common practice for powering up MCU

Discussion in 'General Electronics Chat' started by durable126, Mar 25, 2016.

  1. durable126

    Thread Starter Member

    Feb 20, 2016
    56
    1
    Powering up a an atiny85

    What is the common accepted practice as far as supply and ground voltages go?

    We don't typically just plug the thing into 5 volts supply and ground the other side

    Normal people have some capacitors in place here and there to prevent certain problems correct?

    Can someone make some recommendations on the correct way to set it up?

    Cap across the supply? Cap across the ground? etc
    aka supply filtering common practice

    Thanks
     
    Last edited: Mar 25, 2016
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
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    Follow manufacturer recommendations in the datasheet. Typically one decoupling cap for each pair of supply pins.
     
  3. durable126

    Thread Starter Member

    Feb 20, 2016
    56
    1
    I didnt see anything in data sheet which is 280 pages long

    The sheet talks about noise reduction while using the ADC but thats all i saw?
    Any recommendations?
     
  4. SLK001

    Well-Known Member

    Nov 29, 2011
    812
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    Really? 280 pages and nothing about bypassing the supplies?

    Well, bypass EVERY supply line as close to the pins as possible with at LEAST a 0.1μF ceramic capacitor. One pin should also have a 10μF capacitor as close to the pin as possible.
    (RE: BYPASSING means placing a capacitor between a supply line and ground.)

    Also, it used to be common practice to tie RESET to an RC network, so that the MPU will be fully powered when it comes out of reset.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Section 17.9 (and maybe others)
     
  6. durable126

    Thread Starter Member

    Feb 20, 2016
    56
    1
    why are you telling me to look at 17.9
    You even quoted my above post
    I stated the only talk of bypass caps was in the ADC section which is in FACT 17.9

    There is one sentence about it and its for ADC noise canceling
     
  7. durable126

    Thread Starter Member

    Feb 20, 2016
    56
    1
    What do you mean every supply line.

    there is only one 5volt supply and one ground
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    If you don't have specific supply decoupling data from the manufacturer, use the standard rule of thumb. 10-100uF within a couple inches of the microcontroller and 0.01-0.1uF on the VCC pin to a ground plane.
     
  9. BobaMosfet

    Active Member

    Jul 1, 2009
    109
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    For the 'Tiny, normally +5VDC on the positive rail to start, for learners.
    Blocking/Bypass capacitors are used as a short (for an incredibly brief period of time) between the positive and negative rails until the capacitor develops a field within itself that stops the short and creates a flexible buffer of energy between the rails. If the mcu needs a little extra current-- the capacitor provides it instantly. If a little noise/jitter is on the line, the capacitor helps to stop that. In essence, it acts like a little powe-conditioner. And you want one on both the ADC rails (ARef (+)and Grnd (-)) and on the normal power rails for positive and Gnd.
     
  10. durable126

    Thread Starter Member

    Feb 20, 2016
    56
    1
    yes i understand how a buffer works
    what are you talking about rails. there is only 1 supply pin and one ground as i have stated 3 times now
     
  11. BobaMosfet

    Active Member

    Jul 1, 2009
    109
    11
    supply pin-- think of it as a 'rail'.
    ground pin-- think of it as a 'rail'.

    I apologize about mentioning ARef-- that's for slightly larger package ATMEGA's.

    Just put 0.01uF cap between your Vcc and Gnd. Get a good book on basics of electronics, too :)
     
  12. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    224
    I didn't know how many supply pins your MPU had. If you should put 1 capacitor on every supply line and there is only one supply line, how many caps are you going to place - between supply and ground?
     
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