MAX6649YMUA+ [MAXIM]
Analog Circuit, 1 Func, BICMOS, ROHS COMPLIANT, MO-187C-AA, MICRO MAX PACKAGE-8;
| 型号： | MAX6649YMUA+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Analog Circuit, 1 Func, BICMOS, ROHS COMPLIANT, MO-187C-AA, MICRO MAX PACKAGE-8 传感器 |
| 文件： | 总16页 (文件大小：226K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2540; Rev 1; 7/03
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
General Description
Features
The MAX6646/MAX6647/MAX6649 are precise, two-
channel digital temperature sensors. The devices accu-
rately 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 junc-
tion is typically the emitter-base junction of a common-
collector PNP on a CPU, FPGA, or ASIC.
ꢀ Dual Channel: Measures Remote and Local
Temperature
ꢀ 0.125°C Resolution
ꢀ High Accuracy 1°C ꢀmaꢁx ꢂrom ꢃ+0°C to ꢃ1ꢄ5°C
ꢀRemotex, and 2°C ꢀmaꢁx ꢂrom ꢃ+0°C to ꢃ100°C
ꢀLocalx
The 2-wire serial interface accepts standard system man-
agement bus (SMBus) 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).
ꢀ Measures High-Ideality Thermal Diodes Up to
ꢃ170°C ꢀApparentx
ꢃ1ꢄ5°C ꢀRealx
ꢀ Two Alarm Outputs: ALERT and OVERT
ꢀ Programmable Under/Overtemperature Alarm
Temperature Thresholds
ꢀ Programmable Conversion Rate
ꢀ SMBus-Compatible Interꢂace
ꢀ SMBus Timeout
The MAX6646/MAX6647/MAX6649 provide two system
alarms: ALERT and OVERT. ALERT asserts when any of
four temperature conditions are violated: local overtem-
perature, remote overtemperature, local undertempera-
ture, 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.
Ordering Information
PIN-
MEASURED
PART
TEMP RANGE
PACKAGE TEMP RANGE
Measurements can be done autonomously, at the pro-
grammed conversion rate, or in a single-shot mode. The
adjustable conversion rate allows optimizing supply cur-
rent and temperature update rate to match system needs.
MAX6646MUA -551C to +1251C 8 µMAX
MAX6647MUA -551C to +1251C 8 µMAX
MAX6649MUA -551C to +1251C 8 µMAX
01C to +1451C
01C to +1451C
01C to +1451C
Remote accuracy is ±±1C maꢀimum error between ꢁ6ꢂ1C
and ꢁ±451C with no calibration needed. The
MAX6646/MAX6647/MAX6649 operate from -551C to
ꢁ±251C, and measure temperatures between ꢂ1C and
ꢁ±451C. The MAX6646/MAX6647/MAX6649 are available
in an 8-pin µMAX package.
Typical Operating Circuit
3.3V
Applications
0.1µF
200Ω
Graphics Processors
Desktop Computers
Notebook Computers
Servers
V
CC
10kΩ EACH
MAX6646
MAX6647
MAX6649
DXP
DATA
SDA
CLOCK
SCLK
ALERT
INTERRUPT TO µP
Thin Clients
DXN
2200pF
OVERT
TO FAN DRIVER OR
SYSTEM SHUTDOWN
Workstations
GND
µP
Test and Measurement
Multichip Modules
Selector Guide, Pin Configurations, and Functional Diagram
appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
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.
