MAX6642 [MAXIM]
?癈. SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm ; ？癈。 SMBus兼容，远端/本地温度传感器，带有过温报警\n
| 型号： | MAX6642 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | ?癈. SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
|
| 文件： | 总13页 (文件大小：218K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2920; Rev 0; 8/03
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
General Description
Features
The MAX6642 is a precise, two-channel digital temper-
ature sensor. It accurately measures the temperature of
its own die and a remote PN junction, and reports the
temperature data over a 2-wire serial interface. The
remote PN junction is typically a substrate PNP transis-
tor on the die of a CPU, ASIC, GPU, or FPGA. The
remote PN junction can also be a discrete diode-con-
nected small-signal transistor.
o Dual Channel: Measures Remote and Local
Temperature
o +0.25°C Resolution
o High Accuracy ±±°C ꢀmaꢁx ꢀRemotex and
2°C ꢀLocalx from +60°C to +±00°C
o Measures Remote Temperature Up to +±50°C
o Programmable Overtemperature Alarm
The 2-wire serial interface accepts standard system
management 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 MAX6642 includes an
SMBus timeout. The temperature data format is 10 bit
with the least significant bit (LSB) corresponding to
+0.25°C. The ALERT output asserts when the local or
remote overtemperature thresholds are violated. A fault
queue may be used to prevent the ALERT output from
setting until two consecutive faults have been detected.
Temperature Thresholds
o SMBus/I2CTM-Compatible Interface
o Tiny TDFN Package
Ordering Inforꢃation
PART
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-PACKAGE
6 TDFN
MAX6642ATT90-T
MAX6642ATT92-T
MAX6642ATT94-T
MAX6642ATT96-T
MAX6642ATT98-T
MAX6642ATT9A-T
MAX6642ATT9C-T
MAX6642ATT9E-T
6 TDFN
6 TDFN
Measurements can be done autonomously or in a sin-
gle-shot mode.
6 TDFN
6 TDFN
Remote accuracy is 1°C maꢀimum error between
+60°C and +100°C. The MAX6642 operates from -40°C
to +125°C, and measures remote temperatures
between 0°C and +150°C. The MAX6642 is available in
a 6-pin TDFN package.
6 TDFN
6 TDFN
6 TDFN
SMBus is a trademark of Intel Corp.
2
Purchase of I C components of Maxim Integrated Products, Inc.
or one of its sublicensed Associated Companies, conveys a
license under the Philips I C Patent Rights to use these compo-
nents in an I C system, provided that the system conforms to the
I C Standard Specification as defined by Philips.
Applications
Desktop Computers
Notebook Computers
Servers
2
2
2
Pin Configuration and Functional Diagram appear at end of
data sheet.
Thin Clients
Test and Measurement
Workstations
Typical Operating °ircuit
Graphic Cards
3.3V
ꢀelector Guide
0.1µF
47Ω
TOP
MARK
PART
MEASURED TEMP RANGE
10kΩ EACH
V
CC
MAX6642ATT90-T
MAX6642ATT92-T
MAX6642ATT94-T
MAX6642ATT96-T
MAX6642ATT98-T
MAX6642ATT9A-T
MAX6642ATT9C-T
MAX6642ATT9E-T
0°C to +150°C
0°C to +150°C
0°C to +150°C
0°C to +150°C
0°C to +150°C
0°C to +150°C
0°C to +150°C
0°C to +150°C
AFC
AFD
AFE
AFF
AEW
AFG
AFH
AFI
2200pF
MAX6642
SDA
DATA
DXP
SCLK
CLOCK
ALERT
INTERRUPT TO µP
GND
µP
________________________________________________________________ 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°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND
ESD Protection (all pins, Human Body Model)................ 2000V
Junction Temperature......................................................+150°C
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
V
...........................................................................-0.3V to +6V
CC
