8.3.1 Spectral Responsivity

The TMP006 and TMP006B are optimized to sense IR radiation emitted by objects from approximately 250 K (–23°C) to 400 K (127°C), with maximum sensitivity from approximately 4 µm to 16 µm. The relative spectral response of the TMP006 and TMP006B is shown in Figure 6.

Figure 6. Relative Spectral Response vs Wavelength

8.3.2 Field of View and Angular Response

The TMP006 and TMP006B sense all radiation within a defined field of view (FOV). The FOV (or full-angle of θ) is defined as 2Φ. These devices contain no optical elements, and thus sense all radiation within the hemisphere to the front of the device. Figure 3 shows the angular dependence of the sensor response and the relative power for a circular object that subtends a half angle of phi (Φ). Figure 7 defines the angle Φ in terms of object diameter and distance. Figure 7 assumes that the object is well approximated as a plane that is perpendicular to the sensor axis.

Figure 7. FOV Geometry Definition

In this case, the maximum contribution is from the portion of the object directly in front of the TMP006 or TMP006B (Φ = 0); with the sensitivity per solid angle, dR/dΦ decreases as Φ increases. Approximately 50% of the energy sensed by the TMP006 and TMP006B is within a FOV (θ) = 90°.

This discussion is for illustrative purposes only; in practice the angular response (dR/dΦ) of the TMP006 and TMP006B to the object is affected by the object orientation, the number of objects, and the precise placement relative to the TMP006 or TMP006B. Figure 8 shows the thermopile sensor dimensions.

NOTE: Thermopile sensor is centered in the device.

Figure 8. Thermopile Sensor Dimensions

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, T_hot, and the cold junction, T_cold.

Figure 9. Principle of Thermopile Operation

The cold junction is thermally grounded to the die, and is effectively T_DIE, the die temperature. In thermal equilibrium, the hot junction is determined by the object temperature, T_OBJ. The energy emitted by the object, E_OBJ, minus the energy radiated by the die, E_DIE, determines the temperature of the hot junction. The output voltage, V_OUT, is therefore determined by the relationship shown in Equation 2:

Equation 2.

where

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

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 T_DIE. Estimate T_OBJ by using V_SENSOR and T_DIE. For each 250-ms conversion cycle, the TMP006 and TMP006B measure a value for V_SENSOR and for T_DIE, which are then placed in their respective registers.

For each conversion cycle, the device generates an analog-to-digital converter (ADC) value for T_DIE and V_SENSOR. Bits CR2 to CR0 determine the number of T_DIE 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, T_DIE, result is updated at the end of the Nth ADC conversion with the value shown in Equation 3:

Equation 3.

Similarly, the sensor voltage result is updated at the end of the Nth sensor ADC conversion with the value shown in Equation 4:

Equation 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 T_OBJ are described in the next section.

8.3.4 Object Temperature Calculation

The TMP006 and TMP006B generate a sensor voltage, V_Sensor, in register 00h that is representative of the energy radiated by the object. In an ideal situation, the Stefan-Boltzman law relates the energy radiated by an object to its temperature by the relationship shown in Equation 5:

Equation 5.

where

• σ = Stefan-Boltzman constant = 5.7 × 10^-12 W/cm²/K⁴
• ε = Emissivity, 0 < ε < 1, an object dependent factor, ε = 1 for a perfect black body

A similar relationship holds for the sensing element itself that radiates heat at a rate determined by T_DIE. The net energy absorbed by the sensor is then given by the energy absorbed from the object minus the energy radiated by the sensor, as shown in Equation 6:

Equation 6.

In an ideal situation, the sensor voltage relates to object temperature as shown in Equation 7:

Equation 7.

Equation 8.

where

• S is a system-dependent parameter incorporating the object emissivity (ε), FOV, and sensor characteristics. The parameters S0, A1, and A2 are used in determining S.
• f(V_OBJ) is a function that compensates for heat flow other than radiation, such as convection and conduction, from nearby objects. The parameters B0, B1, and B2 are used to tune this function to a particular system and environment.

The coefficients affect object temperature measurement as described in Table 1.