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND
ESD Protection (all pins, Human Body Model)................ 2000V
Junction Temperature......................................................+1501C
Operating Temperature Range .........................-551C to +1251C
Storage Temperature Range.............................-651C to +1501C
Lead Temperature (soldering, 10s) .................................+3001C
V
...........................................................................-0.3V to +6V
CC
DXP.............................................................-0.3V to (V
+ 0.3V)
CC
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 (T = +701C)
A
8-Pin µMAX (derate 5.9mW/1C above +701C).............471mW
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
(V
= 3.0V to 5.5V, T = -551C to +1251C, unless otherwise specified. Typical values are at V
= 3.3V and T = +1001C.) (Note 1)
CC A
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
3.0
TYP
MAX
UNITS
V
Supply Voltage
V
5.5
CC
0.125
1C
Temperature Resolution
11
Bits
V
T
= 3.3V, T = +1001C,
= +601C to +1451C
CC
RJ
A
-1.0
-1.6
-3.2
+1.0
+1.6
+3.2
V
T
= 3.3V, T = +601C to +1001C,
CC
RJ
A
Remote Temperature Error
Local Temperature Error
1C
= +251C to +1451C
V
T
= 3.3V, T = +01C to +1001C,
CC
RJ
A
= +01C to +1451C
T
T
= +601C to +1001C
= 01C to +1251C
-2.0
-3.0
+2.0
+3.0
A
V
= 3.3V
1C
1C/V
V
CC
A
Supply Sensitivity of Temperature
Error
0.2
2.7
Undervoltage Lockout (UVLO)
Threshold
UVLO
Falling edge of V
disables ADC
2.4
2.95
CC
UVLO Hysteresis
90
2.0
90
3
mV
V
Power-On-Reset (POR) Threshold
POR Threshold Hysteresis
Standby Supply Current
Operating Current
V
falling edge
CC
mV
µA
mA
SMBus static
During conversion
12
0.08
80
0.25 conversions per second
2 conversions per second
40
Average Operating Current
µA
250
125
400
156
+25
100
120
12
Conversion Time
t
From stop bit to conversion completion
95
ms
%
CONV
Conversion Time Error
DXP and DXN Leakage Current
-25
Standby mode
High level
nA
80
8
100
10
Remote-Diode Source Current
I
µA
RJ
Low level
2
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
ELECTRICAL CHARACTERISTICS (continued)
(V
= 3.0V to 5.5V, T = -551C to +1251C, unless otherwise specified. Typical values are at V
= 3.3V and T = +1001C.) (Note 1)
CC A
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ALERT, OVERT
I
I
= 1mA
= 4mA
= 5.5V
0.4
0.6
1
SINK
Output Low Voltage
V
SINK
Output High Leakage Current
V
µA
OH
SMBus-COMPATIBLE INTERFACE (SCLK AND SDA)
Logic Input Low Voltage
V
0.8
+1
V
V
IL
V
V
V
V
= 3.0V
= 5.5V
2.2
2.6
-1
CC
CC
Logic Input High Voltage
V
IH
Input Leakage Current
Output Low-Sink Current
Input Capacitance
I
= GND or V
µA
mA
pF
LEAK
IN
CC
I
= 0.6V
6
SINK
OL
C
5
IN
SMBus-COMPATIBLE TIMING (Note 2)
Serial Clock Frequency
f
(Note 3)
100
kHz
µs
SCLK
Bus Free Time Between STOP
and START Condition
t
4.7
4.7
50
BUF
START Condition Setup Time
µs
Repeat START Condition Setup
Time
t
90% to 90%
ns
SU:STA
START Condition Hold Time
STOP Condition Setup Time
Clock Low Period
t
t
10% of SDA to 90% of SCLK
90% of SCLK to 90% of SDA
10% to 10%
4
4
µs
µs
µs
µs
µs
µs
ns
ns
ms
HD:STA
SU:STO
t
4.7
4
LOW
Clock High Period
t
90% to 90%
HIGH
Data Setup Time
t
(Note 4)
250
HD:DAT
Receive SCLK/SDA Rise Time
Receive SCLK/SDA Fall Time
Pulse Width of Spike Suppressed
SMBus Timeout
t
R
1
t
300
50
F
t
0
SP
TIMEOUT
t
SDA low period for interface reset
25
37
45
Note 1: All parameters tested at a single temperature. Specifications over temperature are guaranteed by design.
Note 2: Timing specifications guaranteed by design.
Note 3: The serial interface resets when SCLK is low for more than t
.
TIMEOUT
Note 4: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK’s falling edge.
_______________________________________________________________________________________
3
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Typical Operating Characteristics
(V
= 3.3V, T = +251C, unless otherwise noted.)
CC
A
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
400
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
5.0
2.0
1.5
4.5
4.0
3.5
3.0
2.5
300
200
100
0
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
T
= +85°C
A
FAIRCHILD 2N3906
3.0
3.5
4.0
4.5
5.0
5.5
0.63 0.13 0.25 0.50 1.00 2.00 4.00
CONVERSION RATE (Hz)
0
25
50
75
100
125
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
LOCAL TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
1.0
0.5
5
4
9
8
V
IN
V
IN
= AC-COUPLED TO DXN
LOCAL ERROR
= 100mV
P-P
7
6
3
0
5
REMOTE ERROR
2
REMOTE ERROR
LOCAL ERROR
4
-0.5
-1.0
-1.5
-2.0
3
1
2
0
1
V
V
= SQUARE WAVE APPLIED TO
WITH NO BYPASS CAPACITOR
CC
CC
0
-1
-2
-1
-2
0
25
50
75
100
125
0.1
1
10
100
1k
10k
100k
1
10
100
1k
10k
100k
TEMPERATURE (°C)
FREQUENCY (Hz)
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
2.0
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
1
0
1.5
1.0
0.5
0
-1
-2
-3
-4
-5
-0.5
-1.0
1
10
100
1k
10k
100k
0.100
1.000
10.000
100.000
FREQUENCY (Hz)
DXP-DXN CAPACITANCE (nF)
4
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Pin Description
PIN
NAME
FUNCTION
Supply Voltage Input, 3V to 5.5V. Bypass V to GND with a 0.1µF capacitor. A 200Ω series
resistor is recommended but not required for additional noise filtering.
