Damping resistor calculating formula of ADV7282A

henry-tang on Nov 1, 2018

Hi ADI expert,

Might you please help to check what's the definition or calculation equation of total Capacitance?

XLSX

And it mentioned each side, do we have to divided by two?

Thank you!!

Henry

Top Replies

PoornimaSubramani
Sep 28, 2021 in reply to TedH4DDV +1 suggested
Hi,

Please find the below comments,

For example, if the external capacitor is 12pF, device pin capacitance is 4pF and PCB is estimated at 2pF, the the value for cell B5 would be 18pF, right ?

We can…

Parents

0 PoornimaSubramani

on Nov 1, 2018 1:24 PM
Hi,

I beleive yes.

Thanks,

Poornima
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 henry-tang on Nov 1, 2018 2:49 PM in reply to PoornimaSubramani

Hi Poornima,

So if my cap and resistance is as below :

load cap(15p)

stray cap(3p)

crystal cap(18p)

my total cap of each side should be (15+3+18) / 2 = 18p

is this correct?

Thank you!

Henry
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 PoornimaSubramani

on Nov 8, 2018 9:26 AM in reply to henry-tang
Hi,

There it is mentioned as total value for each side of XTAL (XTALP, XTALN), So i beleive,

XTALN,C1 as 20PF,

XTALP, C2 as 20PF

I am not sure about the remaining values,Let me check with part specialist on this.

Thanks,

Poornima
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 henry-tang on Nov 22, 2018 10:35 AM in reply to PoornimaSubramani

Hi Poornima,

Excuse me, do you get feedback from specialist? thank you!
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 PoornimaSubramani

on Nov 22, 2018 10:57 AM in reply to henry-tang
Hi,

Sorry for the delay, again checking with part specialist on this.

Thanks,

Poornima
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 TedH4DDV on Sep 24, 2021 2:08 PM in reply to PoornimaSubramani

Is there an update to this (3 years later)?

For example, if the external capacitor is 12pF, device pin capacitance is 4pF and PCB is estimated at 2pF, the the value for cell B5 would be 18pF, right?

Also, are the voltage values in cells E20, E21, F20, F21 meant to be edited? Are these values defined by the ADV728x or for the crystal?
Cancel
Up 0 Down

Reply

Verify Answer

Cancel
0 PoornimaSubramani

on Sep 28, 2021 8:47 AM in reply to TedH4DDV
Hi,

Please find the below comments,

For example, if the external capacitor is 12pF, device pin capacitance is 4pF and PCB is estimated at 2pF, the the value for cell B5 would be 18pF, right ?

    We can calculate the capacitance by referring AN-1260 application note, For example,

    C1 = C2 = 2(Cload - Cstray) - Cpg

    Assume Cstray = 2-3pF, depends on board traces

    Assume Cpg = 4pf, pin capacitance.

C2 & C3 are dependent on the load capacitance specified in the crystal data sheet. As an example a Golledage MA01377 has a load capacitance of 30pF so C2 = C3 = 2 * (30 - 2) - 4 = 52pF, closest real cap. value would be 47pF. These caps adjust the impedance the crystal drivers see to make sure the crystal will oscillate.

   Below we have attached the crystal that was used on our evaluation board,however we can use other crystals as long as we re-calculate the load capacitors based on the following application note.

http://www.analog.com/media/en/technical-documentation/application-notes/AN-1260.pdf

ma01377.pdf

Also, are the voltage values in cells E20, E21, F20, F21 meant to be edited?

   No, the voltage values can't be edited & you will get the voltage value depending upon the value that you are feeding on the calculator tool of section 1

    Please note the purpose of this damping resistor is to limit the current flowing through the XTAL and to limit the voltage across the XTAL amplifier. To define the appropriate value of the damping resistor RDAMP (see the Typical Circuit Connections section), consult the accompanying calculator tool at ADV7182A/ADV728xA Resistor Tool (Rev. A)

Are these values defined by the ADV728x or for the crystal?

      E20, E21, F20, F21 values are defined for the crystal.

Thanks,

Poornima
Cancel
Up +1 Down

Reply

Verify Answer

Reject Answer

Cancel

Reply

0 PoornimaSubramani

on Sep 28, 2021 8:47 AM in reply to TedH4DDV
Hi,

Please find the below comments,

For example, if the external capacitor is 12pF, device pin capacitance is 4pF and PCB is estimated at 2pF, the the value for cell B5 would be 18pF, right ?

    We can calculate the capacitance by referring AN-1260 application note, For example,

    C1 = C2 = 2(Cload - Cstray) - Cpg

    Assume Cstray = 2-3pF, depends on board traces

    Assume Cpg = 4pf, pin capacitance.

C2 & C3 are dependent on the load capacitance specified in the crystal data sheet. As an example a Golledage MA01377 has a load capacitance of 30pF so C2 = C3 = 2 * (30 - 2) - 4 = 52pF, closest real cap. value would be 47pF. These caps adjust the impedance the crystal drivers see to make sure the crystal will oscillate.

   Below we have attached the crystal that was used on our evaluation board,however we can use other crystals as long as we re-calculate the load capacitors based on the following application note.

http://www.analog.com/media/en/technical-documentation/application-notes/AN-1260.pdf

ma01377.pdf

Also, are the voltage values in cells E20, E21, F20, F21 meant to be edited?

   No, the voltage values can't be edited & you will get the voltage value depending upon the value that you are feeding on the calculator tool of section 1

    Please note the purpose of this damping resistor is to limit the current flowing through the XTAL and to limit the voltage across the XTAL amplifier. To define the appropriate value of the damping resistor RDAMP (see the Typical Circuit Connections section), consult the accompanying calculator tool at ADV7182A/ADV728xA Resistor Tool (Rev. A)

Are these values defined by the ADV728x or for the crystal?

      E20, E21, F20, F21 values are defined for the crystal.

Thanks,

Poornima
Cancel
Up +1 Down

Reply

Verify Answer

Reject Answer

Cancel

Children

No Data