Due to STM32’s restrictions , only UART1 to UART 4 has the ability of DMA Write, so

But for your convience, I uploaded all design ideas from Year 1999 to Year 2009, 11 years in all.  You can download them all

[Link]1999-2009.7z

1. How to measure the ripple voltage ?

The methods to measure the ripple voltage are diverse, but there is a standard which is developed by a Japan Power Module Manufacturer (TDK Power). It provide a standard procedure called JEITA-RC9131A to measure a power supply’s output ripple voltage. Here is the detailed method.

It suggest that DUT need to be connect with a special filter circuit like below:

And Prober should not be connected as close as possible to the load and not to the power output pin/terminal. Here is some wrong way to put the prober listed below:

2. What cause the ripple noise ?

Errr… This problem is somebit of difficult. The Main source is from the DC-DC Switch MOSFET‘s transisent current change which called SWITCH CURRENT. Because power supply is working under switch mode, so the distribution parameter of PCB will make a oscillation during the switching on/off period which cause a overshoot or undershoot phenomenon.

So sum it up,  the ripple noise caused by switch current in a switch mode power supply.

3. How to minimize the ripple noise ?

Err..  This is a very  challenging problem to give a proper anwer.  After Googlized the internet, I got some solution to make it works.

Method 1: Use a Passive Filter at the power output pin

(To be continued… Busy working)

So I made a Zener Diode List which from my "Search Job".

Here is the spreadsheet:

1N4099  ~ 1N4135
LOW CURRENT OPERATION 6.8V@250uA IZT
LOW REVERSE LEAKAGE AND LOW NOISE CHARACTERISTICS
1N4158 ~ 1N4193
6.8V@37mA IZT

1N4400 ~ 1N4426
6.8V@37mA IZT

1N4614 ~ 1N4627

1N4678 ~ 1N4717

1N4728 ~ 1N4763

1N5225 ~ 1N5281

1N5333B~1N5388B

They are all Zener Diode, which can be easily got the stores. Here is a PDF which covers all diode

Recently, I solve a problem which make a DA converter very very hot boiler. But thanks god, it works very well.. so other guys just ignore that problem, errr, I want to fix it.

First, I need to check which pin is convert current to pass the chip then work as a resistor heater to heat up the chip. And I find that it is pin 8 – A Reference Voltage Pin which is a input pin to give the DA convert a reference. It can absorb more than 100mA current from a 5V precise voltage source.

So problem is pretty easy. The 5V precisely Voltage source must be in some overvoltage conditon somehow.  So I attach a prober to the 5V ref source, then here is the problem. When system starts, the Voltage can be up to nearly 15V for about 25ms, so it cause the chip to be breakdown.

Reference Voltage Generated from here

And Voltage from DAVREF is here

So. Pretty easy solution to fix it up. Just remove the MJD127. Voltage never go beyond 5V,

So From this issue, I learned that never trust the circuit which already been tested and verfied by other people, you need to doubt while it is obviously wrong.

In a new company, I decide to use OrCAD + Allegro to finish all projects. In next 3~4 weeks, I will write some notes about how to use Allegro to draw a PCB Board. Orcad is somebit of easy job for me because of that I have used a lot in PSpice Simulation Job.

1. How to draw Component’s footprint in Allegro

2. How to Place Component’s footprint

And as an electronics engineer myself, I also have collected many design rule from Internet. Most of them coming from Semiconductor Corp (TI, NSC, LT, Onsemi, ... ). So here I gave my version of PCB Design GuideLine.

It will be the first one of my series Guide Book called -  TGuide Book Series.

So Here is the 1st one.  High Speed PCB Layout Guide Book

High Speed PCB Layout Guide Book

Written by Chenxiang Hsu

Part 1:

My Name is Chenxiang Hsu. And I am an electronics designer which work in a small company dealing with hardware design job.  If you wanna to talk with me, just write a email to me