Maxim MAX6648 Precision smbus-compatible remote/local temperature sensors with overtemperature alarm Datasheet

19-2545; Rev 1; 10/02
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
Features
♦ Dual Channel: Measures Remote and Local
Temperature
♦ 0.125°C Resolution
♦ High Accuracy: ±0.8°C (max) from +25°C to
+125°C (Remote), and ±2°C (max) from +60°C to
+100°C (Local)
♦ Two Alarm Outputs: ALERT and OVERT
♦ Two Default OVERT Thresholds Available
MAX6648: +110°C
MAX6692: +85°C
♦ Programmable Conversion Rate
♦ SMBus-Compatible Interface
♦ SMBus Timeout
♦ Programmable Under/Overtemperature Alarm
Thresholds
Ordering Information
PART
TEMP RANGE
MAX6648MUA -55°C to +125°C 8 µMAX
0°C to +125°C
MAX6692MUA -55°C to +125°C 8 µMAX
0°C to +125°C
MAX6692MSA
0°C to +125°C
Remote accuracy is ±0.8°C maximum error between
+25°C and +125°C with no calibration needed. The
MAX6648/MAX6692 operate from -55°C to +125°C, and
measure temperatures between 0°C and +125°C. The
MAX6648 is available in an 8-pin µMAX package, and the
MAX6692 is available in 8-pin µMAX and SO packages.
-55°C to +125°C 8 SO
Typical Operating Circuit
3.3V
0.1µF
200Ω
Applications
VCC
Desktop Computers
Notebook Computers
Thin Clients
2200pF
Workstations
µP
10kΩ EACH
DXP
SDA
DXN
MAX6648 SCLK
MAX6692
ALERT
Servers
Test and Measurement
PINMEASURED
PACKAGE TEMP RANGE
OVERT
GND
DATA
CLOCK
INTERRUPTED TO µP
TO FAN DRIVER OR
SYSTEM SHUTDOWN
Multichip Modules
SMBus is a trademark of Intel Corp.
Pin Configuration 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
MAX6648/MAX6692
General Description
The MAX6648/MAX6692 are precise, two-channel digital temperature sensors. They 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 common-collector PNP on a
CPU, FPGA, or ASIC.
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 MAX6648/MAX6692
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 MAX6648/MAX6692 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, with the
conversion rate programmed by the user, or in a singleshot mode. The adjustable conversion rate allows the
user to optimize supply current and temperature
update rate to match system needs.
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
ABSOLUTE MAXIMUM RATINGS
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 5.9mW/°C above +70°C) .............471mW
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
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
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 = +85°C.) (Note 1)
PARAMETER
Supply Voltage
SYMBOL
CONDITIONS
VCC
MIN
3.0
MAX
5.5
0.125
Temperature Resolution
Local Temperature Error
-0.8
+0.8
TRJ = +60°C to +100°C
-1.0
+1.0
TRJ = 0°C to +125°C
-1.6
+1.6
VCC = 3.3V, +0°C
TRJ = 0°C to +125°C
≤ TA ≤ +100°C
-3.0
+3.0
TA = +60°C to +100°C
-2.0
+2.0
TA = 0°C to +125°C
-3.0
+3.0
VCC = 3.3V
°C
Supply Sensitivity of Temperature
Error
±0.2
UVLO
V
Bits
TRJ = +25°C to +125°C
VCC = 3.3V,
+60°C ≤ TA ≤
+100°C
Remote Temperature Error
UNITS
°C
10
VCC = 3.3V,
TA = +85°C
Undervoltage Lockout (UVLO)
Threshold
TYP
Falling edge of VCC disables ADC
2.4
UVLO Hysteresis
2.7
°C
°C/V
2.95
V
90
mV
VCC falling edge
2.0
V
Standby Supply Current
SMBus static
3.5
12
µA
Operating Current
During conversion
0.45
0.8
mA
Power-On-Reset (POR) Threshold
POR Threshold Hysteresis
90
Average Operating Current
Conversion Time
tCONV
0.25 conversions per second
40
80
2 conversions per second
250
400
125
156
From stop bit to conversion completion
Conversion Time Error
Remote-Diode Source Current
2
95
-25
DXP and DXN Leakage Current
Standby mode
IRJ
mV
ms
+25
%
100
nA
High level
80
100
120
Low level
8
10
12
_______________________________________________________________________________________
µA
µA
Precision SMBus-Compatible Remote/Local
Temperature 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 = +85°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
250
µs
Data Setup Time
tHD:DAT
(Note 4)
Receive SCLK/SDA Rise Time
tR
1
Receive SCLK/SDA Fall Time
tF
300
ns
Pulse Width of Spike Suppressed
tSP
50
ns
45
ms
SMBus Timeout
Note 1:
Note 2:
Note 3:
