参数资料
| 型号： | ADT7476EBZEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 17/65页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION FOR ADT7476 |
| 产品变化通告： | MFG CHG Notification ADI to ON Semi |
| 标准包装： | 1 |
| 系列： | dBCool® |
| 类型： | 温度传感器 |
| 适用于相关产品： | ADT7476 |
| 所含物品： | 评估板 |
| 其它名称： | EVAL-ADT7476EBZ EVAL-ADT7476EBZ-ND |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页当前第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页第29页第30页第31页第32页第33页第34页第35页第36页第37页第38页第39页第40页第41页第42页第43页第44页第45页第46页第47页第48页第49页第50页第51页第52页第53页第54页第55页第56页第57页第58页第59页第60页第61页第62页第63页第64页第65页
ADT7476
D+
ADT7476
2N3904
NPN
D ?
Figure 26. Measuring Temperature by Using
an NPN Transistor
To reduce the error due to variations in both substrate and
discrete transistors, a number of factors should be taken into
consideration:
? The ideality factor, n f , of the transistor is a measure of
the deviation of the thermal diode from ideal behavior.
The ADT7476 is trimmed for an n f value of 1.008. Use
the following equation to calculate the error introduced
2N3906
PNP
ADT7476
D+
D ?
at a temperature T ( ° C), when using a transistor whose
n f does not equal 1.008 (see the processor ’s data sheet
for the n f values):
D T + (nf * 1.008) 273.15 K ) T (eq. 2)
Figure 27. Measuring Temperature by Using
a PNP Transistor
To factor this in, the user can write the D T value to the
offset register. The ADT7476 then automatically adds
To measure D V BE , the sensor switches between operating
currents of I and N × I. The resulting waveform passes
through a 65 kHz low-pass filter to remove noise and through
a chopper-stabilized amplifier. The amplifier performs the
amplification and rectification of the waveform to produce a
dc voltage proportional to D V BE . This voltage is measured by
the ADC to give a temperature output in 10-bit, twos
complement format. To further reduce the effects of noise,
digital filtering is performed by averaging the results of
16 measurement cycles.
A remote temperature measurement takes nominally
38 ms. The results of remote temperature measurements are
stored in 10-bit, twos complement format, as illustrated in
?
it to or subtracts it from the temperature measurement.
Some CPU manufacturers specify the high and low
current levels of the substrate transistors. The high
current level of the ADT7476, I HIGH , is 180 m A, and
the low level current, I LOW , is 11 m A. If the ADT7476
current levels do not match the current levels specified
by the CPU manufacturer, it could be necessary to
remove an offset. The CPU’s data sheet advises
whether this offset needs to be removed and how to
calculate it. This offset can be programmed to the offset
register. It is important to note that if more than one
offset must be considered, then the algebraic sum of
these offsets must be programmed to the offset register.
Table 10. The extra resolution for the temperature
measurements is held in the Extended Resolution Register 2
(0x77). This gives temperature readings with a resolution of
0.25 ° C.
Noise Filtering
For temperature sensors operating in noisy environments,
previous practice placed a capacitor across the D+ pin and
the D ? pin to help combat the effects of noise. However,
large capacitances affect the accuracy of the temperature
measurement, leading to a recommended maximum
capacitor value of 1,000 pF.
This capacitor reduces the noise but does not eliminate it,
which makes using the sensor difficult in a very noisy
environment. In most cases, a capacitor is not required
because differential inputs by their very nature have a high
immunity to noise.
Factors Affecting Diode Accuracy
Remote Sensing Diode
The ADT7476 is designed to work with substrate
transistors built into processors or with discrete transistors.
Substrate transistors are generally PNP types with the
collector connected to the substrate. Discrete types can be
either PNP or NPN transistors connected as a diode
(base-shorted to the collector). If an NPN transistor is used,
the collector and base are connected to D+ and the emitter
to D ? . If a PNP transistor is used, the collector and base are
connected to D ? and the emitter is connected to D+.
If a discrete transistor is used with the ADT7476, the best
accuracy is obtained by choosing devices according to the
following criteria:
? Base-emitter voltage greater than 0.25 V at 11 m A, at
the highest operating temperature.
? Base-emitter voltage less than 0.95 V at 180 m A,
at the lowest operating temperature.
? Base resistance less than 100 W .
? Small variation in the current gain, h FE , (approximately
50 to 150) that indicates tight control of V BE
characteristics.
Transistors, such as 2N3904, 2N3906, or equivalents in
SOT ? 23 packages, are suitable devices to use.
Nulling Out Temperature Errors
As CPUs run faster, it is more difficult to avoid high
frequency clocks when routing the D+/D– traces around a
system board. Even when recommended layout guidelines
are followed, some temperature errors can still be
attributable to noise coupled onto the D+/D– lines. Constant
high frequency noise usually attenuates, or increases,
temperature measurements by a linear, constant value.
The ADT7476 has temperature offset registers (0x70 and
0x72) for the Remote 1 and Remote 2 temperature channels.
By doing a one-time calibration of the system, the user can
determine the offset caused by system board noise and null
it out using the offset registers. The offset registers
http://onsemi.com
17
相关PDF资料 |
PDF描述 |
|---|---|
| ADT7490ZEVB | BOARD EVALUATION FOR ADT7490 |
| ADZS-21262-1-EZEXT | BOARD DAUGHTER FOR ADSP-21262 |
| ADZS-BF-EZEXT-1 | BOARD DAUGHTER ADSP-BF533/561KIT |
| ADZS-BFAV-EZEXT | BOARD DAUGHT ADSP-BF533,37,61KIT |
| ADZS-BFSHUSB-EZEXT | BOARD DAUGHTER EZ EXTENDER |
相关代理商/技术参数 |
参数描述 |
|---|---|
| ADT7481 | 制造商:AD 制造商全称:Analog Devices 功能描述:Dual Channel Temperature Sensor and Over Temperature Alarm |
| ADT7481ARMZ | 功能描述:板上安装温度传感器 2 CH TEMP SNSR/ALARM 2 WIRE SMBUS INTRFCE RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| ADT7481ARMZ-001 | 功能描述:板上安装温度传感器 2 CH TEMP SNSR/ALARM 2 WIRE SMBUS INTRFCE RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| ADT7481ARMZ-1 | 功能描述:IC SENSOR TEMP 2CH ALARM 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热管理 系列:- 标准包装:1 系列:- 功能:温度监控系统（传感器） 传感器类型:内部和外部 感应温度:-40°C ~ 125°C，外部传感器 精确度:±2.5°C 本地（最大值），±5°C 远程（最大值） 拓扑:ADC，比较器，寄存器库 输出类型:2 线 SMBus? 输出警报:无 输出风扇:无 电源电压:2.7 V ~ 5.5 V 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:SOT-23-8 供应商设备封装:SOT-23-8 包装:Digi-Reel® 其它名称:296-22675-6 |
| ADT7481ARMZ-1R7 | 功能描述:板上安装温度传感器 2 CH TEMP SNSR/ALARM 2 WIRE SMBUS INTRFCE RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
发布紧急采购，3分钟左右您将得到回复。