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參數(shù)資料
| 型號： | MAX6642YATT98+T |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm |
| 中文描述： | DIGITAL TEMP SENSOR-SERIAL, 10BIT(s), 1Cel, SQUARE, SURFACE MOUNT |
| 封裝： | 3 X 3 MM, 0.80 MM HEIGHT, MO-229WEEC, TDFN-6 |
| 文件頁數(shù)： | 3/16頁 |
| 文件大小： | 344K |
| 代理商： | MAX6642YATT98+T |
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).
PC Board 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 PC board contamination must be dealt with
carefully since a 20M
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
3V/°C, and it takes about 200V 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 47
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.
Cable resistance also affects remote-sensor accuracy.
For every 1
of series resistance, the error is approxi-
mately 1/2°C.
Thermal Mass and Self-Heating
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.
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
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
______________________________________________________________________________________
11
MINIMUM
10 mils
THERMAL DIODE CATHODE/GND
THERMAL DIODE ANODE/DXP
GND
Figure 4. Recommended DXP PC Traces
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