Note 4:
tTIMEOUT
0
SDA low period for interface reset
25
37
µs
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
MAX6648/MAX6692
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
2.8
400
300
200
3.5
4.0
4.5
5.0
5.5
-0.5
-2.5
0.63
0.13 0.25 0.50 1.00
2.00
0
4.00
25
50
75
100
125
SUPPLY VOLTAGE (V)
CONVERSION RATE (Hz)
TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
0.4
0.2
0
-0.2
-0.4
-0.6
LOCAL ERROR
1.2
1.0
0.8
0.6
REMOTE ERROR
0.4
MAX6648/92 toc06
1.4
9
VIN = AC-COUPLED TO DXN
VIN = 100mVP-P
8
TEMPERATURE ERROR (°C)
0.6
1.6
MAX6648/92 toc05
0.8
TEMPERATURE ERROR (°C)
MAX6648/92 toc04
1.0
7
REMOTE ERROR
6
5
4
3
2
LOCAL ERROR
1
0
VIN = SQUARE WAVE APPLIED TO VCC
WITH NO 0.1µF VCC CAPACITOR
0.2
-0.8
-1.0
-1
0
25
50
75
100
125
-2
0.1
1
10
TEMPERATURE (°C)
100
1k
1.5
TEMPERATURE ERROR (°C)
1
10
1.0
0.5
0
-0.5
-1.0
VIN = 20mVP-P SQUARE WAVE
APPLIED TO DXP-DXN
100
1k
FREQUENCY (Hz)
1
0
-1
-2
-3
-4
-5
-2.0
10
100
10k
100k
-6
0.100
1k
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
TEMPERATURE ERROR (°C)
MAX6648/92 toc07
2.0
1
100k
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
-1.5
10k
MAX6648/92 toc08
0
4
0.5
TA = +85°C
FAIRCHILD 2N3906
0
3.0
1.5
-1.5
100
2.4
MAX6648/92 toc03
500
2.5
TEMPERATURE ERROR (°C)
3.2
MAX6648/92 toc02
3.6
600
OPERATING SUPPLY CURRENT (µA)
MAX6648/92 toc01
STANDBY SUPPLY CURRENT (µA)
4.0
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TEMPERATURE ERROR (°C)
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
1.000
10.000
100.000
DXP-DXN CAPACITANCE (nF)
_______________________________________________________________________________________
10k
100k
Precision SMBus-Compatible Remote/Local
Temperature 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; tie 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 biased to one
diode drop above 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 user-set
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 MAX6648/MAX6692 are temperature sensors
designed to work in conjunction with a microprocessor
or other intelligence in thermostatic, process-control, or
monitoring applications. Communication with the
MAX6648/MAX6692 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 high
limit or less than the ALERT low limit. ALERT also
asserts 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 thermalmanagement circuitry.
The MAX6648/MAX6692 convert temperatures to digital
data either at a programmed rate or in single conversions. Temperature data is represented as 10 bits plus
sign, 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 7 bits with the final
MSB 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 user can ignore the results of the unused chan-
Table 1. Main Temperature Data Register
Format (00h, 01h)
TEMP (°C)
DIGITAL OUTPUT
130
0 111 1111
127
0 111 1111
126
0 111 1111
25
0 001 1001
0
0 000 0000
<0
0 000 0000
-1
0 000 0000
-25
Diode fault
(short or open)
0 000 0000
1 000 0000
_______________________________________________________________________________________
5
MAX6648/MAX6692
Pin Description
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
nel. If the remote-diode channel is unused, connect
DXP to DXN rather than leaving the pins open.
The DXN input is biased to one VBE above ground by
an internal diode to prepare the ADC inputs for a differential measurement. The worst-case 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.
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
10µA 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 MAX6648/MAX6692 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 500µA (typ). Slowing down the conversion rate
reduces the average supply current (see Typical
Operating Characteristics). Between conversions, the
conversion rate timer consumes about 25µA of supply
current. In standby mode, supply current drops to
about 3µA.
SMBus Digital Interface
From a software perspective, the MAX6648/MAX6692
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. These devices respond to the
same SMBus slave address for access to all functions.
