MAXIM MAX6646

19-2540; Rev 3; 5/07
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Features
The MAX6646/MAX6647/MAX6649 are precise, twochannel digital temperature sensors. The devices accurately measure the temperature of their own die and a
remote PN junction, and report the temperature in digital
form using a 2-wire serial interface. The remote PN junction is typically the emitter-base junction of a commoncollector PNP on a CPU, FPGA, or ASIC.
♦ Dual Channel: Measures Remote and Local
Temperature
The 2-wire serial interface accepts standard system management bus (SMBusTM) write byte, read byte, send byte,
and receive byte commands to read the temperature
data and to program the alarm thresholds. To enhance
system reliability, the MAX6646/MAX6647/MAX6649
include an SMBus timeout. A fault queue prevents the
ALERT and OVERT outputs from setting until a fault has
been detected one, two, or three consecutive times
(programmable).
The MAX6646/MAX6647/MAX6649 provide two system
alarms: ALERT and OVERT. ALERT asserts when any of
four temperature conditions are violated: local overtemperature, remote overtemperature, local undertemperature, or remote undertemperature. OVERT asserts when
the temperature rises above the value in either of the two
OVERT limit registers. The OVERT output can be used to
activate a cooling fan, or to trigger a system shutdown.
Measurements can be done autonomously, at the programmed conversion rate, or in a single-shot mode. The
adjustable conversion rate allows optimizing supply current and temperature update rate to match system needs.
Remote accuracy is ±1°C maximum error between +60°C
and +145°C with no calibration needed. The MAX6646/
MAX6647/MAX6649 operate from -55°C to +125°C, and
measure temperatures between 0°C and +145°C. The
MAX6646/MAX6647/MAX6649 are available in an 8-pin
µMAX® package.
♦ Measures High-Ideality Thermal Diodes Up to
+170°C (Apparent)
+145°C (Real)
♦ 0.125°C Resolution
♦ High Accuracy ±1°C (max) from +60°C to +145°C
(Remote), and ±2°C (max) from +60°C to +100°C
(Local)
♦ Two Alarm Outputs: ALERT and OVERT
♦ Programmable Under/Overtemperature Alarm
Temperature Thresholds
♦ Programmable Conversion Rate
♦ SMBus-Compatible Interface
♦ SMBus Timeout
Ordering Information
PART
TEMP RANGE
PINMEASURED
PACKAGE TEMP RANGE
MAX6646MUA -55°C to +125°C 8 µMAX
0°C to +145°C
MAX6647MUA -55°C to +125°C 8 µMAX
0°C to +145°C
MAX6649MUA -55°C to +125°C 8 µMAX
0°C to +145°C
Typical Operating Circuit
3.3V
Applications
0.1μF
200Ω
Graphics Processors
VCC
Desktop Computers
Notebook Computers
DXP
MAX6646 SDA
MAX6647
MAX6649 SCLK
DXN
ALERT
INTERRUPT TO μP
OVERT
TO FAN DRIVER OR
SYSTEM SHUTDOWN
Servers
Thin Clients
Workstations
Test and Measurement
2200pF
μP
10kΩ EACH
GND
DATA
CLOCK
Multichip Modules
SMBus is a trademark of Intel Corp.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Selector Guide, Pin Configurations, and Functional Diagram
appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX6646/MAX6647/MAX6649
General Description
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
ABSOLUTE MAXIMUM RATINGS
ESD Protection (all pins, Human Body Model) ................±2000V
Junction Temperature ......................................................+150°C
Operating Temperature Range .........................-55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
All Voltages Referenced to GND
VCC ...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (VCC + 0.3V)
DXN .......................................................................-0.3V to +0.8V
SCLK, SDA, ALERT, OVERT.....................................-0.3V to +6V
SDA, ALERT, OVERT Current .............................-1mA to +50mA
DXN Current .......................................................................±1mA
Continuous Power Dissipation (TA = +70°C)
8-Pin µMAX (derate 4.8mW/°C above +70°C) ..........387.8mW
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 5.5V, TA = -55°C to +125°C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +100°C.) (Note 1)
PARAMETER
Supply Voltage
SYMBOL
CONDITIONS
VCC
MIN
Local Temperature Error
°C
Bits
-1.0
+1.0
VCC = 3.3V, TA = +60°C to +100°C,
TRJ = +25°C to +145°C
-1.6
+1.6
VCC = 3.3V, TA = +0°C to +100°C,
TRJ = +0°C to +145°C
-3.2
+3.2
TA = +60°C to +100°C
-2.0
+2.0
TA = 0°C to +125°C
-3.0
+3.0
VCC = 3.3V
±0.2
UVLO
