B1 Intermediate Other 205 Folder Collection
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Hello my name is Andy Reiter, I'm with Microchips Power Supply Applications Group.
The topic we would cover today is our new CIP Hybrid Power Starter Kit.
This starter kit is introducing the PIC16F176X and 7X families of freely
programmable pwm microcontrollers. These microcontrollers
have specific peripherals that are running independently from the core and
are highly configurable so that it can configure them or interconnect them in
specific ways to form some PWM controller architectures. So the
advantage of this freely configurable peripherals are that you can tailor the
PWM controller capabilities specifically to your very application. To allow
designers to utilize these capabilities we also have introduced a new design
tool chain, which is encapsulated in our development environment MPLAB X. So this
is part of our Microchip Code Configurator tool called MCC, and is a
set of sub libraries that allows you to simplify the configuration of multiple
peripherals at the same time. We have set up this assembly in this demo here where
we have a starter kit on the left and here on the right on the screen you see
this MPLAB X environment with the specific switch mode power supply library
subset for Microchips Code Configurator. So this tool now can be used to set up
PWM controllers that support different control modes like peak current load
control, voltage mode control, average motor control. You can combine
multiple control loops, you can add in specific fault handlers and the device
itself then supports you with setting specific thresholds like shutdown levels
for maximum currents, voltage clamping, inputs under voltage
over voltage lockout and further features by utilizing the internal DACs.
So the variety of things you can do with these peripherals is really really wide.
So the switching power supply library helps you to abstract the
capabilities and tailor them to specific topologies. So therefore we also offer
different sets of pre-configurations for targeting specific topologies. So once
you have used that tool to set up a PWM controller for a specific application
and topology, that where you're generating the code, the code is
downloaded into the device, the codes that's generated with the device also
includes functional aspects like soft start, so that you're having a nice
behavior right from the beginning, so that when you fire up the power supply
for the very first time that you can be sure that it won't burn. So once you have
downloaded it, and this is what we are doing in this demo set, is then we have
connected a network analyzer to the output, we are injecting an error signal
and we're using our BODI 100 Network Analyzer to measure the total open-loop
gain in the closed-loop system. So depending on the additional tools you
might have used to design your power supply and to set up your compensation networks,
so to achieve a certain stability of your application, you can then
just measure directly from the kit the final results compared with your
simulation and then you take it from there and in further some iteration
steps you might have quickly achieved your goal.
so before we go into the details about this kit and its software and design
tool chain might be necessary to explain a little bit what hybrid power actually
means the work hybrid is often used in different contexts like hybrid power
supplies is something entirely different from hybrid power controllers so hybrid
in our context means that it's a device which is somewhere between the analog
control domain and the full digital control domain so analog controllers
usually come as fixed Asics covering very specific topologies or specific
applications so the conventional pol controllers for example or you have here
switch switching regulator for flight controllers or resonant converters and
for every single one of them so for every single application you might have
a set of specific Asics to choose from while full digital control then
digitizes even the feedback loop so everything is running and software the
interface is an A to D converter so analog signals continuous time domain
analog signals are converted into digital signals and then processed
through software and then some PWM is adjusted so this the letter 1 full
digital control gives you extreme flexibility in terms of what a
controller can do while analog circuitry is might have a significantly higher
performance but they are nailed to what they have been designed for so that
section between both worlds that is what we're trying to cover with hybrid
controls so it means we have a small device with relatively low power
consumption but and in within the architecture we're combining digital
logic with analog circuits so that we can leverage that in the advantages of
both worlds in one single device so and when we are focusing on these hybrid
devices then it's always a a device which is targeting the
application would have a specific requirement for very specific features
so the basic concept of these products is that in one chip you get a
microcontroller core and a PWM controller peripheral that PWM
controller peripheral always breaks down into three main major blocks consisting
of the compensator so Erin play fire basically and the modulator so the
modulator then determines which control loop control mode you're applying and
there's always an additional fault level that helps you to make sure that the
power supply stays within its safe operating range default is usually tied
into the modulator or uses inputs to the modulator to shut down the passerby in
case something is going wrong so when we're looking into the modulator so here
on the right side we see a specific setup for a voltage or an average
current mode and on the top we see an implementation for a classical picker
remote controller so here on the upper writes in the current note section we