8.3.5 Calibration

The TMP006 and TMP006B default coefficients are calibrated with a black body of emissivity, ε = 0.95, and an FOV (θ) = 110°. Use these coefficients for applications where the object emissivity and geometry satisfy these conditions. For applications with different object emissivity or geometry, calibrate the TMP006 or TMP006B to accurately reflect the object temperature and system geometry. Accuracy is affected by device-to-device or object-to-object variation. For the most demanding applications, calibrate each device individually.

As an overview the calibration procedure includes:

1. Defining the environmental variation range (die and object temperature range, supply voltage, temperature change speed, sampling rate and so on).
2. Making the die temperature measurements and IR sensor voltage measurements over the environmental range.
3. Generate an optimal set of coefficients based on the collected data set.

The best temperature precision is available if every device is calibrated individually. Alternatively, if all the units in the application use the same coefficients, then calibrate a statistically significant number of devices.

Recalibration may be required under any or all of the following conditions:

1. Board layout is changed.
2. Object or objects in the field of view changed.
3. Object distance changed.
4. Angle between device surface and direction to the object changed.
5. Object and local temperature range changed outside the environmental calibration range.
6. Object and local temperature transients significantly changed.
7. Supply voltage changed more than 1 V.
8. Air convection or conduction near the device.

For further information and methods for calibration, refer to user guide SBOU142, TMP007 Calibration Guide

8.3.6 Sensor Voltage Format

The TMP006 and TMP006B provide 16 bits of data in binary twos complement format. The positive full-scale input produces an output code of 7FFFh and the negative full-scale input produces an output code of 8000h. The output clips at these codes for signals that exceed full-scale. Table 2 summarizes the ideal output codes for different input signals. Figure 10 illustrates code transitions versus input voltage. Full-scale is a 5.12-mV signal. The LSB size is 156.25 nV.

Figure 10. Code Transition Diagram

8.3.7 Temperature Format

The temperature register data format of the TMP006 and TMP006B is reported in a binary twos complement signed integer format, as Table 3 shows, with 1 LSB = 1 / 32°C = 0.03125.

Converting the integer temperature result of the TMP006 and TMP006B to physical temperature is done by right-shifting the last two LSBs followed by a divide-by-32 of T_DIE to obtain the physical temperature result in degrees Celsius. T_DIE is the 14-bit signed integer contained in the corresponding register. The sign of the temperature is the same as the sign of the integer read from the TMP006 and TMP006B. In twos complement notation, the MSB is the sign bit. If the MSB is 1, the integer is negative and the absolute value can be obtained by inverting all bits and adding 1. An alternative method of calculating the absolute value of negative integers is abs(i) = i xor FFFFh + 1.

8.3.8 Serial Interface

The TMP006 and TMP006B initially start up with typical settings consisting of a conversion rate of one conversion per second (as specified in the Electrical Characteristics). The internal structure of the digital interface is shown in Figure 11.

Figure 11. Internal Structure

The TMP006 and TMP006B operate only as a slave device on the two-wire bus. Connections to either bus are made via the open-drain I/O lines, SDA, and SCL. The SDA and SCL pins feature integrated spike-suppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. The TMP006 and TMP006B support the transmission protocol for fast (1 kHz to 400 kHz) and high-speed (1 kHz to 3.4 MHz) modes. All data bytes are transmitted MSB first.

8.3.8.3 Two-Wire Timing Diagrams

The TMP006 and TMP006B use a two-wire interface (I²C and SMBus-compatible). Figure 12 and Figure 13 illustrate the timing for the various operations on the TMP006 and TMP006B. Parameters for Figure 12 are defined in Table 5. Bus definitions are given below.

Table 5. Two-Wire Timing Diagram Definitions

PARAMETER	TEST CONDITIONS	FAST MODE		HIGH-SPEED MODE		UNIT
		MIN	MAX	MIN	MAX
fSCL	SCL operating frequency, VS > 1.7 V	0.001	0.4	0.001	3.4	MHz
fSCL	SCL operating frequency, VS < 1.7 V	0.001	0.4	0.001	2.75	MHz
tBUF	Bus free time between STOP and START condition	600		160		ns
tHDSTA	Hold time after repeated START condition. After this period, the first clock is generated.	100		100		ns
tSUSTA	Repeated START condition setup time	100		100		ns
tSUSTO	STOP condition setup time	100		100		ns
tHDDAT	Data hold time	0(1)		0(2)		ns
tSUDAT	Data setup time	100		10		ns
tLOW	SCL clock low period, VS > 1.7 V	1300		160		ns
tLOW	SCL clock low period, VS < 1.7 V	1300		200		ns
tHIGH	SCL clock high period	600		60		ns
tF	Clock/data fall time		300			ns
tR	Clock/data rise time		300		160	ns
tR	Clock/data rise time for SCLK ≤ 100 kHz		1000			ns

(1) For cases with fall time of SCL less than 20 ns and/or the rise or fall time of SDA less than 20 ns, the hold time should be greater than 20 ns.