CC
1
V
CC
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.
2
3
DXP
DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to
ground.
Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is
above the software-programmed threshold.
4
5
OVERT
GND
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
8
SDA
SMBus Serial-Data Input/Output, Open Drain
SMBus Serial-Clock Input
SCLK
ADC and Multiplexer
Detailed Description
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 volt-
age and compute the temperature based on this volt-
age. Both channels are automatically converted once
the conversion process has started, either in free-run-
ning 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.
The MAX6646/MAX6647/MAX6649 are temperature sen-
sors designed to work in conjunction with a microproces-
sor 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 mea-
sured 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 short-
ed 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-man-
agement circuitry.
Table 1. Main Temperature Data Register
Format (00h, 01h)
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 0.1251C. The “main” temperature
data registers (at addresses 00h and 01h) are 8-bit regis-
ters 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).
TEMP (°C)
+145
+130
+128
+25
DIGITAL OUTPUT
1001 0001
1000 0010
1000 0000
0001 1001
0
0000 0000
<0
0000 0000
Diode fault
(short or open)
1111 1111
_______________________________________________________________________________________
5
+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 +0.51C (typ) error per ohm.
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.
Remote Temperature Measurement
Range
The MAX6646/MAX6647/MAX6649 measure remote
temperatures significantly above the +1201C limit of
many temperature sensors. External diode-connected
transistors work well as temperature sensors up to
approximately +1451C, where accuracy begins to
degrade. Thermal diodes on some CPUs have charac-
teristics that produce “apparent temperatures” far
above actual operating temperatures. The MAX6646/
MAX6647/MAX6649 measure apparent temperatures as
high as +1701C, as long as the actual temperature is
less than +1451C.
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 pro-
tocols 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 regis-
ters is 8 bits for each channel, with the LSB representing
11C (Table 1). The MSB is transmitted first.
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 auto-
matically 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.
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 0.1251C 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
0.1251C per LSB (Table 2).
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 configu-
ration byte register (Table 6). All data is retained in mem-
ory, 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.
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
000X XXXX
001X XXXX
010X XXXX
011X XXXX
100X XXXX
101X XXXX
110X XXXX
111X XXXX
0.000
0.125
0.250
0.375
0.500
0.625
0.750
0.875
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 tempera-
ture 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
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
DATA
ACK
P
7 bits
8 bits
8 bits
1
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
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 ACK
S
ADDRESS
RD
ACK
DATA
///
P
7 bits
8 bits
7 bits
8 bits
Slave Address: equiva-
lent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
Send Byte Format
ADDRESS WR ACK COMMAND ACK
7 bits 8 bits
Receive Byte Format
S
P
S
ADDRESS
RD
ACK DATA
///
P
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
Command Byte: sends com-
mand with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
Shaded = Slave transmission
/// = Not acknowledged
Figure 1. SMBus Protocols
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
BUF
SU:STO
t
t
t
SU:DAT
SU:STA HD:STA
A = START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:
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 comple-
tion, immediately read the contents of the tempera-
ture 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.
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 con-
tents of the temperature data registers.
_______________________________________________________________________________________
7
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
HD:DAT
HD:STA
SU:STA
SU:DAT
t
t
SU:STO
BUF
A = START CONDITION
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
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
M = NEW START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
Figure 3. SMBus Read Timing Diagram
Alarm Threshold Registers
ALERT Interrupts
Four registers store ALERT threshold values—one high-
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.
temperature (T
) and one low-temperature (T
)
LOW
HIGH
register each for the local and remote channels. If either
measured temperature equals or exceeds the corre-
sponding ALERT threshold value, the ALERT interrupt
asserts.
