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 | |
| Voice480)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.

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

On Tue, 26 Nov 2013 14:15:20 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

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


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

Source only... ~100mA.


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.

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 | |
| Voice480)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.

On 11/26/2013 1:59 PM, Jim Thompson wrote:
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.

How about classic TTL output schematics?

VLV

On 11/26/2013 03:22 PM, Jim Thompson wrote:
On Tue, 26 Nov 2013 14:15:20 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

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


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

Source only... ~100mA.


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.

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

...Jim Thompson

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

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson
wrote:

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

---
Can you take the hit from a series Schottky?

On Tue, 26 Nov 2013 13:22:33 -0700, Jim Thompson wrote:

On Tue, 26 Nov 2013 14:15:20 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

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

Possible, yes, but easy?


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

Source only... ~100mA.


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.

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

...Jim Thompson

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

On Tue, 26 Nov 2013 15:41:01 -0500, Phil Hobbs
wrote:

On 11/26/2013 03:22 PM, Jim Thompson wrote:
On Tue, 26 Nov 2013 14:15:20 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

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


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

Source only... ~100mA.


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.

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

...Jim Thompson

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

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 | |
| Voice480)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.

On Tue, 26 Nov 2013 14:28:06 -0600, Vladimir Vassilevsky
wrote:

On 11/26/2013 1:59 PM, Jim Thompson wrote:
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.

How about classic TTL output schematics?

VLV

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 | |
| Voice480)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.

On Tue, 26 Nov 2013 16:03:30 -0600, John Fields
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson
wrote:

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

---
Can you take the hit from a series Schottky?

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 | |
| Voice480)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.

On Tue, 26 Nov 2013 16:46:50 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 13:22:33 -0700, Jim Thompson wrote:

On Tue, 26 Nov 2013 14:15:20 -0600, Tim Wescott
wrote:

On Tue, 26 Nov 2013 12:59:44 -0700, Jim Thompson wrote:

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.

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

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

Possible, yes, but easy?

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.



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

Source only... ~100mA.


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.

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

...Jim Thompson

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?

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


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.

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 | |
| Voice480)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.