19-5260; Rev 0; 8/10
EVALUATION KIT
AVAILABLE
±1°C 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 SMBus™ 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.
Features
S Eight Channels to Measure Seven Remote and
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 SMBus/I
S Two Open-Drain Alarm Outputs (ALERT and
2
C-Compatible Interface
OVERT)
S Resistance Cancellation on All Remote Channels
Applications
Desktop Computers
Notebook Computers
Workstations
Servers
Data Communications
MAX6581
Ordering Information/Selector Guide
PART SLAVE ADDRESS PIN-PACKAGE
MAX6581TG9A+ 0X9A 24 TQFN-EP*
MAX6581TG9C+** 0X9C 24 TQFN-EP*
MAX6581TG9E+** 0X9E 24 TQFN-EP*
MAX6581TG98+** 0X98 24 TQFN-EP*
+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.
OPERATING
TEMPERATURE RANGE
-40NC to +125NC -64NC to +150NC
-40NC to +125NC -64NC to +150NC
-40NC to +125NC -64NC to +150NC
-40NC to +125NC -64NC to +150NC
MEASURED
TEMPERATURE RANGE
_______________________________________________________________ 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.
±1°C Accurate 8-Channel Temperature Sensor
ABSOLUTE MAXIMUM RATINGS
(All Voltages Referenced to GND)
V
, SMBCLK, SMBDATA, ALERT,
CC
OVERT, STBY to GND .......................................... -0.3V to +4V
DXP_ to GND ............................................ -0.3V to (V
DXN_ to GND ........................................... -0.3V to (V
+ 0.3V)
CC
+ 0.3V)
CC
SMBDATA, ALERT, OVERT Current .................. -1mA to +50mA
DXN_ Current .................................................................... Q1mA
Continuous Power Dissipation (T
MAX6581
= +70NC)
A
24-Pin Thin QFN (derate 27.8mW/NC above +70NC) ..2222mW
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer 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 CONDITIONS MIN TYP MAX UNITS
Supply Voltage V
Standby Supply Current I
Operating Current
Temperature Resolution
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
I
CC1
I
CC2
CC
SS
SMBus static 4 15
During conversion, RC off 500 600
During conversion, RC on 550 650
= 3.3V
V
CC
V
= 3.3V
CC
V
= 3.3V
CC
V
= 3.3V
CC
Package Junction-to-Ambient Thermal Resistance
(B
) (Note 1) ............................................................36.0NC/W
JA
Package Junction-to-Case Thermal Resistance
(B
) (Note 1) ..............................................................3.0NC/W
JC
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
3.0 3.6 V
11 Bits
0.125
T
= +30NC to +85NC,
A
T
= +60NC to +100NC
RJ
, TRJ = -40NC to +125NC
A
T
= +30NC to +85NC,
A
T
= +100NC to +150NC
RJ
= +30NC to +85NC
T
A
= -40NC to +125NC
A
T
= 0NC to +150NC
A
T
= +30NC to +85NC,
A
T
= +60NC to +100NC
RJ
, TRJ = -40NC to +125NC
A
T
= +30NC to +85NC,
A
T
= +100NC to +125NC
RJ
= +30NC to +85NC
T
A
= -40NC to +125NC
A
T
= 0NC to +150NC
A
-0.85 +0.85
-1.2 +1.2
-2.5 +2.5
-1 +1
-2 +2
-3 +3
-1 +1
-2 +2
-2.75 +2.75
-1.5 +1.5
-2.5 +2.5
-3.5 +3.5
Q0.2 NC/V
FA
FA
NC
NCT
NCT
NCT
NCT
2 ______________________________________________________________________________________
±1°C 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 SYMBOL CONDITIONS MIN TYP MAX UNITS
Resistance cancellation mode off 95 125 156
