Level Shifter 3.3V to 28V

Id like to convert six 3.3v level signals to 28v signals. Very low current.

I've found some ICs, but they only convert 1 signal each and they internally generate the 28V.

Since I have 28v going into the board, I really dont need the IC to generate or charge pump from the low to high voltage. Im just looking for an IC that takes the 3.3v signals and switches it to 28V when 28V is provided to the IC.

How can I do this??

Reply to
benn686
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How about logic level N fets and pull up resistors? I am assuming your

3.3v signal is really ground to 3.3V, and you want ground to 28v out. Granted, the n-fet scheme will invert the signal.
Reply to
miso

SN7406.

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You'll probably need to set up a 5V rail to drive the 7406. but its inputs are guaranteed to treat anything higher tha 2V as a "1" so 3.3V signals should drive it okay.

A common-emitter array of NPN transistors could do the same job, but you'd need a resistor in series with each base to limit the base current. A common-source array of N-channel MOSFETs could skip the gate resistors, saving you a bit more space and the "on" base current.

-- Bill Sloman, Nijmegn

Reply to
bill.sloman

One popular seven-line switching IC from the old days is TI's uln2003, rated at 50 volts max. TI's cost: 64 cents, Toshiba: 55 cents, and ST: 43 cents. Get TI at 22 cents, qty 1k. Mouser has tens of thousands in stock, in various packages, etc., and can ship nearly a million in 10 days. DigiKey has about 150k parts in stock and will ship you 75k on reels for 19 cents each, this afternoon.

Yep, that one is a true jellybean!

If benn has a uP signal source, he may want to consider Allegro's a6b273 or a6b595. The latter are replacements for TI's tpic6b273 and tpic6b595. The '373s use a byte- wide input latch and the '595s use a shift register.

Reply to
Winfield

That is not a "level shifter" technically, which means to preserve the original signal shifted to a new DC baseline. You need a simple 28V switch with a 3.3V input. In the logic world, 28V is *high voltage*, and since the circuit is communicating with non-logic types of loads, it would be called an *interface*. So you want to look under the interface category of "chips."

Reply to
Fred Bloggs

Check Power Logic series buffers from TI.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

A few dual opamps, maybe, running open-loop.

John

Reply to
John Larkin

What does "convert" mean? 0 to 3.3V => 0 to 28V "logic"?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Look at half-hbridge interface ICs, for example: SN754410 or L293D. In some applications these are nicer than the open collector chips: they actively pull up as well as down and will work with 3.3V inputs, but they do need a

5V supply.
--
/*  jhallen@world.std.com AB1GO */                        /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0)
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Reply to
Joseph H Allen

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JF
Reply to
John Fields

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Open-collector voltage comparators. View in Courier:


               Vcc
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Reply to
John Fields

What? No hysteresis ?:-) Smirk-Smirk ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

or, better yet:

Vcc | +28 [R1] +28 | | | [10K] +----|-\\ | | | >--+-->OUT1 IN1>----|----|+/ | U1A | LM339

--
JF
Reply to
John Fields

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Oh, yeah... I forgot about the slow edge rates of 3.3V logic! ;)
Reply to
John Fields

Thanks! I think this might work best for me.. a simple dip with 6 inputs and 6 outputs is ideal! Switching time is not a concern, and the inversion I can take care of in the FPGA so no biggie there, but I do have a dumb question, the data sheet for the SN7406N shows that VCC should be 7 Volts, and that the output will be 30V.. it doesnt require the high voltage as an input to chip, whats the theory on how this chip works?

Reply to
benn686

Use opamps, get active pullup, less parts, and possibly less power consumption, depending on how hard the load needs to be pulled up, which isn't specified here.

John

Reply to
John Larkin

Got a 28V rail-to-rail-output device in mind, John ?:-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

There are lots around, but they're not super cheap. The load, and its swing requirements, aren't specified, so we don't know how close it has to swing, or indeed if it has to pull down at all.

We designed a pulse generator, actually a laser driver, a couple of months ago. It puts a 75-volt, 250 ps wide pulse into 50 ohms, up to a few MHz max. At one point, we needed to go from ecl (0.8 volt swing) to the gate of a gaasfet, with ideal swing from about -2 (to turn it off) to about +0.5 (to enhance it a bit.) The ideal logic level shifter turned out to be an opamp! An AD8009 does it in about 600 ps.

John

Reply to
John Larkin

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Blah, blah, blah, blah, blah.

He said the load on the +28 was "very low", and even if nothing on
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Reply to
John Fields

Since the load and the swing requirements are unspecified, there's not a lot of point arguing the details. Open-loop opamps are sometimes handy in these situations: pullup/pulldown drive, high voltage swing, no external components, low quiescent current, built-in current limiting, cheap and available.

I thought it was about electronics, almost on-topic in s.e.d. I suppose you're not interested in fast level shifters, working with

555's mostly.

And I didn't say "me", I said "we." I didn't design this particular level shifter, I just thought it was cool.

John

Reply to
John Larkin

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