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I'm looking for a pair of otherwise interchangeable 8 bit output shift registers where one has open drain (or open collector) outputs, and the other has "normal logic outputs" (ie a pull up transistor and a pull down transistor, I've seen the term tri-state used, though I'm not certain that's exactly what I need). Can anyone suggest suitable parts?

I'm planning to build a PCB using large mosfets as final outputs, and these shift registers to drive them. I will only decide whether to use N-Chan or P-chan mosfets as high side or low side switches when I populate each board, the overall supply voltage to the mosfets will be anywhere from 3V up to 20 volts (I'm aware of the input voltage limits on mosfets).

For N-Chan mosfets I will use a "normal" shift register to drive the mosfet to 5v, or turn the mosfet off at 0v.

For P-Chan mosfets I will use a the open drain on the shift register to drive the mosfet down to ground, or let a pull up resistor float it up to supply voltage to turn it off.

I can find plenty of "normal" shift registers and a few open drain ones, but none of the parametric search tools are set up for telling me which have the same pinouts, and I'm not familiar enough with the parts to know which parts are a good place to look at. Many of the data sheets completely omit the details of the output circuitry.

Additionally I need latching and ideally PDIP, though I'll make the brave jump to SMD if I really have to. I'd like them to be cost effective, and I intend to run them at 5V, though 3.3v compatibility would be nice.

The closest I've found is the TI sn74ls595 and sn74ls596 which would do the job perfectly but are so old the datasheet on TI's site is scanned in and they cost a fortune to source. An alternative would be a way to use a normal a normal 595 shift register against a 20v pull up, but I'm confident that wouldn't end well without using a row of 8 transistors in the middle, and that's a parts count issue I'd rather avoid.

[edited to fix mosfet naming]

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Most logic devices are designed with push/pull outputs by default. You are more likely to find open-drain outputs in devices that are designed to switch a load current. So when you search for LED drivers, you find something like the TLC6C598 (or TPIC6C596 if you really want DIP).

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  • \$\begingroup\$ The TPIC6C596 perfectly solves half the problem, but I also need a complimentary part with the same pinout in push-pull to solve the whole problem. \$\endgroup\$ – Thingomy Mar 15 '20 at 16:13
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Consider instead a MOSFET driver IC designed for this purpose. Choose any logic you like for your shift register.

Example: https://www.onsemi.com/products/discretes-drivers/gate-drivers/ncp5104

This chip can drive FETs up to 20V. Bonus: you could consider using NFETs for both high and low drive. There are others from Maxim, TI, Linear Tech and other companies.

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  • \$\begingroup\$ While this is an excellent solution in demanding situations, this adds ~£4 BOM cost and achieves the same result as a signal transistor (+ passives) per channel in my circuit. So although this would work great, it doesn't help in my case. \$\endgroup\$ – Thingomy Mar 15 '20 at 1:01
  • \$\begingroup\$ Try Diodes Inc. I bet they’re cheaper. diodes.com/products/power-management/gate-drivers/… \$\endgroup\$ – hacktastical Mar 15 '20 at 1:05

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