6
The MAX6648/MAX6692 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 7 bits plus 1 bit, indicating the diode fault status
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 10 bits plus sign and the resolution to 0.125°C
per LSB (Table 2). An additional 3 bits can be read
from the read internal extended temperature register
(11h), which extends the data to 10 bits (plus 1 bit indicating the diode fault status) 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.
To ensure valid extended data, read extended resolution temperature data using one of the following
approaches:
1) Put the MAX6648/MAX6692 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.
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
_______________________________________________________________________________________
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
MAX6648/MAX6692
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
7 bits
COMMAND
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
S
P
ADDRESS
RD
ACK
7 bits
8 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
tLOW
B
tHIGH
C
D
E
F
G
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
E = SLAVE PULLS SMBDATA LINE LOW
tSU:DAT
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 2. SMBus Write Timing Diagram
2) If the MAX6648/MAX6692 are 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
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
A
B
tLOW
C
D
E
F
G
tHIGH
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:STO
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
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 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 power-on-reset (POR) state of both ALERT THIGH
registers is full scale (0101 0101, or +85°C). The POR
state of both TLOW registers 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 POR state of the
OVERT threshold is 0110 1110 or +110°C for the
MAX6648, and 0101 0101 or +85°C for the MAX6692.
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 1000 0000.
If the fault is an open-circuit fault bit 2 (OPEN) of the
status byte, it is set to 1 and the ALERT condition 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.
ALERT Interrupts
The ALERT interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperature limit (user programmed) or when the remote
diode is disconnected (for continuity fault detection).
8
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 only if the
fault condition no longer exists. Asserting ALERT does
not halt automatic conversion. The ALERT output pin is
open drain, allowing multiple devices to share a common interrupt line.
The MAX6648/MAX6692 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 2 and 3 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.
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
I 2C is a trademark of Philips Corp.
_______________________________________________________________________________________
Precision SMBus-Compatible Remote/Local
Temperature 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
0
Fault queue-length control
bit (see Table 4).
1
FQ0
0
Fault queue-length control
bit (see Table 4).
0
RFU
0
Reserved. Always write
zero to this bit.
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
MAX6648/MAX6692. 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 MAX6648/MAX6692 incorporate collision avoidance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
One-Shot
The one-shot command immediately forces a new conversion cycle to begin. If the one-shot command is
received while the MAX6648/MAX6692 are in standby
Table 4. Fault Queue Length Bit Definition
FQ1
FQ0
FAULT QUEUE LENGTH (SAMPLES)
0
0
1
0
1
2
1
1
3
1
0
—
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 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 MAX6648/MAX6692 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 a conversion is complete
and the fault 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
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.
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-
_______________________________________________________________________________________
9
MAX6648/MAX6692
Table 3. Fault Queue Register Bit Definition
(22h)
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
Table 5. Command-Byte Bit Assignments
REGISTER
ADDRESS
POR STATE
FUNCTION
RLTS
00h
0000 0000
0°C
Read local (internal) temperature
RRTE
01h
0000 0000
0°C
Read remote (external) temperature
RSL
02h
N/A
—
Read status byte
Read configuration byte
RCL
03h
0000 0000
—
RCRA
04h
0000 0111
—
RLHN
05h
0101 0101
+85°C
Read conversion rate byte
Read local (internal) ALERT high limit
Read local (internal) ALERT low limit
RLLI
06h
0000 0000
0°C
RRHI
07h
0101 0101
+85°C
Read remote (external) ALERT high limit
RRLS
08h
0000 0000
0°C
Read remote (external) ALERT low limit
WCA
09h
N/A
—
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
0110 1110
+110°C
Read/write remote (external) OVERT limit (MAX6648)
19h
0101 0101
+85°C
Read/write remote (external) OVERT limit (MAX6692)
RWOI
20h
0101 0101
+85°C
Read/write local (internal) OVERT limit
HYS
21h
0000 1010
10°C
RWOE
Overtemperature hysteresis
QUEUE
22h
1000 0000
—
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.
equipment applications. The conversion rate byte’s
POR state is 07h or 4Hz. The MAX6648/MAX6692 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.
Valid A/D conversion results for both channels are available one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conversion is initiated through the RUN bit, one-shot com10
mand, or initial power-up. Changing the conversion rate
can also affect the delay until new results are available.
Slave Addresses
The MAX6648/MAX6692 have a fixed address of 1001
100. The MAX6648/MAX6692 also respond to the
SMBus alert response slave address (see the Alert
Response Address section).
