TMP006 datasheet(11/38 Pages) TI1

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SENSOR

X 1

Sensor Conversion

DIE

X 1

Local Temp Conversion

OUT

SENSOR

HOT

COLD

OBJ

DIE

C (T

)

Thermopile

Heat Absorbor

Cold Junction

Thot

Tcold

Thot

EHOT ß TDIE

EOBJ ß TOBJ

TMP006, TMP006B

www.ti.com

SBOS518E – MAY 2011 – REVISED APRIL 2015

Feature Description (continued)

8.3.3 Thermopile Principles and Operation

The TMP006 and TMP006B sense radiation by absorbing the radiation on a hot junction. The thermopile then

generates a voltage proportional to the temperature difference between the hot junction, Thot, and the cold

junction, Tcold.

Figure 9. Principle of Thermopile Operation

The cold junction is thermally grounded to the die, and is effectively TDIE, the die temperature. In thermal

equilibrium, the hot junction is determined by the object temperature, TOBJ. The energy emitted by the object,

EOBJ, minus the energy radiated by the die, EDIE, determines the temperature of the hot junction. The output

voltage, VOUT, is therefore determined by the relationship shown in Equation 2:

where

•

C is a constant depending on the design of the sensing element.

(2)

Note that the sensor voltage is related to both the object temperature and the die temperature. A fundamental

characteristic of all thermopiles is that they measure temperature differentials, not absolute temperatures. The

TMP006 and TMP006B contain a highly-accurate, internal temperature sensing element to measure TDIE.

Estimate TOBJ by using VSENSOR and TDIE. For each 250-ms conversion cycle, the TMP006 and TMP006B

measure a value for VSENSOR and for TDIE, which are then placed in their respective registers.

For each conversion cycle, the device generates an analog-to-digital converter (ADC) value for TDIE and VSENSOR.

Bits CR2 to CR0 determine the number of TDIE and sensor ADC results to average before they are loaded into

the respective registers for readout.

After power-on reset (POR), the TMP006 and TMP006B start in four conversions per second (CR[2:0] = 010). In

general, for a mode with N conversions, the local temperature, TDIE, result is updated at the end of the Nth ADC

conversion with the value shown in Equation 3:

(3)

Similarly, the sensor voltage result is updated at the end of the Nth sensor ADC conversion with the value shown

in Equation 4:

(4)

The total conversion time and averages per conversion can be optimized to select the best combination of

update rate versus noise for an application. Additionally, low-power conversion mode is available. In CR settings

101, 110, and 111, the device inserts a standby time before the beginning of the next conversion or conversions.

The method and requirements for estimating TOBJ are described in the next section.

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