK
P
8 BITS
COMMAND BYTE: SENDS COMMAND
WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
S = START CONDITION
P = STOP CONDITION
RD
7 BITS
SEND-BYTE FORMAT
S
ADDRESS
8 BITS
SHADED = SLAVE TRANSMISSION
/// = NOT ACKNOWLEDGED
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
Figure 2. SMBus Protocols
10 �������������������������������������������������������������������������������������
P
±1°C Accurate 8-Channel Temperature Sensor
tLOW
B
C
tHIGH
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:STO
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
tBUF
I = SLAVE PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
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
Figure 3. SMBus Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
I
H
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
E = SLAVE PULLS SMBDATA LINE LOW
tSU:DAT
tHD:DAT
tSU:STO tBUF
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
Figure 4. Read-Timing Diagram
Table 1. Main Temperature Register (High-Byte) Data Format
TEMPERATURE (NC)
DIGITAL OUTPUT
NORMAL FORMAT
EXTENDED FORMAT
Diode fault (open or short)
1111 1111
1111 1111
> +191
1111 1111
1111 1111
+191
1111 1111
1111 1111
+150
1101 0110
1100 1100
+127
1011 1111
1011 1111
+25
0101 1001
1001 1001
0
0100 0000
0100 0000
-39
0001 1001
0101 1001
-64
0000 0000
0000 0000
< -64
0000 0000
0000 0000
______________________________________________________________________________________ 11
MAX6581
A
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Table 2. Extended-Resolution Temperature Register (Low-Byte) Data Format
TEMPERATURE (NC)
DIGITAL OUTPUT
0
000X XXXX
+0.125
001X XXXX
+0.250
010X XXXX
+0.375
011X XXXX
+0.500
100X XXXX
+0.625
101X XXXX
+0.750
110X XXXX
+0.875
111X XXXX
X = Don’t care.
Table 3. Command Byte Register Bit Assignment
ADDRESS
(HEX)
POR
VALUE
(HEX)
READ/
WRITE
Remote 1
01
00
R
Read channel 1 remote temperature
Remote 2
02
00
R
Read channel 2 remote temperature
Remote 3
03
00
R
Read channel 3 remote temperature
Remote 4
04
00
R
Read channel 4 remote temperature
Remote 5
05
00
R
Read channel 5 remote temperature
Remote 6
06
00
R
Read channel 6 remote temperature
Local
07
00
R
Read local temperature
Remote 7
08
00
R
Read channel 7 remote temperature
Remote 1 Extended
Bits*
09
00
R
Read channel 1 remote-diode extended temperature
Manufacturer ID
0A
4D
R
Read manufacturer ID
Revision ID
0F
00
R
Read revision ID
Remote 1 ALERT High
Limit
11
7F
R/W
Read/write channel 1 remote-diode alert high-temperature
threshold limit
Remote 2 ALERT High
Limit
12
7F
R/W
Read/write channel 2 remote-diode alert high-temperature
threshold limit
Remote 3 ALERT High
Limit
13
64
R/W
Read/write channel 3 remote-diode alert high-temperature
threshold limit
Remote 4 ALERT High
Limit
14
64
R/W
Read/write channel 4 remote-diode alert high-temperature
threshold limit
Remote 5 ALERT High
Limit
15
64
R/W
Read/write channel 5 remote-diode alert high-temperature
threshold limit
Remote 6 ALERT High
Limit
16
64
R/W
Read/write channel 6 remote-diode alert high-temperature
threshold limit
Local ALERT High Limit
17
5A
R/W
Read/write local-diode alert high-temperature threshold limit
Remote 7 ALERT High
Limit
18
64
R/W
Read/write channel 7 remote-diode alert high-temperature
threshold limit
Local OVERT High Limit
20
50
R/W
Read/write channel local-diode overtemperature threshold limit
REGISTER
DESCRIPTION
12 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
ADDRESS
(HEX)
POR
VALUE
(HEX)
READ/
WRITE
DESCRIPTION
Remote 1 OVERT High
Limit
21
6E
R/W
Read/write channel 1 remote-diode overtemperature threshold limit
Remote 2 OVERT High
Limit
22
6E
R/W
Read/write channel 2 remote-diode overtemperature threshold limit
Remote 3 OVERT High
Limit
23
6E
R/W
Read/write channel 3 remote-diode overtemperature threshold limit
Remote 4 OVERT High
Limit
24
7F
R/W
Read/write channel 4 remote-diode overtemperature threshold limit
Remote 5 OVERT High
Limit
25
5A
R/W
Read/write channel 5 remote-diode overtemperature threshold limit
Remote 6 OVERT High
Limit
26
5A
R/W
