LT6003 datasheet(20/30 Pages) AD

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LTC2066/LTC2067/LTC2068

Rev. B

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OUT

2066 F10

–

RFB

1.58M

RTD

100k

10k

100k

LT5400-3

GND

LT6656-2.048

11k

110k

0.1%

±2ppm/°C

10µF

VOUT SCALE 10mV/°C

1V AT 25°C ROOM TEMP

ISUPPLY = 43µA

VISHAY PTS SERIES

1k PtRTD, CLASS F0.3

PTS12061B1K00P100

www.vishay.com

0.1µF

2.6V ≤ VSUPPLY ≤ 18V +

–

OUT

LTC2066

131:1 VOLTAGE DIVIDER

Figure 10. RTD Sensor

APPLICATIONS INFORMATION

RTD Sensor

This low power platinum resistance temperature detector

(RTD) sensor circuit draws only 43μA total supply cur-

rent on a minimum 2.6V rail, and is accurate to within

±1°C at room temperature, including all error intrinsic

to the Vishay PTS Class F0.3 Variant RTD. It covers the

temperature range from –40°C to 85°C in 10mV/°C incre-

ments and produces an output of 1V at nominal room

temperature of 25°C.

The LTC2066’s extremely low typical offset of 1μV and

typical input bias current of 5pA allows for the use of a

very low excitation current in the RTD. Thus, self-heating

is negligible, improving accuracy.

The LT5400-3, B-grade, is used to provide a ±0.025%

matched resistor network that is effectively a precision

131:1 voltage divider. This precision divider forms one

half of a bridge circuit, with the 0.1% 110kΩ and RTD in

the other branch. Note that the 110kΩ’s precision require-

ment is to ensure matching with the RTD. The 11kΩ R2

serves to provide a DC offset for the entire bridge so

that the output is 1V at room temperature. Since bridge

imbalances can lead to error, it is recommended to mini-

mize the length of the leads connecting the RTD to reduce

additional lead resistance.

The LT6656-2.048 reference helps create a known excita-

tion current in the RTD at each temperature of operation,

and also acts as a supply for the LTC2066, all while using

less than 1μA itself. The LT6656 can accept input voltages

anywhere between 2.6V and 18V, allowing for flexibility

in selection of supply voltage while maintaining a fixed

output range. The LT6656 reference can easily source

the 43μA required to run the entire circuit, thanks to the

LTC2066’s 10μA maximum supply current and ability to

handle microvolt signals produced by the RTD under low

excitation current.

Care should be taken to minimize thermocouple effects by

preventing significant thermal gradients between the two

op amp inputs. It is also important to choose feedback

and series resistors that are low-tempco to minimize error

due to drift over the entire temperature range.

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