Falling edge of VCC disables ADC
2.4
UVLO Hysteresis
2.7
VCC falling edge
POR Threshold Hysteresis
Standby Supply Current
SMBus static
Operating Current
During conversion
Average Operating Current
2.95
tCONV
V
90
mV
3
0.08
mA
250
400
125
Standby mode
IRJ
µA
2 conversions per second
-25
DXP and DXN Leakage Current
12
80
95
V
2.0
40
From stop bit to conversion completion
°C
mV
0.25 conversions per second
Conversion Time Error
°C
°C/V
90
Power-On-Reset (POR) Threshold
2
V
VCC = 3.3V, TA = +100°C,
TRJ = +60°C to +145°C
Supply Sensitivity of Temperature
Error
Remote-Diode Source Current
UNITS
5.5
11
Remote Temperature Error
Conversion Time
MAX
0.125
Temperature Resolution
Undervoltage Lockout (UVLO)
Threshold
TYP
3.0
156
ms
+25
%
100
nA
High level
80
100
120
Low level
8
10
12
_______________________________________________________________________________________
µA
µA
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
(VCC = 3.0V to 5.5V, TA = -55°C to +125°C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +100°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ALERT, OVERT
Output Low Voltage
Output High Leakage Current
ISINK = 1mA
0.4
ISINK = 4mA
0.6
VOH = 5.5V
1
µA
0.8
V
V
SMBus-COMPATIBLE INTERFACE (SCLK AND SDA)
Logic Input Low Voltage
Logic Input High Voltage
VIL
VIH
VCC = 3.0V
2.2
VCC = 5.5V
2.6
Input Leakage Current
ILEAK
VIN = GND or VCC
-1
Output Low-Sink Current
ISINK
VOL = 0.6V
6
Input Capacitance
CIN
V
+1
µA
mA
5
pF
SMBus-COMPATIBLE TIMING (Note 2)
Serial Clock Frequency
fSCLK
Bus Free Time Between STOP
and START Condition
tBUF
(Note 3)
START Condition Setup Time
100
kHz
4.7
µs
4.7
µs
Repeat START Condition Setup
Time
tSU:STA
90% to 90%
50
ns
START Condition Hold Time
tHD:STA
10% of SDA to 90% of SCLK
4
µs
STOP Condition Setup Time
tSU:STO
90% of SCLK to 90% of SDA
4
µs
Clock Low Period
tLOW
10% to 10%
4.7
µs
Clock High Period
tHIGH
90% to 90%
4
µs
Data Setup Time
tHD:DAT
(Note 4)
250
µs
Receive SCLK/SDA Rise Time
tR
1
µs
Receive SCLK/SDA Fall Time
tF
300
ns
Pulse Width of Spike Suppressed
SMBus Timeout
Note 1:
Note 2:
Note 3:
Note 4:
tSP
tTIMEOUT
0
SDA low period for interface reset
25
37
50
ns
55
ms
All parameters tested at a single temperature. Specifications over temperature are guaranteed by design.
Timing specifications guaranteed by design.
The serial interface resets when SCLK is low for more than tTIMEOUT.
A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK’s falling edge.
_______________________________________________________________________________________
3
MAX6646/MAX6647/MAX6649
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
3.5
3.0
1.5
TEMPERATURE ERROR (°C)
4.0
2.0
MAX6649 toc02
OPERATING SUPPLY CURRENT (μA)
4.5
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
400
MAX6649 toc01
300
200
100
1.0
0.5
0
-0.5
-1.0
TA = +85°C
FAIRCHILD 2N3906
-1.5
2.5
0
3.5
4.0
4.5
-2.0
5.5
5.0
0.63
0.13
0.25
0.50
1.00
2.00 4.00
75
100
125
TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
LOCAL TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
5
MAX6649 toc04
LOCAL ERROR
0
-0.5
-1.0
-1.5
3
REMOTE ERROR
2
1
0
VCC = SQUARE WAVE APPLIED TO
VCC WITH NO BYPASS CAPACITOR
-1
-2.0
75
125
100
6
5
REMOTE ERROR
4
3
2
LOCAL ERROR
1
0
-2
0.1
1
TEMPERATURE (°C)
10
100
1k
10k
100k
1
10
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
1
0
TEMPERATURE ERROR (°C)
1.5
1.0
0.5
0
-0.5
100
-1
-2
-3
-4
-1.0
1
10
100
1k
FREQUENCY (Hz)
10k
100k
-5
0.100
1k
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6649 toc07
2.0
TEMPERATURE ERROR (°C)
7
MAX6649 toc08
50
VIN = AC-COUPLED TO DXN
VIN = 100mVP-P
8
-1
-2
25
9
TEMPERATURE ERROR (°C)
4
TEMPERATURE ERROR (°C)
0.5
4
50
CONVERSION RATE (Hz)
1.0
0
25
0
SUPPLY VOLTAGE (V)
MAX6649 toc05
3.0
MAX6649 toc06
STANDBY SUPPLY CURRENT (μA)
5.0
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX6649 toc03
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TEMPERATURE ERROR (°C)
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
1.000
10.000
100.000
DXP-DXN CAPACITANCE (nF)
_______________________________________________________________________________________
10k
100k
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
PIN
NAME
FUNCTION
1
VCC
Supply Voltage Input, 3V to 5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 200Ω series
resistor is recommended but not required for additional noise filtering.