find a subset of codes lay or labeled with PRG so that stands for programmable
RAM generator so we are utilizing this ramp generator to generate a negative
ramp which is modulated onto the reference input to our modulator that
then is used usually in Picard mode for slope computation but it can also be
used in voltage mode this is when you look below you also see a voltage range
on the upper right where we use a positive ramp to generate an analog PWM
signal the next therefore we find in this modulator are fast comparators so
in the current mode section on the top we find that comparative
between the RAM generator and our so-called Co G which is actually our PWM
output logic block so that comparator is used to tie in the current feedback so
that we can trip on peaks of the inductor current while in voltage and
average card mode that comes very same comparator is now used to compare the
reference from the Aaron profile to the artificially generated ramp and when the
ramp exceeds the reference voltage level then it changes its output strips and
and it's our latch and this then influences our PWM output so in both
motivators we always use a PWM module and the so called CEO cheese or the
complimentary output generator or in other devices it's called
a complimentary waveform generator cwg but these blocks to is actually said
they give to get to the capability to start out from a single PWM signal and
split it up into complementary waveforms allowing you to adjust that x or you can
split it up up to a full bridge drive so it also offers additional inputs for
false signals so fault triggers that come from different peripherals or from
external circuits can also be fed into the PWM logic and some additional glue
logics and also would allow you to establish something like conditional
fault handing so the third level is the compensator the compensator on these
devices usually just a are just consisting of an errand to fire so this
is actually a general-purpose operational amplifier then you get a
deck to adjust reference and then the reference itself which is called the
fixed voltage reference F we are
so in addition to help you to condition signals for especially false signals of
to define fault levels to trip on there is a an additional set of comparators
and attack with a lower resolution so usually you get five bit tags that help
you to set up thresholds that five bits might not be sufficient for in some
cases so when you need a higher resolution then it is possible to use
external resistors to create a window which is then still scalable with five
bit and then you send it around a threshold range you would like to set up
so once we have picked these three blocks we now can use these to set up an
entire analog feedback loop here we see the first architecture so on the right
we have a power supply so in this case it's just for the purposes of a sake of
an example it's a boost converter that offers a voltage feedback coming from a
voltage divider and we have a peak current signal which is taken from below
the boost mains which using a shunt resistor so the voltage feedback now is
fed into the outer loop portion of our architecture which is then our air
amplifier so the amplifier compares that signal to our reference which is
internally set by attack the output of that amplifier is fed into the
programmable Ram generator and this part we are modulating a negative frame onto
this reference voltage to apply a slope compensation for our inner p-card load
control loop then we are entering then or we are taking this output of this
program of a ramp generator feed it into a comparator that comparator compares
that reference signal to the peak current signal that's coming from our
shunt resistor and then that output of that comparator trips our
PWM output logic and effectively true hates the duty cycle so to set up the
switching frequency we are now using a digital PWM oniel which allows us to set
up a fixed period with a maximum duty cycle so in case the comparator does not
trip the pwm module in time it's the only time base of the pwm module which
makes sure that the duty cycle is not hitting hundred percent and maybe with a
bad outcome when your inductor saturates and then your power supplies effectively
going out of control
so one thing we see here in this particular example is because of these
devices are highly configurable and can practically drive any kind of topology
it is very hard to define our C Network values that might be necessary to set up
an appropriate computation for every single different topology out there so
therefore all of the compensation networks need to be external with these
devices so we see here in the lower around the OPA so the operational
amplifier that the input as well as it's the output is connected to a device pin
so these device pins are usually sitting right next to each other so that it's
very easy that it can place your RC components of the conversation that are
very close to the device so after having established this basic feedback loop we
are now adding the fault level so the fault level consists of a comparator
with five attack in this case we are using it as an additional over current
shut down and then we can feed that output of the comparator directly into
the CG so that it asynchronously overrides anything that's coming from
the software from the rest of the European architecture
and we can truncate the duty cycle and turn off the PWM immediately as fast as
possible so usually these comparators have a propagation delay of between 30
and 50 nanoseconds and this is the timeframe in which she can shut down can
you respond to fault and shut down the power supply economy so what we can do
with these PWM controllers now is a lot so as I said potentially you can support
all kind of different configurations for specific topologies it does not only
