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PDF MAX6649MUA Data sheet ( Hoja de datos )
| Número de pieza | MAX6649MUA | |
| Descripción | +145C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms | |
| Fabricantes | Maxim Integrated | |
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19-2540; Rev 1; 7/03
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
General Description
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.
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).
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.
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.
Remote accuracy is ±1°C maximum error between +60°C
and +145°C with no calibration needed. The
MAX6646/MAX6647/MAX6649 operate from -55°C to
+125°C, and measure temperatures between 0°C and
+145°C. The MAX6646/MAX6647/MAX6649 are available
in an 8-pin µMAX package.
Applications
Graphics Processors
Desktop Computers
Notebook Computers
Servers
Thin Clients
Workstations
Test and Measurement
Multichip Modules
Features
o Dual Channel: Measures Remote and Local
Temperature
o 0.125°C Resolution
o High Accuracy ±1°C (max) from +60°C to +145°C
(Remote), and ±2°C (max) from +60°C to +100°C
(Local)
o Measures High-Ideality Thermal Diodes Up to
+170°C (Apparent)
+145°C (Real)
o Two Alarm Outputs: ALERT and OVERT
o Programmable Under/Overtemperature Alarm
Temperature Thresholds
o Programmable Conversion Rate
o SMBus-Compatible Interface
o SMBus Timeout
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
MEASURED
TEMP RANGE
MAX6646MUA -55°C to +125°C 8 µMAX 0°C to +145°C
MAX6647MUA -55°C to +125°C 8 µMAX 0°C to +145°C
MAX6649MUA -55°C to +125°C 8 µMAX 0°C to +145°C
Typical Operating Circuit
0.1µF
3.3V
200Ω
VCC
DXP MAX6646 SDA
MAX6647
MAX6649 SCLK
DXN
2200pF
ALERT
OVERT
µP GND
10kΩ EACH
DATA
CLOCK
INTERRUPT TO µP
TO FAN DRIVER OR
SYSTEM SHUTDOWN
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.
1 page  
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Pin Description
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.
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. DO
2 DXP NOT LEAVE DXP FLOATING; connect DXP to DXN if no remote diode is used. Place a 2200pF
capacitor between DXP and DXN for noise filtering.
3
DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to
ground.
4
OVERT
Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is
above the software-programmed threshold.
5
GND
Ground
SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds limits
6
ALERT
(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.
7
SDA
SMBus Serial-Data Input/Output, Open Drain
8
SCLK
SMBus Serial-Clock Input
Detailed Description
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.
The MAX6646/MAX6647/MAX6649 convert temperatures
to digital data either at a programmed rate or in single
conversions. Temperature data is represented as 11 bits,
with the LSB equal to 0.125°C. The “main” temperature
data registers (at addresses 00h and 01h) are 8-bit 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).
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 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.
Table 1. Main Temperature Data Register
Format (00h, 01h)
TEMP (°C)
+145
+130
+128
+25
0
<0
Diode fault
(short or open)
DIGITAL OUTPUT
1001 0001
1000 0010
1000 0000
0001 1001
0000 0000
0000 0000
1111 1111
_______________________________________________________________________________________ 5
5 Page 
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
Table 7. Status Register Bit Assignments (02h)
BIT NAME
7 (MSB) BUSY
6 LHIGH
5 LLOW
4 RHIGH
3 RLOW
2 FAULT
1 EOT
0 IOT
POR
STATE
0
0
0
0
0
0
0
0
FUNCTION
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.
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.
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.
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
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).
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 = 2.7V typ).
Table 8. Conversion-Rate Control Byte
(04h)
DATA
00h
01h
02h
03h
04h
05h
06h
07h
08h-FFh
CONVERSION
RATE (Hz)
0.0625
0.125
0.25
0.5
1
2
4
4
Reserved
Power-up defaults include:
Power-Up Defaults
• Interrupt latch is cleared.
• ADC begins autoconverting at a 4Hz rate.
• Command byte is set to 00h to facilitate quick local
temperature receive byte queries.
• Local (internal) THIGH limit is set to +85°C.
• Local (internal) TLOW limit is set to 0°C.
• Remote (external) THIGH limit is set to +85°C
(MAX6649)/+95°C (MAX6646/MAX6647)
• OVERT (internal) limit is set to +85°C
• OVERT (external) limit is set to +85°C (MAX6649)/
+125°C (MAX6646/MAX6647)
Table 9. Slave Addresses
PART
MAX6646
MAX6647
MAX6649
SLAVE ADDRESS
1001 101
1001 110
1001 100
______________________________________________________________________________________ 11
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