TMS320F28069 - Internal vs External Oscillator

Tackle the 1st question first.

C1 and C2 are actual capacitors that you need to connect in the circuit . They need to be highly stable (COG, NPO dielectric, 1% tolerance). Typically say for a 20Mhz quartz crystal, 22pf C1 and C2 will be good. For other crystal values you need to check the crystal datasheet for the resonance capcitors to be attached.

Vivek

Randy,

I wanted to clarify some.  I know that the documentation can be complicated.  For the Piccolo F28069 there are several clock source choices:
1) Internal oscillator 1 (no external components needed; source is generated in-chip)
2) Internal oscillator 2 (no external components needed; source is generated in-chip; osc 2 is often used as a backup for internal osc 1)
3) Crystal/resonator + load capacitors for use with on-chip crystal oscillator
4) External clock source via external oscillator

Option 1 and 2 will be less precise over temperature than the other options and therefore may not 'by default' meet some timing specs for certain applications.  (I say 'by default' because there is a way to calibrate the oscillator at different temps during operation, but this will use up some cycles). 

However, I would say that the majority of the F2806x's customers use option 1.  Option 3 is a bit more precise over temperature and option 4 is the most precise (but also the most expensive).

Running CAN on an MCU (and meet CAN's specifications) is an example of a situation which may require connecting something external.

Vivek above has accurately described the setup for Option 3 which is what you asked about.

See page 76 of the following for more information: http://www.ti.com/lit/spruh18


Thank you,
Brett

Hi,

Your description suits the user manual, but for the F28069 controller-card's

data sheet appears that between the X1 and X2 pins a 20MHz oscillator is connected, instead of a

crystal/resonator - see figure:

It's quiet confusing - is it a crystal or an oscillator? am I missing something out?

The data sheet is attached below.

Thanks,

Amitai

F28069controlCARD-SCH[R1.1].pdf

Hi Amitai,

If you take a look at the Bill Of Materials for the F28069 ISO controlCARD (which matches the schematic you attached), you'll find that the component X1 is actually a crystal. 

I understand that this is a bit confusing since the schematic labels X1 as an OSC.  I will file a bug to have this label removed in a future version of the schematic.

Hopefully this helps!


Thank you,
Brett

Thanks much,

Amitai