2A sink and source voltage regulator

[mihaibl]

Does anybody know of a single IC voltage regulator (5V input) that would be capable of both sourcing and sinking up to 1.5A or 2A (when the output is at 3V)?

Thank you

 

[IRstuff]

Probably not.

Most VR's are constructed with a pass transistor that does the heavy hauling for current output and will not work correctly in sink mode.

If you run the VR output into a high-current unity gain buffer, it might work. Either that, or you'll need to build your own high current push-pull output stage.

TTFN

 

[Lewish]

Definitely NOT! You are asking for regulator to go from being a positive voltage reduction to an inverting or negative regulator when you go from source to sink. A Howland current source can be made to do that for a few milliamps, but not Amps.
What is your application?

 

[electricuwe]

Lewish,

I guess you didn't understand mihaibls question. The voltage-current-plane has four quadrants ! I guess IRstuffs approach will be useful for mihaibl.

 

[Lewish]

Gee, electricuwe, I thought I did, did you? He said single IC voltage regulator. A unity gain buffer is not a regulator, so you need something to get from your 5V source to 3V reference if you are going to use a buffer. And the last time I checked, you can only sink current if your terminal voltage is lower than the load voltage. So, how are you going to sink current if the load voltage goes to zero?

Maybe the problem is, I assume people are engineers, since this is what this forum is for, and that they know what they are asking for.

 

[IRstuff]

Please do not get into fisticuffs! ;-)

It was clear that the poster was trying to use a crowbar as a screwdriver, (possibly literally). The voltage regulator with buffer follower offered the simplest match to his posted requirements.

It's also clear that are a number of approaches that might do the intended job more efficiently.

TTFN

 

[mihaibl]

First of all let me thank everybody for his/her input.
My intention though was not to start a complicated thread, so please people do not fight over this question. I think each of you provided interesting and valuable feedback!

The application is to provide termination voltage (3V) to a bus used with both TTL-type drivers and also so-called "active negation" drivers. Think of it like similar to the DDR SDRAM, or more exactly like SCSI-3. The input to the regulator is always 5V.

One such bus termination "regulator" is made by Fairchild (FAN6555), as I just found out in the weekend. The problem with this is that it seems nobody else makes a perfect replacement, so it's a single source. Philips and National have variants of this "DDR bus termination reference", but support different pinouts and currents/inputs.

I specified "single IC" just because I want to keep down the number of components (cost, MTBF, etc). It's true that following either IRStuff's or Lewish's approaches I can achieve my design goal, depending on how you look at the problem.

Thanks again to everybody. Let me know if by any chance you stumble across an exact equivalent of the FAN6555. And yes, we are all engineers, even (or especially) if sometimes we try to use crowbars as screwdrivers.

 

[Lewish]

I don't know if this helps, but the FAN6555 was originally made by Samsung.

In reality, what you are asking for is an active pullup-pulldown terminator. The FAN6555 is fairly sophisticated, so I don't think you will find an exact second source, unless it is the same part number.

 

[IRstuff]

Your expanded description rules out any possible replacement with an ad hoc solution. The termination supply requires careful control of impedance/inductance, which is why there are dedicated devices.

You may simply need to look at alternate suppliers with lower power ratings.

 

[electricuwe]

Lewish,

no one asked for a device capable of sinking current when the load voltage goes to zero.

 

[VITORA]

Try the LM1118 of Linear Technology.

Vitor Amorim