The MAX6646/MAX6647 local (internal) ALERT T
HIGH
register POR state is 0101 0101, or +851C, while the
remote (external) ALERT T register POR state is
HIGH
0101 1111, or +951C.The MAX6649 POR state of both
ALERT T
registers is 0101 0101, or +851C. The POR
HIGH
state of the local and remote T
devices is 0000 0000, or 01C.
registers for all
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.
LOW
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
+851C, while the remote (external) OVERT register POR
state is 0111 1101, or +1251C. The MAX6649 POR state
of both OVERT registers is 0101 0101, or +851C.
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).
Diode Fault Alarm
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 gen-
erated an interrupt attempts to identify itself by putting
its own address on the bus.
A continuity fault detector at DXP detects an open cir-
cuit between DXP and DXN, or a DXP short to V
,
CC
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 sta-
tus 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
_______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Table 4. Fault Queue Length Bit Definition
Table 3. Fault Queue Register Bit Definition
(22h)
FQ1
FQ0
FAULT QUEUE LENGTH (SAMPLES)
POR
STATE
0
0
1
1
0
1
1
0
1
2
3
1
BIT
NAME
RFU
RFU
FQ1
FUNCTION
Reserved. Always write 1 to
this bit.
7
1
Reserved. Always write
zero to this bit.
6 to 3
0
1
1
0
One-Shot
The one-shot command immediately forces a new con-
version 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 one-
shot conversion is in progress when a one-shot com-
mand 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 con-
version rate timer is reset, and the next automatic conver-
sion takes place after a full delay elapses.
Fault queue-length control
bit (see Table 4).
2
1
0
Fault queue-length control
bit (see Table 4).
FQ0
Reserved. Always write
zero to this bit.
RFU
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 arbitra-
tion 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 com-
pletion of the read alert response protocol clears the
interrupt latch, provided the condition that caused the
alert no longer exists.
Configuration Byte Functions
The configuration byte register (Table 6) is a read-write
register with several functions. Bit 7 is used to mask (dis-
able) 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.
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 trig-
ger 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.
When autoconverting, if the T
and T
limits are
HIGH
LOW
close together, it is possible for both high-temp and low-
temp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances, it
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.
The MAX6646/MAX6647/MAX6649 incorporate collision
avoidance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
2
Purchase of I C components of Maxim Integrated Products, Inc. or one of its sublicensed Associated Companies, conveys a license
2
2
2
under the Philips I C Patent Rights to use these components in an I C system, provided that the system conforms to the I C Standard
Specification as defined by Philips.
_______________________________________________________________________________________
9
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Table 5. Command-Byte Bit Assignments
REGISTER
RLTS
ADDRESS
00h
POR STATE
0000 0000
FUNCTION
Read local (internal) temperature
01C
01C
—
RRTE
RSL
01h
0000 0000
N/A
Read remote (external) temperature
Read status byte
02h
RCL
03h
0000 0000
0000 0111
0101 0101
0000 0000
0101 1111
0101 0101
0000 0000
N/A
—
Read configuration byte
RCRA
RLHN
RLLI
04h
—
Read conversion rate byte
05h
+851C
01C
+951C
+851C
01C
—
Read local (internal) ALERT high limit
Read local (internal) ALERT low limit
Read remote (external) ALERT high limit (MAX6646/MAX6647)
Read remote (external) ALERT high limit (MAX6649)
Read remote (external) ALERT low limit
Write configuration byte
06h
RRHI
07h
RRLS
WCA
08h
09h
0Ah
0Bh
0Ch
0Dh
0Eh
0Fh
10h
11h
WCRW
WLHO
WLLM
WRHA
WRLN
OSHT
REET
N/A
—
Write conversion rate byte
N/A
—
Write local (internal) ALERT high limit
Write local (internal) ALERT low limit
Write remote (external) ALERT high limit
Write remote (external) ALERT low limit
One-shot
N/A
—
N/A
—
N/A
—
N/A
—
0000 0000
0000 0000
0111 1101
0101 0101
0101 0101
0000 1010
1000 0110
0100 1101
0101 1001
01C
01C
+1251C
+851C
+851C
101C
—
Read remote (external) extended temperature
Read local (internal) extended temperature
Read/write remote (external) OVERT limit (MAX6646/MAX6647)
Read/write remote (external) OVERT limit (MAX6649)
Read/write local (internal) OVERT limit
Overtemperature hysteresis
RIET
RWOE
19h
RWOI
HYS
QUEUE
—
20h
21h
22h
FEh
FFh
Fault queue
—
Read manufacture ID
—
—
Read revision ID
Table 6. Configuration-Byte Bit Assignments (03h)
BIT
7 (MSB)
6
NAME
MASK
RUN
POR STATE
FUNCTION
Masks ALERT interrupts when set to 1.