Read/write channel 6 remote-diode overtemperature threshold limit
Remote 7 OVERT High
Limit
27
5A
R/W
Read/write channel 7 remote-diode overtemperature threshold limit
30
00
R/W
Read/write all channels alert low-temperature threshold limit
REGISTER
ALERT Low Limits (all
channels)
Configuration
41
00
R/W
Read/write configuration
ALERT Mask
42
00
R/W
Read/write ALERT mask
OVERT Mask
43
00
R/W
Read/write OVERT mask
ALERT High Status
44
00
R
Read ALERT high status
OVERT Status
Diode Fault Status
45
00
R
46
00
R
Read OVERT status
Read diode fault status
ALERT Low Status
47
00
R
Read ALERT low status
ALERT Low Disable
Resistance Cancellation
48
FF
R/W
4A
00
R/W
Read/write ALERT low disable
Read/write resistance cancellation enable bits (1 = On, 0 = Off)
Transistor Ideality
4B
00
R/W
Read/write ideality value for remote-sense transistor
Ideality Select
4C
00
R/W
Read/write ideality value selection bits (1 = selected transistor
ideality, 0 = 1.008)
Offset
4D
00
R/W
Read/write temperature offset value
Offset Select
4E
00
R/W
Read/write offset value selection bits (1 = value in Offset Select
register, 0 = 0)
Remote 1 Extended
Bits*
51
00
R
Read channel 1 remote extended temperature
Remote 2 Extended Bits
52
00
R
Read channel 2 remote extended temperature
Remote 3 Extended Bits
53
00
R
Read channel 3 remote extended temperature
Remote 4 Extended Bits
54
00
R
Read channel 4 remote extended temperature
Remote 5 Extended Bits
55
00
R
Read channel 5 remote extended temperature
Remote 6 Extended Bits
56
00
R
Read channel 6 remote extended temperature
Local Extended Bits
57
00
R
Read local channel extended temperature
*Duplicate entries.
______________________________________________________________________________________ 13
MAX6581
Table 3. Command Byte Register Bit Assignment (continued)
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Diode Fault Detection
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.
Alarm Threshold Registers
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.
OVERT Overtemperature Alarms
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.
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.
ALERT Interrupt Mode
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.
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.
ALERT Responses Address
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.
Command Byte Register Functions
Configuration Register (41h)
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).
ALERT Mask Register (42h)
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).
OVERT Mask Register (43h)
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).
14 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
BIT
NAME
POR
VALUE
7 (MSB)
STOP
0
Standby-Mode Control Bit. If STOP is set to logic 1, the MAX6581 stops converting
and enters standby mode.
6
POR
0
Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is selfclearing.
5
TIMEOUT
RESERVED
0
Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.
4
0
Reserved. Must be set to 0.
3
RESERVED
0
Reserved. Must be set to 0.
2
RESERVED
0
Reserved. Must be set to 0.
FUNCTION
1
EXTRANGE
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.
0
RESERVED
0
Reserved. Must be set to 0.
Table 5. ALERT Mask Register (42h)
BIT
NAME
POR
VALUE
7 (MSB)
Mask ALERT 7
0
Channel 7 Alert Mask. Set to logic 1 to mask channel 7 ALERT.
6
Mask Local
ALERT
0
Local Alert Mask. Set to logic 1 to mask local channel ALERT.
5
Mask ALERT 6
0
Channel 6 Alert Mask. Set to logic 1 to mask channel 6 ALERT.
4
Mask ALERT 5
0
Channel 5 Alert Mask. Set to logic 1 to mask channel 5 ALERT.
3
Mask ALERT 4
0
Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT.
2
Mask ALERT 3
0
Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT.
1
Mask ALERT 2
0
Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT.
0
Mask ALERT 1
0
Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.
FUNCTION
Table 6. OVERT Mask Register (43h)
BIT
NAME
POR
VALUE
7 (MSB)
Mask OVERT 7
0
Channel 7 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 7 OVERT.
