How to check the circuit schematic

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Http://ticktick.blog.51cto.com/823160/305471

 

I have been working on an embedded system and drawing a schematic diagram recently. Finally, in order to ensure the accuracy of the schematic diagram, it took me nearly two weeks to check the schematic diagram. Here, I would like to summarize my experience in checking the schematic diagram for your reference, you are welcome to point out something wrong.

After we draw the circuit schematic diagram, we also know to check, but where should we start? What should I pay attention to when checking the schematic diagram? Let me talk about it one by one based on my experience.

1. check whether all chip package diagram pins are correct.

Of course, I am referring to the chip encapsulation I have drawn. I used to reverse the two pins of a chip in the project. As a result, the patch cord had to be taken after the last version.

Therefore, before checking and schematic diagram, we must start with the chip encapsulation and resolutely put the wrong encapsulation in the cradle!

2. Use the tools-> ERC electrical rule check of PROTEL to troubleshoot errors according to the generated files.

This refers to the ERC electrical rule check of protel99, and dxp should also have a corresponding menu to complete such a check. It is very useful. It can help you find a lot of errors. Based on the error file generated by it, check your schematic against the error file. You should be amazed: "I draw pictures so carefully, are there so many errors?"

3. check whether all network node net connections are correct (important)

Common Errors include:

(1) originally, the two net should be connected, but they were accidentally marked as inconsistent. For example, I used to set the DDR clock pin of the main chip as ddr_clk, the clock pin corresponding to the DDR chip is labeled as ddrclk. Because the names are inconsistent, the two legs are not connected together.

(2) Some net only marks one and the other end of the net forgets to mark somewhere.

(3) The same net label is used repeatedly in multiple places, resulting in all of them connected together.

4. check whether all functional pins of each chip are correctly connected. check whether all chips have missing pins and do not connect to X

Do not connect the function pins of the chip to the wrong ones. For example, the audio processing chip I use has three clock pins: lclk, bclk, and mclk, which must correspond to the three audio clock pins of the main chip one by one, A single record cannot work.

Whether there are missing pins is actually very easy to troubleshoot, carefully observe the various chips to see if there are any missing pins that are not connected out, check datasheet to see what features of the pin, if not needed in the system, use X to remove the pin X.

5. Check whether the values of all external capacitors, inductors, and resistors are correct, rather than random values.

In fact, when you draw a schematic diagram, you often do not know how to set values for some peripheral resistors and capacitors, these peripheral circuit resistors and Capacitor values are often described in The Datasheet of the chip. Some datasheet also provides a typical reference circuit, or some calculation formulas of the resistance and capacitor, as long as you are careful enough, you can find the basis for most of the values of resistance and capacitance. Occasionally, you cannot find the basis. You can search for other people's design cases or typical connections on the Internet. For more information, see. In short, do not set these values at will.

6. Check whether capacitor filtering is applied to all chips.

I don't need to talk about the importance of Capacitive filtering on the power supply end. In fact, people who have done hardware should know it. In general, some ripple will be introduced at the input end of the circuit power supply. To prevent these ripple from causing too much impact on the chip logic, some capacitors such as 0.1uf need to be added next to the chip power supply end to achieve some filtering effect. when checking the circuit schematic, you can take a closer look at whether such a filter circuit is added to the necessary chip power supply end?

7. detect all interface circuits of the system

The interface circuit generally includes the input and output of the system. Check whether the input has proper protection and whether the output has sufficient driving capabilities.

Input protection generally includes reverse current protection, photocoupler isolation, and overvoltage protection.

When the output drive capability is insufficient, you need to add some pull-up resistors to improve the drive capability.

8. Check whether each chip has the order of power-on and reset requirements. If yes, design the corresponding delay circuit.

For example, the dm6467 chip used in my project requires that the power-on of the power supply voltage be sequential. First, the power supply must be provided to the 1.2v power supply end, then the power supply to the 1.8v power supply end, and finally the 3.3v power supply end. Therefore, we use a delay chip to process the three voltages produced by the power chip (in fact, we can also use a transistor to use the clamp voltage), and then transmit them to the main chip in sequence.

9. Check the location of each chip, the analog location, whether the analog location is connected to the digital location, and whether the numbers are separated from the analog location.

Generally, the chips used to process analog signals include sensor chips, analog signal acquisition chips, adconverter chips, power amplifier chips, filter chips, carrier chips, DA conversion chips, and analog signal output chips, generally, only chips or circuits in the system that process analog signals involve analog and digital locations.

Generally, the chip grounding pin can be connected by datasheet in both analog and digital ways.

10. check whether there are better solutions for each module (optional)

In fact, when you design the first draft of the schematic diagram, you often don't think so much about it. After the whole system is built, you will often find that there are actually many places that can be improved and optimized. The power supply module in our project has been revised four times before and after. Every time, we often find a better solution. The current power supply solution is concise and practical, and the effect is much higher, I think this is the benefit of continuous improvement and optimization!