(2) For cases with a fall time of SCL less than 10 ns and/or the rise or fall time of SDA less than 10 ns, the hold time should be greater than 10 ns.

Bus Idle: Both SDA and SCL lines remain high.

Start Data Transfer: A change in the state of the SDA line from high to low while the SCL line is high defines a START condition. Each data transfer is initiated with a START condition.

Stop Data Transfer: A change in the state of the SDA line from low to high while the SCL line is high defines a STOP condition. Each data transfer terminates with a STOP or a repeated START condition.

Data Transfer: The number of data bytes transferred between a START and a STOP condition is not limited and is determined by the master device. The receiver acknowledges the transfer of data.

Acknowledge: Each receiving device, when addressed, is obliged to generate an Acknowledge bit. A device that acknowledges must pull down the SDA line during the Acknowledge clock pulse in such a way that the SDA line is stable low during the high period of the Acknowledge clock pulse. Setup and hold times must be taken into account. On a master receive, data transfer termination can be signaled by the master generating a Not-Acknowledge on the last byte that has been transmitted by the slave.

In order for the two-wire bus to operate at frequencies above 400 kHz, the master device must issue a High-speed mode (Hs-mode) master code (0000100X) as the first byte after a START condition to switch the bus to high-speed operation. The TMP006 and TMP006B do not acknowledge this byte, but switch the input filters on SDA and SCL and the output filter on SDA to operate in Hs-mode, allowing transfers at up to 3.4 MHz. After the Hs-mode master code has been issued, the master transmits a two-wire slave address to initiate a data transfer operation. The bus continues to operate in Hs-mode until a STOP condition occurs on the bus. Upon receiving the STOP condition, the TMP006 and TMP006B switch the input and output filter back to fast-mode operation.

1.

NOINDENT:

Slave address 1000000 shown. Slave address changes for the TMP006 and TMP006B depend on the ADR1 and ADR0 pin connection. See Table 4 for more details.

Figure 12. Two-Wire Timing Diagram For Write Word Format

1.

NOINDENT:

Slave address 1000000 shown.

2.

NOINDENT:

Master must leave SDA high to terminate a two-byte read operation.

Figure 13. Two-Wire Timing Diagram For Two-Byte Read Format

Table 6. Register Map

8.5.1 Sensor Voltage Result (V_SENSOR) Register (address = 00h) [reset = 0000000000000000]

The sensor voltage register is a 16-bit result register in binary twos complement format. One least significant bit (LSB) is 156.25 nV. The full-scale value is a ±5.12 mV signal. Data from this register (Figure 14) are used in conjunction with data from the Temperature register to calculate the object temperature. Figure 14 summarizes the Sensor Voltage register. The equation for the resultant object temperature is discussed in the TMP006 User Guide (SBOU107).

8.5.2 Temperature (T_DIE) Register (address = 01h) [reset = 0000000000000000]

The temperature register of the TMP006 and TMP006B is configured as a 14-bit, read-only register (as shown in Figure 15) that stores the result of the most recent conversion for the die temperature, T_DIE. Following power-up or a software reset, the Temperature Register reads 0°C (0000h) until the first conversion is complete.

8.5.3 Configuration Register (address = 02h) [reset = 0111010000000000]

Figure 16 describes the configuration register. This register determines the operational modes, conversion rate, DRDY control, initiates a single conversion, performs a software reset, or puts the device into shutdown mode. This register is read/write, and the pointer address is 02h.

8.5.4 Manufacturer and Device ID Registers

The TMP006 and TMP006B have two identification registers: manufacturer ID (address FEh) shown in Figure 17, and device ID (address FFh) shown in Figure 18. The manufacturer ID reads 5449h and the device ID is 0067h.