Conversion Time per Channel t
Remote-Diode Source Current I
CONV
RJ
Resistance cancellation mode on or beta
compensation on
High level
Low level 8 10 12
High level
Resistance cancellation
mode off
Resistance cancellation
190 250 312
80 100 120
160 200 240
mode on or beta
Low level 16 20 24
DXP_ and DXN_ Leakage
Current
Standby mode 100 nA
Undervoltage Lockout Threshold UVLO Falling edge of V
compensation on
disables ADC 2.25 2.80 2.95 V
CC
Undervoltage Lockout Hysteresis 90 mV
Power-On-Reset (POR)
Threshold
falling edge 1.3 2.0 2.2 V
V
CC
POR Threshold Hysteresis 90 mV
ALERT and OVERT
I
= 1mA 0.01
Output Low Voltage V
Input Leakage Current I
OL
LEAK
SINK
= 6mA 0.3
I
SINK
-1 +1
SMBus INTERFACE, STBY
Logic Input Low Voltage V
Logic Input High Voltage V
VCC = 3.6V 0.8 V
IL
VCC = 3.0V 2.2 V
IH
Input Leakage Current -1 +1
I
Output Low Voltage V
Input Capacitance C
OL
IN
= 6mA 0.1 V
SINK
5 pF
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 3)
Serial-Clock Frequency f
Bus Free Time Between STOP
and START Condition
SMBCLK
t
BUF
START Condition Setup Time f
Repeated START Condition
Setup Time
START Condition Hold Time t
STOP Condition Setup Time t
Clock Low Period t
Clock High Period t
Data-In Hold Time t
Data-In Setup Time t
t
SU:STA
HD:STA
SU:STO
LOW
HIGH
HD:DAT
SU:DAT
(Note 4) 400 kHz
f
SMBCLK
SMBCLK
90% of SMBCLK to 90% of SMBDATA,
f
SMBCLK
10% of SMBDATA to 90% of SMBCLK,
f
SMBCLK
90% of SMBCLK to 90% of SMBDATA,
f
SMBCLK
10% to 10%, f
= 400kHz 1.6
= 400kHz 0.6
= 400kHz
= 400kHz
= 400kHz
SMBCLK
= 400kHz 1
50 ns
0.6
0.6
90% to 90% 0.6
0 0.9 us
(Note 5) 100 ns
ms
FA
V
FA
FA
Fs
Fs
Fs
Fs
Fs
Fs
MAX6581
_______________________________________________________________________________________ 3
±1°C 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 SYMBOL CONDITIONS MIN TYP MAX UNITS
Receive SMBCLK/SMBDATA
Rise Time
Receive SMBCLK/SMBDATA Fall
Time
MAX6581
Data-Out Hold Time t
Pulse Width of Spike Suppressed t
SMBus Timeout t
Note 2: All parameters are tested at T
Note 3: Timing specifications are guaranteed by design.
Note 4: The serial interface resets when SMBCLK is low for more than t
Note 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, V
= VCC, TA = +25NC, unless otherwise noted.)
STBY
t
R
t
F
DH
SP
TIMEOUT
= +85NC. Specifications over temperature are guaranteed by design.
A
SMBDATA low period for interface reset 25 37 45 ms
TIMEOUT
.
50 ns
0 50 ns
300 ns
300 ns
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
STANDBY SUPPLY CURRENT (µA)
HARDWARE OR SOFTWARE
0.5
STANDBY SUPPLY CURRENT
0
3.0 3.6
SUPPLY VOLTAGE (V)
AVERAGE OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGE
400
RESISTANCE
395
MAX6581 toc01
3.53.43.33.23.1
CANCELLATION OFF
390
385
380
375
370
365
AVERAGE OPERATING SUPPLY CURRENT (µA)
360
3.0 3.6
SUPPLY VOLTAGE (V)
MAX6581 toc02
3.53.43.1 3.2 3.3
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
REMOTE-DIODE TEMPERATURE ERROR (°C)
-8
-9
-10
-10 130
REMOTE-DIODE TEMPERATURE (°C)
MAX6581 toc03
1109050 703010
4 ______________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Typical Operating Characteristics (continued)
(VCC = +3.3V, V
= VCC, TA = +25NC, unless otherwise noted.)
