Trans-Conductance

Hi James,

In DM816x datasheet (Table 8-6. Input Requirements for Crystal Circuit on the Device Oscillator) is provided only the data you need to select your external crystal. As this crystal is external for the DM816x device, not all the data is provided in the DM816x datasheet, but only the data needed. Other external crystal data should be documented in the manufacture documentation of this external crystal.

BR
Pavel

Hello Pavel,

I would completely agree with your response, IF I was selecting an external crystal.  But I am not, I have a customer who is using the DM816x chip and is having intermitten problems with start-up.  We are reviewing the crystal drive circuit.  I have completed a Negative Resistance and Drive Level test in efforts to trouble-shoot the problem.  A different approach is to use a calculation finding Gm Critical and in this calculation it uses the trans-conductance of the Amplifier or driver circuit (this is within the DM816x IC).  This information has to come from the manufacture of the IC, (TI).  TI either will or will not give me this information. Other IC manufactures do offer this information, I'm just asking if TI will do the same.

Regards, James

James,

In DM816x TI EVM, the crystal is external and is manufactured by Abracon corporation - ABM7-27.000MHZ-D2Y-T

From what I see in the DM816x datasheet, we have internal oscillator, but the crystal is external. I do not think we have internal crystal (internal to the DM816x device).

BR
Pavel

Pavel,

I know the crystal external, BUT inside the IC between pins A19 and C19 is an amplifier, (this may be what your calling the internal oscillator), something has to provide power to  the crystal, and that power exits and enters the DM816x through these two pins (A19 and C19).  The IC circuity (amplifier or oscillator) that provides this power has a trans-conductance value, that is the value that I need for my calculation.  I don't need assistance in choosing a crystal, I know the crystal is external.  Crystals are passive components, they need a power source and that power source comes from the IC.

Regards, James

James,

So you need a value regarding the internal oscillator, value (trans-conductance) that is not documented in the DM816x public datasheet. Let me check with the HW team if we have such value and if we can disclose it in a public forum.

BR
Pavel

Hello Pavel,

It has been more than 6 weeks and I haven't heard any response.  Does this mean the HW team will not allow the transconductance value to be displayed?

Regards,
James

James,

I have checked with the HW team, but I was not able to find this info.

Regards,
Pavel