IRC Oscillator vs. System Oscillator

lpcware · ‎06-15-2016

Content originally posted in LPCWare by kralux on Fri Apr 09 16:54:49 MST 2010
Could someone please explain the differences between the IRC oscillator and the system oscillator from a circuit point of view as well as stability over temperature and supply?

Is the IRC oscillator a Resonant Crystal osc. on chip or is it a more typical R-C (resistor-capacitor) oscillator?
What is the system oscillator made of? I could not find any info.

Since the time base is very important in our application, we need to understand these differences (and we can't really afford a crystal on the BOM).

Thank you!

Original Attachment has been moved to: 1100279_onewire.zip

lpcware · ‎06-15-2016

Content originally posted in LPCWare by BichoBus on Tue Sep 18 08:08:20 MST 2012

Quote: glenn_mark
Hi,

Maybe his thread is too old but I'll post my query anyway.

Is it OK to use the IRC for USB Applications?
I'm also confused with the system oscillator. And I think the initial question of 'what a system oscillator is made of' was not yet answered. Is it an external component (crystal) or is this an internal oscillator?

|-----------------------------------------------------------|

As far as I know,

"System Oscillator" is the on-chip circuitry that drives the external quartz crystal, and generates the square wave of same frecuency that the crystal frecuency. Is the circuitry connected to XTALIN and XTALOUT pins.
It is not the internal oscillator (the internal oscillator is the "IRC" oscillator, and it is an accuracy R-C on-chip oscillator; or same kind of precise oscillator)

Some NXP microcontrollers, like LPC1227, can "connect" or "disconnect" the "system oscillator".
I think this is: Imagine we have an external square wave (clock), and we want to use this for "clocking" the LPC1227. We connect the signal to XTALIN (as described in Data-Sheet), and left floating XTALOUT (disconnected). Then we disconnect the "system oscillator": register SYSOSCCTRL, bit 0 "BYPASS" = 1; => "bypass enabled" (because we are not using any external crystal).

lpcware · ‎06-15-2016

Content originally posted in LPCWare by xinbadaz on Fri Jan 07 00:24:48 MST 2011

Quote: kralux
Could someone please explain the differences between the IRC oscillator and the system oscillator from a circuit point of view as well as stability over temperature and supply?

Is the IRC oscillator a Resonant Crystal osc. on chip or is it a more typical R-C (resistor-capacitor) oscillator?
What is the system oscillator made of? I could not find any info.

Since the time base is very important in our application, we need to understand these differences (and we can't really afford a crystal on the BOM).

Thank you!

as i konw,
the IRC is a chip built-in resonant crystal,
and system oscillator is the external crystal

lpcware · ‎06-15-2016

Content originally posted in LPCWare by glenn_mark on Wed Jan 05 18:07:27 MST 2011
Thanks gbm for the reply.

I also made a thorough research yesterday and it is clear to me now that we need an external clock source for USB Application esp. for NXP's LPC1342/43.

I also found out that instead of using an expensive crystal, we can use resonators to drive the MCU. See link below:

http://ics.nxp.com/support/documents/microcontrollers/pdf/report.r_10003.pdf

Good luck to everyone. :)

lpcware · ‎06-15-2016

Content originally posted in LPCWare by gbm on Wed Jan 05 03:15:38 MST 2011
No. USB requires < 0.5% deviation. There are some micros with precise laser-trimmed internal oscs providing this accuracy, produced by SiliconLabs. So far not too many vendors offer USB chips with internal oscillators.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by glenn_mark on Tue Jan 04 19:09:00 MST 2011
Hi,

Maybe his thread is too old but I'll post my query anyway.

Is it OK to use the IRC for USB Applications?
I'm also confused with the system oscillator. And I think the initial question of 'what a system oscillator is made of' was not yet answered. Is it an external component (crystal) or is this an internal oscillator?

lpcware · ‎06-15-2016

Content originally posted in LPCWare by leon_heller on Sat Apr 10 16:50:03 MST 2010
1% is fine for many applications, and should be OK for RS-232. If a crystal is too expensive and you need something better than 1% you could use a ceramic resonator. Some include the feedback capacitors.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by rmteo on Fri Apr 09 19:29:43 MST 2010

Quote: kralux
....and we can't really afford a crystal on the BOM.

Thank you!

I guess the downside to having a low-cost MCU is that it makes the support components look really expensive. :D:D:D

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Luis Digital on Fri Apr 09 19:06:36 MST 2010
Hello,

I performed some tests a few days ago, and the results were as follows (temperature 30 C or so:)):

[LIST]
[*]Crystal Osc. + PLL / 72 (72 MHz / 72)
[/LIST]
[INDENT]1000118 Hz (A deviation of 118 Hz)[/INDENT]
[LIST]
[*]IRC / 72 (12 MHz / 72)
[/LIST]
[INDENT]166490 Hz (A deviation of 177 Hz)

[/INDENT]You say you need an accurate clock, then simply choose a good crystal, the cost is not a priority in these cases.

Check out these comments, if you want to test temperature and voltage, and measure the deviation.

I hope that NXP is working to have these data available soon.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by rmteo on Fri Apr 09 18:44:56 MST 2010
This is the only info from the data sheet.

Quote:
12 MHz internal [B]RC oscillator trimmed to 1% accuracy[/B] that can optionally be used as a system clock.