“There are many types of temperature sensors and their applications are extremely wide. There are one to several temperature sensors in automobiles, consumer electronics, household appliances and other products that we need every day. Compared with other types of sensors, temperature sensors are the first to appear. Various temperature sensors such as thermocouple sensors, RTD platinum resistance and integrated semiconductor temperature sensors have appeared one after another. With the development of technology, new types of temperature sensors are still emerging.
There are many types of temperature sensors and their applications are extremely wide. There are one to several temperature sensors in automobiles, consumer electronics, household appliances and other products that we need every day. Compared with other types of sensors, temperature sensors are the first to appear. Various temperature sensors such as thermocouple sensors, RTD platinum resistance and integrated semiconductor temperature sensors have appeared one after another. With the development of technology, new types of temperature sensors are still emerging.
What this article is going to introduce is a new type of temperature sensor-Nanocore Microelectronics D-NTC? series of high-precision two-pin digital pulse output temperature sensor chip NST1001. Here will introduce its product features and application circuits, so that everyone can fully understand this revolutionary digital temperature measurement product.
Comparison of commonly used temperature measurement solutions
Temperature sensors are widely used, ranging from temperature transmitters in industrial process control to small household Electronic thermometers that require temperature sensors to achieve temperature detection, but in these application scenarios, the temperature measurement scheme used Is different.
According to the principle of temperature measurement, the temperature measurement program mainly includes the following categories:
Platinum resistance RTD
CMOS temperature sensor
Figure 1: Different types of temperature measurement solutions
The thermocouple has the widest temperature range, up to -200°C to 2000°C, and requires an external reference terminal when used, which is more complicated. The platinum resistance RTD has high precision and a wide range, but the cost is high and the peripheral circuit is complicated. NTC thermistor has low cost, but its accuracy is limited, and it has the characteristics of large temperature coefficient and nonlinear output. CMOS temperature sensor is also called IC temperature sensor, including two types of analog output and digital output. Compared with the above three temperature sensors, the CMOS temperature sensor has very high linearity, low system cost, high function integration, simple peripherals, and can support digital output. The main disadvantage is that the temperature measurement range is generally concentrated in -40℃~125 ℃, more limited.
Use a chart to compare, more intuitive:
Table 1: Comparison of several common temperature measurement schemes
Through the above comparison, everyone has already understood the differences of several temperature measurement solutions, and these differences also determine different application scenarios. The thermocouple and RTD solutions have a wide temperature measurement range and are complicated to use, so they are basically limited to industrial applications. The thermistor NTC has a wide range of applications due to its low cost and relatively easy-to-use advantages, such as water temperature, oil temperature, engine intake temperature, cylinder temperature to exhaust temperature in automobiles, air conditioners in household appliances and small appliances, refrigerators, rice cookers And so on, these are the main battlefields of NTC. The ambient temperature measurement, water temperature probes, and electronic thermometers in IoT applications also use NTC-based temperature measurement solutions.
In the past, CMOS digital temperature sensors mainly existed in the form of ICs, using standard IC SOP8-pin packages, and used for board-level temperature measurement in electronic products, such as hard disks and motherboards. The output signal is mainly I2C interface, and some of them use analog voltage output. With the development of Moore’s Law, the performance of digital temperature sensors based on CMOS technology is getting better and better, and the cost is getting lower and lower.
Why NST1001 is a revolutionary temperature sensor product
Through the above description, it can be found that NTC is the most widely used, but essentially as a resistor, the grassroots properties of passive devices also bring its inherent shortcomings. The accuracy mainly depends on the production process and sorting, and there is no internal circuit. There is no calibration capability, and it relies on external reference resistor divider detection when used. The traditional CMOS digital temperature sensor is more like a standard IC. The SOP8 package size used is also larger, the response time is longer, and there are many pins, so it cannot be directly replaced with NTC.
Nanocore Microelectronics D-NTC? series NST1001 products combine the advantages of both the thermistor and CMOS digital temperature sensor, combined with Nanocore’s solid mixed-signal chain IC design capabilities and innovative patented technology, to measure traditional NTC temperature The market has brought about a whole new revolution. NST1001 itself is an IC with a complete internal power supply circuit, digital circuit, analog circuit, and data processing and storage capabilities. It has a 100% factory-calibrated temperature accuracy guarantee, and uses a minimalist 2-pin package with peripheral circuits. It is also directly compatible with NTC, and the reference resistor supports pull-up and pull-down.
NST1001 offers two packages, TO-92S and DFN2L. The former is convenient for the second package of the probe, and the latter has a very fast response time of 0.12S and a shape compatible with 0603 chip resistors, which is more suitable for fast response temperature measurement applications and board-level measurements. Wen scene.