2
DXP
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. DO
NOT LEAVE DXP FLOATING; connect DXP to DXN if no remote diode is used. Place a 2200pF
capacitor between DXP and DXN for noise filtering.
3
DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to
ground.
4
OVERT
5
GND
Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is
above the software-programmed threshold.
Ground
SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds limits
(high or low temperature). ALERT stays asserted until acknowledged by either reading the status
register or by successfully responding to an alert response address, provided that the fault
condition no longer exists. See the ALERT Interrupts section.
6
ALERT
7
SDA
SMBus Serial-Data Input/Output, Open Drain
8
SCLK
SMBus Serial-Clock Input
Detailed Description
The MAX6646/MAX6647/MAX6649 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in thermostatic, process-control,
or monitoring applications. Communication with the
MAX6646/MAX6647/MAX6649 occurs through the
SMBus-compatible serial interface and dedicated alert
and overtemperature outputs. ALERT asserts if the measured local or remote temperature is greater than the
software-programmed ALERT high limit or less than the
ALERT low limit in the MAX6649. ALERT also asserts, in
the MAX6649, if the remote-sensing diode pins are shorted or unconnected. The overtemperature alarm, OVERT,
asserts if the software-programmed OVERT limit is
exceeded. OVERT can be connected to fans, a system
shutdown, a clock throttle control, or other thermal-management circuitry.
The MAX6646/MAX6647/MAX6649 convert temperatures
to digital data either at a programmed rate or in single
conversions. Temperature data is represented as 11 bits,
with the LSB equal to 0.125°C. The “main” temperature
data registers (at addresses 00h and 01h) are 8-bit registers that represent the data as 8 bits with the full-scale
reading indicating the diode fault status (Table 1). The
remaining 3 bits of temperature data are available in the
“extended” registers at addresses 11h and 10h (Table 2).
ADC and Multiplexer
The averaging ADC integrates over a 60ms period
(each channel, typically), with excellent noise rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward voltage and compute the temperature based on this voltage. Both channels are automatically converted once
the conversion process has started, either in free-running or single-shot mode. If one of the two channels is
not used, the device still performs both measurements,
and the results of the unused channel can be ignored.
If the remote-diode channel is unused, connect DXP to
DXN rather than leaving the inputs open.
Table 1. Main Temperature Data Register
Format (00h, 01h)
TEMP (°C)
DIGITAL OUTPUT
+145
1001 0001
+130
1000 0010
+128
1000 0000
+25
0001 1001
0
0000 0000
<0
Diode fault
(short or open)
0000 0000
1111 1111
_______________________________________________________________________________________
5
MAX6646/MAX6647/MAX6649
Pin Description
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
The DXP-DXN differential input voltage range is 0.25V to
0.95V. Excess resistance in series with the remote diode
causes +0.5°C (typ) error per ohm.
Remote Temperature Measurement
Range
The MAX6646/MAX6647/MAX6649 measure remote
temperatures significantly above the +120°C limit of
many temperature sensors. External diode-connected
transistors work well as temperature sensors up to
approximately +145°C, where accuracy begins to
degrade. Thermal diodes on some CPUs have characteristics that produce “apparent temperatures” far
above actual operating temperatures. The MAX6646/
MAX6647/MAX6649 measure apparent temperatures as
high as +170°C, as long as the actual temperature is
less than +145°C.
A/D Conversion Sequence
A conversion sequence consists of a local temperature
measurement and a remote temperature measurement.
Each time a conversion begins, whether initiated automatically in the free-running autonomous mode (RUN =
0) or by writing a one-shot command, both channels are
converted, and the results of both measurements are
available after the end of a conversion. A BUSY status bit
in the status byte indicates that the device is performing a
new conversion. The results of the previous conversion
are always available, even if the ADC is busy.
Low-Power Standby Mode
Standby mode reduces the supply current to less than
12µA by disabling the ADC and timing circuitry. Enter
standby mode by setting the RUN bit to 1 in the configuration byte register (Table 6). All data is retained in memory, and the SMBus interface is active and listening for
SMBus commands. Standby mode is not a shutdown
mode. With activity on the SMBus, the device draws more
supply current (see Typical Operating Characteristics). In
standby mode, the MAX6646/MAX6647/MAX6649 can be
forced to perform A/D conversions through the one-shot
command, regardless of the RUN bit status.
If a standby command is received while a conversion is
in progress, the conversion cycle is truncated, and the
data from that conversion is not latched into a temperature register. The previous data is not changed and
remains available.
Supply-current drain during the 125ms conversion period
is 250µA (typ). Slowing down the conversion rate reduces
the average supply current (see Typical Operating
Characteristics). Between conversions, the conversion
rate timer consumes 25µA (typ) of supply current. In
standby mode, supply current drops to 3µA (typ).
