TMP05/06 Temperature Sensor and Its Application

Abstract: This paper introduces the working principle and performance characteristics of TMP05/TMP06 temperature sensors , and gives its application examples. Keywords: digital temperature sensor; microcontroller; pulse width modulation; daisy chain mode 1 Working principle of TMP05/06 1.1 Internal structure and pin function The internal structure block diagram of TMP05/06 is shown in Figure 1.

Pin functions: (1) OUT digital output terminal, pulse width modulation PWM output is a square wave signal with a certain relationship with temperature; (2) CONV/IN digital input terminal, in single conversion mode and continuous conversion mode, the three input states of this pin determine the conversion ratio during temperature measurement; in daisy chain mode, it is connected to the PWM output terminal of the previous TMP05/06 as an input pin; (3) FUNC digital input terminal, by setting its high, low, and floating states to select different working modes; (4) VDD positive power supply voltage 3V~5.5V; (5) GND analog and digital ground. 1.2 Temperature measurement principle The working principle of TMP05/06 is to convert the analog quantity of the measured temperature into a digital quantity and encode the digital signal into the form of time ratio (TH/TL). TH and TL are continuous in time, and the ratio of the two can be obtained using the same clock. Therefore, the temperature signal is related to the time ratio. The output of TMP05/06 is a square wave signal. At 25℃, the period of the output square wave is 116ms (typical value, CONV/IN pin is floating). The duration of the high level TH is fixed, while the duration of the low level varies with the temperature. When the CONV/IN pin is set to low or floating, the temperature can be calculated by formula (1): t(℃)=421-751TH/TL(1) If it is set to high level, it is calculated by formula (2): t(℃)=421-93.875TH/TL(2) Among them, the values ​​of TH and TL can be easily read through the timing/counting port of the microprocessor, and then the above algorithm can be implemented by programming to obtain the measured temperature value. 1.3 Performance characteristics The accuracy is ±1℃ in the temperature range of 0℃～70℃, and ±0.5℃ at 25℃; The operating range is -40℃～+150℃; 3V～5.5V single power supply; The maximum power consumption is 70μW under 3.3V power supply; Ultra-small package (SC70 and SOT23 package forms), low power consumption. 2 TMP05/06 working mode TMP05/06 has three working modes. The user can select the appropriate working mode according to the state of the FUNC pin as needed (Table 1).

2.1 Single conversion mode

In single conversion mode, when the microcontroller sends a request, TMP05/06 outputs a square wave signal related to the temperature. The microcontroller first sets the OUT pin to a low level and then releases it, indicating a request for output; when the OUT pin is released, the temperature measurement results TH and TL are output (as shown in Figure 2).

In this mode, the internal resistor is switched into the circuit and the OUT pin of the TMP05 is configured as a push-pull output. This resistor protects the TMP05 from short-circuit current when the microcontroller pulls the OUT pin low to start temperature conversion.

2.2 Continuous Conversion Mode

In continuous conversion mode, the TMP05/06 continuously outputs a square wave signal. The frequency of the square wave is determined by setting the state of the CONV/IN pin. And after power-on, any changes to the CONV/IN pin will not affect the original setting.

2.3 Daisy Chain Operation Mode

By setting the FUNC pin to a high state, multiple TMP05/06s on a printed circuit board can be connected in daisy chain operation mode. Therefore, the microcontroller is allowed to use a dedicated input line to receive all temperature measurements (as shown in Figure 3).

In this working mode, FUNC is configured as a high level, and the CONV/IN pin is used as the input of the daisy chain. It converts at a standard ratio when measuring temperature, so the measured temperature is calculated according to formula (1). Another line of the microcontroller is used to generate a start pulse with a pulse width of less than 25μs to start the first TMP05/06 to convert and output the measurement result. The output of this TMP05/06 provides a start pulse for the next one. Figure 4 shows the waveforms of the start signal and the output signal on the daisy chain respectively.

When the start pulse does not reach the TMP05/06, this component acts as a buffer for the previous temperature measurement. Once the start signal is detected, the conversion is started immediately and the result is output, so the start pulse is provided for the next TMP05/06, and the cycle is repeated. The final output result is shown in Figure 4c. The CONV/IN pin of the first TMP05/06 must be kept low until the last piece outputs the start pulse, and then set high. This is the entire process of the daisy chain working mode.

3 Application of TMP05/06

TMP05/06 can be ideally used as a temperature monitor in various portable electronic devices due to its high-precision measurement results and ultra-small package. For example, it can be used to monitor the temperature of high-speed MCU chips in electronic devices, which is more suitable for surface-mounted chips (install TMP05/06 under the MCU chip and as close to the chip as possible to measure the surface temperature of the chip). Its unique daisy chain working mode can easily connect multiple integrated circuit temperature sensors, simplifying the design of hardware circuits.

TMP05/06 is a single-wire PWM output, which can be easily connected to the microcontroller with only a single line, so the hardware circuit design is relatively simple (as shown in Figure 5).

After TMP05/06 is equipped with a single-chip microcomputer, it is easy to use the counter in the single-chip microcomputer to measure the values ​​of TH and TL respectively, and then program to calculate the temperature value. The specific steps are as follows (TMP05/06 is configured in single-shot conversion mode):

(1) Counters 0 and 1 are initialized;
(2) 80C51 sends a request signal, that is, pulls the OUT pin to a low level and then releases it;
(3) When the OUT pin is released, P1.0 inputs a high level, counter 0 starts working, and counts TH;
(4) When P1.0 becomes low, counter 0 stops, counter 1 starts, and counts TL;
(5) Calculate the temperature value according to the above formula;
(6) Display the temperature. If it exceeds the limit, an alarm will be issued or the cooling device will be started.

References
[1] American AD Company Product Information [Z]. 2003.
[2] Sha Zhanyou, et al. Principles and Applications of Intelligent Integrated Temperature Sensors [M]. Beijing: Machinery Industry Press, 2002