Switching Regulator - Watchdog Timer, etc...

[superflux]

I'm looking to move from a Linear Regulator to a Switching Regulator with as little fuss as possible. I have found this (TLE 4271) unit from Mouser and would like some insight.

I am using a PIC 16F series chip. The input voltage to the regulator is 14~15.5 and the output will be 5 volts drawing at most 150mA.

I really don't know if I need Pins 2, 3, or 6 or how to bypass them if possible.

1) The reset (pin 3) appears to be internally connected to the output. Anything else need to be done?
2) Not sure why I would need the Watchdog Input - do I need to connect it to something?
3) Can someone explain what INHIBIT (pin 2) means?

In a nutshell, I would like to see if the circuit below would satisfy my needs and what to do with those pins (2,3,6).

Typical Circuit and Pin Layout at bottom.

Thanks,

SF

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EDIT: Not sure why the images were not showing up - here are direct links:

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[mneary]

TLE-4721 appears to be a linear regulator with some extra features.

I've been very impressed with the specs on the TPS63031, although I have never used it myself. Someone else here is using it and has problems so you might want to watch how that goes.

 

[superflux]

I guess Mouser had that VR categorized incorrectly. I'll look at the model you posted.

Thanks,

SF

 

[crutschow]

If you don't need the extra bells and whistles of the TLE-4721, why not use a 7805 which is cheap and readily available.

 

[superflux]

I want to get away from Linear Regulators. They run too hot when dropping 9-10 volts.

 

[crutschow]

At 150mA it will dissipate about 1.5W which a small heatsink will readily dissipate.

Otherwise you might consider a Black Regulator. It's simple and cheap.

 

[superflux]

I'm going to try a switching regulator that is contained within a small footprint: AP1507-50D5L-13 Diodes Inc. Switching Converters, Regulators & Controllers

It should keep the heat low with minimal changes to my layout.

 

[crutschow]

That should work for you. It requires two capacitors, a diode, and an inductor for operation.

 

[superflux]

They're not very clear on what size capacitors or what hertz the inductor should be. I'm going to try a 47uH for the 5 volt as in their adjustable circuit example.

Any thoughts?

SF

 

[crutschow]

Inductors are rated in Henrys (H) not Hertz (Hz). The 47µH should be fine, the exact value is not critical.

10µF in parallel with a 0.1µF ceramic at the input, along with a 100µF in parallel with a 0.1µF at the output should work. For minimum output ripple use several smaller output caps in parallel, such as four 22µF, to minimize the ESR of the capacitors.

Make sure you wire the caps and inductor with short leads to the chip, and use some type of ground plane for proper circuit operation and minimum noise.

 

[superflux]

Inductors are rated in Henrys (H) not Hertz (Hz). The 47µH should be fine, the exact value is not critical.

I knew it was Henrys... just testing you. Can't believe I typed Hertz. Is there any other value that relates to the inductor or are they fairly generic?

10µF in parallel with a 0.1µF ceramic at the input, along with a 100µF in parallel with a 0.1µF at the output should work. For minimum output ripple use several smaller output caps in parallel, such as four 22µF, to minimize the ESR of the capacitors.

Awesome! I usually have a 100uf and a .1uf on the input side and just a .1uf before the microprocessor on the output. I will add to the output.

Make sure you wire the caps and inductor with short leads to the chip, and use some type of ground plane for proper circuit operation and minimum noise.

Not a problem. The board I designed with the linear regulator used the entire backside as a heatsink / ground plane.

Thanks for taking the time, Carl, to help me out!

SF

 

[Mike - K8LH]

superflux,

I upgraded to a switching regulator a couple years ago for the similar reasons -- I'm using surplus Laptop power 'bricks' with outputs ranging from 13 to 17 vdc and I was concerned about how hot 7805 type linear regulators were getting when I would draw more then about 50 ma through them.

I ended up sampling some 1-amp Micrel 200-KHz switching regulators (MIC45745) which look very similar to the 150-KHz device you're looking at. The switching regulator runs cool to the touch without a heatsink. Pay close attention to the layout and the recommended low ESR capacitors and low resistance inductors.

Cheerful regards, Mike

 

[superflux]

Thanks, Mike. I'll look into that model as well.