6
SMBus Digital Interface
From a software perspective, the MAX6646/MAX6647/
MAX6649 appear as a set of byte-wide registers that
contain temperature 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 MAX6646/MAX6647/MAX6649 employ four standard
SMBus protocols: write byte, read byte, send byte, and
receive byte (Figures 1, 2, and 3). The shorter receive
byte protocol allows quicker transfers, provided that the
correct data register was previously selected by a read
byte instruction. Use caution when using the shorter protocols in multimaster systems, as a second master could
overwrite the command byte without informing the first
master.
Temperature data can be read from the read internal
temperature (00h) and read external temperature (01h)
registers. The temperature data format for these registers is 8 bits for each channel, with the LSB representing
1°C (Table 1). The MSB is transmitted first.
An additional 3 bits can be read from the read external
extended temperature register (10h), which extends
the data to 11 bits and the resolution to 0.125°C per
LSB. An additional 3 bits can be read from the read
internal extended temperature register (11h), which
extends the data to 11 bits and the resolution to
0.125°C per LSB (Table 2).
When a conversion is complete, the main temperature
register and the extended temperature register are
updated simultaneously. Ensure that no conversions
are completed between reading the main register and
the extended register, so that both registers contain the
result of the same conversion.
Table 2. Extended Resolution Temperature
Register Data Format (10h, 11h)
FRACTIONAL TEMP (°C)
DIGITAL OUTPUT
0.000
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
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
MAX6646/MAX6647/MAX6649
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
DATA
8 bits
Slave Address: equivalent to chip-select line of
a 3-wire interface
ACK
P
8 bits
Command Byte: selects which
register you are writing to
1
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Read Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
S
8 bits
Slave Address: equivalent to chip-select line
ADDRESS
RD
ACK
Command Byte: selects
which register you are
reading from
///
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
COMMAND
7 bits
ACK
P
S
8 bits
ADDRESS
RD
ACK
7 bits
DATA
///
P
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
Command Byte: sends command with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
DATA
7 bits
Send Byte Format
S
ADDRESS
Shaded = Slave transmission
/// = Not acknowledged
Figure 1. SMBus Protocols
A
B
tLOW
C
D
E
F
G
tHIGH
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA tHD:STA
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
tSU:STO
tSU:DAT
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
tBUF
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram
To ensure valid extended data, read extended resolution temperature data using one of the following
approaches:
1) Put the MAX6646/MAX6647/MAX6649 into standby
mode by setting bit 6 of the configuration register to 1.
Initiate a one-shot conversion using command byte
0Fh. When this conversion is complete, read the contents of the temperature data registers.
2) If the MAX6646/MAX6647/MAX6649 is in run mode,
read the status byte. If the BUSY bit indicates that a
conversion is in progress, wait until the conversion is
complete (BUSY bit set to zero) before reading the
temperature data. Following a conversion completion, immediately read the contents of the temperature data registers. If no conversion is in progress,
the data can be read within a few microseconds,
which is a sufficiently short period of time to ensure
that a new conversion cannot be completed until
after the data has been read.
_______________________________________________________________________________________
7
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tHD:DAT
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = MASTER PULLS DATA LINE LOW
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 3. SMBus Read Timing Diagram
Alarm Threshold Registers
Four registers store ALERT threshold values—one hightemperature (THIGH) and one low-temperature (TLOW)
register each for the local and remote channels. If either
measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT interrupt
asserts.
The MAX6646/MAX6647 local (internal) ALERT THIGH
register POR state is 0101 0101, or +85°C, while the
remote (external) ALERT THIGH register POR state is
0101 1111, or +95°C.The MAX6649 POR state of both
ALERT THIGH registers is 0101 0101, or +85°C. The POR
state of the local and remote T LOW registers for all
devices is 0000 0000, or 0°C.
Two additional registers store remote and local alarm
threshold data corresponding to the OVERT output. The
values stored in these registers are high-temperature
thresholds. If either of the measured temperatures equals
or exceeds the corresponding alarm threshold value, an
OVERT output asserts. The MAX6646/MAX6647 local
(internal) OVERT register POR state is 0101 0101, or
+85°C, while the remote (external) OVERT register POR
state is 0111 1101, or +125°C. The MAX6649 POR state
of both OVERT registers is 0101 0101, or +85°C.
Diode Fault Alarm
A continuity fault detector at DXP detects an open circuit between DXP and DXN, or a DXP short to VCC,
GND, or DXN. If an open or short circuit exists, the
external temperature register is loaded with 1111 1111.
If the fault is an open-circuit fault bit 2 (OPEN), the status byte is set to 1. In the MAX6649, ALERT is activated
at the end of the conversion. Immediately after POR,
the status register indicates that no fault is present. If a
fault is present upon power-up, the fault is not indicated
until the end of the first conversion.