cover fixed frequency you can also setup the peripherals to support user 80
controls like internal time constant of time quasi resonant converters resonant
converters so the variety of possibilities is really really wide so
for just to keep things simple let's just start with fixed frequency
operation off a standard topology and this is what we are doing with this
starter kit so this starter kit we have used a simple synchronous buck converter
not only because it's safe to operate it easy to compensate but also because
everyone is very familiar with this topology so this starter kit now comes
with multiple options so that it can play an experiment and explore a little
bit the capabilities of the part play with different configurations and see
how you can solve different design challenges by using different
modifications of a preset of provided examples so when we are looking into the
hardware we find that this port is as a power supply on the lower side so this
is where we find our synchronous buck converter so that buck converter has
been designed for a power level of approximately 25 watts so the maximum
current call from the outputs at 3.3 volt is
roughly at around 8 m/s so you're above this is where we have find our
controller so that controller is bigger than it would be necessary for that
single topology so we have picked our superset device providing up to four
independent pwm controller peripheral sets the reason why we have done that is
to allow you to switch between different control modes so we have set up one PWM
control of the voltage mode another one for pico remote control in the third one
for average current mode control we use the peripherals of the fourth one to add
more advanced functions one of them for example is VCR sensing so one of the
current feedback options provided by the power plant is a RC network which is
tied in parallel to the main inductor and which can be used to to use a
lossless sensing technique which is fairly popular especially in low voltage
here will applications to implement that function we need an additional append so
as the op-amp is still available from the fourth PWM controller architecture
we can now utilize it to create an additional option which then is tied
into one of the other PDM controllers so that kit now is supported by the power
supply library NCC so when we are now trying to utilize
this extreme flexibility of the Percel we really rely on tools which try to
keep the complexity as low as possible during the design process so for that
particular purpose we have created this switching power supply library which is
available in the microchip code configurator
so the basic architecture so the ones of you who are familiar with MCC might know
that it is a graphical tool that helps you to configure specific settings of
one independent peripheral so usually when you set up an application you pick
one person like a UART and then you use that school to set up moderate or very
specific details of that very powerful and then you're generating hold and the
generated code is then called during startup of the device and putting that
function provided by the person in place so now as we have seen that a switchman
power supply controller is more than just one single peripheral the
configuration of multiple blocks can get very tricky so eventually you might end
up with seven to nine different peripheral blocks that need to be
connected in a very specific way to achieve a certain function so to
simplify that design process we have now added additional layers to our MCC
design tool so here on the bottom of that diagram we see that classical MCC
layer this is what most of you are maybe familiar with and this is what contains
all the different configuration sets of every single powerful so here in that
list you see all the peripherals that are used to form that function of a PWM
controller so here we find this program a program generator the complimentary
output output generator the PWM module a timer comparators digital to analog
converters fixed voltage references op amps and so forth so these blocks mell
are merged into that functional blocks of a modulator here on the left for peak
current mode control and compensator block which consists of an op-amp attack
and the fixed voltage reference here in the right we
another set and this is the model a box for voltage not control or average more
control so once you have you know which control mode you would like to use then
we can tie together compensator and model a the block to form a control mode
block in this case we have two options the card mode control or voltage or
average mode control now this block is still very generic and it's not really
tailored to a specific topology so to make the right position on the
switch configuration which kind of dead times you need we now need to nail down
the topology you would like a pro apply this control block for so this brings us
up to the next level which is the topology level until specifically for
our starter kits we are using a synchronous buck converter block so that
block now when we pick one of these blocks we know exactly what the PWM
output configuration needs to be we know which feedback signals we need to
consider and we can pick all the peripherals to form a PWM controller so
that you as a designer and up with a system that is already pre-configured
and the only remaining options that need to be picked to make this block work or
where should the feedback signals go into the device where is the pillar of
iam coming out of the device and what is your preference value for your feedback
and what is the definition of your switch node so switching frequency and
that times need to be specified so eventually instead of diving into the
peripherals and spending quite some time to set up all these different blocks
functional blocks you now practically just configure the entire system on a
very high level by just using physical values coming from your area application
