Newer Model Instrumentation Amp
in [Design]
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From: Jim Thompson on 21 Jun 2010 11:10 On Sun, 20 Jun 2010 15:28:53 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sun, 20 Jun 2010 22:01:24 GMT, paulhendersen(a)qualcomm.com (Paul >Henderson) wrote: > >>On Sun, 20 Jun 2010 07:38:00 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On a current design, I had to make my own. I wanted lots of >>>overvoltage protection, logic-switchable gains from 0.05 to 256, high >>>precision, and at least +-12 volts of common-mode range, 120 dB CMRR >>>at high gain. I wound up with a classic 3-opamp diffamp, using an >>>LT1124 dual opamp, four Supertex depletion mode fets for protection, a >>>discrete string of thinfilm resistors, one DPDT gain switch relay, two >>>analog muxes, and an INA154 as the second stage. Two tiny trimpots >>>tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! >>> >> >>If that's not a proprietary design John, any chance of posting a link >>to the schematic? >> >>Paul Hendersen > > >Yes, it is proprietary but, hell, I *am* the boss, so here it is: > >ftp://jjlarkin.lmi.net/22S490B_ch12.pdf > >in hopes that it will invoke an entertaining flurry of pecking and >clucking. > >I don't totally like the style of the schematic; I drew it on D-size >vellum "my way" and The Brat entered it into PADS. It would be too >much work to push 16 channels of stuff around at this point. > >John > Young Buck Alarm: Driving Inductive loads directly from CMOS logic is NOT recommended without some kind of protective elements. Allowing CMOS body diodes to be exposed to flyback currents can be hazardous, possibly fatal to the chip if latch-up occurs. Observe data sheet current limits carefully. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Where is Joe McCarthy when you need him ??
From: Spehro Pefhany on 21 Jun 2010 11:58 On Mon, 21 Jun 2010 08:10:45 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Sun, 20 Jun 2010 15:28:53 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Sun, 20 Jun 2010 22:01:24 GMT, paulhendersen(a)qualcomm.com (Paul >>Henderson) wrote: >> >>>On Sun, 20 Jun 2010 07:38:00 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On a current design, I had to make my own. I wanted lots of >>>>overvoltage protection, logic-switchable gains from 0.05 to 256, high >>>>precision, and at least +-12 volts of common-mode range, 120 dB CMRR >>>>at high gain. I wound up with a classic 3-opamp diffamp, using an >>>>LT1124 dual opamp, four Supertex depletion mode fets for protection, a >>>>discrete string of thinfilm resistors, one DPDT gain switch relay, two >>>>analog muxes, and an INA154 as the second stage. Two tiny trimpots >>>>tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! >>>> >>> >>>If that's not a proprietary design John, any chance of posting a link >>>to the schematic? >>> >>>Paul Hendersen >> >> >>Yes, it is proprietary but, hell, I *am* the boss, so here it is: >> >>ftp://jjlarkin.lmi.net/22S490B_ch12.pdf >> >>in hopes that it will invoke an entertaining flurry of pecking and >>clucking. >> >>I don't totally like the style of the schematic; I drew it on D-size >>vellum "my way" and The Brat entered it into PADS. It would be too >>much work to push 16 channels of stuff around at this point. >> >>John >> > >Young Buck Alarm: Driving Inductive loads directly from CMOS logic is >NOT recommended without some kind of protective elements. Allowing >CMOS body diodes to be exposed to flyback currents can be hazardous, >possibly fatal to the chip if latch-up occurs. Observe data sheet >current limits carefully. > > ...Jim Thompson Good advice in general. I've used emitter followers from CMOS for the unipolar latching type, which don't require diodes. Not sure which ones JL used, but some of those relays only draw 8mA or so at 4.5V, and the diodes are shunted by MOSFETs under normal conditions so it ought to work okay. In pathological conditions (say a sudden drop of Vdd to 0 during the brief pulse when the relay is energized) the diodes would conduct, but something like 8mA maximum is pretty conservative for that particular part- data sheet says 100mA or 50mA. A 20-cent H-bridge...
