3.3V to 1.8V problems

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 01:29 PM
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Hi,

 

I have just switched from powering my micro with 3.3v to 1.8v and now the micro and i think usart does not work.  I cannot test the output of the usart because the ttl level is below 3v.

 

I am running 4MHz and 9600 baud.  Is this to much for a 1.8v supply.  Should I drop down to 1MHz.

 

Other than swapping from 3.3v to 1.8v I have changed nothing else.  Do I need to changed anything else when dropping the supply voltage?

 

thanks.

 

 

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AVR Microcontrollers, megaAVR and tinyAVR
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valusoft
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Posted by valusoft: Wed. Sep 7, 2016 - 01:52 PM
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And your micro is which model? What does its datasheet say about supply voltage options and operating frequency limits?

Ross McKenzie ValuSoft Melbourne Australia

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awneil
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Posted by awneil: Wed. Sep 7, 2016 - 01:54 PM
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Tuurbo46 wrote:
 my micro

and you expect us to guess which micro that might be?!

 

I cannot test the output of the usart because the ttl level is below 3v.

So how can you tell it's not working?

 

What were you expecting to connect to it?

 

Is this to much for a 1.8v supply.  

What does the datasheet say?

 

 

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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 01:58 PM
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Tuurbo46 wrote:
Other than swapping from 3.3v to 1.8v I have changed nothing else.

Such as BOD level?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 02:04 PM (Reply to #4)
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Oh sorry, its a ATmega324P

 

Just trying to find the voltage baud cross over.

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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 02:07 PM
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Tuurbo46 wrote:

...  I cannot test the output of the usart because the ttl level is below 3v.

 

That got me curious.

 

First, why couldn't it be "tested" by looking with a 'scope?

 

Then for fun I went to DigiKey and found 1.8V or lower RS232 transceivers from several manufacturers.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 02:07 PM
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Hi,

 

page 324 displays I am right on the edge of working.  should I therefore drop my clk speed?

 

thanks

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valusoft
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Posted by valusoft: Wed. Sep 7, 2016 - 02:08 PM
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Well I guess you are out of luck.

 

Ross McKenzie ValuSoft Melbourne Australia

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 02:14 PM (Reply to #8)
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Hi Valusoft.

 

Well this could be my problem!!

 

What page did you find that on?

 

On page 2 of the datasheet (ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P ) it quotes the below:

 

Operating voltage 1.8V - 5.5V.

 

 

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valusoft
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Posted by valusoft: Wed. Sep 7, 2016 - 02:22 PM
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Page 2 of http://www.atmel.com/Images/Atme... (Atmel-42743B-ATmega324P/V_Datasheet_Summary-08/2016)

 

Ross McKenzie ValuSoft Melbourne Australia

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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 02:22 PM
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Tuurbo46 wrote:
On page 2 of the datasheet (ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P ) it quotes the below: Operating voltage 1.8V - 5.5V.

And right below:

 

So you are within spec.  But you still haven't answered why you think it is not working.  Nor about BOD level.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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valusoft
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Posted by valusoft: Wed. Sep 7, 2016 - 02:34 PM
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Lee, the datasheet that I have quoted from above is dated August 2016. I guess it and "yours" could be contradictory but as the OP is experiencing problems below 2.7Volts.... well draw your own conclusions.

 

I am out.

 

Cheers,

 

Ross

 

Ross McKenzie ValuSoft Melbourne Australia

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DAFlippers
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Posted by DAFlippers: Wed. Sep 7, 2016 - 02:46 PM
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I'm with Ross. 

 

David

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Brian Fairchild
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Posted by Brian Fairchild: Wed. Sep 7, 2016 - 02:51 PM
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Tuurbo46 wrote:

Oh sorry, its a ATmega324P

 

Do you have a '324P-20', a '324PV-10', a '324A' or a '324PA'?

 

 

[E2A]

 

and for completeness there was also a '324-20' and a '324V-10'.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

Last Edited: Wed. Sep 7, 2016 - 02:55 PM
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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 02:56 PM
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valusoft wrote:
Lee, the datasheet that I have quoted from above is dated August 2016. I guess it and "yours" could be contradictory but as the OP is experiencing problems below 2.7Volts.... well draw your own conclusions. I am out. Cheers, Ross

 

DAFlippers wrote:
I'm with Ross. David

 

[edit]  Doh!  I was reading '328 when OP said '324.  Sorry.  BOD level and how testing is done still applies.  ;)  lht

 

There is no "safe" BOD level for 1.8V...

