How to plan a schematic design review?

First of all, we must clarify the purpose of the schematic review: to identify problems in advance and improve the product design.

Therefore, before the review, we have to list out the possible problems with the product design experience and make a targeted review. The process is pragmatic and the reviewers are multi-faceted in their assessment of the design. The schematic review mainly involves hardware engineers (and procurement engineers) and embedded software engineers.

★Drawing inspection：

•A modular design is recommended for the schematic diagram, with a general diagram on the first page describing the relationship between the modules logically and clearly.

•Each module is labeled with the relevant power consumption calculation, key elementary parameters are labeled, the power supply section indicates the input and output, and EMC test standards.

•Clear logic between modules, smooth signal flow and easy to understand network signage.

★Component inspection

•The selection of individual components in the schematic diagram shall meet the common derating criteria.

•Clearly marked component specifications in the schematic diagram and clearly filled in package information (eg: AD software can be filled in Parameters).

•Preference for components is given to the corresponding company's standing materials to avoid increasing the company's material procurement pressure.

•To meet the requirements of product development, key components are preferred to national brands, and if foreign brands have to be used, the supply risk of components should be considered.

★Rule Check

•This step is particularly important as the error checking rules are set uniformly according to the mapping software.

★Power supply check

•Confirmation with the structure of the product installation method, confirming whether the product needs to be connected to earth.

•Power supply interface plus protection, following the product should be tested standard targeted design, to avoid copying the use, not take the design development.

•Power supply design basic protection against reverse connection, overvoltage and overload, short circuit, etc., plug-in interfaces to consider anti-dumbing design.

•Isolation and separation between digital circuits and analogue/sensitive circuit modules power supply, independent grounding treatment.

•Placement of decoupling capacitors at the input of the power supply chip and large current-continuing capacitors near the power supply of heavily loaded modules.

•Evaluation of the current between individual modules to ensure that the supply module is 1.5 times the maximum value of the load.

★MCU and peripheral IC section

•MCU clock circuitry to ensure safety and reliability, and to do ground wrapping if necessary.

•MCU burn-in port using a unified interface to avoid extra work caused by incorrect burn-in port wire sequence at a later stage.

•MCU reset circuit resistance and capacitance selection, check the MCU reset time requirements and select the appropriate capacitance value.

•MCU and peripheral IC unused pins handling issues, ground, pull up or overhang? Check the reference manual or ask the chip manufacturer.

•Problems involving communication between the MCU and peripherals, pay attention to the issue of matching between communication levels and evaluate common level conversion methods.

★PCB Layout

•After the Layout is completed, the Layout can be exported to a 3D format file and sent to a structural engineer to assess whether there are interference problems.

•The board layout should consider EMC design, the important EMC issues in product reliability design are half designed by the schematic and half by the Layout and structure design. Attention should be paid to the location of the plug-in, the location design between the wire harness alignment and the structure outlet, all of which will affect the direction of the common mode interference current and thus determine the success or failure of the product EMC design.

•The PCB also requires a targeted review, involving mainly hardware engineers, PCB Layout engineers, structural engineers and electronic process engineers.

Seektronics believes that no matter how to do design or other things, experience is certainly important, but remember not to blindly push experience, sometimes push back, often have unexpected gains. The process can refer to the 5W+1H principle: that is, the selected project, process or operation, from the reason (Why), object (What), place (Where), time (When), personnel (Who), method (How) and other six aspects of the question to think about.

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