8
ALERT Interrupts
The ALERT interrupt occurs when the internal or external
temperature reading exceeds a high- or low-temperature
limit (programmed) or in the MAX6649, when the remote
diode is disconnected (for continuity fault detection). The
ALERT interrupt output signal is latched and can be
cleared only by either reading the status register or by
successfully responding to an alert response address. In
both cases, the alert is cleared if the fault condition no
longer exists. Asserting ALERT does not halt automatic
conversion. The ALERT output is open drain, allowing
multiple devices to share a common interrupt line.
The MAX6646/MAX6647/MAX6649 respond to the
SMBus alert response address, an interrupt pointer
return-address feature (see the Alert Response
Address section). Prior to taking corrective action,
always check to ensure that an interrupt is valid by
reading the current temperature.
Fault Queue Register
In some systems, it may be desirable to ignore a single
temperature measurement that falls outside the ALERT
limits. Bits 1 and 2 of the fault queue register (address
22h) determine the number of consecutive temperature
faults necessary to set ALERT (see Tables 3 and 4).
Alert Response Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a receive byte transmission
to the alert response slave address (0001 100).
Following such a broadcast, any slave device that generated an interrupt attempts to identify itself by putting
its own address on the bus.
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
BIT
7
6 to 3
NAME
RFU
RFU
POR
STATE
FUNCTION
1
Reserved. Always write 1 to
this bit.
0
Reserved. Always write
zero to this bit.
2
FQ1
1
Fault queue-length control
bit (see Table 4).
1
FQ0
1
Fault queue-length control
bit (see Table 4).
0
RFU
0
Reserved. Always write
zero to this bit.
The alert response can activate several different slave
devices simultaneously, similar to the I2C general call. If
more than one slave attempts to respond, bus arbitration
rules apply, and the device with the lower address code
wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until
cleared. (The conditions for clearing an ALERT vary,
depending on the type of slave device). Successful completion of the read alert response protocol clears the
interrupt latch, provided the condition that caused the
alert no longer exists.
OVERT Overtemperature Alarm/Warning
Outputs
OVERT asserts when the temperature rises to a value
stored in one of the OVERT limit registers (19h, 20h). It
deasserts when the temperature drops below the stored
limit, minus hysteresis. OVERT can be used to activate a
cooling fan, send a warning, invoke clock throttling, or trigger a system shutdown to prevent component damage.
Command Byte Functions
The 8-bit command byte register (Table 5) is the master
index that points to the various other registers within the
MAX6646/MAX6647/MAX6649. The register’s POR state
is 0000 0000, so a receive byte transmission (a protocol
that lacks the command byte) that occurs immediately
after POR, returns the current local temperature data.
The MAX6646/MAX6647/MAX6649 incorporate collision
avoidance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
Table 4. Fault Queue Length Bit Definition
FQ1
FQ0
FAULT QUEUE LENGTH (SAMPLES)
0
0
1
0
1
2
1
1
3
1
0
1
One-Shot
The one-shot command immediately forces a new conversion cycle to begin. If the one-shot command is
received while the MAX6646/MAX6647/MAX6649 are in
standby mode (RUN bit = 1), a new conversion begins,
after which the device returns to standby mode. If a oneshot conversion is in progress when a one-shot command is received, the command is ignored. If a one-shot
command is received in autonomous mode (RUN bit = 0)
between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses.
Configuration Byte Functions
The configuration byte register (Table 6) is a read-write
register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6646/MAX6647/
MAX6649 into standby mode (STOP) or autonomous
(RUN) mode.
Status Byte Functions
The status byte register (Table 7) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether the ADC is converting and
whether there is an open-circuit fault detected in the
external sense junction. After POR, the normal state of
all flag bits is zero, assuming no alarm conditions are
present. The status byte is cleared by any successful
read of the status byte, after conversion is complete
and if the fault condition no longer exists. Note that the
ALERT interrupt latch is not automatically cleared when
the status flag bit indicating the ALERT is cleared. The
fault condition must be eliminated before the ALERT
output can be cleared.
When autoconverting, if the THIGH and TLOW limits are
close together, it is possible for both high-temp and lowtemp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances, it
is best not to rely on the status bits to indicate reversals in
long-term temperature changes. Instead use a current
temperature reading to establish the trend direction.
