Difference between "Low Power" and "Full Swing" Crystal Oscillator

[Blade87]

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?

1 – Full swing crystal oscillator not supported
The full swing crystal oscillator functionality is not available in revision K.
Fix/Workaround:
Use alternative clock sources available in the device.

I 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 about Low Power Crystal Oscillator and Full 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 typical HC-49 low power or full swing?

[Psi]

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.

[reboots]

In page 51 and 52 of ATmega328P datasheet, there are information about Low Power Crystal Oscillator and Full 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 typical HC-49 low power or full swing?

The 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.

[PCB.Wiz]

The low power oscillator has been improved and has made the high power full swing hardware a bit redundant.

Almost, I think Atmel goofed a little there, and made Low Power 16MHz spec, vs 20MHz for full swing ?  Not sure what they were thinking.

For example, is typical HC-49 low power or full swing?

HC-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')

[T3sl4co1l]

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

[iMo]

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.

[bingo600]

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

[Psi]

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

So no more overclocking them to 65mhz with LN2 then

[LC333]

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-1179301
https://media.digikey.com/pdf/PCNs/Atmel/WC154601-cancel.pdf