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LM318 pin 8 usage

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  • David C. Partridge
    This is my first post here. I m looking at a circuit that has a 1uF ceramic capacitor between Pin 2 and pin 8 on an LM318 op-amp. Regardless of whose
    Message 1 of 7 , Nov 3, 2011
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      This is my first post here.

      I'm looking at a circuit that has a 1uF ceramic capacitor between Pin 2 and pin 8 on an LM318 op-amp.

      Regardless of whose data-sheet I look at for the LM318, I can find little or nothing about the use of this pin (other than that it is used for feed-forward compensation). The other two pins (1 and 5) that can also be used (apparently) for this purpose are only shown being used for offset (balance) correction.

      Where can I find some documentation that addresses the choice of the components to use in the feed-forward network?

      Thanks
      Dave
    • Derek
      Increase slew rate for inverter application with 150V/us capability (double band width) - National Semi s and TI s data sheet. ... high speed and fast
      Message 2 of 7 , Nov 3, 2011
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        Increase slew rate for inverter application with 150V/us capability
        (double band width) - National Semi's and TI's data sheet. "... high
        speed and fast settling time ... useful in A/D converters, oscillators,
        ..." There is also an internal circuit equivalent showing the connection
        of pin 8. Check out TI's web site for additional information and on-line
        training. I have not looked through this much, but it appears to be
        documented. If all else fails, us the TI forum support e2e.ti.com and
        ask questions.


        Derek Koonce
        DDK Interactive Consulting Services


        On 11/3/2011 2:41 AM, David C. Partridge wrote:
        >
        > This is my first post here.
        >
        > I'm looking at a circuit that has a 1uF ceramic capacitor between Pin
        > 2 and pin 8 on an LM318 op-amp.
        >
        > Regardless of whose data-sheet I look at for the LM318, I can find
        > little or nothing about the use of this pin (other than that it is
        > used for feed-forward compensation). The other two pins (1 and 5) that
        > can also be used (apparently) for this purpose are only shown being
        > used for offset (balance) correction.
        >
        > Where can I find some documentation that addresses the choice of the
        > components to use in the feed-forward network?
        >
        > Thanks
        > Dave
        >
        >
      • David C. Partridge
        I don t call that text you quoted as useful information on choosing components. It is just fluff . D. ... From: Electronics_101@yahoogroups.com
        Message 3 of 7 , Nov 3, 2011
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          I don't call that text you quoted as useful information on choosing components. It is just "fluff".

          D.
          -----Original Message-----
          From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of Derek
          Sent: 03 November 2011 14:32
          To: Electronics_101@yahoogroups.com
          Subject: Re: [Electronics_101] LM318 pin 8 usage

          Increase slew rate for inverter application with 150V/us capability (double band width) - National Semi's and TI's data sheet. "... high speed and fast settling time ... useful in A/D converters, oscillators, ..." There is also an internal circuit equivalent showing the connection of pin 8. Check out TI's web site for additional information and on-line training. I have not looked through this much, but it appears to be documented. If all else fails, us the TI forum support e2e.ti.com and ask questions.


          Derek Koonce
          DDK Interactive Consulting Services


          On 11/3/2011 2:41 AM, David C. Partridge wrote:
          >
          > This is my first post here.
          >
          > I'm looking at a circuit that has a 1uF ceramic capacitor between Pin
          > 2 and pin 8 on an LM318 op-amp.
          >
          > Regardless of whose data-sheet I look at for the LM318, I can find
          > little or nothing about the use of this pin (other than that it is
          > used for feed-forward compensation). The other two pins (1 and 5) that
          > can also be used (apparently) for this purpose are only shown being
          > used for offset (balance) correction.
          >
          > Where can I find some documentation that addresses the choice of the
          > components to use in the feed-forward network?
          >
          > Thanks
          > Dave
          >
          >


          ------------------------------------

          Please trim excess when replyingYahoo! Groups Links
        • AlienRelics
          Hm. Nice 2nd post. ; ) http://www.national.com/ds/LM/LM118.pdf Pins 1 and 5 are used for offset balance and overcompensation. Do you understand what
          Message 4 of 7 , Nov 3, 2011
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            Hm. Nice 2nd post. ;')

            http://www.national.com/ds/LM/LM118.pdf

            Pins 1 and 5 are used for offset balance and overcompensation. Do you understand what feedforward compensation is, or is that what you are asking about?