_______________________________________________________________________________________
9
MAX6646/MAX6647/MAX6649
Table 3. Fault Queue Register Bit Definition
(22h)
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Table 5. Command-Byte Bit Assignments
REGISTER
ADDRESS
POR STATE
FUNCTION
RLTS
00h
0000 0000
0°C
RRTE
01h
0000 0000
0°C
Read local (internal) temperature
RSL
02h
N/A
—
Read status byte
RCL
03h
0000 0000
—
Read configuration byte
RCRA
04h
0000 0111
—
Read conversion rate byte
Read remote (external) temperature
RLHN
05h
0101 0101
+85°C
Read local (internal) ALERT high limit
RLLI
06h
0000 0000
0°C
Read local (internal) ALERT low limit
RRHI
07h
0101 1111
+95°C
Read remote (external) ALERT high limit (MAX6646/MAX6647)
0101 0101
+85°C
Read remote (external) ALERT high limit (MAX6649)
RRLS
08h
0000 0000
0°C
WCA
09h
N/A
—
Read remote (external) ALERT low limit
Write configuration byte
WCRW
0Ah
N/A
—
Write conversion rate byte
WLHO
0Bh
N/A
—
Write local (internal) ALERT high limit
WLLM
0Ch
N/A
—
Write local (internal) ALERT low limit
WRHA
0Dh
N/A
—
Write remote (external) ALERT high limit
WRLN
0Eh
N/A
—
Write remote (external) ALERT low limit
OSHT
0Fh
N/A
—
One-shot
REET
10h
0000 0000
0°C
Read remote (external) extended temperature
RIET
11h
0000 0000
0°C
Read local (internal) extended temperature
RWOE
19h
0111 1101
+125°C
Read/write remote (external) OVERT limit (MAX6646/MAX6647)
0101 0101
+85°C
Read/write remote (external) OVERT limit (MAX6649)
RWOI
20h
0101 0101
+85°C
HYS
21h
0000 1010
10°C
Read/write local (internal) OVERT limit
Overtemperature hysteresis
QUEUE
22h
1000 0110
—
Fault queue
—
FEh
0100 1101
—
Read manufacture ID
—
FFh
0101 1001
—
Read revision ID
Table 6. Configuration-Byte Bit Assignments (03h)
BIT
NAME
POR STATE
FUNCTION
7 (MSB)
MASK
0
Masks ALERT interrupts when set to 1.
6
RUN
0
Standby mode control bit; if set to 1, standby mode is initiated.
5 to 0
RFU
0
Reserved.
Conversion Rate Byte
The conversion rate register (Table 8) programs the time
interval between conversions in free-running autonomous
mode (RUN = 0). This variable rate control can be used
to reduce the supply current in portable-equipment applications. The conversion rate byte’s POR state is 07h or
4Hz. The MAX6646/MAX6647/MAX6649 look only at the 3
LSBs of this register, so the upper 5 bits are “don’t care”
bits, which should be set to zero. The conversion rate tolerance is ±25% at any rate setting.
10
Valid A/D conversion results for both channels are available two total conversion times (250ms nominal, 312ms
maximum) after initiating a conversion, whether conversion is initiated through the RUN bit, one-shot command, or initial power-up. Changing the conversion rate
can also affect the delay until new results are available.
______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
BIT
NAME
POR
STATE
7 (MSB)
BUSY
0
A/D is busy converting when 1.
6
LHIGH
0
Local (internal) high-temperature alarm has tripped when 1; cleared by POR or readout of the
status byte if the fault condition no longer exists.
5
LLOW
0
Local (internal) low-temperature alarm has tripped when 1; cleared by POR or readout of the
status byte if the fault condition no longer exists.
4
RHIGH
0
Remote (external) high-temperature alarm has tripped when 1; cleared by POR or readout of the
status byte if the fault condition no longer exists.
3
RLOW
0
Remote (external) low-temperature alarm has tripped when 1; cleared by POR or readout of the
status byte if the fault condition no longer exists.
2
FAULT
0
A 1 indicates DXN and DXP are either shorted or open; cleared by POR or readout of the status
byte if the fault condition no longer exists.
1
EOT
0
A 1 indicates the remote (external) junction temperature exceeds the external OVERT threshold.
0
IOT
0
A 1 indicates the local (internal) junction temperature exceeds the internal OVERT threshold.
FUNCTION
Slave Addresses
The MAX6646/MAX6647/MAX6649 have fixed slave
addresses (see Table 9). All devices also respond to the
SMBus alert response slave address (see the Alert
Response Address section).
Table 8. Conversion-Rate Control Byte
(04h)
DATA
CONVERSION
RATE (Hz)
POR and UVLO
00h
0.0625
To prevent ambiguous power-supply conditions from
corrupting the data in memory and causing erratic
behavior, a POR voltage detector monitors VCC and
clears the memory if VCC falls below 2.0V (typ). When
power is first applied and VCC rises above 2.0V (typ),
the logic blocks begin operating, although reads and
writes at VCC levels below 3V are not recommended. A
second VCC comparator, the ADC UVLO comparator,
prevents the ADC from converting until there is sufficient
headroom (VCC = 2.7V typ).
01h
0.125
02h
0.25
03h
0.5
04h
1
05h
2
06h
4
07h
4
08h-FFh
Reserved
Power-Up Defaults
Power-up defaults include:
• Interrupt latch is cleared.
• ADC begins autoconverting at a 4Hz rate.
• Command byte is set to 00h to facilitate quick local
temperature receive byte queries.
• Local (internal) THIGH limit is set to +85°C.
• Local (internal) TLOW limit is set to 0°C.