so we have seen the basic concept of the MCC smps library I would say just let's
give it a try and configure or switch mode power supply so for that purpose I
take my starter kit and I plug it it with my using the micro USB cable and
what happens now when I do this when we look into MPLAB X as soon as the tool
connects we see the product page coming up so MPLAB X is detecting the board and
the board comes with a specific feature that it mounts a thumb drive on which
all the information is stored that is now displayed in that window so now from
that window on you can directly click on go to the kids home page and on that
development kids home page you find all the documents and collaterals we offer
with the device so as of today what you find is a user guide for the kids the
configuration user guide for the switch composed by libraries which concludes
the installation process the library itself so did not be already included in
your envelop X installation you can always download the latest version from
that website and then you find further documentation like schematics and the
detailed data sheet of the chip we are using which is in this case the
pic16f877a so let's get started so to set up a power supply controller on on
that chip what I do first is I create a new project
so I create a standalone project continue I picked the device I'm using
but just pick 16 F one seven seven nine
okay next now I have to check when my tool is and here I think to find the CIP
hyper tower starter kit so I select this one click next choose my compiler and
then I need to give it project name so I call this CIP high HP test choose a
and click finish
so now with in this new generators project I'm now opening MCC
and as well as the mcc modules have floated I can save the configuration I'm
going to build in a specific file which is usually stored in the project
directory so the very first thing and this might be a little bit out of the
scope of normal power supply designs is I have to determine which frequency I
would like to have running on that device so to make sure that all the
peripherals including pwms interrupts input capture you are and everything
else you might use in your application works at decent performance we pick the
eight megahertz oscillator and we enable the PLL which then gives us an effective
CPU frequency of thirty-two megahertz so based on that timing this is the base
for all the other timings we are going to set up in on that chip so later on in
the modules we will find specifications for switching frequencies for dead times
and so forth and all these timings always refer to the specific frequency
we have set in this window so from that point on we are ready to go and dive
into the configuration of the power supply peripherals so to make our life
easy we are now referring to the switching power supply library so when
we look into the device resources we find here this SMPS power controllers so
when we open those then we find either soft blocks or the highest level would
then be power supply topologies so when you recall that diagram we have just
seen at the bottom there were all the peripherals then above they were already
pre-configured sets of peripherals forming modulators and compensators
above that we found encapsulated blocks for control modes and above that there
was our topology so we going to start at the highest level let's say this highest
abstraction layer and as we see there are a couple of different topologies
already with can pick from in this case we pick a
generic synchronous buck converter double click it and now it's loaded into
our project resources when we load that project item then first we end up in a
short page with some short description about what this block is all about the
second one is then our configuration window so if you consider the number of
peripherals who would have to put together for one PWM controller so all
of that is now already pre-configured so we know exactly which peripherals we
need to pick how they need to be interconnected because we know what you
are going to design so the number of parameters then need to be set now comes
down to a very very short list so this now is starts with the switching
frequency so for this particular starter kit we pick 500 kilohertz the maximum
duty cycle this determines some certain clamping value so for that starter kit
it's 90% but it's really highly the application dependent and it really
depends on the topology and your safety levels you're trying to achieve so we
leave it at the 90% for that for our demo setup here the reference voltage
relies on your feedback signal so the voltage divider we used on the starter
kit gives us feedback signals of exactly 2.5 volts when the converter is
producing 3.3 volt at the output so to achieve that 3.3 volts stable output
control we need to set the reference at 2.5 volt then we have leading-edge
blanking so and that depends on the current feedback we are going to use so
the starter kit offers three different current sensing options the first one is
a current Stinson's fauna which is located above the high side switch so
when we switch over into the third top then we see
a simplified schematic that gives us some indication where we find our
current sensing option and how feedbacks and interconnects are done so here we
see that complementary PWM that's connected to the highside and low-side
switch of our half bridge then the current sense gives us the inductor
current so the first option would be this is the one we're going use would be
the currents in some format so that guy is located here just before the hiset
switch that location that is indicated here in is just idolized indicating that
we are always measuring the inductor current in truth the second option would
be the shunt which is located between the inductor and the output capacitor so
at this place and then we have a third option which is called TC our sensing so
