Question about C674x Vref for 1.2V

Hi,

As per my understanding, Vref for 3.3V and 1.8V are given in figure-6.2 of chapter 6.1.1.1 because they are I/O Voltage whereas 1.2V is not an I/O Voltage.

As shown in figure-6.3, Vref for Rise and Fall times are considered for clocks and it is given as Vih-min and Vil-max respectively for input clocks and Voh-min and Voh-max resp. for output clocks.

Suresh-san,

Thanks for your prompt reply.  It is helpful.

Could you let me ask more in detail?

Suresh K said:

As per my understanding, Vref for 3.3V and 1.8V are given in figure-6.2 of chapter 6.1.1.1 because they are I/O Voltage whereas 1.2V is not an I/O Voltage.

I could not fully understand this.  The title of Figure 6.2 is "Input and Output Voltage Reference Levels for AC Timing Measurements"
So, I thought the Vref on figure-6.2 was the reference point for AC timing regardless whether it was I/O voltage or not.
How does it affect to the Vref if 1.2V is not an I/O voltage?..

Suresh K said:

As shown in figure-6.3, Vref for Rise and Fall times are considered for clocks and it is given as Vih-min and Vil-max respectively for input clocks and Voh-min and Voh-max resp. for output clocks.

 So, more concretely, what do you recommend, for example, clock frequency and pulse width?

Is it OK to quote to customers,
   Tc (OSCIN) cycle time (20ns)  is " Vih-min to the next Vih-min"?
   Tw(OSCINH)  (0.4*tc) is "Vih-min to the next Vil-max"
   Tw(OSCINL) (0.4*tc) is "Vil-max to the next Vih-min"

 Thanks.

Best regards,
Kenichi Yoshii

Hi Kenichi Yoshii-san,

I read the name as "Input and Output Voltage Reference Levels for AC Timing Measurements".
So I thought that since 1.2V is not an I/O Voltage, its not mentioned in that figure.  If there is any misunderstanding from my side regarding this, please let me know.

Suresh-san,

Thanks for your reply.
Maybe, I'm confused.   Sorry, but please let me keep asking some more?

By "input and output voltage", do you mean if the device has the power supply for that voltage?
I am not sure how that is related to the AC timing.
In chapter 6.1.1.1, the datasheet says "All input and output timing parameters are referenced to Vref for both "0" and "1" logic levels."
So, I can't understand how to read this for 1.2V input (ie, OSCIN & RTC).

Probably, if you can give me the answer to the following my last question, it will be helpful for me to talk with customers about OSCIN&RTC timing.

Yoshii said:

 So, more concretely, what do you recommend, for example, clock frequency and pulse width?

Is it OK to quote to customers,
   Tc (OSCIN) cycle time (20ns)  is " Vih-min to the next Vih-min"?
   Tw(OSCINH)  (0.4*tc) is "Vih-min to the next Vil-max"
   Tw(OSCINL) (0.4*tc) is "Vil-max to the next Vih-min"

Thank in advance.

Best regards,
Kenichi Yoshii

Yoshii-san,

I think the parameters you are looking for are in Section 5.2, Recommended Operating Condition of SPRS377D (page 56).

VIl for the OSCIN pin is 0.3 * CVdd.

VIh for the OSCIN pin is 0.7 * CVdd.

The maximum transition time for OSCIN is 25% or the input clock cycle (max) or 10 ns whichever is smaller (faster).

Regards,

Clay

Clay-san,

Thank you.
Yes, I know what the Vil and Vih are.  Those are used as Vref for transition time (Figure 6-3 of C6747 datasheet(SPRS377D), p59).

What I want to know is the Vref for pulse width and cycle time of OSCIN (& RTC).
While the Vref for transition time are defined as Vil and Vih ((Figure 6-3 of SPRS377D, p59), the Vref for AC timing measurements for 1.2V is not defined (Figure 6-2 of SPRS377D, p59).

So, my question again is,

Yoshii said:

Is it OK to quote to customers,
   Tc (OSCIN) cycle time (20ns)  is " Vih-min to the next Vih-min"?
   Tw(OSCINH)  (0.4*tc) is "Vih-min to the next Vil-max"
   Tw(OSCINL) (0.4*tc) is "Vil-max to the next Vih-min"

Should I suggest the Vref for transition time (defined in Figure 6-3) to measure the pulse width and cycle time for OSCIN (& RTC)?

Thanks.
Best regards,
Kenichi Yoshii