            The late, great Bob Widlar wrote up a bit about Feedforward Compensation as used in the LM101 OpAmp:
            http://www.national.com/ms/LB/LB-2.pdf

            What specifically are you wanting to know? How to calculate the capacitance?

            Steve Greenfield AE7HD


            --- In Electronics_101@yahoogroups.com, "David C. Partridge" <david.partridge@...> wrote:
            >
            > I don't call that text you quoted as useful information on choosing components. It is just "fluff".
            >
            > D.
            > -----Original Message-----
            > From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of Derek
            > Sent: 03 November 2011 14:32
            > To: Electronics_101@yahoogroups.com
            > Subject: Re: [Electronics_101] LM318 pin 8 usage
            >
            > Increase slew rate for inverter application with 150V/us capability (double band width) - National Semi's and TI's data sheet. "... high speed and fast settling time ... useful in A/D converters, oscillators, ..." There is also an internal circuit equivalent showing the connection of pin 8. Check out TI's web site for additional information and on-line training. I have not looked through this much, but it appears to be documented. If all else fails, us the TI forum support e2e.ti.com and ask questions.
            >
            >
            > Derek Koonce
            > DDK Interactive Consulting Services
            >
            >
            > On 11/3/2011 2:41 AM, David C. Partridge wrote:
            > >
            > > This is my first post here.
            > >
            > > I'm looking at a circuit that has a 1uF ceramic capacitor between Pin
            > > 2 and pin 8 on an LM318 op-amp.
            > >
            > > Regardless of whose data-sheet I look at for the LM318, I can find
            > > little or nothing about the use of this pin (other than that it is
            > > used for feed-forward compensation). The other two pins (1 and 5) that
            > > can also be used (apparently) for this purpose are only shown being
            > > used for offset (balance) correction.
            > >
            > > Where can I find some documentation that addresses the choice of the
            > > components to use in the feed-forward network?
            > >
            > > Thanks
            > > Dave
            > >
            > >
            >
            >
            > ------------------------------------
            >
            > Please trim excess when replyingYahoo! Groups Links
            >
          • David C. Partridge
            Steve, Yes, I had found Bob Widlar s note on the LM101. Yes, I do understand feed forward compensation in principle, you bypass the slow and phase shifty first
            Message 5 of 7 , Nov 3, 2011
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              Steve,

              Yes, I had found Bob Widlar's note on the LM101.

              Yes, I do understand feed forward compensation in principle, you bypass the slow and phase shifty first stage of the opamp, and inject the higher frequency signals into the later stages directly, thus increasing the effective slew rate and avoiding oscillation (by cutting out a good bit of the phase shift).

              The problem is that of where to find the necessary data to allow me to understand (calculate) the effect a particular compensation network (or single specific capacitor value) between pins 2 and 8, or indeed applied to the other two compensation pins. None of the data sheets appear to give this information, and none of the books I have on opamps discuss this either save to say "specialised pins for external compensation".

              The comment on fluff wasn't directed at the respondent - it was a bitch about lack of detailed information in the data sheets on using these pins. I would have thought this would merit an application note in its own right.

              Maybe I don't own the right books on opamps or have failed my Google exam :(

              Regards,
              David Partridge
              -----Original Message-----
              From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of AlienRelics
              Sent: 03 November 2011 16:10
              To: Electronics_101@yahoogroups.com
              Subject: [Electronics_101] Re: LM318 pin 8 usage

              Hm. Nice 2nd post. ;')

              http://www.national.com/ds/LM/LM118.pdf

              Pins 1 and 5 are used for offset balance and overcompensation. Do you understand what feedforward compensation is, or is that what you are asking about?

              The late, great Bob Widlar wrote up a bit about Feedforward Compensation as used in the LM101 OpAmp:
              http://www.national.com/ms/LB/LB-2.pdf

              What specifically are you wanting to know? How to calculate the capacitance?

