LH001-55: Pressure Transmitter Solution

The pressure sensor is a kind of sensor commonly used in industrial practice and instrument control. It is widely used in various industrial automatic control environment, including water conservancy and hydropower, railway transportation, automatic production control, aerospace, military industry, petrochemical, oil well, electric power, ship, machine tool, pipeline, etc. At present, the pressure sensor has also been significantly improved in the medical industry application, and there is a breakthrough development in its precision, reliability, stability, volume and other parameters compared with the past, and it plays a key role in respiratory apparatus, infusion pumps, pressure pumps, diagnostic devices and various monitors and it promotes the medical digitalization process. What is a pressure sensor? Pressure sensor refers to the apparatus or device that can convert pressure signal into available and output electric signal according to certain rules, usually composed of pressure sensitive element and signal processing unit. It mainly consists of the load cell sensor, measuring circuit, process connector, etc. (intake pressure sensor). The pressure sensor market research shows that in the global market, the share of pressure sensor in the overall sensor market is about 20%, second only to the flow sensor, and it is the second largest type of sensor product The global pressure MEMS market has reached USD 1.685 billion and is expected to drop slightly to USD 1.645 billion by 2020 due to COVID-19 pandemic. By 2026, the overall market is expected to grow to USD 2.214 billion, with a compound annual growth rate of 4%. As the core component of industrial control measurement system, ADC (analog-to-digital converter) is used for analogue-to-digital conversion of analog signal of pressure sensor and sending it to main control MCU for correction and other series of processing.


Figure 1 Pressure Transmitter Scheme


LH001-55 Pressure Transmitter Solution

LH001-55 launched by Legendsemi is a low noise 24-bit Σ△ADC that provides a complete high resolution measurement solution. The maximum effective number of bits (ENOB) can reach 23 bits. The integrated multiplexing MUX and gain adjustable PGA can be used for flexible processing of differential or single-ended signals. The programmable filter allows the user to make the optimal choice between resolution and output rate. The programmable excitation current source and temperature sensor are integrated inside the chip. The 12-bit voltage output type DAC is also integrated. The 4-wire SPI interface supports daisy chain to extend multiplex ADCs to achieve simultaneous sampling. Figure 2 shows the structure diagram of bit chip. Another highlight of the chip is that it can accurately measure the absolute negative pressure signal less than -0.1 V under the condition of positive supply voltage.


Figure 2 Structure Diagram


Figure 3 shows the evaluation board of LH001-55, mainly consisting of AFE (LH001-55), general MCU, etc. Legendsemi provides a complete set of software demonstration solutions. The demonstration program can perform the sampling ADC input signals and send data over a baud rate of 1500000 serial ports. The data can be read using the serial debugging assistant. The data format is channel, ADCCODE, voltage (mV), routine, DAC and current source output.


Figure 3 LH001-55 Evaluation Board


Figure 4 Application Example of Pressure Transmitter


LH001-55 Key Indicators

Low noise programmable gain amplifier (PGA) and high resolution 24-bit analog-to-digital converter (ADC)
    - Maximum effective number of bits (ENOB) - 23 bits
    - Programmable gain: 1/2/4/6/8/12/24/48
    - 4-way differential input or 8-way single-ended input
    - Support self-calibration of gain error and offset error
    - Maximum integral nonlinearity: 13PPM/FS
    - Programmable output rate: 2.5SPS-30kSPS
    - Continuous sampling mode: 525µA
    - Sleep current: 0.2μA
12-bit voltage output type digital-to-analog converter (DAC)
    - Output range: 0~2.5V
    - Support maximum resistive load 1kΩ and capacitive load 200pF
Integrated temperature sensor
Integrated two-way programmable excitation current source:
    - 100nA/50μA/100μA/250μA/500μA/ 750μA/1mA 
Built-in 16MHz oscillator with ±3% precision
Power supply
    - Analog 2.4V to 3.6V
    - Digital: 1.7V to 3.6V