From: Jim Thompson on 21 Jun 2010 12:10 On Mon, 21 Jun 2010 11:58:27 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Mon, 21 Jun 2010 08:10:45 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Sun, 20 Jun 2010 15:28:53 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sun, 20 Jun 2010 22:01:24 GMT, paulhendersen(a)qualcomm.com (Paul >>>Henderson) wrote: >>> >>>>On Sun, 20 Jun 2010 07:38:00 -0700, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On a current design, I had to make my own. I wanted lots of >>>>>overvoltage protection, logic-switchable gains from 0.05 to 256, high >>>>>precision, and at least +-12 volts of common-mode range, 120 dB CMRR >>>>>at high gain. I wound up with a classic 3-opamp diffamp, using an >>>>>LT1124 dual opamp, four Supertex depletion mode fets for protection, a >>>>>discrete string of thinfilm resistors, one DPDT gain switch relay, two >>>>>analog muxes, and an INA154 as the second stage. Two tiny trimpots >>>>>tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! >>>>> >>>> >>>>If that's not a proprietary design John, any chance of posting a link >>>>to the schematic? >>>> >>>>Paul Hendersen >>> >>> >>>Yes, it is proprietary but, hell, I *am* the boss, so here it is: >>> >>>ftp://jjlarkin.lmi.net/22S490B_ch12.pdf >>> >>>in hopes that it will invoke an entertaining flurry of pecking and >>>clucking. >>> >>>I don't totally like the style of the schematic; I drew it on D-size >>>vellum "my way" and The Brat entered it into PADS. It would be too >>>much work to push 16 channels of stuff around at this point. >>> >>>John >>> >> >>Young Buck Alarm: Driving Inductive loads directly from CMOS logic is >>NOT recommended without some kind of protective elements. Allowing >>CMOS body diodes to be exposed to flyback currents can be hazardous, >>possibly fatal to the chip if latch-up occurs. Observe data sheet >>current limits carefully. >> >> ...Jim Thompson > >Good advice in general. I've used emitter followers from CMOS for the >unipolar latching type, which don't require diodes. > >Not sure which ones JL used, but some of those relays only draw 8mA or >so at 4.5V, and the diodes are shunted by MOSFETs under normal >conditions so it ought to work okay. In pathological conditions (say a >sudden drop of Vdd to 0 during the brief pulse when the relay is >energized) the diodes would conduct, but something like 8mA maximum is >pretty conservative for that particular part- data sheet says 100mA or >50mA. What John did is AOK, the SN74LVC2G02 is rated for �24mA drive, so I'd expect the body diodes can cope. These "simple" gate parts have few, if any, sneak paths for latch-up. Just don't try it with a complex chip. > >A 20-cent H-bridge... Yep. I've recently been involved in designing chips for security cameras. Besides the usual video functions, there are actuators, for example... iris control and day/night filters. So I've developed a special-purpose H-bridge for such applications that needs no diodes to cope with flyback. As usual I can't divulge details until the patent applications are in place :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Where is Joe McCarthy when you need him ??
From: John Larkin on 21 Jun 2010 12:13 On Mon, 21 Jun 2010 11:58:27 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Mon, 21 Jun 2010 08:10:45 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Sun, 20 Jun 2010 15:28:53 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sun, 20 Jun 2010 22:01:24 GMT, paulhendersen(a)qualcomm.com (Paul >>>Henderson) wrote: >>> >>>>On Sun, 20 Jun 2010 07:38:00 -0700, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On a current design, I had to make my own. I wanted lots of >>>>>overvoltage protection, logic-switchable gains from 0.05 to 256, high >>>>>precision, and at least +-12 volts of common-mode range, 120 dB CMRR >>>>>at high gain. I wound up with a classic 3-opamp diffamp, using an >>>>>LT1124 dual opamp, four Supertex depletion mode fets for protection, a >>>>>discrete string of thinfilm resistors, one DPDT gain switch relay, two >>>>>analog muxes, and an INA154 as the second stage. Two tiny trimpots >>>>>tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! >>>>> >>>> >>>>If that's not a proprietary design John, any chance of posting a link >>>>to the schematic? >>>> >>>>Paul Hendersen >>> >>> >>>Yes, it is proprietary but, hell, I *am* the boss, so here it is: >>> >>>ftp://jjlarkin.lmi.net/22S490B_ch12.pdf >>> >>>in hopes that it will invoke an entertaining flurry of pecking and >>>clucking. >>> >>>I don't totally like the style of the schematic; I drew it on D-size >>>vellum "my way" and The Brat entered it into PADS. It would be too >>>much work to push 16 channels