              Steve Greenfield AE7HD
            • Howard Hansen
              Hello David, There is some information on using feed forward compensation with the LM318 in National Semiconductors LB -17. At one time National Semiconductor
              Message 6 of 7 , Nov 3, 2011
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                Hello David,

                There is some information on using feed forward compensation with the
                LM318 in National Semiconductors LB -17. At one time National
                Semiconductor used the designation LM118, LM218 and LM318 to refer to
                similar devices with different temperature ratings. Hence what the
                Linear Brief says about feed forward compensation for the LM118 also
                applies to the LM318. See:
                <http://www.national.com/an/LB/LB-17.pdf>

                I get the impression the value of the feed forward capacitor is not that
                critical. More important is the value of the feed forward resistor.

                Because of the difficulty of finding detailed feed forward design
                information for It looks like a better approach is to build the circuit
                on a bread board and do some testing.

                Howard


                On 11/3/2011 10:51 AM, David C. Partridge wrote:
                >
                > Steve,
                >
                > Yes, I had found Bob Widlar's note on the LM101.
                >
                > Yes, I do understand feed forward compensation in principle, you
                > bypass the slow and phase shifty first stage of the opamp, and inject
                > the higher frequency signals into the later stages directly, thus
                > increasing the effective slew rate and avoiding oscillation (by
                > cutting out a good bit of the phase shift).
                >
                > The problem is that of where to find the necessary data to allow me to
                > understand (calculate) the effect a particular compensation network
                > (or single specific capacitor value) between pins 2 and 8, or indeed
                > applied to the other two compensation pins. None of the data sheets
                > appear to give this information, and none of the books I have on
                > opamps discuss this either save to say "specialised pins for external
                > compensation".
                >
                > The comment on fluff wasn't directed at the respondent - it was a
                > bitch about lack of detailed information in the data sheets on using
                > these pins. I would have thought this would merit an application note
                > in its own right.
                >
                > Maybe I don't own the right books on opamps or have failed my Google
                > exam :(
                >
                > Regards,
                > David Partridge
                > -----Original Message-----
                > From: Electronics_101@yahoogroups.com
                > <mailto:Electronics_101%40yahoogroups.com>
                > [mailto:Electronics_101@yahoogroups.com
                > <mailto:Electronics_101%40yahoogroups.com>] On Behalf Of AlienRelics
                > Sent: 03 November 2011 16:10
                > To: Electronics_101@yahoogroups.com
                > <mailto:Electronics_101%40yahoogroups.com>
                > Subject: [Electronics_101] Re: LM318 pin 8 usage
                >
                > Hm. Nice 2nd post. ;')
                >
                > http://www.national.com/ds/LM/LM118.pdf
                >
                > Pins 1 and 5 are used for offset balance and overcompensation. Do you
                > understand what feedforward compensation is, or is that what you are
                > asking about?
                >
                > The late, great Bob Widlar wrote up a bit about Feedforward
                > Compensation as used in the LM101 OpAmp:
                > http://www.national.com/ms/LB/LB-2.pdf
                >
                > What specifically are you wanting to know? How to calculate the
                > capacitance?
                >
                > Steve Greenfield AE7HD
                >
                >



                [Non-text portions of this message have been removed]
              • David C. Partridge
                Howard, Thank you for that pointer, it looks like this is one of those less well documented areas. Strange that the Tektronix circuit I m looking at only has
                Message 7 of 7 , Nov 4, 2011
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                  Howard,

                  Thank you for that pointer, it looks like this is one of those "less well documented" areas.

                  Strange that the Tektronix circuit I'm looking at only has a 1uF capacitor (no feed forward resistor) between pins 2 and 8, and just a pair of 27k resistors to ground on pins 1 and 5.

                  Should anyone be interested this is on the Display Board on the 7854 oscilloscope, schematic <34>.

                  Regards,
                  David Partridge
                  -----Original Message-----
                  From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of Howard Hansen
                  Sent: 03 November 2011 18:44
                  To: Electronics_101@yahoogroups.com
                  Subject: Re: [Electronics_101] Re: LM318 pin 8 usage

                  Hello David,

                  :
                  :
                  See:
                  <http://www.national.com/an/LB/LB-17.pdf>

                  :

                  Because of the difficulty of finding detailed feed forward design information for It looks like a better approach is to build the circuit on a bread board and do some testing.

                  Howard
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