0
0
0
Standby mode control bit; if set to 1, standby mode is initiated.
Reserved.
5 to 0
RFU
Valid A/D conversion results for both channels are avail-
able one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conver-
sion is initiated through the RUN bit, one-shot com-
mand, or initial power-up. Changing the conversion rate
can also affect the delay until new results are available.
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 appli-
cations. 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 tol-
erance is 25% at any rate setting.
10 ______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Table 7. Status Register Bit Assignments (02h)
POR
STATE
BIT
7 (MSB)
6
NAME
BUSY
FUNCTION
0
A/D is busy converting when 1.
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.
LHIGH
0
0
0
0
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.
5
4
3
2
LLOW
RHIGH
RLOW
FAULT
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.
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.
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
0
EOT
IOT
0
0
A 1 indicates the remote (external) junction temperature exceeds the external OVERT threshold.
A 1 indicates the local (internal) junction temperature exceeds the internal OVERT threshold.
Slave Addresses
Table 8. Conversion-Rate Control Byte
(04h)
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).
CONVERSION
DATA
RATE (Hz)
00h
01h
0.0625
POR and UVLO
To prevent ambiguous power-supply conditions from
corrupting the data in memory and causing erratic
0.125
02h
0.25
behavior, a POR voltage detector monitors V
and
CC
03h
0.5
clears the memory if V
falls below 2.0V (typ). When
CC
04h
1
power is first applied and V
rises above 2.0V (typ),
CC
05h
2
the logic blocks begin operating, although reads and
writes at V
levels below 3V are not recommended. A
comparator, the ADC UVLO comparator,
CC
06h
4
4
second V
CC
07h
prevents the ADC from converting until there is sufficient
headroom (V = 2.7V typ).
08h-FFh
Reserved
CC
Power-Up Defaults
Table 9. Slave Addresses
Power-up defaults include:
PART
SLAVE ADDRESS
1001 101
• Interrupt latch is cleared.
MAX6646
MAX6647
MAX6649
• ADC begins autoconverting at a 4Hz rate.
1001 110
• Command byte is set to 00h to facilitate quick local
1001 100
temperature receive byte queries.
• Local (internal) T
• Local (internal) T
limit is set to +851C.
limit is set to 01C.
HIGH
LOW
• Remote (external) T
limit is set to +851C
HIGH
(MAX6649)/+951C (MAX6646/MAX6647)
•
•
OVERT (internal) limit is set to +851C
OVERT (external) limit is set to +851C (MAX6649)/
+1251C (MAX6646/MAX6647)
______________________________________________________________________________________ 11
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Applications Information
µV
Ω
90
°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 tempera-
ture of a discrete diode-connected transistor.
= 0.453
µV
°C
Ω
198.6
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
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.
°C
Ω
3Ω × 0.453
=1.36°C
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 cal-
culated by adding error due to series resistance with
error due to ideality factor:
Assume a remote-diode sensor designed for a nominal
1.361C - 2.131C = -0.771C
ideality factor n
is used to measure the tem-
NOMINAL
for a diode temperature of +851C.
perature of a diode with a different ideality factor n .
1
The measured temperature T can be corrected using:
M
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
n
1
T
= T
M
ACTUAL
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.
n
NOMINAL
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:
Avoid violating the A/D input voltage range by using a
small-signal transistor with a relatively high forward volt-
age. The forward voltage at the highest expected tem-
perature 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 man-
ufacturer has good process controls and that the
n
1.008
1.002
NOMINAL
T
= T
= T
= T (1.00599)
M
ACTUAL
M
M
n
1
For a real temperature of +851C (358.15 K), the mea-
sured temperature is +82.911C (356.02 K), which is an
error of -2.131C.
devices have consistent V characteristics.
BE
Table 10. Remote-Sensor Transistor
Manufactures
Effect of Series Resistance
Series resistance in a sense diode contributes addition-
al errors. For nominal diode currents of 10µA and
100µA, change in the measured voltage is:
MANUFACTURER
Central Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
MODEL NO.
CMPT3904
SST3904
∆V =R (100µA −10µA) = 90µA ×R
S
M
S
KST3904-TF
SMBT3904
Siemens (Germany)
Since 11C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
Zetex (England)
FMMT3904CT-ND
Note: Discrete transistors must be diode connected (base
shorted to collector).