• Remote (external) T HIGH limit is set to +85°C
(MAX6649)/+95°C (MAX6646/MAX6647)
• OVERT (internal) limit is set to +85°C
• OVERT (external) limit is set to +85°C (MAX6649)/
+125°C (MAX6646/MAX6647)
Table 9. Slave Addresses
PART
SLAVE ADDRESS
MAX6646
1001 101
MAX6647
1001 110
MAX6649
1001 100
______________________________________________________________________________________
11
MAX6646/MAX6647/MAX6649
Table 7. Status Register Bit Assignments (02h)
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Applications Information
90
Ω = 0.453 °C
μV
Ω
198.6
°C
Remote-Diode Selection
The MAX6646/MAX6647/MAX6649 can directly measure
the die temperature of CPUs and other ICs that have
on-board temperature-sensing diodes (see Typical
Operating Circuit), or they can measure the temperature of a discrete diode-connected transistor.
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 MAX6646/MAX6647/MAX6649
are optimized for n = 1.008, which is the typical value for
the Intel® Pentium® III and the AMD Athlon MP model 6.
If a sense transistor with a different ideality factor is used,
the output data is different. Fortunately, the difference is
predictable.
Assume a remote-diode sensor designed for a nominal
ideality factor nNOMINAL is used to measure the temperature of a diode with a different ideality factor n1.
The measured temperature TM can be corrected using:
⎛
⎞
n1
TM = TACTUAL ⎜
⎟
⎝ nNOMINAL ⎠
where temperature is measured in Kelvin.
As mentioned above, the nominal ideality factor of the
MAX6646/MAX6647/MAX6649 is 1.008. The following
example uses the MAX6646/MAX6647/MAX6649 with a
CPU that has an ideality factor of 1.002. If the diode has
no series resistance, the measured data is related to
the real temperature as follows:
⎛n
⎞
⎛ 1.008 ⎞
TACTUAL = TM ⎜ NOMINAL ⎟ = TM ⎜
⎟ = TM (1.00599)
⎝ 1.002 ⎠
n1
⎝
⎠
For a real temperature of +85°C (358.15 K), the measured temperature is +82.91°C (356.02 K), which is an
error of -2.13°C.
Effect of Series Resistance
Series resistance in a sense diode contributes additional errors. For nominal diode currents of 10µA and
100µA, change in the measured voltage is:
ΔVM = RS (100μA − 10μA) = 90μA × RS
μV
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
3Ω × 0.453
°C
= 1.36°C
Ω
The effects of the ideality factor and series resistance
are additive. If the diode has an ideality factor of 1.002
and series resistance of 3Ω, the total offset can be calculated by adding error due to series resistance with
error due to ideality factor:
1.36°C - 2.13°C = -0.77°C
for a diode temperature of +85°C.
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor,
short the collector to the base. Table 10 lists examples
of discrete transistors that are appropriate for use with
the MAX6646/MAX6647/MAX6649.
Avoid violating the A/D input voltage range by using a
small-signal transistor with a relatively high forward voltage. The forward voltage at the highest expected temperature must be greater than 0.25V at 10µA, and the
forward voltage at the lowest expected temperature
must be less than 0.95V at 100µA. Do not use large
power transistors. Ensure that the base resistance is
less than 100Ω. Tight specifications for forward current
gain (50 < ß < 150, for example) indicate that the manufacturer has good process controls and that the
devices have consistent VBE characteristics.
Table 10. Remote-Sensor Transistor
Manufactures
MANUFACTURER
MODEL NO.
Central Semiconductor (USA)
CMPT3904
Rohm Semiconductor (USA)
SST3904
Samsung (Korea)
Since 1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
Intel and Pentium are registered trademarks of Intel Corp.
AMD and Athlon are trademarks of Advanced Micro Devices, Inc.
12
KST3904-TF
Siemens (Germany)
Zetex (England)
SMBT3904
FMMT3904CT-ND
Note: Discrete transistors must be diode connected (base
shorted to collector).
______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
10 MILS
10 MILS
DXP
10 MILS
DXN
MINIMUM
10 MILS
GND
Figure 4. Recommended DXP-DXN PC Traces
ADC Noise Filtering
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-supply hum. In noisy environments, high-frequency noise
reduction is needed for high-accuracy remote measurements. The noise can be reduced with careful PC
board layout and proper external noise filtering.
High-frequency EMI is best filtered at DXP and DXN with
an external 2200pF capacitor. Larger capacitor values
can be used for added filtering, but do not exceed
3300pF because larger values can introduce errors due
to the rise time of the switched current source.
PC Board Layout
Follow these guidelines to reduce the measurement
error of the temperature sensors:
1) Place the MAX6646/MAX6647/MAX6649 as close as
is practical to the remote diode. In noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). This length can be
increased if the worst noise sources are avoided.
