Difference between "Low Power" and "Full Swing" Crystal Oscillator - Page 1
Forum section: electronics / general

author: Blade87
author_rank: Contributor
timestamp: April 03, 2019, 01:31:54 pm
content: Hello everyone,Recently, I saw this in ATmega328P errata and I thought maybe new ATmega328P won't work correctly with "Full swing crystal oscillator". Am I right?QuoteI haven't experienced any problem when I used crystal oscillators, but this new data made me curious.In page 51 and 52 of ATmega328P datasheet, there are information aboutLow Power Crystal OscillatorandFull Swing Crystal Oscillator. I read some crystal oscillator datasheets, but there aren't any information that if they are "low power" or "full swing". How should I identify these types of crystal oscillators? For example, is typicalHC-49low power or full swing?

author: Psi
author_rank: Super Contributor
timestamp: April 03, 2019, 01:42:03 pm
content: The low power oscillator has been improved and has made the high power full swing hardware a bit redundant.Unless you have a design that's running the AVR outside its clock spec i doubt you will any any problems.But it could cause problems if a design had the wrong capacitors on the crystal and the high power oscillator had been able to push past this.The low power oscillator might not be able to work without correct caps.

author: reboots
author_rank: Regular Contributor
timestamp: April 03, 2019, 03:28:13 pm
content: Quote from: Blade87 on April 03, 2019, 01:31:54 pmThe datasheet is referring to oscillator circuitry internal to the AVR, which drives an external crystal at different power levels. The same crystal would be used for both "low power" and "full swing" modes.There are also complete crystal oscillator parts, which incorporate both a crystal and oscillator circuitry. These parts can be identified by their need for an external power supply. The AVR does not need to drive this type of part; you would select "external clock" as detailed in the datasheet.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: April 03, 2019, 11:45:41 pm
content: Quote from: Psi on April 03, 2019, 01:42:03 pmAlmost, I think Atmel goofed a little there, and made Low Power 16MHz spec, vs 20MHz for full swing ? Not sure what they were thinking.Quote from: Blade87 on April 03, 2019, 01:31:54 pmHC-49 is a package type for a crystal. That package should work in either AVR setting.All Xtal amplifiers are analog elements, so you need to test to confirm they have operating margin.That's usually only an issue when pushing MHz up, or trying to use smallest package crystals. (smaller xtals have higher ESR, which makes them 'harder to start')

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 04, 2019, 01:41:16 am
content: High power may be of interest in high-noise environments, or for use with low ESR crystals.For general purpose application, and a crystal selected for reasonable ESR (suited to the drive power available), it's not needed.Tim

author: iMo
author_rank: Super Contributor
timestamp: April 04, 2019, 07:56:51 am
content: FYI - as we messed with atmega1284p in past the low power vs. high swing was the method how to overcome an annoyance with an "inter-pin" noise between the adjacent Xtal1 input and serial Rx pins. The high swing usually solved that issue.

author: bingo600
author_rank: Super Contributor
timestamp: April 14, 2019, 10:23:23 am
content: ISTR some of the new Atmel Mega chips wont do 20MHz , due to the new (lack off) oscillator swing.Not sure if it was new M328's too/Bingo

author: Psi
author_rank: Super Contributor
timestamp: April 14, 2019, 10:32:41 am
content: Quote from: bingo600 on April 14, 2019, 10:23:23 amSo no more overclocking them to 65mhz with LN2 then

author: LC333
author_rank: Newbie
timestamp: October 25, 2023, 07:20:48 am
content: Just for anyone coming across this doing a search as I have, revision K that would have removed Full Swings support was cancelled by Microchip, so there are no 328P's in the wild that ONLY support a low power mode on the crystal, they will all do Full Swing or Low power as chosen by the fuses.https://www.avrfreaks.net/s/topic/a5C3l000000UY3ZEAW/t144707?comment=P-1179301https://media.digikey.com/pdf/PCNs/Atmel/WC154601-cancel.pdf