- 您现在的位置：买卖IC网 > Sheet目录1194 > ADT7468ZEVB (ON Semiconductor)BOARD EVAL FOR ADT7468
ADT7468
produce a dc voltage proportional to ?V BE . The ADC digitizes
this voltage, and a temperature measurement is produced. To
reduce the effects of noise, digital filtering is performed by
averaging the results of 16 measurement cycles.
The results of remote temperature measurements are stored in
10-bit, twos complement format, as illustrated in Table 7. The
extra resolution for the temperature measurements is held in
the Extended Resolution Register 2 (Reg. 0x77). This gives
temperature readings with a resolution of 0.25°C.
Noise Filtering
For temperature sensors operating in noisy environments,
previous practice was to place a capacitor across the D+ and D?
pins to decrease the effects of noise. However, large capacitances
affect the accuracy of the temperature measurement, leading to a
recommended maximum capacitor value of 1000 pF. A capacitor
of this value reduces the noise, but does not eliminate it, making
use of the sensor difficult in a very noisy environment.
The ADT7468 has a major advantage over other devices for
eliminating the effects of noise on the external sensor. Using the
series resistance cancellation feature, a filter can be constructed
between the external temperature sensor and the part. The effect
typically, up to 3 k? of resistance. By using an advanced
temperature measurement method, this is transparent to the
user. This feature allows resistances to be added to the sensor
path to produce a filter, allowing the part to be used in noisy
environments. See the Noise Filtering section for details.
Factors Affecting Diode Accuracy
Remote Sensing Diode
The ADT7468 is designed to work with either 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 is connected to D?. If a
PNP transistor is used, the collector and base are connected to
D? and the emitter is connected to D+.
To reduce the error due to variations in both substrate and
discrete transistors, a number of factors should be taken into
consideration:
of any filter resistance seen in series with the remote sensor is
automatically canceled from the temperature result.
The construction of a filter allows the ADT7468 and the remote
temperature sensor to operate in noisy environments. Figure 24
shows a low-pass R-C-R filter, with the following values:
R = 100 ?, C = 1 nF.
This filtering reduces both common-mode noise and
differential noise.
100 ?
?
The ideality factor, n f , of the transistor is a measure of the
deviation of the thermal diode from ideal behavior. The
ADT7468 is trimmed for an n f value of 1.008. Use the
following equation to calculate the error introduced at a
temperature T (°C), when using a transistor whose n f does
not equal 1.008. See the processor data sheet for the
n f values.
? T = ( n f ? 1.008) × (273.15 K + T )
To correct for this error, the user can write the ?T value to
the offset register. The ADT7468 then automatically adds
REMOTE
D+
or subtracts it from the temperature measurement.
TEMPERATURE
SENSOR
100 ?
1nF
D–
?
Some CPU manufacturers specify the high and low current
levels of the substrate transistors. The high current level of
Figure 24. Filter Between Remote Sensor and ADT7468
Series Resistance Cancellation
Parasitic resistance to the ADT7468 D+ and D? inputs (seen in
series with the remote diode) is caused by a variety of factors,
including PCB track resistance and track length. This series
resistance appears as a temperature offset in the remote sensor’s
temperature measurement. This error typically causes a
0.5°C offset per ? of parasitic resistance in series with the
remote diode.
the ADT7468, I HIGH , is 96 μA and the low level current,
I LOW , is 6 μA. If the ADT7468 current levels do not match
the current levels specified by the CPU manufacturer, it
might be necessary to remove an offset. The CPU’s data
sheet should advise 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, the
algebraic sum of these offsets must be programmed to the
offset register.
The ADT7468 automatically cancels out the effect of this series
resistance on the temperature reading, giving a more accurate
result, without the need for user characterization of this
resistance. The ADT7468 is designed to automatically cancel,
If a discrete transistor is used with the ADT7468, the best
accuracy is obtained by choosing devices according to the
following criteria:
Rev. 3 | Page 19 of 81 | www.onsemi.com
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
ADT7473ZEVB
BOARD EVALUATION FOR ADT7473
ADT7475EBZEVB
BOARD EVALUATION FOR ADT7475
ADT7476EBZEVB
BOARD EVALUATION FOR ADT7476
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
ADT7470
制造商:AD 制造商全称:Analog Devices 功能描述:Temperature Sensor Hub and Fan Controller
ADT7470_13
制造商:AD 制造商全称:Analog Devices 功能描述:Temperature Sensor Hub and Fan Controller
ADT7470ARQ
制造商:Analog Devices 功能描述:Temp Sensor Digital Serial (I2C) 16-Pin QSOP
ADT7470ARQ-REEL
制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述:
ADT7470ARQ-REEL7
制造商:Analog Devices 功能描述:Temp Sensor Digital Serial (I2C) 16-Pin QSOP T/R
ADT7470ARQZ
功能描述:IC SENSOR TEMP FAN CTRLR 16QSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热管理 系列:- 标准包装:3,000 系列:- 功能:温度开关 传感器类型:内部 感应温度:85°C 分界点 精确度:±6°C（最小值） 拓扑:ADC（三角积分型），比较器，寄存器库 输出类型:开路漏极 输出警报:是 输出风扇:是 电源电压:2.7 V ~ 5.5 V 工作温度:-55°C ~ 125°C 安装类型:表面贴装 封装/外壳:SC-74A，SOT-753 供应商设备封装:SOT-23-5 包装:带卷 (TR) 其它名称:ADT6501SRJZP085RL7-ND
ADT7470ARQZ-REEL
功能描述:IC SENSOR TEMP FAN CTRLR 16QSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热管理 系列:- 标准包装:2,500 系列:SilentSense™ 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:-55°C ~ 125°C，外部传感器 精确度:±2°C 本地（最大），±3°C 远程（最大） 拓扑:ADC（三角积分型），比较器，寄存器库 输出类型:I²C?/SMBus? 输出警报:是 输出风扇:是 电源电压:2.7 V ~ 5.5 V 工作温度:-55°C ~ 125°C 安装类型:表面贴装 封装/外壳:8-TSSOP，8-MSOP（0.118"，3.00mm 宽） 供应商设备封装:8-MSOP 包装:带卷 (TR) 其它名称:MIC284-2BMMTRMIC284-2BMMTR-ND
ADT7470ARQZ-REEL7
功能描述:IC SENSOR TEMP FAN CTRLR 16QSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热管理 系列:- 标准包装:2,500 系列:SilentSense™ 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:-55°C ~ 125°C，外部传感器 精确度:±2°C 本地（最大），±3°C 远程（最大） 拓扑:ADC（三角积分型），比较器，寄存器库 输出类型:I²C?/SMBus? 输出警报:是 输出风扇:是 电源电压:2.7 V ~ 5.5 V 工作温度:-55°C ~ 125°C 安装类型:表面贴装 封装/外壳:8-TSSOP，8-MSOP（0.118"，3.00mm 宽） 供应商设备封装:8-MSOP 包装:带卷 (TR) 其它名称:MIC284-2BMMTRMIC284-2BMMTR-ND