The National College Student Electronic Competition is coming, the data acquisition system is a project that cannot be ignored in the competition. For now, data collection is a key function of robots and industrial networks. From a energy acquisition source to multiple sensors, the ability to capture subsystems, allowing capture data from more venues to be possible, and reduces the need for charging or replacing the battery.
Multi-channel data acquisition subsystems can use solar cells or thermoelectric power generation (TEG) power supply, but power consumption is a key consideration. Using ultra-low power consumption approximation analog to digital converter (such as Analog Devices 12-bit AD7091R-5), such a subsystem having a smaller shape can be constructed. This is an increasingly important consideration because the data acquisition board needs to be installed to a smaller position that does not provide the main power supply.
Figure 1 shows the combination of AD7091R with high energy collection circuits based on Analog Devices-based ADP5090 boosting regulators. This boost regulator is input to four single-ended analog sensors. When sampled at a maximum 22 kSPS sampling rate, the ADC uses a typical power consumption of 3 V single power supply to 100 μW, and 1 kHz input signal has a 68 DB typical signal to noise ratio (SNR).
12-bit SAR ADC uses 2.7 V to 5.25 V single power supply, including the I2C interface of the I2C interface, an accurate reference, and the I2C interface operated in 100 kHz standard mode and 400 kHz fast mode. When additional filtering is required to appear an input signal of the source channel on the Muxout pin, the multiplexer output will make each channel no signal adjustment circuit. The filter before the VIN pin has a cutoff frequency of approximately 8.6 MHz, which can be weak noise at the ADC input, and reduce the charge response from the ADC using the low-series resistance value; there is a suitable capacitor, pull out and Infink the high frequency charge of the ADC. If more filtering or signal adjustment do not need, the MUXOUT pin will be directly connected to the ADCIN.
Stable reference voltages are critical to data acquisition, so the film 2.5 V is available on the REFIN / REFOUT pin, and the chip can work with this reference or external application. The logic status of the P_DOWN LSB bit in the configuration register determines whether the internal reference is used. When the P_Down LSB bit is set to 1, the internal reference will be selected for the ADC. When the P_DOWN LSB bit is set to 0, the external reference of the 2.5 V to VDD range can be connected to the device via the REFIN / REFOUT pin to reduce jitter and improve accuracy.
The internal reference circuit consists of 2.5 V band gap reference and a reference buffer, and is disabled by default, so that external reference can be used. Then, change the configuration bit when starting can allow 2.5 V internal references to be used on the REFIN / REFOUT pin, which is usually used to ground 2.2 μF capacitors that require 50 ms to be powered to ground. It is recommended to buffer the internal benchmark before applying it to other places in the system.
The conversion process and data acquisition are controlled by the I2C interface and an internal oscillator, and the data can be read after the conversion to reach the highest throughput of 22.22 KSPS in the fast mode.
Sampling mode uses a convst / gpo1 pin and the ADC conversion is implemented after switching, and the command mode uses the readings of the conversion result register to switch to provide a stable data stream. However, this device also has an automatic loop mode to operate in autonomous mode, so that events that exceed the user-defined range. This is particularly suitable for setting an alarm conditions. These patterns are shown in the I2C configuration mode in Figure 2.
Four single-ended analog input channels include a channel sequencer that allows sequential conversion by sequential selection results, and the user can use a different working condition, such as power management, alarm function, and Busy instructions, channel sequencing, and universal output pins. The MUXOUT and ADCIIN pins also allow signal adjustment to multiplexer outputs before the ADC acquisition data.
The AD7091R-5 uses two power pins, which has a certain impact on energy collection power supplies. VDRIVE allows direct connection between 1.8 V to 5.25 V, but in order to reduce the number of power supplies, VDRIVE and VDD can be connected together.
In addition, the ADC is not sensitive to the power supply in the wide frequency range, so it can easily use the energy collection source. The ADC will automatically power down at the end of each conversion phase, which means that the power supply will extend linearly as the sampling rate is linearly extended, and the power-off function support is even a few Hz low sampling rates to meet the very low energy consumption. Application.
Then integrated with the ADP5090 integrated boost regulator, converts the DC power source from the photovoltaic or the thermoelectric generator to charge the rechargeable battery or supercapacitor. The CN-0372 board shown in Figure 3 uses a supercapacitor to power the electronic device and the battery system.
The plate is input to the power supply in 16 μW to 200 MW, and the working loss is less than 1 micro. With internal cold boot circuits, the rectifier can start working at input voltages as low as 380 mV. This solution does not require external batteries to supply power to the circuit, and can fully use the available collectible energy.
By sensing the input voltage of the VIN pin, the control loop keeps the input voltage ripple in a fixed range to maintain a stable DC-DC boost conversion. The VIN sensing and programmable adjustment point of the input voltage allows the highest energy to be collected from the photovoltaic or TEG collector.
For solar cells, the lowest programmable working threshold (Minop) can support boost shutoffs under low light conditions, and the charging control function can protect the battery voltage to protect the battery voltage, including programmable charging ends. Press the voltage and discharge shutdown voltage.
The circuit in FIG. 4 can convert the power from the connected energy source to the J4 terminal, store the charge in the supercapacitor (C26) and powered through the SYS voltage input.
The energy collected from the photovoltaic or TEG is introduced in the Energy_IN pin. When this voltage exceeds 380 mV, the chip will enter the cold start state until the main boost device is enabled, and the SYS voltage exceeds VSYS_TH usually 1.93 V. The logic high level on the PGOOD is equal to the SYS voltage, and when the battery terminal voltage is reached, the main boost charger is turned off.
This allows the regulator to operate at the pulse frequency mode (PFM), transmit energy stored in the input capacitor to SYS and 50 mF, 3.5 V Super Capacitor (C26). The PGOOD threshold is set by an external connector indicating that the SYS voltage is at an acceptable voltage level.
The ADP5090 is also equipped with a battery overcharge and depth discharge protection threshold, which is also set by an external resistor.
Assess the circuit
Connect low-power, high impedance DC power (e.g., photovoltaic cells or teg) to the J4 terminal, and then placed SL4 and SL5 in position a, which can use the ADP5090 energy collection circuit as a system power source. The PC-based ADI evaluation software can then be used in conjunction with the EVAL-CN0372-PMDZ board and connect the PC via a USB.
in conclusion
Developing multi-channel data acquisition subsystems powered by environmental energy requires a boost converter optimized for low power ADCs and designed for energy collection. Integrated multiplexing and filtering functions in the ADC can reduce the complexity of the design, while different configuration options (especially based on autonomous threshold patterns) can achieve multiple sensors at minimum power consumption. The ADC is then bonded to the boost converter, and the boost converter is used under low voltage, supports monitoring the rechargeable battery or supercapacitor to store the collected energy. All of these features are integrated in the evaluation board, and designers can learn how to capture data.
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