I am creating a project for my self that's going to control 40 LED's in which use five TPIC6B595's. For the people that use these IC's I just want to ask a few questions.
First off. I know I need to use 0.1uf cap on the VCC - GND as close as possible to the VCC pin of the IC. Now my project requires 40 LED's which means I am using one LED per output on the shift registers. So (5x8=40) max 20-30 mA per pin as my LED's require. I have some questions to ask when I am etching my design of PCB.
First off, I am thinking that I need a bigger trace width for VCC for when all LED's or IC's are drawing their MAX capacity ?
2nd, Is grounding the bottom and top layer via copper pour better for the IC's (Copper pour for GND connected) is it better for less interference etc for the IC's ? or should I just do one layer ?
3rd, when I am using a external PSU for the +5 VCC I can never know how much noise it makes, is it better to have a electrolytic capacitor on the feed as well with low ESR even I have the 0.1uF caps by the VCC -GND pins by the IC's ?
Wow, that is some fast replies, Grumpy_Mike thanks for the information regarding my questions, I never thought that a copper pour on the top side (IC's) for VCC and bottom GND would be efficient like that. I have a calculator here that will give me the proper mm for trace for VCC connections that should be ok regarding in air ambient temp and high temp to the data sheet, but should I trust it ?
I have a new DSO on order, I can measure the noise from about 4 various PSU's pumping out 5v, I presume I should make my calculations for a generic +5volt PSU or PC, etc. Hence the cap value in which I need to calculate that fits all or most.
@ CrossRoads
I see your board, and it looks nice etc, but I don't understand your answer to my above questions ? Unless you want me to look at your board candy ? or is it an advert ?
regards
Thank you so much to both of your for everything !
Although I would Mike look at my reply and respond given my last reply.
EDIT: I forgot to mention I am using SMT versions of the TPIC6B595
I have a calculator here that will give me the proper mm for trace for VCC connections that should be ok regarding in air ambient temp and high temp to the data sheet, but should I trust it ?
Yes you can trust it but using a flooded Vcc gives you better noise protection and also adds a bit of distributed capacitance with the lower layer.
I can measure the noise from about 4 various PSU's pumping out 5v,
Normally this is not much of an issue, just have a large cap and small cap. If you want to be extra sure then add a series inductor with cap either side for each shift register or group of shift registers.
My board was supporting 100 LEDs at 20mA. Power traces are 60mil wide, with ceramic 0.1uF cap per each shift register, and ground plane on the top & bottom layers. 10uF caps before & after the 5V regulator.
You've not mentioned doing any analog processing, so the extra series inductors and extra electrolytics should not be needed.
CrossRoads:
My board was supporting 100 LEDs at 20mA. Power traces are 60mil wide, with ceramic 0.1uF cap per each shift register, and ground plane on the top & bottom layers. 10uF caps before & after the 5V regulator.
You've not mentioned doing any analog processing, so the extra series inductors and extra electrolytics should not be needed.
I am not going to be doing any sort of analog processing, its a normal signal process regarding the clock, data and latch stuff, but I was thinking of putting another cap on the external VCC etc just to make sure about external noise that might be introduced into the circuit even I have 0.1uF caps by the VCC of each IC pin, and the other aspect was the ground plane attached to the GND on top and bottom or just the top where my IC's are.
Thanks CrossRoads for your input. You have a been a great help !