 

It's pretty close anyway. ;)  (In bench tests some years back on a model in this family it ran very reliably to a bit below 1V including EEPROM.)

 

There are '328Ps and '328Ps.  As I recall, '328 (or maybe '328P) was already the A process when it came out.  So without date code and die version and such it is really hard to tell.

 

The latest I have downloaded is as below, doc 8271 rev. J 11/2015.  The "omnibus" covering the family.

 

 

 

 

 

 

Anyway, OP has to tell us what "doesn't work" means, and BOD level.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Wed. Sep 7, 2016 - 03:13 PM
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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 04:01 PM
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OK after double checking the chip, at some point it has moved from an ATmega324P to now using a ATmega324PA AU1522.

 

Yes I have tried changing the BOD levels but not luck.  But when I switch back to 3.3V the circuit works correctly.  I cannot even flash an led at 1.8V.

 

Thanks for your help.

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Brian Fairchild
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Posted by Brian Fairchild: Wed. Sep 7, 2016 - 04:11 PM
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Well, a 'PA' should be good for 4MHz.

 

What oscillator are you using? If it's an external crystal, try setting it to 'full-swing'.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 04:14 PM
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Hi Brain,

 

I am using the internal oscillator.

 

So you think 4MHz, 9600 baud, 1.8v should be ok?

 

thanks.

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Brian Fairchild
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Posted by Brian Fairchild: Wed. Sep 7, 2016 - 04:36 PM
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Tuurbo46 wrote:

I am using the internal oscillator.

 

 

The internal RC oscillator runs at 8MHz so to run at 4MHz you are setting up a divide by two in CLKPR?

 

What's not clear from the datasheet is if the RC oscillator will run on 1.8V.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 04:43 PM (Reply to #16)
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Tuurbo46 wrote:

Yes I have tried changing the BOD levels but not luck. 

Did you turn it off?  Did you see above that the is no "safe" BOD level for 1.8V?

 

Re the LED:  What is the forward voltage?

 

When you ramp up the supply V, at what voltage does it start "working"?

 

 

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 06:36 PM
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Brian,

 

Yes I am dividing by two in CLKPR.  This works correctly at 3.3V.

 

Theusch,

 

BOD: I did see there is not a safe level for 1.8V, but I tried anyway.

 

LED: yes you are correct, the led will not work because the voltage drop is 1.8V, well spotted.

 

Power Supply: I do not have a bench power supply, only a battery.  I can only confirm it works correctly at 3.3V but not 1.8V.

 

 

I may just resort back to 3.3V as a few articles on google quote some chips will not run close to there minimum VDD.

 

Thanks for your help everybody.

 

 

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theusch
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Posted by theusch: Wed. Sep 7, 2016 - 06:43 PM
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Tuurbo46 wrote:
BOD: I did see there is not a safe level for 1.8V, but I tried anyway.

Sheesh--did you try >>disabling<< the brownout?!?

 

Tuurbo46 wrote:
Power Supply: I do not have a bench power supply, only a battery.

And for a sanity check, you have no potentiometer and voltmeter available to manipulate the voltage for a few minutes of experimentation?

 

Think it through a bit.  Tell more about the purpose of the exercise of 1.8V.  (Are there common batteries with that nominal voltage?  I see none at DigiKey.)  Tell, with proper transceiver, why the UART won't work.  Tell what you connect the UART to, and what you expect.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Wed. Sep 7, 2016 - 06:44 PM
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Tuurbo46
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Posted by Tuurbo46: Wed. Sep 7, 2016 - 07:57 PM
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Hi theusch,

 

So my project is nearly finished, and I am just trying to put it into low low power mode.

 

I had a bad power consumption problem, and a design over-site, I have found out I was trying to control a CMOS logic level modem CTS and TX lines with 3.3V.

 

To resolve this problem I can either power the micro with 1.8V or put a potential divider in the CTS and TX lines.  A level shifter chip would require a new board design which I cannot do at this stage.

 

So what is the best solution, 1.8V or potential divider.  I can cut the board and put the potential dividers in without a problem.

 

Thanks,

 

Tuurbo46

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