Noise sources include CRTs, clock generators,
memory buses, and ISA/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 30°C error, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any higher
voltage traces, such as 12VDC. Leakage currents
from PC board contamination must be dealt with
carefully since a 20MΩ leakage path from DXP to
ground causes about 1°C error. If high-voltage traces
are unavoidable, connect guard traces to GND on
either side of the DXP-DXN traces (Figure 4).
4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.
5) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. A copper-solder thermocouple
exhibits 3µV/°C, and takes about 200µV of voltage
error at DXP-DXN to cause a 1°C measurement
error. Adding a few thermocouples causes a negligible error.
6) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10mil widths
and spacing recommended in Figure 4 are not
absolutely necessary, as they offer only a minor
improvement in leakage and noise over narrow
traces. Use wider traces when practical.
7) Add a 200Ω resistor in series with VCC for best noise
filtering (see Typical Operating Circuit).
8) Copper cannot be used as an EMI shield; only ferrous materials such as steel work well. Placing a
copper ground plane between the DXP-DXN traces
and traces carrying high-frequency noise signals
does not help reduce EMI.
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor
for remote-sensor distance 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 like that 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 to DXP and DXN and
the shield to GND. Leave the shield unconnected at the
remote sensor.
For very long cable runs, the cable’s parasitic capacitance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy.
For every 1Ω of series resistance, the error is approximately 0.5°C.
Thermal Mass and Self-Heating
When sensing local temperature, these devices are
intended to measure the temperature of the PC board
to which the devices are soldered. The leads provide a
good thermal path between the PC board traces and
the die. Thermal conductivity between the die and the
ambient air is poor by comparison, making air temperature measurements impractical. Because the thermal
mass of the PC board is far greater than that of the
MAX6646/MAX6647/MAX6649, the device follows temperature changes on the PC board with little or no perceivable delay.
______________________________________________________________________________________
13
MAX6646/MAX6647/MAX6649
GND
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
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 sensors, smaller packages, such as SC70s or SOT23s,
yield the best thermal response times. Take care to
account for thermal gradients between the heat source
and the sensor, and ensure that stray air currents
across the sensor package do not interfere with measurement accuracy.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
worst-case error occurs when autoconverting at the
fastest rate and simultaneously sinking maximum current at the ALERT output. For example, with V CC =
5.0V, at a 4Hz conversion rate and with ALERT sinking
1mA, the typical power dissipation is:
5.0V x 500µA + 0.4V x 1mA = 2.9mW
ø J-A for the 8-pin µMAX package is +221°C/W, so
assuming no copper PC board heat sinking, the resulting temperature rise is:
ΔT = 2.9mW x +221°C/W = +0.6409°C
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
Functional Diagram
VCC
MAX6646/MAX6647/MAX6649
2
DXP
MUX
REMOTE
DXN
CONTROL
LOGIC
ADC
LOCAL
DIODE
FAULT
SMBus
ALERT
S
Q
8
READ
8
WRITE
SDA
SCLK
R
REGISTER BANK
7
COMMAND BYTE
REMOTE TEMPERATURE
OVERT
S
Q
R
ADDRESS
DECODER
LOCAL TEMPERATURE
ALERT THRESHOLD
ALERT RESPONSE ADDRESS
GND
14
OVERT THRESHOLD
______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
POR VALUES
ALERT ASSERTED
WHILE DIODE OPEN
PKG
CODE
+95
No
U8-1
+95
No
U8-1
+85
Yes
U8-1
PART
ADDRESS
EXTERNAL OVERT
LIMIT (°C)
EXTERNAL ALERT
THIGH LIMIT (°C)
MAX6646
1001 101
+125
MAX6647
1001 110
+125
MAX6649
1001 100
+85
Pin Configuration
Chip Information
TRANSISTOR COUNT: 14,764
PROCESS: BiCMOS
TOP VIEW
VCC
1
DXP
2
DXN
3
OVERT
4
8
MAX6646
MAX6647
MAX6649
SCLK
7
SDA
6
ALERT
5
GND
μMAX
______________________________________________________________________________________
15
MAX6646/MAX6647/MAX6649
Selector Guide
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
4X S
8
8
INCHES
DIM
A
A1
A2
b
E
Ø0.50±0.1
H
c
D
e
E
H
0.6±0.1
L
1
1
α
0.6±0.1
S
BOTTOM VIEW
D
MIN
0.002
0.030
MAX
0.043
0.006
0.037
0.014
0.010
0.007
0.005
0.120
0.116
0.0256 BSC
0.120
0.116
0.198
0.188
0.026
0.016
6°
0°
0.0207 BSC
8LUMAXD.EPS
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
MILLIMETERS
MAX
MIN
0.05
0.75
1.10
0.15
0.95
0.25
0.36
0.13
0.18
2.95
3.05
0.65 BSC
2.95
3.05
4.78
5.03
0.41
0.66
0°
6°
0.5250 BSC
TOP VIEW
A1
A2
A
α
c
e
b
L
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0036
REV.
J
1
1
Revision History
Pages changed at Rev 3: 1, 2, 9, 10, 15, 16
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.