DXP.............................................................-0.3V to (V
+ 0.3V)
CC
SCLK, SDA, ALERT ..................................................-0.3V to +6V
SDA, ALERT Current...........................................-1mA to +50mA
Continuous Power Dissipation (T = +70°C)
A
6-Pin TDFN (derate 24.4mW/°C above +70°C) .........1951mW
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 = -40°C to +125°C, unless otherwise specified. Typical values are at V = +3.3V and T = +25°C.) (Note 1)
CC
A
CC
A
PARAMETER
Supply Voltage
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
3.0
5.5
CC
0.25
10
°C
Temperature Resolution
Remote Temperature Error
Local Temperature Error
Bits
T
T
= +60°C to +100°C,
= +25°C to +85°C
RJ
-1.0
+1.0
A
V
V
= 3.3V
= 3.3V
°C
CC
CC
T
T
T
T
= 0°C to +125°C
-3.0
-3.5
-2.0
-3.0
+3.0
+3.5
+2.0
+3.0
RJ
= +125°C to +150°C
RJ
= +60°C to +100°C
= 0°C to +125°C
A
A
°C
Supply Sensitivity of Temperature
Error
0.2
°C/V
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Power-On-Reset (POR) Threshold
POR Threshold Hysteresis
Standby Supply Current
Operating Current
UVLO
Falling edge of V
disables ADC
2.4
1.5
2.7
90
2.95
2.4
V
CC
mV
V
V
falling edge
2.0
90
CC
mV
µA
mA
µA
ms
Hz
SMBus static
During conversion
3
10
0.5
260
125
8
1.0
Average Operating Current
Conversion Time
t
f
From stop bit to conversion completion
106
143
CONV
CONV
Conversion Rate
High level
Low level
80
8
100
10
120
12
Remote-Diode Source Current
ALERT
I
µA
RJ
V
V
V
= 0.4V
= 0.6V
1
4
OL
OL
OH
Output-Low Sink Current
Output-High Leakage Current
mA
µA
= V
1
CC
2
_______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
ELECTRICAL CHARACTERISTICS (continued)
(V = +3.0V to +5.5V, T = -40°C to +125°C, unless otherwise specified. Typical values are at V = +3.3V and T = +25°C.) (Note 1)
CC
A
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus-COMPATIBLE INTERFACE (SCLK and SDA)
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
Output Low Sink Current
Input Capacitance
V
0.8
V
V
IL
V
V
V
V
= 3.0V
CC
2.2
-1
6
IH
I
f
= GND or 5.5V
= 0.6V
+1
µA
mA
pF
LEAK
IN
I
OL
OL
C
5
IN
SMBus TIMING (Note 2)
Serial Clock Frequency
(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
20
28
40
Note 1: All parameters tested at T = +25°C. Specifications over temperature are guaranteed by design.
A
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
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
Typical Operating °haracteristics
(V
= 3.3V, T = +25°C, unless otherwise noted.)
CC
A
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
5.0
2
1
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0
-1
-2
-3
-4
2N3906
0
25
50
75
100
125
0.01
0.1
1
10
100
TEMPERATURE (°C)
CLOCK FREQUENCY (kHz)
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
2.0
1.5
1.0
0.5
0
3
2
REMOTE ERROR
LOCAL ERROR
1
0
-1
-2
-3
-0.5
-1.0
-1.5
V
= 100mV SQUARE WAVE
P-P
IN
APPLIED TO V WITH NO BYPASS CAPACITOR
CC
0
25
50
75
100
125
0.0001 0.001 0.01
0.1
1
10
100
TEMPERATURE (°C)
FREQUENCY (kHz)
TEMPERATURE ERROR
vs. DXP NOISE FREQUENCY
TEMPERATURE ERROR
vs. DXP-GND CAPACITANCE
100
90
80
70
60
50
40
30
20
10
0
2.0
1.0
V
V
= AC-COUPLED TO DXP
IN
IN
= 100mV SQUARE WAVE
P-P
0
REMOTE ERROR
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
LOCAL ERROR
0.001
0.01
0.1
1
10
100
0.1
1
10
100
FREQUENCY (kHz)
DXP-GND CAPACITANCE (nF)
4
_______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
Pin Description
PIN
1
NAME
FUNCTION
Supply Voltage Input, +3V to +5.5V. Bypass V to GND with a 0.1µF capacitor. A 47Ω series resistor is
CC
V
CC
recommended but not required for additional noise filtering.