Intel and Pentium are registered trademarks of Intel Corp.
AMD and Athlon are trademarks of Advanced Micro Devices, Inc.
12 ______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
5) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
GND
thermocouples. A copper-solder thermocouple
10 MILS
exhibits 3µV/1C, and takes about 200µV of voltage
10 MILS
10 MILS
DXP
error at DXP-DXN to cause a 11C measurement
MINIMUM
error. Adding a few thermocouples causes a negligi-
DXN
ble error.
10 MILS
6) Use wide traces. Narrow traces are more inductive
GND
and tend to pick up radiated noise. The 10mil widths
and spacing recommended in Figure 4 are not
Figure 4. Recommended DXP-DXN PC Traces
absolutely necessary, as they offer only a minor
improvement in leakage and noise over narrow
traces. Use wider traces when practical.
ADC Noise Filtering
7) Add a 200Ω resistor in series with V
for best noise
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-sup-
ply hum. In noisy environments, high-frequency noise
reduction is needed for high-accuracy remote mea-
surements. The noise can be reduced with careful PC
board layout and proper external noise filtering.
CC
filtering (see Typical Operating Circuit).
8) Copper cannot be used as an EMI shield; only fer-
rous 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.
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.
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 micro-
phones. For example, Belden 8451 works well for dis-
tances 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.
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 environ-
ments, such as a computer motherboard, this dis-
tance 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.
For very long cable runs, the cable’s parasitic capaci-
tance 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 approxi-
mately 0.51C.
2) Do not route the DXP-DXN lines next to the deflec-
tion coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily intro-
duce 301C 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 11C error. If high-voltage traces
are unavoidable, connect guard traces to GND on
either side of the DXP-DXN traces (Figure 4).
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 tempera-
ture measurements impractical. Because the thermal
mass of the PC board is far greater than that of the
MAX6646/MAX6647/MAX6649, the device follows tem-
perature changes on the PC board with little or no per-
ceivable delay.
4) Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects.
______________________________________________________________________________________ 13
+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 virtu-
ally no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, 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 mea-
surement 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 cur-
rent 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
øJ-A for the 8-pin µMAX package is +2211C/W, so
assuming no copper PC board heat sinking, the result-
ing temperature rise is:
∆T = 2.9mW x +2211C/W = +0.64091C
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
Functional Diagram
V
CC
MAX6646/MAX6647/MAX6649
2
DXP
DXN
MUX
REMOTE
CONTROL
LOGIC
ADC
LOCAL
DIODE
FAULT
SMBus
SDA
8
8
READ
ALERT
S
R
SCLK
WRITE
Q
Q
REGISTER BANK
7
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
ADDRESS
DECODER
OVERT
GND
S
R
ALERT RESPONSE ADDRESS
OVERT THRESHOLD
14 ______________________________________________________________________________________
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Selector Guide
POR VALUES
ALERT ASSERTED
WHILE DIODE OPEN
PART
ADDRESS
EXTERNAL OVERT
LIMIT (°C)
EXTERNAL ALERT
T
LIMIT (°C)
HIGH
MAX6646
MAX6647
MAX6649
1001 101
1001 110
1001 100
+125
+125
+85
+95
+95
+85
No
No
Yes
Chip Information
TRANSISTOR COUNT: 14,764
Pin Configuration
TOP VIEW
PROCESS: BiCMOS
V
1
2
3
4
8
7
6
5
SCLK
SDA
CC
DXP
DXN
MAX6646
MAX6647
MAX6649
ALERT
GND
OVERT
µMAX
______________________________________________________________________________________ 15
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
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
MILLIMETERS
INCHES
DIM MIN
MAX
MAX
MIN
-
-
0.043
0.006
0.037
0.014
0.007
0.120
1.10
0.15
0.95
0.36
0.18
3.05
A
0.002
0.030
0.010
0.005
0.116
0.05
0.75
0.25
0.13
2.95
A1
A2
b
E
H
ÿ 0.50 0.1
c
D
e
0.0256 BSC
0.65 BSC
0.6 0.1
E
H
0.116
0.188
0.016
0∞
0.120
2.95
4.78
0.41
0∞
3.05
5.03
0.66
6∞
0.198
0.026
6∞
L
1
1
α
S
0.6 0.1
0.0207 BSC
0.5250 BSC
BOTTOM VIEW
D
TOP VIEW
A1
A2
A
c
α
e
L
b
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0036
J
1
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
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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