TPS65950: Tr/Tf time for HFCLKIN of TS65950

mike zeng

Part Number: TPS65950

For TPS65950, the max. Tr/Tf of HFCLKIN is 5ns(in the page 134 of datasheet), the oscillator (26M HZ) is connected to HFCLKIN, but Tr/Tf of Oscillator is 6ns, my question is:

1.Is it accpeted for this oscillator connected to HFCLKIN?

2.what kind of negative impact will be caused?

over 4 years ago

0 Kevin LaRosa over 4 years ago

TI__Genius 17380 points

Hi Mike,

TPS65950 is NRND so support will be limited.

I would not recommend using an oscillator / circuit that can't meet the design specification. Perhaps you can modify the behavior with component changes.

Unfortunately I can't provide a clear risk for the additional 1 ns of rise time. It would fall outside the simulated test cases so I have no data to know.

0 Nathan Kro1 over 4 years ago in reply to Kevin LaRosa

Prodigy 40 points

Kevin

Can you confirm the Tr/Tf is with the stated Vih of 1V and Vil of 0.6V?

0 Kevin LaRosa over 4 years ago in reply to Nathan Kro1

TI__Genius 17380 points

Hi Nathan,

You are correct that the timing is based on Vih and Vil for the PMIC.

0 Nathan Kro1 over 4 years ago in reply to Kevin LaRosa

Prodigy 40 points

Thanks

0 Brad Brown over 4 years ago in reply to Kevin LaRosa

Prodigy 165 points

Kevin,

I have that vIL = 0.6V and vIH = 1.0 making the tr/tf from 33% to 56%.

This forum post link below appears to state the tr/tf is from 10% to 90%.

e2e.ti.com/.../752

Can you please confirm which is correct?

0 Kevin LaRosa over 4 years ago in reply to Brad Brown

TI__Genius 17380 points

Hi Brad,

The specification is for Vil and Vih.

Kartik may have been referencing the simulated use case or just providing a conservative answer. Back in 2009 they were still doing new designs for this device so 10%-90% is a safer recommendation.

If you have are having an issue with this pin, it may help to provide an eye diagram showing what it looks like.

0 Brad Brown over 4 years ago in reply to Kevin LaRosa

Prodigy 165 points

Kevin,

I have an oscillator that specifies the tr/tf at 6nS from 10% to 90% for it's output.

I have that the TI TPS65950 input tr/tf 5nS from 33% (vil = 0.6V) to 56% (vih=1.0V).

Using linear calculation, I would the calculate the effective tr/tf for the oscillator to be 1.4nS when using 33% to 56%.

This would seem to be well with in the 5nS tr/tf specified by the TPS65950. Would you agree?

0 Kevin LaRosa over 4 years ago in reply to Brad Brown

TI__Genius 17380 points

Hi Brad,

I would agree, this seems to be within specification.

One note I can add is that if you were operating at the 38.4 MHz setting, this would not be sufficient to meet the pulse duration requirement (1/38 MHz = 26.3 ns period, so to have a pulse width of 11.84 ns, it would require a rise time of 1.32 ns).

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TPS65950: Tr/Tf time for HFCLKIN of TS65950