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I. Preface
When measuring the performance of the 1117 regulator chip earlier, the single-chip microcomputer was burned. The following is to test the noise of the regulator chip. This also provides a basis for the design of the subsequent data sampling circuit. The following is a redesign of the measurement circuit.
2. Circuit production
The test circuit consists of a microcontroller and an AS1117 regulated power supply. Later, change the type and capacitance of its output filter capacitor to measure the AC noise in the output power supply. At the same time, the power supply is divided by the microcontroller, and the data noise after acquisition is viewed. Design a single-sided PCB, and get the finished circuit board in one minute. The circuit board is very complete. The following is the welding commissioning.
▲ Figure 1.1.1 Schematic diagram of test circuit
▲ Figure 1.1.2 Test circuit PCB
3. Measurement results
The circuit is soldered, cleaned and placed on the test shelf, and the microcontroller has not yet been programmed. Use a probe clip to plug the 5V power supply into the circuit. The quiescent current is 5.1mA. Measure the 1117 output voltage at this time, and the voltage is 3.3V. The voltage is very stable.
Use the AC gear of the DM3068 digital multimeter to measure fluctuations in the 3.3V power supply. The results show that the AC component in the power supply is 0. In other words, no small noise is measured. Maybe it's a problem with this multimeter, maybe it doesn't have enough resolution.
The AC noise of the power supply at this time is measured using the AC setting of the FLUKE45 with an amplitude of 0.165mV. This shows that the AC gear of the DM3068 multimeter is indeed problematic and cannot reflect the noise in the actual signal. At this point, the 1117 output has a 10 microfarf and a 0.1 microfarf surface-mount capacitor in parallel. The microcontroller did not work.
Download a working program and the LEDs on the board start flashing, at which point there is no other action on the circuit. Measure the corresponding power supply noise at this time. The voltage fluctuation increases to 0.28mV, which is an increase of about 40%. This shows that the operation of the single-chip microcomputer has brought large fluctuations to the power supply.
A microcontroller was used to collect 512 ADC data, which is the voltage signal of the supply voltage through two 10k ohm dividers. Data for 2012. The standard deviation of the calculated data is around 1.98. This data shows that the last two digits of the collected data are fluctuating. Below remove the power supply 10 micro-method filter capacitor, and you can see that the variance of the collected data has not changed. Replacing the capacitor with a 10 microfaring tantalum capacitor has no effect on the variance of the acquired data, and the supply noise fluctuates around 0.18mV.
※Summary※
In this paper, the influence of the filter capacitor of the 3.3V regulator chip on the circuit noise of the MCU is recorded. It can be seen that the output voltage noise of chip 1117 is only about 0.2mV, and replacing its output filter capacitor reduces 0.1 microfarnet, or replacing it with tantalum capacitor, which does not have much impact on the collected data noise. This experimental experience supports the design of future circuits.
Resources
[1]
LM1117: https://www.ti.com.cn/product/cn/LM1117#:~:text=%E6%95%B0%E6%8D%AE%E8%A1%A8%20LM1117%20800mA%20%E4%BD%8E%E5%8E%8B%E9%99%8D%E7%BA%BF%E6%80%A7%E7%A8%B3%E5%8E%8B%E5%99%A8%20%E6%95%B0%E6%8D%AE%E8%A1%A8,%28Rev.%20Q%29%20PDF%20%7C%20HTML