2
GND
DXP
Ground
Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF
capacitor between DXP and GND for noise filtering.
3
4
5
SCLK
SDA
SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of V
.
CC
SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of V
.
CC
SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See
the ALERT Interrupts section.
6
ALERT
remote temperature is measured eight times per sec-
Detailed Description
ond. The results of the previous conversion are always
The MAX6642 is a temperature sensor for local
and remote temperature-monitoring applications.
Communication with the MAX6642 occurs through the
SMBus-compatible serial interface and dedicated alert
pins. ALERT asserts if the measured local or remote
temperature is greater than the software-programmed
ALERT limit.
available, even if the ADC is busy.
/owꢂPower ꢀtandꢄy Mode
Standby mode reduces the supply current to less than
10µA by disabling the ADC and timing circuitry. Enter
standby mode by setting the RUN bit to 1 in the config-
uration byte register (Table 4). All data is retained in
memory, and the SMBus interface is active and listen-
ing for SMBus commands. Standby mode is not a shut-
down mode. With activity on the SMBus, the device
draws more supply current (see the Typical Operating
Characteristics). In standby mode, the MAX6642 can
be forced to perform ADC conversions through the
one-shot command, regardless of the RUN bit status.
The MAX6642 converts temperatures to digital data
either at a programmed rate of eight conversions per
second or in single conversions. Temperature data is
represented by 8 data bits (at addresses 00h and 01h),
with the LSB equal to +1°C and the MSB equal to
+128°C. Two additional bits of remote temperature data
are available in the “extended” register at address 10h
and 11h (Table 2) providing resolution of +0.25°C.
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.
AD° and Multiplexer
The averaging ADC integrates over a 60ms period
(each channel, typ), 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 user can ignore the results of the unused chan-
nel. If the remote-diode channel is unused, connect
DXP to GND rather than leaving DXP open.
Supply-current drain during the 125ms conversion peri-
od is 500µA (typ). In standby mode, supply current
drops to 3µA (typ).
ꢀMꢁus Digital Interface
From a software perspective, the MAX6642 appears as
a set of byte-wide registers that contain temperature
data, alarm threshold values, and control bits. A stan-
dard SMBus-compatible 2-wire serial interface is used
to read temperature data and write control bits and
alarm threshold data.
The conversion time per channel (remote and internal)
is 125ms. If both channels are being used, then each
channel is converted four times per second. If the
external conversion-only option is selected, then the
The MAX6642 employs 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
_______________________________________________________________________________________
5
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
register was previously selected by a Write Byte
instruction. Use caution when using the shorter proto-
cols in multimaster systems, as a second master could
overwrite the command byte without informing the first
master.
ters. The temperature data format for these registers is
8 bits for each channel, with the LSB representing +1°C
(Table 1).
Read the additional bits from the read extended tem-
perature byte register (10h, 11h), which extends the
data to 10 bits and the resolution to +0.25°C per LSB
(Table 2).
Read temperature data from the read internal tempera-
ture (00h) and read external temperature (01h) regis-
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
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
7 BITS
RD
ACK
DATA
///
P
7 BITS
8 BITS
8 BITS
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP SELECT LINE
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
REDING 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
RECEIVE BYTE FORMAT
S
ADDRESS
WR
ACK
COMMAND
ACK
P
S
ADDRESS
RD
ACK
DATA
///
P
7 BITS
8 BITS
7 BITS
8 BITS
COMMAND BYTE: SENDS COM-
MAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
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
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
6
_______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
When a conversion is complete, the main temperature
Table 1. Main Temperature Register
(High Byte) Data Format
register and the extended temperature register are
updated.