STBY
MAX6581
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
5
4
3
2
1
0
-1
-2
-3
LOCAL TEMPERATURE ERROR (°C)
-4
-5
-10 100
DIE TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
5
4
3
2
1
0
-1
-2
-3
LOCAL TEMPERATURE ERROR (°C)
-4
-5
0.001 10
POWER-SUPPLY NOISE FREQUENCY (MHz)
100mV
10.10.01
REMOTE-DIODE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
5
4
MAX6581 toc04
908060 7010 20 30 40 500
3
2
1
0
-1
-2
-3
-4
REMOTE-DIODE TEMPERATURE ERROR (°C)
-5
0.001 10
POWER-SUPPLY NOISE FREQUENCY (MHz)
100mV
P-P
TRJ = +85°C
10.10.01
MAX6581 toc05
REMOTE-DIODE TEMPERATURE ERROR
vs. CAPACITANCE
P-P
MAX6581 toc06
5
4
3
2
1
0
-1
-2
-3
-4
REMOTE-DIODE TEMPERATURE ERROR (°C)
-5
1 100
CAPACITANCE (nF)
100mV
P-P
TRJ = +85°C
10
MAX6581 toc07
REMOTE-DIODE TEMPERATURE ERROR
vs. RESISTANCE
50
TRJ = +85°C
45
40
35
30
RESISTANCE
25
CANCELLATION OFF
20
15
10
5
REMOTE-DIODE TEMPERATURE ERROR (°C)
0
-5
0 100
RESISTANCE
CANCELLATION ON
RESISTANCE (I)
MAX6581 toc08
908060 7020 30 40 5010
_______________________________________________________________________________________ 5
±1°C Accurate 8-Channel Temperature Sensor
Pin Configuration
MAX6581
TOP VIEW
SMBDATA
SMBCLK
GND
N.C.
DXP1
DXN1
19
20
21
22
23
24
CC
V
ALERT
1718 16 14 13
OVERT
I.C.
STBY
15
MAX6581
*EP
1 2
DXP2
DXN2
*EP = EXPOSED PAD, CONNECT TO GND
3
DXP3
4 5 6
DXP4
DXN3
DXP7
N.C.
12
DXN7
DXP6
11
DXN6
10
9
DXN5
DXP5
8
DXN4
7
Pin Description
PIN NAME FUNCTION
Combined Current Source and ADC Positive Input for Channel 2 Remote Diode. Connect DXP2 to
1 DXP2
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-diode-
2 DXN2
connected 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
3 DXP3
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-diode-
4 DXN3
connected 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
5 DXP4
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.
6 ______________________________________________________________________________________
±1°C 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-diode-
7 DXN4
8 DXP5
9 DXN5
10 DXN6
11 DXP6
connected 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 substrate pnp (e.g., on a CPU
die), connect the base of the 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.
MAX6581
Cathode Input for Channel 7 Remote Diode. Connect the cathode of the channel 7 remote-diode-
12 DXN7
13 DXP7
14
15 I.C. Internally Connected. I.C. is internally connected to V
16
17 V
18
19 SMBDATA SMBus Serial-Data Input/Output. Connect SMBDATA to a pullup resistor.
20 SMBCLK SMBus Serial-Clock Input. Connect SMBCLK to a pullup resistor.
STBY
OVERT
CC
ALERT
connected 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.
. Connect I.C. to VCC or leave unconnected.
CC
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.
_______________________________________________________________________________________ 7
±1°C Accurate 8-Channel Temperature Sensor
Pin Description (continued)
PIN NAME FUNCTION
21 GND Ground
Combined Current Source and ADC Positive Input for Channel 1 Remote Diode. Connect DXP1 to
23 DXP1
MAX6581
24 DXN1
— EP Exposed Pad. Connect EP to GND.
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 DXN1. 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.
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.
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 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.
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:
N 1 2 N
+ ×
I I I
= + ×
AV CC1 CC2
where:
N
= the number of remote channels that are operating
N
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.