we are using a parallel RC network which is sitting in parallel to the inductor
and that would actually give us that indicated current position although this
is more an an emulated current feedback signal so precise but is lossless
because it's not sitting really in the power path so it doesn't create losses
that is the advantage of DC are the penalty is it's not that accurate so the
three different current sensing options have three very different
characteristics so the advantage of a current sentence former is that it's
very fast and it gives you a very nice resolution so it's a large signal so the
signal noise ratio is very good the downside is because it's located above
the high sites which is that we only see half of the current waveform so we only
see current feedbacks when the current when the switch is closed and current is
flowing through that current transformer so we don't see the discharge current
towards the node and the output capacitor the second sensing option the
shunt has the advantage that it shows us the entire current waveform
however the shunt needs to be very small to create as little losses as possible
so we need to amplify that signal to get it up to a size that we can actually
work with it so this is done with a high set current sense amplifier these
amplifiers have limited bandwidth which usually results in a tiny phase shift
and usually some damping on the amplitude so instead of a razor-sharp
triangular current waveform you might get I mean something that's a little bit
more sinusoidal and face shifted the third option the DCR sensing is equally
sensitive so the signal won't be very large so we also need to amplify it and
it is a signal which need also needs to be taken from the high side so we need a
high cycle or higher voltage differential amplifier so the advantage
in this low voltage buck providing 3.3 volt is that the output voltage is still
below the supply voltage of our device so what we can do nervous we can utilize
an on-board amplifier as differential amplifier for the DCR sensing so these
are the three options we have in this first configuration we will start out
with the current sensors form so the Continentals former has a very
particular signal waveform so every time the switch closes it creates a tiny
spike so we see a turn-on spike and that peak of that spike might be higher than
the peak or peak current mode control is triggering on so we have to make sure
that this peak is not accidentally tripping our comparator we're achieving
this by setting up a so-called leading edge blanking window so this time frame
we are setting will disable the comparator during that time between the
start of the cycle until the end of our leading edge blanking period so when we
are going to set this up okay on this particular design we know already it
needs to be 200 15 nanoseconds so the 250 nanoseconds
are counted from the point our internal pwm module is generating the leading
edge so there's the first delay we have to consider is the delay between our
signal generator and the propagation delay through the complementary output
generator logic to the through the pin driver towards the most driver the
propagation delay of the most driver until the MOSFET eventually turns on so
that delay is already 55 milliseconds and then we see that spike of that
current sentence former and the width of the spike is roughly 120 nanoseconds and
to be a little bit on the safe side to account for additional switching noise
we add some safety margin this altogether that delay chain that brings
us up to 250 nanoseconds so the third setting we have to make is dead times so
we have a half bridge converter that means when we are closing both switches
at the same time simultaneously we're practically shortening out the input
voltage and that will potentially or very probably blow our switches so we
have to make sure that this never ever happens this dead time setting is based
on a high resolution delay line which is part of the complimentary own output
generator so we cannot just dead times with a resolution of five nanoseconds
per tick so when we set up a value of three then we get 15 nanoseconds dead
time so here in this mask all the values were entering our physical values so
using physical units so in this case we're just entering 15 nanoseconds if
you try to enter 12 it might sit there with 12 but eventually it will just be
15 anyways so your choices are 5 10 15 20 and so forth
so the rising edge with 50 nanoseconds sounds very short and that the reason
why the dead time needs to be support is the MOSFETs we're using on this starter
kit so these are high speed high speed silicon MOSFETs which turned on in
roughly eight nanoseconds so between five and eight nanoseconds is typically
rise and fall time of these MOSFETs so they're extremely fast and the edges
don't change so any Miller plateau or any additional delays so we can position
them very close to each other to ensure a most efficient operation of our power
stage so the rising edge is 15 in this case the falling edge that time is named
with 60 nanoseconds so the mismatch between both dead times also mainly come
from that delay between our signal generator edge through the entire output
logic MOSFET or our master travel delays and then we have to account for all
these additional and late delays in addition to our appropriate dead time
setting so the best way to figure out how what the appropriate dead time is is
always starting out with a very safe setting which is usually derived from
the data sheets of the components here using so look into your into the data
sheets of the most drivers try to figure out what the corrugation delay is there
look into the most read data sheets look for the typical rise and fall times when
driven by a driver at a certain voltage and then you get some good ballpark
number where that data might be at a little bit of safety margin and fire up