TEMP (°C)
DIGITAL OUTPUT
1 000 0010
0 111 1111
0 111 1110
0 001 1001
0 000 0000
0 000 0000
1 111 1111
Alarꢃ Threshold ꢅegisters
Two registers store ALERT threshold values—one each
for the local and remote channels. If either measured
temperature equals or exceeds the corresponding
ALERT threshold value, the ALERT interrupt asserts
unless the ALERT bit is masked.
130.00
127.00
126.00
25
0.00
<0.00
The power-on-reset (POR) state of the local ALERT
T
register is +70°C (0100 0110). The POR state of
HIGH
Diode fault (short or open)
the remote ALERT T
register is +120°C (0111 1000).
HIGH
Table 2. Extended Resolution
Temperature Register (Low Byte) Data
Format
Diode Fault Detection
A continuity fault detector at DXP detects an open cir-
cuit on DXP, or a DXP short to V
or GND. If an open
CC
or short circuit exists, the external temperature register
is loaded with 1111 1111 and status bit 2 (OPEN) of the
status byte is set to 1. Immediately after POR, the sta-
tus 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. Diode faults do not set
the ALERT output.
FRACTIONAL TEMP (°C)
DIGITAL OUTPUT
00XX XXXX
0.000
0.250
0.500
0.750
01XX XXXX
10XX XXXX
11XX XXXX
ALERT Interrupts
The ALERT interrupt occurs when the internal or external
temperature reading exceeds a high temperature limit
(user programmed). The ALERT interrupt output signal is
latched and can be cleared only by reading the status
register after the fault condition no longer exists or by
successfully responding to the alert response address. If
the ALERT is cleared by responding to the alert
response address and the temperature fault condition
still exists, ALERT is reasserted after the next tempera-
ture-monitoring cycle. To clear ALERT while the tempera-
ture is above the trip threshold, write a new high limit that
is higher than the current temperature. The ALERT out-
put is open drain, allowing multiple devices to share a
common interrupt line.
Alert ꢅesponse Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices like
temperature sensors. Upon receiving an ALERT inter-
rupt signal, the host master can broadcast a Receive
Byte transmission to the alert response slave address
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
_______________________________________________________________________________________
7
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
(0001 100). Following such a broadcast, any slave
Table 3. Command-Byte Assignments
device that generated an interrupt attempts to identify
ADDRESS
POR STATE
00h (0000 0000)
00h (0000 0000)
N/A
FUNCTION
itself by putting its own address on the bus.
00h
Read local temperature
Read remote temperature
Read status byte
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 completion of the alert response protocol
clears the interrupt latch. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
01h
02h
03h
10h (0001 0000)
46h (0100 0110) +70°C
Read configuration byte
Read local high limit
05h
07h
78h (0111 1000) +120°C Read remote high limit
09h
N/A
N/A
N/A
N/A
Write configuration byte
Write local high limit
Write remote high limit
Single shot
0Bh
0Dh
0Fh
Read remote extended
temperature
10h
0000 0000
°oꢃꢃand ꢁyte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the various other registers within the
MAX6642. The register’s POR state is 0000 0000, so a
Receive Byte transmission (a protocol that lacks the
Read internal extended
temperature
11h
FEh
0000 0000
4Dh (0100 1101)
Read manufacturer ID
Table 4. Configuration-Byte Bit Assignments
BIT
7 (MSB)
6
NAME
MASK1
POR STATE
FUNCTION
0
0
A 1 masks off (disables) the ALERT interrupts.
A 1 puts the MAX6642 into standby mode.
STOP/RUN
A 1 disables local temperature measurements so that only
remote temperature is measured. The measurement rate
becomes 8Hz.
5
External only
0
Fault
queue
0: ALERT is set by a single fault. 1: Two consecutive faults
are required to set ALERT.