I
= the average operating power-supply current
CC1
during a conversion in normal mode.
I
= the average operating power-supply current
CC2
during a conversion in RC mode.
N R
N 2 N 1 N 2 N 1
+ × + + × +
N R N R
8 ______________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
V
CC
DXP1
MAX6581
DXN1
MAX6581
DXP2
DXN2
DXP3
DXN3
DXP4
DXN4
DXP5
DXN5
DXP6
DXN6
DXP7
I
RJ
+
INPUT
BUFFER
-
REF
SMBus INTERFACE
COUNT
COUNTER
REMOTE TEMPERATURES
ALERT RESPONSE ADDRESS
ALARM
ALU
REGISTER BANK
COMMAND BYTE
LOCAL TEMPERATURES
ALERT THRESHOLD
OVERT THRESHOLD
OVERT
ALERT
STBY
DXN7
Figure 1. Internal Block Diagram
_______________________________________________________________________________________ 9
LOCAL
TRANSISTOR
SMBCLK SMBDATA
±1°C Accurate 8-Channel Temperature Sensor
SMBus Digital Interface
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.
MAX6581
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 ACK PDATA ACKCOMMAND
7 BITS 18 BITS8 BITS
SLAVE ADDRESS: EQUIVALENT
TO CHIP-SELECT LINE OF
A 3-WIRE INTERFACE
READ-BYTE FORMAT
S ADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND
7 BITS 7 BITS 8 BITS8 BITS
SLAVE ADDRESS: EQUIVALENT
TO CHIP SELECT LINE
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
READING FROM
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.
DATA BYTE: DATA GOES INTO THE REGISTER
SET BY THE COMMAND BYTE (TO SET
THRESHOLDS, CONFIGURATION MASKS, AND
SAMPLING RATE)
SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATAFLOW DIRECTION
DATA BYTE: READS FROM
THE REGISTER SET BY THE
COMMAND BYTE
SEND-BYTE FORMAT
S PADDRESS WR ACK ACKCOMMAND
7 BITS 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
RECEIVE-BYTE FORMAT
S PADDRESS RD ACK ///DATA
7 BITS 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 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
MAX6581
A B C D
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
SU:STAtHD: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
Figure 3. SMBus Write Timing Diagram
A B C D
t
LOWtHIGH
SMBCLK
SMBDATA
t
t
HD:STA
SU: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
t
SU:DAT
F G
E
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
E
F G H
t
SU:DAT
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
t
HD:DAT
H I J
I = SLAVE PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
I
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
t
SU:STOtBUF
t
SU:STO
L MK
K
J
t
BUF
Figure 4. Read-Timing Diagram
Table 1. Main Temperature Register (High-Byte) Data Format
TEMPERATURE (NC)
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
DIGITAL OUTPUT
±1°C Accurate 8-Channel Temperature Sensor
Table 2. Extended-Resolution Temperature Register (Low-Byte) Data Format
TEMPERATURE (NC)
0 000X XXXX
+0.125 001X XXXX
+0.250 010X XXXX
+0.375 011X XXXX
MAX6581
X = Don’t care.
+0.500 100X XXXX
+0.625 101X XXXX
+0.750 110X XXXX
+0.875 111X XXXX
Table 3. Command Byte Register Bit Assignment
DIGITAL OUTPUT
REGISTER
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*
Manufacturer ID 0A 4D R Read manufacturer ID
Revision ID 0F 00 R Read 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
ADDRESS
(HEX)
09 00 R Read channel 1 remote-diode extended temperature
11 7F R/W
12 7F R/W
13 64 R/W
14 64 R/W
15 64 R/W
16 64 R/W
17 5A R/W Read/write local-diode alert high-temperature threshold limit
18 64 R/W
20 50 R/W Read/write channel local-diode overtemperature threshold limit
POR
VALUE
(HEX)
READ/
WRITE
DESCRIPTION
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 channel 7 remote-diode alert high-temperature
threshold limit
12 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Table 3. Command Byte Register Bit Assignment (continued)
MAX6581
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 41 00 R/W Read/write configuration
ALERT Mask
OVERT Mask
ALERT High Status
OVERT Status
Diode Fault Status 46 00 R Read diode fault status
ALERT Low Status
ALERT Low Disable
Resistance Cancellation 4A 00 R/W 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
Offset 4D 00 R/W Read/write temperature offset value
Offset Select 4E 00 R/W
Remote 1 Extended
Bits*
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.