of stuff around at this point. >>> >>>John >>> >> >>Young Buck Alarm: Driving Inductive loads directly from CMOS logic is >>NOT recommended without some kind of protective elements. Allowing >>CMOS body diodes to be exposed to flyback currents can be hazardous, >>possibly fatal to the chip if latch-up occurs. Observe data sheet >>current limits carefully. >> >> ...Jim Thompson > >Good advice in general. I've used emitter followers from CMOS for the >unipolar latching type, which don't require diodes. > >Not sure which ones JL used, but some of those relays only draw 8mA or >so at 4.5V, and the diodes are shunted by MOSFETs under normal >conditions so it ought to work okay. In pathological conditions (say a >sudden drop of Vdd to 0 during the brief pulse when the relay is >energized) the diodes would conduct, but something like 8mA maximum is >pretty conservative for that particular part- data sheet says 100mA or >50mA. > >A 20-cent H-bridge... The relays are Fujitsu FTR-B3GB4.5Z-B10, 4.5 volts at 25 mA. Wonderful little parts, second-sourced by Omron. They will turn on/off in under a millisecond if you drive them right. Yes, this driver is prefectly safe from latchup, for the two reasons you mention. We've shipped about 8000 so far, no problems. This is the second time in recent days that this old hen has criticized my design suggestions without bothering to understand them first. Or bothering to be constructive. John
From: Jim Thompson on 21 Jun 2010 12:23
On Mon, 21 Jun 2010 09:13:14 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 21 Jun 2010 11:58:27 -0400, Spehro Pefhany ><speffSNIP(a)interlogDOTyou.knowwhat> wrote: > >>On Mon, 21 Jun 2010 08:10:45 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>>On Sun, 20 Jun 2010 15:28:53 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Sun, 20 Jun 2010 22:01:24 GMT, paulhendersen(a)qualcomm.com (Paul >>>>Henderson) wrote: >>>> >>>>>On Sun, 20 Jun 2010 07:38:00 -0700, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On a current design, I had to make my own. I wanted lots of >>>>>>overvoltage protection, logic-switchable gains from 0.05 to 256, high >>>>>>precision, and at least +-12 volts of common-mode range, 120 dB CMRR >>>>>>at high gain. I wound up with a classic 3-opamp diffamp, using an >>>>>>LT1124 dual opamp, four Supertex depletion mode fets for protection, a >>>>>>discrete string of thinfilm resistors, one DPDT gain switch relay, two >>>>>>analog muxes, and an INA154 as the second stage. Two tiny trimpots >>>>>>tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! >>>>>> >>>>> >>>>>If that's not a proprietary design John, any chance of posting a link >>>>>to the schematic? >>>>> >>>>>Paul Hendersen >>>> >>>> >>>>Yes, it is proprietary but, hell, I *am* the boss, so here it is: >>>> >>>>ftp://jjlarkin.lmi.net/22S490B_ch12.pdf >>>> >>>>in hopes that it will invoke an entertaining flurry of pecking and >>>>clucking. >>>> >>>>I don't totally like the style of the schematic; I drew it on D-size >>>>vellum "my way" and The Brat entered it into PADS. It would be too >>>>much work to push 16 channels of stuff around at this point. >>>> >>>>John >>>> >>> >>>Young Buck Alarm: Driving Inductive loads directly from CMOS logic is >>>NOT recommended without some kind of protective elements. Allowing >>>CMOS body diodes to be exposed to flyback currents can be hazardous, >>>possibly fatal to the chip if latch-up occurs. Observe data sheet >>>current limits carefully. >>> >>> ...Jim Thompson >> >>Good advice in general. I've used emitter followers from CMOS for the >>unipolar latching type, which don't require diodes. >> >>Not sure which ones JL used, but some of those relays only draw 8mA or >>so at 4.5V, and the diodes are shunted by MOSFETs under normal >>conditions so it ought to work okay. In pathological conditions (say a >>sudden drop of Vdd to 0 during the brief pulse when the relay is >>energized) the diodes would conduct, but something like 8mA maximum is >>pretty conservative for that particular part- data sheet says 100mA or >>50mA. >> >>A 20-cent H-bridge... > >The relays are Fujitsu FTR-B3GB4.5Z-B10, 4.5 volts at 25 mA. Wonderful >little parts, second-sourced by Omron. They will turn on/off in under >a millisecond if you drive them right. > >Yes, this driver is prefectly safe from latchup, for the two reasons >you mention. We've shipped about 8000 so far, no problems. > >This is the second time in recent days that this old hen has >criticized my design suggestions without bothering to understand them >first. Or bothering to be constructive. > >John Do pay attention, John! ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Where is Joe McCarthy when you need him ?? |