4
1
3 to 0
—
0000
Reserved.
Table 5. Status-Byte Bit Assignments
BIT
NAME
POR STATE
FUNCTION
7 (MSB)
BUSY
0
A 1 indicates the MAX6642 is busy converting.
A 1 indicates an internal high-temperature fault. Clear
LHIGH with a POR or by reading the status byte.
6
5
4
3
LHIGH
—
0
0
0
0
Reserved.
A 1 indicates an external high-temperature fault. Clear
RHIGH with a POR or by reading the status byte.
RHIGH
—
Reserved.
A 1 indicates a diode open condition. Clear OPEN with a
POR or by reading the status byte when the condition no
longer exists.
2
OPEN
0
0
1 to 0
—
Reserved.
8
_______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
command byte) that occurs immediately after POR
returns the current local temperature data.
POꢅ and UV/O
To prevent ambiguous power-supply conditions from
corrupting the data in memory and causing erratic
ꢀingleꢂꢀhot
The single-shot command immediately forces a new
conversion cycle to begin. If the single-shot command
is received while the MAX6642 is in standby mode
(RUN bit = 1), a new conversion begins, after which the
device returns to standby mode. If a single-shot con-
version is in progress when a single-shot command is
received, the command is ignored. If a single-shot
command is received in autonomous mode (RUN bit =
0), the command is ignored.
behavior, a POR voltage detector monitors V
and
CC
clears the memory if V
falls below 2.1 (typ). When
CC
power is first applied and V
rises above 2.1 (typ),
CC
the logic blocks begin operating, although reads and
writes at V levels below 3V are not recommended. A
CC
second V
comparator, the ADC undervoltage lockout
CC
(UVLO) comparator prevents the ADC from converting
until there is sufficient headroom (V = +2.7V typ).
CC
PowerꢂUp Defaults
Power-up defaults include:
°onfiguration ꢁyte Functions
The configuration byte register (Table 4) is a read-write
register with several functions. Bit 7 is used to mask
(disable) interrupts. Bit 6 puts the MAX6642 into stand-
by mode (STOP) or autonomous (RUN) mode. Bit 5 dis-
ables local temperature conversions for faster (8Hz)
remote temperature monitoring. Bit 4 prevents setting
the ALERT output until two consecutive measurements
result in fault conditions.
• ALERT output is cleared.
• ADC begins autoconverting at a 4Hz rate.
• Command byte is set to 00h to facilitate quick
local Receive Byte queries.
• Local (internal) T
limit set to +70°C.
HIGH
• Remote (external) T
limit set to +120°C.
HIGH
Applications Inforꢃation
ꢀtatus ꢁyte Functions
The status byte register (Table 5) 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 on 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 the overtemperature fault
condition no longer exists.
ꢅeꢃoteꢂDiode ꢀelection
The MAX6642 can directly measure the die temperature
of CPUs and other ICs that have on-board temperature-
sensing diodes (see the 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 MAX6642 is optimized for n
= 1.008, which is the typical value for the Intel Pentium
III. A thermal diode on the substrate of an IC is normally
a PNP with its collector grounded. DXP should be con-
nected to the anode (emitter) and the cathode should
be connected at GND of the MAX6642.
ꢀlave Addresses
The MAX6642 has eight fixed addresses available.
These are shown in Table 6.
The MAX6642 also responds to the SMBus alert
response slave address (see the Alert Response
Address section).
If a sense transistor with an ideality factor other than
1.008 is used, the output data is different from the data
obtained with the optimum ideality factor. Fortunately,
the difference is predictable.
Table 6. Slave Address
PART NO. SUFFIX
MAX6642ATT90
MAX6642ATT92
MAX6642ATT94
MAX6642ATT96
MAX6642ATT98
MAX6642ATT9A
MAX6642ATT9C
MAX6642ATT9E
ADDRESS
1001 000
1001 001
1001 010
1001 011
1001 100
1001 101
1001 110
1001 111
Assume a remote-diode sensor designed for a nominal
ideality factor n
is used to measure the tem-
NOMINAL
perature of a diode with a different ideality factor n .
