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viscomjim
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Joined: 08/01/2014
Location: United States
Posts: 925

Posted: 04:25pm 19 Sep 2015

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I am working on a project and will need to use 12 io pins on the uMite to SINK 5 volts. If all 12 pins are on, can they all sink 20mA at one time? If not, how can I figure out what the max current 12 pins can sink at one time? These will all be 5v tolerant pins on a 44 pinner.

Thanks!!!!

MicroBlocks

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Joined: 12/05/2012
Location: Thailand
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Posted: 05:15pm 19 Sep 2015

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First page datasheet. Nominal 10ma per pin source/sink.

Page 301 'Absolute Maximum ratings'

Sink per pin 15ma.
Source per pin 15ma.
Maximum current sink by all pins 200ma.
Maximum current sourced by all pins 200ma.

Microblocks. Build with logic.

BobD

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Joined: 07/12/2011
Location: Australia
Posts: 935

Posted: 05:23pm 19 Sep 2015

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Jim
Have a look at the attachment and see if that does it for you. The datasheet may be a bit antique but is probably fairly accurate.
Bob
2015-09-20_032236_Capture.zip

Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3303

Posted: 06:03pm 19 Sep 2015

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When you are sinking or sourcing a significant current there is also the voltage drop across the internal PIC32 driver to consider. This graph comes from the MX170 data sheet.

I don't know why they extended the graph above the "Absolute Maximum". Perhaps to prove how tough it is.

Geoff

Geoff Graham - http://geoffg.net

MicroBlocks

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Joined: 12/05/2012
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Posted: 07:43pm 19 Sep 2015

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I keep always well below those Absolute Maximum Ratings.
About 100ma total sinking/sourcing is what i would recommend.
With LEDS you can get away with very fast multiplexing.

I actually designed a pcb for that purpose, alas it is not in production yet as i have to take it through some rigorous testing.

Here is the schematic, it might help you get on with your project.
The transistors are NPN Switching. The diodes are only needed when using it for switching relais or motors.

2015-09-20_054318_ioOC10.pdf

This will be the PCB (23x18mm)

Edited by TZAdvantage 2015-09-21

Microblocks. Build with logic.

viscomjim
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Joined: 08/01/2014
Location: United States
Posts: 925

Posted: 05:01am 20 Sep 2015

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Great info! Thanks. I will have to use a driver of some sort for sure.

TZ, that is a nice little board. The bat54c is a nice part for this. Just out of curiosity, why did you go for 10 outputs instead of 8? Also how do your "Blocks" get put together, it looks very interesting.

MicroBlocks

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Posted: 05:29am 20 Sep 2015

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I am actually considering a BAV70L diode as the bat54c is hard to get where i live. They are functionally the same and also the same package.

I put ten on the board because that is how many i could cram in there.

My first choice was to make one with 4, then i changed my mind and made one with 8. Having pins and PCB room left i though well why not 10.
I also recently ran into a requirement that needed 10. See micromite keyboard thread where i use a 4017 to provided 10 outputs for the rows of a matrix. These are not OC so having a small board like this comes in handy. Then you have things like servos, stepper motors, etc that can require many OC outputs. (Think robots, xyz platforms for 3d printers/cnc etc).
Having a single version of a small pcb is also more cost effective. 'Competitors' already offer 4 or 8 versions so need to differentiate.
That being said. I am still considering a smaller pcb with 4 of them. Just to have the smallest pcb available and you not have more outputs that you really need.
The Microblocks should only deliver what is needed. Finding the right balance is difficult and at this moment i try to make 'blocks' that have a single function and are as small as possible.

Microblocks. Build with logic.

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