______________________________________________________________________________________
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
BIT
NAME
POR
STATE
7 (MSB)
BUSY
0
A/D is busy converting when 1.
FUNCTION
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.
POR and UVLO
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 = 2.8V typ).
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 set to +85°C.
• Local (internal) TLOW limit set to 0°C.
• Remote (external) THIGH limit set to +85°C.
• Remote (external) TLOW limit set to 0°C.
• OVERT internal limit is set to +85°C; every external
limit is set to +110°C (MAX6648).
• OVERT limits are set to +85°C (MAX6692).
Table 8. Conversion-Rate Control Byte
(04h)
DATA
CONVERSION
RATE (Hz)
00h
0.0625
01h
0.125
02h
0.25
03h
0.5
04h
1
05h
2
06h
4
07h
4
08h-FFh
Reserved
Applications Information
Remote-Diode Selection
The MAX6648/MAX6692 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.
______________________________________________________________________________________
11
MAX6648/MAX6692
Table 7. Status Register Bit Assignments (02h)
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
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 MAX6648/MAX6692 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
MAX6648/MAX6692 is 1.008. As an example, assume
you want to use the MAX6648/MAX6692 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:
∆VM = RS (100µA − 10µA) = 90µA × RS
Since 1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
90
µV
Ω = 0.453 °C
µV
Ω
198.6
°C
Assume that the diode being measured has a series
Intel and Pentium are registered trademarks of Intel Corp.
12
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.
For best accuracy, the discrete transistor should be a
small-signal device with its collector and base connected together. Table 9 lists examples of discrete transistors that are appropriate for use with the MAX6648/
MAX6692.
Table 9. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
MODEL NO.
Central Semiconductor (USA)
CMPT3904
Rohm Semiconductor (USA)
SST3904
Samsung (Korea)
KST3904-TF
Siemens (Germany)
SMBT3904
Note: Transistors must be diode connected (base shorted to
collector).
The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage at
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected temperature, 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 VBE characteristics.
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 mea-
______________________________________________________________________________________
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
10MILS
10MILS
DXP
10MILS
DXN
MINIMUM
10MILS
GND
Figure 4. Recommended DXP-DXN PC Traces
surements. 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 MAX6648/MAX6692 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
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 they 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 MAX6648/
MAX6692, the devices follow temperature changes on
the PC board with little or no perceivable delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
______________________________________________________________________________________
13
MAX6648/MAX6692
GND
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.
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
MAX6648/MAX6692
Functional Diagram
VCC
MAX6648
MAX6692
2
DXP
MUX
REMOTE
DXN
CONTROL
LOGIC
ADC
LOCAL
DIODE
FAULT
SMBus
ALERT
S
Q
8
READ
SMBDATA
8
WRITE
SMBCLK
R
REGISTER BANK
7
COMMAND BYTE
REMOTE TEMPERATURE
OVERT
S
LOCAL TEMPERATURE
R
ALERT THRESHOLD
Q
ADDRESS
DECODER
ALERT RESPONSE ADDRESS
OVERT THRESHOLD
When measuring temperature with discrete remote sensors, smaller packages, such as 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
14
at the ALERT output. For example, with VCC = 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 about +221°C/W,
so assuming no copper PC board heat sinking, the
resulting temperature rise is:
∆T = 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.
______________________________________________________________________________________
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
Chip Information
TRANSISTOR COUNT: 14,764
PROCESS: BiCMOS
TOP VIEW
SCLK
VCC
1
8
DXP
2
7
SDA
DXN
3
6
ALERT
OVERT
4
5
GND
MAX6648
MAX6692
µMAX/SO*
*SO PACKAGE AVAILABLE FOR MAX6692 ONLY.
______________________________________________________________________________________
15
MAX6648/MAX6692
Pin Configuration
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
E
ÿ 0.50±0.1
8
INCHES
DIM
A
A1
A2
b
H
c
D
e
E
H
0.6±0.1
1
L
1
α
0.6±0.1
S
BOTTOM VIEW
D
MIN
0.002
0.030
MAX
0.043
0.006
0.037
0.010
0.014
0.005
0.007
0.116
0.120
0.0256 BSC
0.116
0.120
0.188
0.198
0.016
0.026
0∞
6∞
0.0207 BSC
8LUMAXD.EPS
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature 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
e
FRONT VIEW
A
α
c
b
L
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0036
16
______________________________________________________________________________________
REV.
J
1
1
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
9LUCSP, 3x3.EPS
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX6648/MAX6692
Package Information (continued)
(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.)
Similar pages