at90usb1286 power supply (first pcb)

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Hey everyone, first post. I searched for "at90usb1286" and read several threads before deciding to make this post.

 

I am designing a pcb for a mechanical keyboard, am pretty new to pcb design, and need to understand how the power circuit from a mini usb port should work. I spent a good amount of time reading some of the datasheet about it, but I'm having some difficulty parsing the information. I sort of designed what I have now after looking at the Teensy++ schematic and another tutorial for an atmega32u4. 

 

Any help would be appreciated, as well as any comments about my schematic so far.

Attachment(s): 

I never knew what I was doing

Last Edited: Mon. Dec 9, 2019 - 06:04 PM
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Atmel put the AT90USB1287 on the AT90USBKEY which is a very good test bed for all things 1286/1287 based. I think there'll be a published schematic some where. That will also be a good reference for "best practice" in the PSU and USB interface design.

 

EDIT: complete schematics in the last pages of:  http://ww1.microchip.com/downloads/en/DeviceDoc/doc7627.pdf

Last Edited: Mon. Dec 9, 2019 - 01:58 PM
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Thanks for the reply! I studied that schematic and put this together. Any thoughts?

Attachment(s): 

I never knew what I was doing

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Old_Gold_Hand wrote:
Any thoughts?

 

Based on the schematics in both posts:

 

1) Change your transorbs on the D=/D- lines to SP0503BAHTG.  Its a three 'zorb device.  The third 'zorb goes to the VBus line.  The other two go to teh respective D lines

2) Where is your ISP connection for the AVR?  You need to program it some how.

3) you need a filter capacitor very close to the output of your regulator.

4) you need to place a .1uF cap at each Vcc pin, and one at the AVcc pin as well.

5) Ucap id not connected...might want to fix that.

6) C3, C4, C5, C6 need to be identified as to their location(s) on your board.

 

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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If you are planning to use the ADC, then add a 100nf cap to the AREF pin to gnd as well.

 

Jim

 

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Thanks for the advice! sorry for late responses, but here they are:

1) Looking at the symbol for  SP0503BAHTG , do the D+/D- go to their own pins on the  SP0503BAHTG ? the Vbus goes to it's own? then what comes out of the other side? I have uploaded a sketch about my questions

2) Can I not flash the AVR through usb? is this not commonly done? the firmware is called QMK and is common for use with mechanical keyboards. 

3) any idea what rating? should it be just output into the cap and "filtered output" (not sure what to call it) going out into the vcc circuit?

4) not pictured is a bunch of .1uF decoupling capacitors, one for each vcc pin

5) The connection from ucap to ID is made, it is just cropped out of the image

6) C3 is .1uF and between AREF and ground. 4,5,6 are decoupling caps and are cropped out. new image should be more clear.

 

Attached picture is some changes based on your advice. The schematic does not reflect the pcb very well, I can move the decoupling caps closer to their pins when laying out the pcb, for instance. Another question that arises is that when I shop for USB breakout boards, they often come with only 5 pins, like this one 

 

https://www.adafruit.com/product/1764?gclid=CjwKCAiAis3vBRBdEiwAHXB29IM4EGCIIk8bAlU4I0pbMUjVuJ3cQKpB61QjMdlgkud3Xzco6Oh0EhoCRq8QAvD_BwE

 

In the case of the usb breakout board listed, do I just ignore the shielding? Is shielding important for a device that will only ever recieve power from a computer's usb port (which is already protected i presume)?

 

Thanks again for all your advice

Attachment(s): 

I never knew what I was doing

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There is one of those already there, just cropped out of the schematic. Thanks for your insight!

I never knew what I was doing

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The common pin for the part i called out goes to your ground plane. The other three pins go to D+ D- and Vbus respectavely.

Out of the tube i do not believe you can program the part through USB. You would need to load a USB bootloader througl ISP first

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Like this? 

Attachment(s): 

I never knew what I was doing

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Old_Gold_Hand wrote:

Like this? 

 

For teh surge suppressors, yes

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user