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參數(shù)資料
| 型號： | G768D |
| 英文描述： | ± 3oC remote thermal sensor with one fan control and SMBus interface.|Thermal Sensor / Detector Series |
| 中文描述： | ± 3oC遠(yuǎn)程溫度傳感器一個風(fēng)扇控制和SMBus接口。|熱傳感器/探測器系列 |
| 文件頁數(shù)： | 6/16頁 |
| 文件大?。?/td> | 323K |
| 代理商： | G768D |
Ver: 1.4
May 23, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
6
G768D
Global Mixed-mode Technology Inc.
Fig 1. Functional Diagram
A/D Conversion Sequence
If a Start command is written (or generated automati-
cally in the free-running auto-convert mode), both two
channels are converted, and the results of both meas-
urements are available after the end of conversion. A
BUSY status bit in the status byte shows that the de-
vice is actually performing a new conversion; however,
even if the ADC is busy, the results of the previous
conversion are always available.
Remote-Diode Selection
Temperature
good-quality, diode-connected small-signal transistor.
Accuracy has been experimentally verified for all of
the devices listed in Table 1. The G768D can also
directly measure the die temperature of CPUs and
other integrated circuits having on-board tempera-
ture-sensing diodes. 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 must be greater than 0.25V at
10μA; check to ensure this is true at the highest ex-
pected temperature. The forward voltage must be less
than 0.95V at 200A; check to ensure this is true at the
lowest expected temperature. Large power transistors
don't work at all. Also, ensure that the base resistance
is less than 100
. Tight specifications for forward
current gain (+50 to +150, for example) indicate that
the manufacturer has good process controls and that
the devices have consistent VBE characteristics.
accuracy
depends
on
having
a
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the G768D's
effective accuracy. The thermal time constant of the
SSOP-16 package is about 140sec in still air. For the
G768D junction temperature to settle to within +1°C
after a sudden +100°C change requires about five
time constants or 12 minutes. The use of smaller
packages for remote sensors, such as SOT23s, im-
proves the situation. Take care to account for thermal
gradients between the heat source and the sen-
sor ,and ensure that stray air current across the sen-
sor package do not interfere with measurement accu-
racy.
Table 1. Remote-Sensor Transistor Manufacturers
MANUFACTURER
Philips
Motorola (USA)
National Semiconductor (USA)
Note:Transistors must be diode-connected (base short
-ed to collector).
MODEL NUMBER
PMBS 3904
MMBT3904
MMBT3904
DXP2
FAN CONTROL
LOGIC
LOGIC
REGISTERS
MUX
ADC
CIRCUIT
FANVCC
FG
TH_SHUT
SMBCLK
SMBDATA
ALERT
RESET
V
CC
+
+
DXP1
DXN
+
INTERNAL GROUND
CLK
V
CC
THERMAL SHUTDOWN
CONTROL
SMBUS
RESET
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