6
Mask Local
OVERT
0
Local Overt Mask. Set to logic 1 to mask local channel OVERT.
5
FUNCTION
Mask OVERT 6
0
Channel 6 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 6 OVERT.
4
Mask OVERT 5
0
Channel 5 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 5 OVERT.
3
Mask OVERT 4
0
Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4 OVERT.
2
Mask OVERT 3
0
Channel 3 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 3 OVERT.
1
Mask OVERT 2
0
Channel 2 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 2 OVERT.
Mask OVERT 1
0
Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1 OVERT.
0
______________________________________________________________________________________ 15
MAX6581
Table 4. Configuration Register (41h)
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Status Register Functions
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
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
POR
STATE
FUNCTION
7 (MSB)
Remote ALERT
High 7
0
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.
6
Local ALERT
High
0
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.
5
Remote ALERT
High 6
0
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.
4
Remote ALERT
High 5
0
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.
3
Remote ALERT
High 4
0
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.
2
Remote ALERT
High 3
0
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.
1
Remote ALERT
High 2
0
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.
0
Remote ALERT
High 1
0
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.
16 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
BIT
NAME
POR
STATE
7 (MSB)
Remote OVERT 7
0
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.
6
Local OVERT
0
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.
5
Remote OVERT 6
0
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.
4
Remote OVERT 5
0
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.
3
Remote OVERT 4
0
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.
2
Remote OVERT 3
0
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.
1
Remote OVERT 2
0
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.
0
Remote OVERT 1
0
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.
FUNCTION
Table 9. Diode Fault Status Register (46h)
BIT
NAME
POR
STATE
7 (MSB)
RESERVED
0
—
6
Diode Fault 7
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.
5
Diode Fault 6
0
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.
4
Diode Fault 5
0
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.
3
Diode Fault 4
0
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.
2
Diode Fault 3
0
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.
1
Diode Fault 2
0
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.
0
Diode Fault 1
0
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.
FUNCTION
______________________________________________________________________________________ 17
MAX6581
Table 8. OVERT Status Register (45h)
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Table 10. ALERT Low Status Register
BIT
NAME
POR
STATE
7 (MSB)
Remote ALERT
Low 7
0
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.
6
Local ALERT Low
0
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.
5
Remote ALERT
Low 6
0
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.
4
Remote ALERT
Low 5
0
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.
3
Remote ALERT
Low 4
0
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.
2
Remote ALERT
Low 3
0
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.
1
Remote ALERT
Low 2
0
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.
0
Remote ALERT
Low 1
0
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.
FUNCTION
Effect of Ideality Factor
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)
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.
18 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
REGISTER
0x4B
B7
B6
B5
B4
B3
B2
B1
B0
IDEALITY
FACTOR
HEX
X
X
X
0
0
0
0
0
.999
0x00
X
X
X
0
0
0
0
1
1.000
0x01
X
X
X
0
0
0
1
0
1.001
0x02
X
X
X
0
0
0
1
1
1.002
0x03
X
X
X
0
0
1
0
0
1.003
0x04
X
X
X
0
0
1
0
1
1.004
0x05
X
X
X
0
0
1
1
0
1.005
0x06
X
X
X
0
0
1
1
1
1.006
0x07
X
X
X
0
1
0
0
0
1.007
0x08
X
X
X
0
1
0
0
1
1.008
0x09
X
X
X
0
1
0
1
0
1.009
0x0A
X
X
X
0
1
0
1
1
1.010
0x0B
X
X
X
0
1
1
0
0
1.011
0x0C
X
X
X
0
1
1
0
1
1.012
0x0D
0x0E
X
X
X
0
1
1
1
0
1.013
X
X
X
0
1
1
1
1
1.014
0x0F
X
X
X
1
0
0
0
0
1.015
0x10
X
X
X
1
0
0
0
1
1.016
0x11
X
X
X
1
0
0
1
0
1.017
0x12
X
X
X
1
0
0
1
1
1.018
0x13
X
X
X
1
0
1
0
0
1.019
0x14
X
X
X
1
0
1
0
1
1.020
0x15
X
X
X
1
0
1
1
0
1.021
0x16
X
X
X
1
0
1
1
1
1.022
0x17
X
X
X
1
1
0
0
0
1.023
0x18
X
X
X
1
1
0
0
1
1.024
0x19
X
X
X
1
1
0
1
0
1.025
0x1A
X
X
X
1
1
0
1
1
1.026
0x1B
X
X
X
1
1
1
0
0
1.027
0x1C
X
X
X
1
1
1
0
1
1.028
0x1D
X
X
X
1
1
1
1
0
1.029
0x1E
X
X
X
1
1
1
1
1
1.030
0x1F
X = Don’t care.
