参数资料
型号: ADT7476AARQZ-RL7
厂商: ON Semiconductor
文件页数: 16/66页
文件大小: 945K
描述: IC REMOTE THERMAL CTLR 24-QSOP
产品变化通告: MFG CHG Notification ADI to ON Semi
QSOP 24ld Pkg (MSL) Change 17/Jun/2010
Product Discontinuation 30/Sept/2011
标准包装: 1,000
系列: dBCool®
功能: 风扇控制,温度监控器
传感器类型: 内部和外部
感应温度: -40°C ~ 125°C
精确度: ±2.5%
拓扑: ADC,比较器,风扇速度计数器,多路复用器,寄存器库
输出类型: SMBus?
输出警报:
输出风扇:
电源电压: 3 V ~ 3.6 V
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 24-SSOP(0.154",3.90mm 宽)
供应商设备封装: 24-QSOP
包装: 带卷 (TR)
ADT7476A
http://onsemi.com
16
Table 14. TWOS COMPLEMENT TEMPERATURE DATA
FORMAT
Temperature
Digital Output (10-bit) (Note 1)
128癈
1000 0000 00 (Diode Fault)
50癈
1100 1110 00
25癈
1110 0111 00
10癈
1111 0110 00
0癈
0000 0000 00
+10.25癈
0000 1010 01
+25.5癈
0001 1001 10
+50.75癈
0011 0010 11
+75癈
0100 1011 00
+100癈
0110 0100 00
+125癈
0111 1101 00
+127癈
0111 1111 00
1.  Bold numbers denote 2 LSB of measurement in the Extended
Resolution Register 2 (0x77) with 0.25癈 resolution.
Table 15. EXTENDED RANGE, TEMPERATURE DATA
FORMAT
Temperature
Digital Output (10-bit) (Note 1)
64癈
0000 0000 00 (Diode Fault)
1癈
0011 1111 00
0癈
0100 0000 00
1癈
0100 0001 00
10癈
0100 1010 00
25癈
0101 1001 00
50癈
0111 0010 00
75癈
1000 1001 00
100癈
1010 0100 00
125癈
1011 1101 00
191癈
1111 1111 00
1.  Bold numbers denote 2 LSB of measurement in the Extended
Resolution Register 2 (0x77) with 0.25癈 resolution.
Remote Temperature Measurement
The ADT7476A can measure the temperature of two
remote diode sensors or diode-connected transistors
connected to Pin 17 and Pin 18, or Pin 15 and Pin 16.
The forward voltage of a diode or diode-connected
transistor operated at a constant current exhibits a negative
temperature coefficient of about 2 mV/癈. Unfortunately,
the absolute value of V
BE
 varies from device to device, and
individual calibration is required to null this out. As a result,
this technique is unsuitable for mass production. The
technique used in the ADT7476A is to measure the change
in V
BE
 when the device is operated at two different currents.
This is given by:
(eq. 1)
DV
BE
+
kT
q
  In
(
N
)
where:
k is the Boltzmanns constant.
q is the charge on the carrier.
T is the absolute temperature in Kelvin.
N is the ratio of the two currents.
Figure 25 shows the input signal conditioning used to
measure the output of a remote temperature sensor. This
figure shows the external sensor as a substrate transistor,
which is provided on some microprocessors for temperature
monitoring. It could also be a discrete transistor such as a
2N3904/2N3906.
If a discrete transistor is used, the collector is not grounded
and is linked to the base. If a PNP transistor is used, the base
is connected to the D input and the emitter to the D+ input.
If an NPN transistor is used, the emitter is connected to the
D input and the base to the D+ input. Figure 26 and
Figure 27 show how to connect the ADT7476A to an NPN
or PNP transistor for temperature measurement. To prevent
ground noise from interfering with the measurement, the
more negative terminal of the sensor is not referenced to
ground, but is biased above ground by an internal diode at
the D input.
Figure 25. Signal Conditioning for Remote Diode Temperature Sensors
LOW-PASS FILTER
f
C
 = 65 kHz
REMOTE
SENSING
TRANSISTOR
BIAS
DIODE
D+
D
V
DD
I
BIAS
I
N ?I
V
OUT+
V
OUT
To ADC
THERMDA
THERMDC
CPU
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