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I'm looking for either a high-side driver or bus driver that can be tri-stated and then withstand its output being driven above rail with very little or any back current flow.

But I'm drawing a blank finding something like that off-the-shelf. ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson
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It sounds like a difficult part to realize -- perhaps that's why?

Speeds, currents, type of load? Does it just need to source current, or does it need to sink it, too?

If your current and speed needs were modest, and an on-off source would work, then a depletion-mode N-channel FET would do, but you'd need to find one.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

I know, from re-working Moto/ON-Semi logic to fit a new foundry process, that kind of tri-state is possible.

Source only... ~100mA.

Alternatively I could use a discrete P-channel capable of 10A+ with VGS=4V ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

How about classic TTL output schematics?

VLV

Reply to
Vladimir Vassilevsky

How about:

back-to-back BSS84 PFETs (S-S), G-G shorted), resistor from S to G, NFET from G to ground.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs 

--
Can you take the hit from a series Schottky?
Reply to
John Fields

Possible, yes, but easy?

I thought of that. But that only works if your output rail isn't going to float much above the input, or if you somehow pull the gate up to the highest of either the output or the input rail. And then it'll want to be slow.

I don't pay much attention to Vgs on FETs, except to know that if it's a

12V-rated part, the Vgs is way lower. Is your 4V realistic?

That's what made me think of depletion-mode N-fet: the higher the source gets, the more "off" the thing turns. But your P-channel is probably easier to find.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

Thanks! I found a P-channel PowerMOS: CSD25401Q3 (TI) which will do the trick. The customer was playing a charge pump game to drive an NMOS, and I thought I was stuck with their approach, but the PMOS fixes the issue and loses not only a couple of capacitors, and a couple of diodes, but a power supply rail as well ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

I'm rail value limited, so the Vbe drop would be a killer. But I found a PMOS solution: CSD25401Q3 (TI) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

I found: CSD25401Q3 (TI), solves the problem straight away. But thanks, anyway! ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

In the chip world? Trivial. Discrete world, too many components. Though an open drain high-side driver that could do a full tri-state disconnect from rail would have worked. I suspect there's one out there, I'm just not calling it by its right name.

Stuck with it. You know the drill, someone f...ed it up and I get called it to patch it, without changing anything ;-)

Yep. CSD25401Q3 ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

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