______________________________________________________________________________________ 19
MAX6581
Table 11. Transistor Ideality Register
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Series-Resistance Cancellation
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.
Applications Information
Remote-Diode Selection
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.
Discrete Remote Diodes
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.
Table 12. Resistance Cancellation Register (4Ah)
NAME
POR
STATE
7 (MSB)
X
0
—
6
RESISTANCE
CANCELLATION 7
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.
5
RESISTANCE
CANCELLATION 6
0
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.
4
RESISTANCE
CANCELLATION 5
0
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.
3
RESISTANCE
CANCELLATION 4
0
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.
2
RESISTANCE
CANCELLATION 3
0
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.
1
RESISTANCE
CANCELLATION 2
0
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.
0
RESISTANCE
CANCELLATION 1
0
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.
BIT
FUNCTION
X = Don’t care.
20 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
MAX6581
Table 13. Remote Sensors Transistor Suppliers (for Channels 1–7)
MODEL NO.
SUPPLIER
PNP
NPN
Central Semiconductor Corp. (USA)
CMPT3906
2N3906
CMPT3904
2N3904
Fairchild Semiconductor (USA)
MMBT3906
2N3906
2N3904
Infineon (Germany)
SMBT3906
—
ON Semiconductor (USA)
MMBT3906
2N3906
2N3904
ROHM Semiconductor (USA)
SST3906
SST3904
Samsung (Korea)
KST3906-TF
KST3904-TF
Siemens (Germany)
SMBT3906
SMBT3904
Zetex (England)
FMMT3906CT-ND
FMMT3904CT-ND
Note: Discrete transistors must be diode connected (base shorted to collector).
Unused Diode Channels
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.
Thermal Mass and Self-Heating
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
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.
ADC Noise Filtering
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.
Slave Address
The slave address for the MAX6581 is shown in Table 14.
Table 14. Slave Address
DEVICE ADDRESS
A7
A6
A5
A4
A3
A2
A1
A0
1
0
0
1
1
0
1
R/W
______________________________________________________________________________________ 21
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
GND
5–10 mils
5–10 mils
DXP_
MINIMUM
5–10 mils
DXN_
5–10 mils
GND
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.
PCB Layout
Follow the guidelines below to reduce the measurement
error when measuring remote temperature:
1) P
lace 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) D
o 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) R
oute 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
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) R
oute through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.
5) U
se 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) W
hen the power supply is noisy, add a resistor (up to
47I) in series with VCC.
Twisted-Pair and Shielded Cables
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.
22 �������������������������������������������������������������������������������������
±1°C Accurate 8-Channel Temperature Sensor
+3.3V
4.7kI
4.7kI 4.7kI
4.7kI
100pF
TO µP
TO µP
CPU
24
DXN1
1
23
DXP1
22
21
GND
N.C.
20
19
SMBCLK SMBDATA
DXP2
ALERT
DXN2
VCC
18
TO µP
100pF
2
3
0.1µF
DXP3
OVERT
100pF
4
5
MAX6581
DXN3
I.C.
DXP4
STBY
6
17
16
TO µP
15
14
N.C.
DXP7
100pF
DXN4
7
DXNP5
8
DXN5
DXN6
9
10
100pF
13
DXP6 DXN7
11
12
100pF
FPGA
ASIC
Package Information
Chip Information
PROCESS: BiCMOS
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.
LAND
PATTERN No.
24 TQFN-EP
T2444+4
21-0139
90-0022
______________________________________________________________________________________ 23
MAX6581
Typical Application Circuit
MAX6581
±1°C Accurate 8-Channel Temperature Sensor
Revision History
REVISION
NUMBER
REVISION
DATE
0
8/10
DESCRIPTION
Initial release
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
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Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.