Datasheet > ADT70*

ADT70*

更新时间： 2024-01-22 16:33:54

品牌	Logo	应用领域
其他 - ETC		控制器
页数	文件大小	规格书
14页	154K
描述
PRTD Conditioning Circuit and Temperature Controller

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中文翻译

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技术参数
数据手册

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ADT70* 技术参数

是否无铅：	含铅	是否Rohs认证：	不符合
生命周期：	Obsolete	包装说明：	SOIC-20
Reach Compliance Code：	not_compliant	ECCN代码：	EAR99
HTS代码：	8542.33.00.01	风险等级：	5.91
其他特性：	RAIL-TO-RAIL OUTPUT, TEMPERATURE COEFFICIENT +/- 15 PPM/DEG C	主体宽度：	7.5 mm
主体高度：	2.5 mm	主体长度或直径：	12.8 mm
外壳：	PLASTIC	JESD-609代码：	e0
安装特点：	THROUGH HOLE MOUNT	最大工作电流：	3 mA
最高工作温度：	125 °C	最低工作温度：	-40 °C
最大输出电压：	2.5 V	封装形状/形式：	RECTANGULAR
传感器/换能器类型：	TEMPERATURE SENSOR,ANALOG,VOLTAGE OUTPUT	最大供电电压：	5.5 V
最小供电电压：	4.5 V	表面贴装：	NO
端子面层：	Tin/Lead (Sn85Pb15)	端接类型：	SOLDER
Base Number Matches：	1

ADT70* 数据手册

ADT70

would contribute to the difference in voltage drop between the

RTD and the reference resistor. Thus, an error in reading the ac-

tual temperature could occur.

As shown above, this is a significant inaccuracy, especially for ap-

plications where the PRTD would be hundreds of feet away from

the ADT70. To reduce lead-wire error it is recommended to use

a larger sensitivity RTD; 1 kΩ instead of 100 Ω. Furthermore, in

the application circuit section, Figure 28 illustrates how to elimi-

nate such error by using the part’s general purpose op amp.

Table I. Copper Wire Gauge Size to Resistance Table.

Lead-wire AWG

Ohms/foot at +25ºC

Self-Heating Effect

Another contributor to measurement error is the self-heating ef-

fect on the RTD. As with any resistive element, power is dissi-

pated in an amount equal to the square of the excitation current

times the resistance of the element. The error contribution of the

heat generated by this power dissipation can easily be calculated.

For example, if the package thermal resistance is 50°C/W, the

RTD nominal resistance is 1 kΩ and the element is excited with a

1 mA current source, then the artificial increase in temperature

(∆ºC) as a result of self-heating is:

0.0016

0.0026

0.0041

0.0065

0.0103

0.0162

0.0257

0.0413

0.0651

0.1027

∆°C = I²R₀× θ_PACKAGE

From Table I the amount of lead-wire resistance effect in the

circuit can be estimated. For example, connect 100 feet of

AWG 22 wire to a 100 Ω Platinum RTD (PF element). The

lead-wire resistance will be: R = 100 ft 3 0.0162 Ω/ft = 1.62 Ω.

Thus the total resistance you have with the PRTD will be:

∆°C = 1mA ²×1000 Ω ×50°C /W

(

)

∆°C = 0.05°C

where:

_PACKAGE= thermal resistance of package

R₀= value of RTD resistance

␪

R_TOTAL=100 Ω +1.62 Ω =101.62 Ω

Since the 100 Ω reference resistor is assumed to be relatively close

to the ADT70, the lead-wire resistance is negligible. This shows

1.62 Ω of inaccuracy.

APPLICATION INFORMATION

As shown in Figure 27, using a 1 kΩ PRTD, 1 kΩ reference

resistor, 49.9 kΩ resistor between RG_A(Pin 11) and RG_B(Pin

12), and shorting BIAS (Pin 4) with V_REFOUT(Pin 3) together,

the output of OUT_IA(Pin 14) will have a transfer function of

From the PRTD’s data sheet, the PRTD’s sensitivity rating

(Ω/°C) can be used with the lead-wire resistance to approximate

the accuracy error in temperature degree (°C). Following the ex-

ample above, the sensitivity of the 100 Ω PRTD is 0.385 Ω/°C

(taken from PRTD data sheet). Hence the approximate error is:

V_OUT=1.299mV /Ω × ∆R ₍_{PRTD RESISTANCE − REFERENCE RESISTANCE}

)

Error =1.62 Ω/0.385Ω/°C = 4.21°C

assuming the reference resistor is constant at 100 Ω throughout

the temperature range.

+5V

50k⍀

POTENTIOMETER

IS USED TO

NULLA

NULLB

BIAS

2.5V

REFOUT

ACHIEVE HIGHER

PRECISION OF

MATCHING

ADT70

CURRENT.

OUT

OUTA

MATCHED

CURRENT

SOURCES

+IN

OUTB

INDEPENDENT

OP AMP

؊IN

2.5V

REF

؊IN

SHUTDOWN

INST

AMP

SHUT-

DOWN

+IN

1k⍀

REF

RESISTOR

1k⍀

PRTD

RGA

RGB GND OUT

AGND

؊V

DGND

SENSE

49.9k⍀

؊1V < ؊V < ؊5V

@ 5mV/؇C

OUT

Figure 27. Basic Operational Diagram

–9–

REV. 0

1...6 7 8910 11 12...14

中文翻译

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