Digital peak current mode control

Hello everybody,

As I am new to chip design and peak current mode control, I have a project where I am asked to design a digital peak current mode control of boost converter and implement it on ASIC.
so please, if you have any good references where i can learn to design such hardware share it with me.

best regards

You'll have to be more specific about what you mean by "digital." Does this mean you'll use ADCs for sampling output voltage, and a DSP for control?

Peak current mode control is best done by sampling the current waveform with a simple comparator, since sampling with an ADC has too much latency. The reference of the comparator is digitally generated with a DAC, and if the DAC is fast enough it can digitally implement slope compensation as well.

I'd recommend studying app notes for digital controllers based on microcontrollers, like TI or microchip.

Peak current mode control is best done by sampling the current waveform with a simple comparator

Click to expand...

I think "sampling" in this context is misleading. The current waveform is always acquired and provided to the input of the comparator i.e. analogically. The fact that the comparator changes state only when the current reaches the reference makes it look like it is sampled at that point, but it is not. The current is acquired continuously.

All Boost converters work to some extent by regulating the ramped or integrated current and flyback from a pulse voltage.

But trying to design anything without any input and output specs is a waste of time.

Everybody loves to talk about the bright sweet future
of digital control for regulators and converters, even if
they can't list one actual upside for the case at hand.

I have rubbed up against a digital POL DC-DC design
with a digital core and as others have said, the current
compare is indeed a simple (autozeroed) comparator.
The design is not mine to share.

Since nobody gave you (since you didn't give us, I
assume) any more detailed specs I suppose you are
at liberty to define just what the current mode control
scheme must be. Follow the notion of a DAC reference
and a comparator, assume the "code" is Somebody
Else's Problem, and all you have left is a bit-field, a
compare and a digital "stop, now" output that goes
to the power farm FET drivers' front end logic.

Your compare could even be pretty dumb - like a
current summing node - if you have a low enough
min pulse width. Current mode DAC pulls, and a
"senseFET" tap on the high side switch pushes,
at some point the sum will reverse and there is
your comparison. Of course this node would need
to be lightly loaded or clever (or both) to get speed
and gain. That's why they call it design and not
catalog shopping.

Thank you everyone for your quick reply. in order to get helped, you have asked me more detail and specification.
I would live to know what do you mean by these 02 criterions, specifications and requirements.
for me what I know is that , I have to control the boost converter (input 5V,output 12V) digitaly, and as some of few mentionned, I will need a DAC and ADC for sampling the voltage and current(as was asked) and write a code in C (microcontroller) and later using just digital circuit (vhdl code).
as you can see, I am quite novice and this project is quite big i belive,this is why I am bit confused.I have read some scientific articles, Power electronics book of Ned mohan(usefull for understanding the working principles), but I still fell to learn a lot.
that is why I am asking some guidelines and thank you again

So you'll need a few building blocks:
1. Digital PWM synthesizer
2. ADC (for sampling Vout, maybe more)
3. Comparator (for sampling current)
4. Digital controller to tie it all together.

Is your task to design every block from scratch, or just implement the digital controller?

There is another topology alternative, hysteretic fixed
on time control, which could be viable depending on
your "customer" (real or imaginary). There is no PWM,
rather PFM and PFM can either be burst mode or linear
to error voltage. Burst mode is really simple and stable
(bang, bang).

Fixed on time and DCM plays nicely with simple boost
where you have to respect the inductor's saturation
current, but know it always starts from zero. Boundary
and CCM get trickier, as I understand things (only have
dabbled in DCM boost converters myself).

mtwig,My task is to design everything from scratch.I have through the book of Ned Mohan Na d I found out he is calculating the transfert function of dc/dc converter and PWM modulator in time variant mode. should I do the same and then use Z-transform for the digital mode?
Dick_freebird, thank you for the suggestion but my Prof has asked me the igital peak current mode control