ADDRESS
(HEX)
21 6E R/W Read/write channel 1 remote-diode overtemperature threshold limit
22 6E R/W Read/write channel 2 remote-diode overtemperature threshold limit
23 6E R/W Read/write channel 3 remote-diode overtemperature threshold limit
24 7F R/W Read/write channel 4 remote-diode overtemperature threshold limit
25 5A R/W Read/write channel 5 remote-diode overtemperature threshold limit
26 5A R/W Read/write channel 6 remote-diode overtemperature threshold 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
42 00 R/W
43 00 R/W
44 00 R
45 00 R
47 00 R
48 FF R/W
51 00 R Read channel 1 remote extended temperature
POR
VALUE
(HEX)
READ/
WRITE
DESCRIPTION
Read/write ALERT mask
Read/write OVERT mask
Read ALERT high status
Read OVERT status
Read ALERT low status
Read/write ALERT low disable
Read/write ideality value selection bits (1 = selected transistor
ideality, 0 = 1.008)
Read/write offset value selection bits (1 = value in Offset Select
register, 0 = 0)
______________________________________________________________________________________ 13
±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
MAX6581
diode fault is detected, the MAX6581 goes to the next
channel in the conversion sequence.
Alarm Threshold Registers
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 Interrupt Mode
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 I
2
C general call.
If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address
code wins. The losing device does not generate an
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
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.
Command Byte Register Functions
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 (00h).
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
Table 4. Configuration Register (41h)
BIT NAME
7 (MSB) STOP 0
6 POR 0
5
4 RESERVED 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.
1 EXTRANGE 0
0 RESERVED 0 Reserved. Must be set to 0.
TIMEOUT
Table 5. ALERT Mask Register (42h)
BIT NAME
7 (MSB)
6
5
4
3
2
1
0
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
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.
0 Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.
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.
POR
VALUE
0
Channel 7 Alert Mask. Set to logic 1 to mask channel 7 ALERT.
0
Local Alert Mask. Set to logic 1 to mask local channel ALERT.
0
Channel 6 Alert Mask. Set to logic 1 to mask channel 6 ALERT.
0
Channel 5 Alert Mask. Set to logic 1 to mask channel 5 ALERT.
0
Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT.
0
Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT.
0
Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT.
0
Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.
FUNCTION
FUNCTION
MAX6581
Table 6. OVERT Mask Register (43h)
BIT NAME
7 (MSB)
6
5
4
3
2
1
0
Mask OVERT 7
Mask Local
OVERT
Mask OVERT 6
Mask OVERT 5
Mask OVERT 4
Mask OVERT 3
Mask OVERT 2
Mask OVERT 1
______________________________________________________________________________________ 15
POR
VALUE
0
0
0
0
0
0
0
0
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.
FUNCTION
±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
MAX6581
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
Table 7. ALERT High Status Register (44h)
BIT NAME
7 (MSB)
6
5
4
3
2
1
0
Remote ALERT
Local ALERT
Remote ALERT
Remote ALERT
Remote ALERT
Remote ALERT
Remote ALERT
Remote ALERT
High 7
High
High 6
High 5
High 4
High 3
High 2
High 1
POR
STATE
0
0
0
0
0
0
0
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.
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.
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.
