Hi, we discussed this new die a few days ago. It appears to match the schematic from National datasheet and I think it's a bandgap, crazy as it sounds.
Look at transistors Q21 and Q22, the latter made of ten paralleled Q21 emitters, and the resistors between them. If I understand correctly, that's exactly what a bandgap reference is supposed to look like. Read my post from February 14th, where I explained why I think that VREF output is determined solely by a need to keep Q21 and Q22 currents equal (maybe up to a constant, not sure what the influence of R8 is). This is achieved by driving their bases to some appropriate level and no higher.
And I just calculated from the values of the resistive divider that with VREF=7.15V their base voltage is about 1.23V, go figure.*
We have also seen a different National part (or so Noopy's eBay vendor said
), which used a similar bias generator to this one but otherwise was identical with all the mainstream xx723s. Perhaps an older National version, maybe a fake, or maybe they really put different dice in the J and CJ versions
You can verify which version you have by testing resistance from VREF to GND. It should show open circuit on the classic design chips and about 15kΩ on this National weirdo.
*There is a bit of influence by Q23 and Q24 collector current. This part of the circuit is completely above my head, but I think it makes little difference because emitter resistors are relatively high and base voltages are only 600~650mV above ground. Maybe I should do the math instead of guessing but I'm lazy