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PDF MAX6642 Data sheet ( Hoja de datos )
| Número de pieza | MAX6642 | |
| Descripción | SMBus-Compatible Remote/Local Temperature Sensor | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-2920; Rev 3; 10/09
EVAALVUAAILTAIOBNLEKIT
www.DataSheet4U.com
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
General Description
The MAX6642 precise, two-channel digital temperature
sensor accurately measures the temperature of its own
die and a remote PN junction and reports the tempera-
ture data over a 2-wire serial interface. The remote PN
junction is typically a substrate PNP transistor on the
die of a CPU, ASIC, GPU, or FPGA. The remote PN
junction can also be a discrete diode-connected small-
signal transistor.
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.
Measurements can be done autonomously or in a sin-
gle-shot mode.
Remote accuracy is ±1°C maximum 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 with an exposed pad.
Desktop Computers
Notebook Computers
Servers
Thin Clients
Test and Measurement
Workstations
Graphic Cards
Applications
Selector Guide
PART
MEASURED TEMP RANGE
MAX6642ATT90-T
0°C to +150°C
MAX6642ATT92-T
0°C to +150°C
MAX6642ATT94-T
0°C to +150°C
MAX6642ATT96-T
0°C to +150°C
MAX6642ATT98-T
0°C to +150°C
MAX6642ATT9A-T
0°C to +150°C
MAX6642ATT9C-T
0°C to +150°C
MAX6642ATT9E-T
0°C to +150°C
SMBus is a trademark of Intel Corp.
TOP
MARK
AFC
AFD
AFE
AFF
AEW
AFG
AFH
AFI
Features
o Dual Channel: Measures Remote and Local
Temperature
o +0.25°C Resolution
o High Accuracy ±1°C (max) (Remote) and
±2°C (Local) from +60°C to +100°C
o Measures Remote Temperature Up to +150°C
o Programmable Overtemperature Alarm
Temperature Thresholds
o SMBus/I2C-Compatible Interface
o Tiny TDFN Package with Exposed Pad
Ordering Information
PART
MAX6642ATT90-T
MAX6642ATT92-T
MAX6642ATT94-T
MAX6642ATT96-T
MAX6642ATT98-T
MAX6642ATT9A-T
MAX6642ATT9C-T
MAX6642ATT9E-T
T = Tape and reel.
*EP = Exposed pad.
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-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
Pin Configuration and Functional Diagram appear at end of
data sheet.
Typical Operating Circuit
0.1μF
3.3V
47Ω
VCC
2200pF
MAX6642
DXP
SDA
SCLK
ALERT
μP GND
10kΩ EACH
DATA
CLOCK
INTERRUPT TO μP
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
www.DataSheet4U.com
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
Pin Description
PIN NAME
FUNCTION
1
VCC
Supply Voltage Input, +3V to +5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 47Ω series resistor is
recommended but not required for additional noise filtering.
2 GND Ground
3
DXP
Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF
capacitor between DXP and GND for noise filtering.
4 SCLK SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of VCC.
5 SDA SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of VCC.
6
ALERT
SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See
the ALERT Interrupts section.
—
EP
Exposed Pad. Internally connected to GND. Connect to a PCB ground pad for optimal performance. Not
intended as an electrical connection point.
Detailed Description
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.
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.
ADC 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.
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
remote temperature is measured eight times per sec-
ond. 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 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.
If a standby command is received while a conversion is
in progress, the conversion cycle is truncated, and the
data from that conversion is not latched into a tempera-
ture register. The previous data is not changed and
remains available.
Supply-current drain during the 125ms conversion peri-
od is 500µA (typ). In standby mode, supply current
drops to 3µA (typ).
SMBus 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 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
5 Page 
www.DataSheet4U.com
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
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.
ADC 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 PCB
layout and proper external noise filtering.
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
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).
PCB Layout
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.
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.
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 PCB contamination must be dealt with careful-
ly 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.
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.
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.
8) Add a 47Ω resistor in series with VCC for best noise
filtering (see the Typical Operating Circuit).
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.
Twisted-Pair and Shielded Cables
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.
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.
10 mils
GND
THERMAL DIODE ANODE/DXP
10 mils
THERMAL DIODE CATHODE/GND
GND
Figure 4. Recommended DXP PC Traces
10 mils
MINIMUM
10 mils
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MAX6642.PDF ] | |
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