FUNCTION
16 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Table 8. OVERT Status Register (45h)
BIT NAME
7 (MSB)
Remote OVERT 7
6
5
Remote OVERT 6
4
Remote OVERT 5
3
Remote OVERT 4
2
Remote OVERT 3
1
Remote OVERT 2
0
Remote OVERT 1
Local OVERT
POR
STATE
0
0
0
0
0
0
0
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
Table 9. Diode Fault Status Register (46h)
BIT NAME
7 (MSB) RESERVED 0 —
6 Diode Fault 7 0
5 Diode Fault 6 0
4 Diode Fault 5 0
3 Diode Fault 4 0
2 Diode Fault 3 0
1 Diode Fault 2 0
0 Diode Fault 1 0
______________________________________________________________________________________ 17
POR
STATE
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 V
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 V
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 V
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 V
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 V
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 V
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 V
FUNCTION
.
CC
.
CC
.
CC
.
CC
.
CC
.
CC
.
CC
±1°C Accurate 8-Channel Temperature Sensor
Table 10. ALERT Low Status Register (47h)
BIT NAME
7 (MSB)
MAX6581
6
5
4
3
2
1
0
Remote ALERT
Low 7
Local ALERT Low
Remote ALERT
Low 6
Remote ALERT
Low 5
Remote ALERT
Low 4
Remote ALERT
Low 3
Remote ALERT
Low 2
Remote ALERT
Low 1
POR
STATE
0
0
0
0
0
0
0
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.
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 (emit-
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.
ter) and DXN_ must be connected to the cathode (base)
18 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Table 11. Transistor Ideality Register
MAX6581
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
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
X X X 0 1 1 1 0 1.013 0x0E
0x4B
X = Don’t care.
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
IDEALITY
FACTOR
HEX
______________________________________________________________________________________ 19
±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 inter-
MAX6581
connection 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 V
characteristics. Manufacturers of discrete
BE
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)
BIT NAME
7 (MSB) X 0 —
6
5
4
3
2
1
0
X = Don’t care.
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
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
20 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Table 13. Remote Sensors Transistor Suppliers (for Channels 1–7)
MAX6581
SUPPLIER
Central Semiconductor Corp. (USA)
Fairchild Semiconductor (USA)
Infineon (Germany) SMBT3906 —
ON Semiconductor (USA)
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).
CMPT3906
2N3906
MMBT3906
2N3906
MMBT3906
2N3906
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
PNP NPN
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.
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
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.
MODEL NO.
CMPT3904
2N3904
2N3904
2N3904
ADC Noise Filtering
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
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
Slave Address
R/W
______________________________________________________________________________________ 21
±1°C Accurate 8-Channel Temperature Sensor
traces away from any higher voltage traces, such as
GND
5–10 mils
5–10 mils
DXP_
DXN_
MAX6581
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) 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
5–10 mils
MINIMUM
5–10 mils
+12V
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 V
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.
. Leakage currents from PCB contamination
DC
.
CC
Twisted-Pair and Shielded Cables
22 _____________________________________________________________________________________
±1°C Accurate 8-Channel Temperature Sensor
Typical Application Circuit
+3.3V
4.7kI 4.7kI4.7kI 4.7kI
CPU
100pF
100pF
100pF
24 23 22 21 20 19
SMBDATA
SMBCLK
DXN1
1
DXP2 ALERT
2
DXN2
3
DXP3
4
DXN3
5
DXP4
DXP1
N.C.
MAX6581
GND
V
OVERT
I.C.
STBY
18
17
CC
µF
0.1
16
15
14
TO
TO
TO
TO
µP
µP
µP
µP
MAX6581
6
N.C.
100pF
DXP5DXN4 DXN5
87 9
FPGA
ASIC
Chip Information
PROCESS: BiCMOS
13
DXP7
DXN6 DXP6
10 11
100pF100pF
DXN7
12
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages.
“-” 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
24 TQFN-EP T2444+4
Note that a “+”, “#”, or
OUTLINE
NO.
PATTERN NO.
21-0139 90-0022
LAND
______________________________________________________________________________________ 23
±1°C Accurate 8-Channel Temperature Sensor
Revision History
REVISION
NUMBER
0 8/10 Initial release —
REVISION
DATE
MAX6581
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 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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