1
The measured temperature T can be corrected using:
M
n1
TM = T
ACTUAL
n
NOMINAL
_______________________________________________________________________________________
9
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
where temperature is measured in Kelvin and
NOMIMAL
Table 7. Remote-Sensor Transistor
Manufacturers
n
for the MAX6642 is 1.008.
As an example, assume you want to use the MAX6642
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:
MANUFACTURER
MODEL NO.
CMPT3906
Central Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
SST3906
n
1.008
1.002
NOMINAL
KST3906-TF
SMBT3906
T
= T
= T
M
=
ACTUAL
M
n
1
Siemens (Germany)
T (1.00599)
Zetex (England)
FMMT3906CT-ND
M
Note: Discrete transistors must be diode connected (base short-
ed to collector).
For a real temperature of +85°C (358.15K), the mea-
sured temperature is +82.91°C (356.02K), an error of
-2.13°C.
Discrete ꢅeꢃote Diodes
When the remote-sensing diode is a discrete transistor,
its collector and base should be connected together.
Table 7 lists examples of discrete transistors that are
appropriate for use with the MAX6642.
Effect of Series Resistance
Series resistance in a sense diode contributes addition-
al errors. For nominal diode currents of 10µA and
100µA, the change in the measured voltage due to
series resistance is:
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage at
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected tempera-
ture, the forward voltage must be less than 0.95V at
100µA. Large power transistors must not be used. Also,
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
∆V = R (100µA - 10µA) = 90µA ✕ R
S
M
S
Since +1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
µV
Ω
90
°C
Ω
= 0.453
V
BE
characteristics.
µV
°C
198.6
Manufacturers of discrete transistors do not normally
specify or guarantee ideality factor. This is normally not
a problem since good-quality discrete transistors tend
to have ideality factors that fall within a relatively narrow
range. We have observed variations in remote tempera-
ture readings of less than 2°C with a variety of dis-
crete transistors. Still, it is good design practice to
verify good consistency of temperature readings with
several discrete transistors from any manufacturer
under consideration.
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
°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:
AD° Noise Filtering
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.
1.36°C - 2.13°C = -0.77°C
High-frequency EMI is best filtered at DXP with an
external 2200pF capacitor. Larger capacitor values can
be used for added filtering, but do not exceed 3300pF
because excessive capacitance can introduce errors
for a diode temperature of +85°C.
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
10 ______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
due to the rise time of the switched current source.
Nearly all noise sources tested cause the temperature
conversion results to be higher than the actual temper-
ature, typically by +1°C to +10°C, depending on the
frequency and amplitude (see the Typical Operating
Characteristics).
9) 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.
TwistedꢂPair and ꢀhielded °aꢄles
Use a twisted-pair cable to connect the remote sensor
for remote-sensor distances longer than 8in or in very
noisy environments. Twisted-pair cable lengths can be
between 6ft and 12ft before noise introduces excessive
errors. For longer distances, the best solution is a
shielded twisted pair 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 GND and
the shield to GND. Leave the shield unconnected at the
remote diode.
P° ꢁoard /ayout
Follow these guidelines to reduce the measurement
error of the temperature sensors:
1) Connect the thermal-sense diode to the MAX6642
using two traces—one between DXP and the
anode, the other between the MAX6642’s GND and
the cathode. Do not connect the cathode to GND at
the sense diode.
2) Place the MAX6642 as close as is practical to the
remote thermal 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.
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 1/2°C.
3) Do not route the thermal diode lines next to the
deflection coils of a CRT. Also, do not route the
traces across fast digital signals, which can easily
introduce a 30°C error, even with good filtering.
Therꢃal Mass and ꢀelfꢂHeating
When sensing local temperature, this device is intend-
ed to measure the temperature of the PC board to
which it is 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 measure-
ments impractical. Because the thermal mass of the PC
board is far greater than that of the MAX6642, the
device follows temperature changes on the PC board
with little or no perceivable delay.
