收藏本站
NCT65
REMOTE
100 W
Theory of Operation
The NCT65 is a remote trip point temperature sensor for
use in a vide variety of applications from smart phones to
embedded systems. The remote temperature is measured by
the NCT65 and then compared with a fixed limit set by the
internal device reference. The limit for the THERM1 pin is
70 ? C and the limit for the THERM2 pin is 85 ? C. If either the
remote temperature exceeds the defined limits the open
drain THERM pins are asserted low. Each THERM pin self
clears when the temperature drops 5 ? C below the THERM
limit. This is to prevent THERM jitter, where the
temperature hovers around the THERM limit.
THERM2 = 85
Hyst = 5
THERM1 = 70
Hyst = 5
Time
THERM2
THERM1
Figure 2. Trippoints
Measurement Method
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, or the
base-emitter voltage of a transistor, operated at constant
current. Unfortunately, this technique requires calibration to
null out the effect of the absolute value of V BE , which varies
from device to device.
The technique used in the NCT65 is to measure the change
in V BE when the device is operated at three different
currents.
This is given by:
q
D V BE + (n f ) kT In(N) (eq. 1)
Where:
k is Boltzmann’s constant (1.38 ? 10 –23 ).
q is the charge on the electron (1.6 ? 10 –19 Coulombs).
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
n f is the ideality factor of the thermal diode.
The NCT65 is trimmed for an ideality factor of 1.008.
To prevent ground noise 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. If the sensor is operating in a
noisy environment an optional filter can be added. Its value
should be no more than 1,000 pF. See the Layout
Considerations section for more information on C1.
To measure D V BE , the operating current through the
sensor is switched among three related currents.
N1 ? I and N2 ? I are different multiples of the current, I.
The currents through the temperature diode are switched
between I and N1 ? I, giving D V BE1 ; and then between I and
N2 ? I, giving D V BE2 . The temperature is then calculated
using the two D V BE measurements. This method also
cancels the effect of any series resistance on the temperature
measurement. The resulting waveform is passed through a
65 kHz low-pass filter to remove noise, and then to a
chopper-stabilized amplifier that performs the functions of
amplification and rectification of the waveform to produce
a dc voltage proportional to D V BE . This voltage is input into
two comparators with a reference voltage. If the voltage
exceeds the reference voltage then the THERM output
asserts low.
Applications Information
Noise Filtering
For temperature sensors operating in noisy environments,
the industry standard practice was to place a capacitor across
the D+ and D ? pins 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. Although this
capacitor reduces the noise, it does not eliminate it, making
it difficult to use the sensor in a very noisy environment.
The NCT65 has a major advantage over other devices
when it comes to eliminating the effects of noise on the
external sensor. The series resistance cancellation feature
allows a filter to be constructed between the external
temperature sensor and the part. The effect of any filter
resistance seen in series with the remote sensor is
automatically cancelled from the temperature result.
The construction of a filter allows the NCT65 and the
remote temperature sensor to operate in noisy environments.
The figure below shows a low-pass R-C-R filter, where
R = 100 W and C = 1 nF. This filtering reduces both
common-mode and differential noise.
100 W
D+
TEMPERATURE 1 nF
SENSOR
D ?
Figure 3. Filter between Remote Sensor and Factors
Affecting Diode Accuracy
http://onsemi.com
4
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
相关PDF资料
NCV8440STT1G MOSFET N CH 2.6A 59V SOT-223-4
NDB5060L MOSFET N-CH 60V 26A D2PAK
NDB6060 MOSFET N-CH 60V 48A TO-263AB
NDB7060 MOSFET N-CH 60V 75A D2PAK
NDC7001C MOSFET N+P 60V 340MA SSOT6
NDC7002N_SB9G007 MOSFET N-CH DUAL 50V 6-SSOT
NDC7003P MOSFET 2P-CH 60V 340MA SSOT6
NDD03N50ZT4G MOSFET N-CH 500V 2.6A DPAK
相关代理商/技术参数
NCT6627UD 制造商:Nuvoton Technology Corp 功能描述:IC LPC SUPER I/O 128LQFP
NCT675 制造商:New Concept Tools 功能描述:TOOLS, DRILL BITS; Kit Contents:31 Pieces of 5 Straight, 4 Phillips, 4 Pozidrive, 10 Hex, & 10 Torx Bits ;RoHS Compliant: NA
NCT6776D 制造商:Nuvoton Technology Corp 功能描述:IC LPC SUPER I/O 128LQFP
NCT6776F 制造商:Nuvoton Technology Corp 功能描述:LPC SUPER I/O, PECI 3.0, SST*, 制造商:Nuvoton Technology 功能描述:LPC SUPER I/O, PECI 3.0, SST*,
NCT6779D 制造商:Nuvoton Technology Corp 功能描述:NEW 128-PIN SIO, BASICALLY PIN
NCT72CMNR2G 功能描述:板上安装温度传感器 REMOTE THERMAL SENSOR 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
NCT72CMTR2G 功能描述:板上安装温度传感器 REMOTE THERMAL SENSOR 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
NCT72DMNR2G 功能描述:板上安装温度传感器 DIGTEMPSEN2WIREINTF 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