Figure 1: Comparison of the size of NST1001 (DFN2L package) and 1 yuan coin
Features of NST1001
Two-pin simplifies temperature measurement without additional components
Two-pin connection, saving wiring resources
Wide temperature range C50°C to 150°C
High resolution, up to 0.0625℃
Maintain high accuracy in the full temperature range
-20℃ ~ 85℃: 0.5℃ (maximum)
-50℃ ~ -20 ℃: 0.75 ℃ (maximum)
+85℃ ~ 150 ℃: 0.75 ℃ (maximum)
Pulse number type digital output, without AD conversion interface
Single temperature conversion time 50ms
Working current is only 30uA during conversion, zero standby power consumption
Wide power supply range, 1.65V to 5.5V
TO-92s(4mm x 3mm)
DFN2L (1.6mm x 0.8mm)
NST1001 pin definition and function description
Figure 2: NST1001 package outline and pin definition
Table 2: NST1001 pin function description
NST1001 typical application circuit
The biggest advantage of D-NTC? is simple to use. NST1001 supports two connection methods of pull-up and pull-down resistors, which is easy to use. Next, we will introduce in detail:
Pull-up resistor connection and output waveform:
Figure 3: Schematic diagram of NST1001 pull-up resistor connection application circuit
Figure 3 is a typical application connection diagram of the pull-up connection of NST1001. The pull-up resistor R1 can be directly connected to the VDD of the MCU, or it can supply power to the NST1001 through a separate GPIO (GPIO1 in the figure), so that the power supply can be turned off when not in use to save power consumption. Some MCU GPIOs come with configurable pull-up resistors, which can also replace the external resistor R1. In some applications, in order to improve the ability to resist external interference, a capacitor C1 can be added near the NST1001. See below for the value of C1. Figure 4 is a typical DQ output waveform in the pull-up resistor connection mode.
Figure 4: NST1001 pull-up resistor DQ pulse waveform
Pull-down resistor connection and output waveform:
Figure 5: Schematic diagram of NST1001 pull-down resistor connection application circuit
Figure 5 is a typical application connection diagram of the pull-down resistor connection of NST1001, which is similar to the common NTC temperature acquisition scheme. The corresponding output waveform is shown in Figure 6. ????????????????? jQuery18302645242388558837_1551665054558
Figure 6: NST1001 pull-down resistance pulse test waveform
The values of R1 and C1 in a typical circuit
Next, expand to introduce the values of R1 and C1 in a typical circuit:
The pull-up or pull-down resistor R1 can be selected from 500 ohm to 10k ohm. The specific value needs to be a compromise between the lowest operating voltage, power consumption and transmission distance. Since the NST1001 has a maximum current of 45uA during temperature conversion, the smaller the R1, the smaller the voltage drop on it, and the higher the power supply voltage for the chip. The minimum value of VDD can be estimated with the following formula:
On the other hand, the power consumption during temperature data transmission increases as the resistance decreases. Therefore, in order to minimize power consumption, it is necessary to use a larger resistance as much as possible. In some cases where long-distance transmission is required, considering the influence of parasitic capacitance on data transmission, in order to ensure that the temperature pulse signal can be sent out normally, the resistance R1 cannot be too large.
Figure 7 DQ pulse waveform in pull-up mode
As shown in Figure 7, in the pull-up mode, since the switch resistance of the DQ pin is only about 50ohm, the output pull-down speed is generally faster. The transmission capacity is mainly limited by the output pull-up from low to 95 when the output changes from low to high. The time TLH of% steady-state value can be calculated by the following formula.
Among them, C1 is the external filter capacitor, and Cpar is the parasitic capacitance of the wiring harness to the ground. TLH needs to be less than the shortest time of DQ high pulse 4us. Assuming that R1 is 5.1k ohm, regardless of Cpar, C1 needs to be no greater than 261pF.
In actual use, users need to compromise between the three factors of minimum operating voltage, power consumption and transmission distance according to the actual application.
NST1001 temperature calculation formula and corresponding temperature table
NST1001 is easy to use. In addition to the small number of pins, it is also reflected in the easy acquisition of temperature measurement data. The temperature value after calibration can be directly obtained through the following equation:
Temperature calculation equation:
Among them: Temp is the temperature value (-50 ℃? ~ 150 ℃), Num is the number of pulses (1 ~ 3201).
The next issue will introduce the use of the NST1001 evaluation kit. Friends who are interested are welcome to leave a message to request the evaluation kit.
Figure 8: NST1001 USB evaluation board in kind?
Figure 9: NST1001 USB evaluation software