4) Route the thermal diode 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 trace (Figure 4).
5) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.
When measuring 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
6) When introducing a thermocouple, make sure that
both the thermal diode paths have matching ther-
mocouples. A copper-solder thermocouple exhibits
3µV/°C, and it takes about 200µV of voltage error at
DXP to cause a +1°C measurement error. Adding a
few thermocouples causes a negligible error.
GND
10 mils
10 mils
THERMAL DIODE ANODE/DXP
7) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10-mil
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.
MINIMUM
10 mils
THERMAL DIODE CATHODE/GND
GND
10 mils
8) Add a 47Ω resistor in series with V
for best noise
CC
Figure 4. Recommended DXP PC Traces
filtering (see the Typical Operating Circuit).
______________________________________________________________________________________ 11
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, smaller packages, such as SOT23s, yield the best
thermal response times. Take care to account for ther-
mal gradients between the heat source and the sensor,
and ensure that stray air currents across the sensor
package do not interfere with measurement accuracy.
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
°hip Inforꢃation
TRANSISTOR COUNT: 7744
PROCESS: BiCMOS
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-
Pin °onfiguration
rent at the ALERT output. For example, with V
=
TOP VIEW
CC
+5.0V, at an 8Hz conversion rate and with ALERT sink-
MAX6642
ing 1mA, the typical power dissipation is:
V
1
2
3
6
5
4
ALERT
SDA
CC
5.0V x 450µA + 0.4V x 1mA = 2.65mW
GND
DXP
ø
for the 6-pin TDFN package is about +41°C/W, so
J-A
SCLK
assuming no copper PC board heat sinking, the result-
ing temperature rise is:
TDFN
(BUMPS ON BOTTOM)
∆T = 2.65mW x 41°C/W = +0.11°C
Functional Diagraꢃ
V
CC
2
MUX
REMOTE
DXP
CONTROL
LOGIC
ADC
LOCAL
DIODE
FAULT
SMBus
SDA
8
READ
ALERT
S
R
SCLK
8
WRITE
7
Q
REGISTER BANK
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
MAX6642
ADDRESS
DECODER
ALERT RESPONSE
ADDRESS
12 ______________________________________________________________________________________
±±1°C ꢀMꢁusꢂ°oꢃpatiꢄle ꢅeꢃoteꢆ/ocal
Teꢃperature ꢀensor with Overteꢃperature Alarꢃ
Package Inforꢃation
(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.)
L
A
D2
D
A2
PIN 1 ID
1
N
1
C0.35
b
[(N/2)-1] x e
REF.
E
E2
PIN 1
INDEX
AREA
DETAIL A
e
k
A1
C
L
C
L
L
L
e
e
A
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
1
2
21-0137
D
COMMON DIMENSIONS
SYMBOL
MIN.
0.70
2.90
2.90
0.00
0.20
MAX.
A
0.80
3.10
3.10
0.05
0.40
D
E
A1
L
k
0.25 MIN.
0.20 REF.
A2
PACKAGE VARIATIONS
PKG. CODE
T633-1
N
6
D2
E2
e
JEDEC SPEC
b
[(N/2)-1] x e
1.90 REF
1.95 REF
2.00 REF
1.50–0.10 2.30–0.10 0.95 BSC
1.50–0.10 2.30–0.10 0.65 BSC
MO229 / WEEA
MO229 / WEEC
0.40–0.05
0.30–0.05
T833-1
8
T1033-1
10
1.50–0.10 2.30–0.10 0.50 BSC MO229 / WEED-3 0.25–0.05
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
2
2
21-0137
D
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.
Maxiꢃ Integrated ProductsC ±20 ꢀan Gaꢄriel DriveC ꢀunnyvaleC °A 94086 408ꢂ737ꢂ7600 ____________________ 13
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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