CV/CC synchronous buck -- do they exist?!

Switching regulator datasheets are the pits IME. Modern parts all seem to have so much internal 'intelligence' that they're about as predictable as Eddie the shipboard computer in HHGTTG. The worst ones lie through their teeth, such as the one for the MCP16312, which claims that it keeps PWMing down to zero load, which it does not.

I never use a new switcher without prototyping it very carefully.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

The old venerable UCC3825 and derivatives can be conrilled like you want. You do need to add high side driver though

Cheers

Klaus

My fave lately is LTM8078, which can be run in always-switch mode (burpless) and does have an LT Spice model.

You can use half, or both halves in parallel for more current, or get two separate voltages out, of either polarity.

But it is BGA. There is some standard LTC chip inside.

You could add a couple of parts to some dumb switcher, to add a current component to the feedback.

Some of the old National Simple Switchers had cycle-by-cycle (peak) current limiting. Nice, reliable, dumb parts. I just used an LM2576HV to convert 48 volts to 12, at some absurdly low switching frequency.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

gled

I think the Rohm BD9E30x series might work for you. I recently used the BD

9E301 for my first-ever "flybuck", kind of fun. I'm actually using an exte rnal current limit, since the 5A internal limit is too high for my magnetic s (so I couldn't find the perfect part either. If you find a 1.5-2A equiva lent let me know).

"Short Circuit Protection (SCP) The short circuit protection block compares the FB terminal voltage with the internal reference voltage VREF. When the FB terminal voltage has fallen below 0.85V (Typ) and remained in that state for 1.0msec (Typ), SCP activates andstops the operation for 16msec (Typ) and subsequently initiates a restart."

TL;DR: no CC mode.

Best regards, Piotr

For my Class H TEC driver, I just dork the feedback pin with another resistor to a DAC. You ought to be able to do the same thing with an op amp to make a CC mode, if your switcher isn't too whizzy.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

There is a Linear Technology design which has two of their linear regulators (LT1086 I think) preceded bij switcher pre-regulator, which is set to keep de voltage over the linears constant (1.7 V or so) . The linears do the actual current limiting an regulation, it could go down to 0 V. I don't have the pdf or link handy, but I recall they have a small pcb with everything on it, I think it was named "lab supply".

Mat Nieuwenhoven

After more research, I believe it is the simplest solution. TPS54302 looks dumb enough; mainly, it seems not to have the output under-voltage "protection". It should be then possible to fool it sufficiently to get CC mode with a low-side sensing opamp.

I am literally shocked by my findings. Most of my effort goes into the battle with the "intelligence" of the "modern" parts, not into the actual design. What has happened to the predictability of our designs? Now I have crystal clear understanding of JL's pervy art of blowing parts. I used to attribute it to curiosity, but it actually is a survival strategy.

Best regards, Piotr

Check out the Rohm BD9E302EFJ Not quite 3.5 amps but 3.0 amps anyway... Close.

7.0V?28V Input, 3A Integrated MOSFET Single Synchronous Buck DC/DC Converter

Re. CV/CC

Typically, voltage feedback is given back to the chip but you could certainly send it a current feedback signal or combination with extra ciruitry.

The point is to avoid the circuitry. I was used to the belief that CC/CV is a pretty standard application for a switcher and was using that every now and then back in the UCC384x days.

Now it looks like the CC mode capability is an eccentric need, let alone CC/CV. Sending the current feedback signal to the part might end up in an endless reset sequence, as most of the newest controllers check if the FB voltage is above some internal threshold and turn off if not. One is either dead in the water or is about to start a peek-a-boo game with the IC designer. An uphill battle, given the fact that he is being paid full-time for making your life harder.

I am afraid that the 0 to VREF FB days are gone.

Best regards, Piotr

If you inject a little current into the FB pin, the chip will still regulat e the FB pin at its normal voltage. The output voltage will sag to compens ate. It works really well as long as you keep the extra current-derived lo op slower than the normal loop; 10x slower works well. I'm using this tech nique in one of my current designs and you can drive into a short just fine .

The plan for now is to check if the TPS54428 wants to mate with the INA199. According to the datasheet the controller, there should be no hiccup. I will share the results in due course.

Best regards, Piotr