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I was comparing the datasheets for the three related CMOS Op Amps from TI: TLC2252, TLC2262, and TLC2272. TLC2252 is the micropower version; TLC2272 is the high-performance version; TLC2262 is offered as a compromise between them.

The equivalent schematics only seem to differ in the area around Q9. In TLC2272, Q9 is part of a current mirror. In TLC2252, it is diode-connected. In TLC2262 just hanging there as a "one-terminal device" (unless the substrate connection is significant.)

TLC2272 Schematic TLC2252 Schematic TLC2262 Schematic

Does Q9 have a function in TLC2262, or is this just an artifact of the manufacturing process? (I.e. are they all made from the same die and trimmed to make the three different versions?)

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    \$\begingroup\$ Errors in data sheets do happen, thus, probably an error in the schematic. Without that connection, Q12 would not act as the intended current source. \$\endgroup\$
    – qrk
    Jun 21, 2021 at 17:16
  • \$\begingroup\$ This IS an error in the schematic, the schematic shown for the TLC2262 simply cannot work like that. It should have been drawn like the schematic of the TLC2272. How do I know? I design CMOS circuits like this as my daily job. OK: With Q12's gate only connected to Q10 like that, Q12 would not be able to be turned off so the output cannot be pulled low. \$\endgroup\$
    – Bimpelrekkie
    Jun 21, 2021 at 18:50
  • \$\begingroup\$ @Bimpelrekkie Can you comment on the one answer here, or post an answer suggesting how the schematic should be? \$\endgroup\$
    – Theodore
    Jun 23, 2021 at 21:51
  • \$\begingroup\$ As I wrote: "It should have been drawn like the schematic of the TLC2272", all that is needed is to add a connection between the drain of Q9 and the drain of Q10. At least, that is the simplest "fix" I see to make the circuit able to work. \$\endgroup\$
    – Bimpelrekkie
    Jun 24, 2021 at 7:39

1 Answer 1

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It is intended to show how the 2262 is a compromise between the higher current & performance of the 2272 and ultra low current of the 2252. This is accommodated by the simple changes in the current mirrors from the same design, where the 2262 does not need Q9 to achieve this.

The 2252 reduces the bias current with the added R to lower the mirrored output, which also lowers the bandwidth and raises the impedance with only 50uA per channel.

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    \$\begingroup\$ So, in fact a way to make clear that its only R6 that is varied from zero R to some R to infty R between the devices. \$\endgroup\$
    – asdfex
    Jun 21, 2021 at 18:20
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    \$\begingroup\$ You got it………… leave shorted or cut the shunt across R or cut before the R to isolate , so only 1 of 2 cuts or none. \$\endgroup\$
    – Tony Stewart EE75
    Jun 21, 2021 at 18:31
  • \$\begingroup\$ So it really is fabricated this way then. (Otherwise they would just omit Q9 from the 2262 entirely in the diagram.) \$\endgroup\$
    – Theodore
    Jun 21, 2021 at 20:18

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