6

O

6

(1.8639

V

2.1962 10

3.88 10

)

T

1481.96





u

u







GND

NC

VO

V

+

LMT89

+2.4V to +5.5V

To MCU ADC

LMT89

www.ti.com

SNIS176A – MARCH 2013 – REVISED JANUARY 2015

NOTE

Either placement of resistor, as shown in Figure 2 and Figure 3, is just as effective.

8.2 Typical Applications

8.2.1 Full-Range Centigrade Temperature Sensor

Figure 4. Full-Range Celsius (Centigrade) Temperature Sensor (

−55°C to 130°C) Operating from a Single

Li-Ion Battery Cell

8.2.1.1 Design Requirements

Design requirements related to layout are also important because the LMT89 device is a simple temperature

sensor that provides an analog output, refer to Layout for a detailed description.

8.2.1.2 Detailed Design Procedure

The LMT89 device output is shown in Equation 4.

VO = (−3.88 × 10

−6 × T2) + (−1.15 × 10−2 × T) + 1.8639

(4)

Solve for T as shown in Equation 5:

where

•

T is temperature, and VO is the measured output voltage of the LMT89 device. Equation 5 is the most accurate

equation that can be used to calculate the temperature of the LMT89 device.

(5)

An alternative to the quadratic equation a second order transfer function can be determined using the least

squares method shown in Equation 6.

T = (

−2.3654 × VO

2) + (−78.154 × V

O ) + 153.857

where

•

T is temperature express in °C and VO is the output voltage expressed in volts.

(6)

A linear transfer function can be used over a limited temperature range by calculating a slope and offset that give

best results over that range. A linear transfer function can be calculated from the parabolic transfer function of

the LMT89 device. The slope of the linear transfer function can be calculated using Equation 7.

m =

−7.76 × 10

−6× T − 0.0115,

where

•

T is the middle of the temperature range of interest and m is in V/°C. For example for the temperature range of

TMIN = −30 to TMAX = 100°C

(7)

T = 35°C

(8)

and

m =

−11.77 mV/°C

(9)

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