your power supply for the first time look at the scope measure it and
optimize it so this is the more typical a little bit pragmatic but not a useful
way in setting up these values good so once we have gone through that list so
now the last setting here would be this computation so slope computation is not
available yet because we first have to have a peripheral which we need to
program so at that point there's nothing else we can do so now we have all the
settings we need to at least set up the architecture we're doing this by
selecting one out of four pwm controllers so the peak current mode
control controller is located here in a specific corner of the device so the pin
out of the device is divided in four sections so I'm here in the upper left
this is where we find the in and outputs of the first PWM controller then here is
number two number three and number four so that peanut has been arranged in a
way that when you're designing multiple power supplies that it can route the
signals on to the device in the most ideal way without crossing other lines
especially trying to keep analog separated from digital and so forth to
prevent any conflicts with signal integrity so on the starter kits the
peak current load control is wired up to PWM controller number three so I pick
that one from the list and now I can upload all the modules that are required
so I'm uploading the configuration for all the people peripherals so this takes
a moment
and here we are now in the project resources we see decide that one power
supply topology we have added first there is now a list of peripherals so
now we see all the sub blocks so which is then here
for example the comparative digital to analog converter and op-amp for the area
fire our fixed voltage reference at the complementary output generator the ramp
generator and the basic period is switching on PWM so and as you soon see
every time I click on one of these modules I see all the configurations
which are available for that particular powerful so if you go into the register
map you see this there are endless options of configurations that could
potentially be done but as we have done all this already all these settings have
been done for you ready so I can just skip that peripheral level go back into
my sync rectifier and now as attack is loaded and I know what the resolution of
the deck is now we can set a new revenue rate of our slope compensation ramp
generator so for that particular design we need a slope of 0.35 volt per
microsecond so that ramp that is modulated onto the reference of the air
amplifier now decreases over time with a ratio of 350 millivolt per microsecond
so now we are all set so I save my configuration and now I generate the
and in which the help would we know
until the process has completed
and I see this is stunned first when the progress bras have disappeared and when
I find a line that says save configuration' in final my path so when
I now switch over into the project and I open the header then I see that the MCC
generated files folder in which all the search and possible configurations have
been generated - and then there's another folder called SPS and in this
folder I find software functions that already have been generated in addition
to the basic peripheral configurations so what we providing as a standard
generated code block is a soft starter team especially in half bridge
configurations at high input voltages if you would just snap on the PWM with a
certain duty cycle the chances are very high that it will just blow up or not to
be switches so usually half which drives especially with high speed MOSFETs like
those needs needed is vitally need to be soft starter so and that code is now
part of your project already so this is a function you can call the right key
and you don't have to be concerned about your some sort behavior anymore
so when we go into the source files we find also a main which contains the main
program and years our MCC generated block with all the peripheral
configurations and here also this which will power supply software function
blocks so why did I look into my main the first line within Maine is system
initialize so inside that system initialize I see the configuration of my
pin out oscillator settings what's your timer settings and then all
the peripherals for most which one power supply PWM
controller including the to sink park and PCM C Block software blocks which
include the soft start
within Maine there's nothing else to find so there's just a while loop so the
only modification we have to do manually is to decide when that power supply
should be turned on so where to place my soft start function call so the first
thing is we have to figure out how that function is called so we have to go into
the PCMC header to learn how that function Hall looks like and how its
named so it's called PCMC underscore soft start easy to remember and we would
like to soft start that over to start the power supply immediately it just
before we enter the while loop so I place that function call here and this
is it now we are ready to go so now I hit compile compile the project
just to make sure that the generated code doesn't produce any errors
and I get a built succeed and now can program my device
okay so now we see programming verify complete so the program has been
successfully programmed okay so now here we are with a programmed board now we
have to test if it's really working now I'm connecting this port to the power
supplies and the load which is part of that development kit so for that purpose
I'm stealing the input voltage from that input terminals connected to my freshly
program port
and I take the load module we have here on this side and connect it to the
output and then here on the display you see an operative of 3.3 volt at already
close to four amps so regulation seems to work to make sure that it's really
working we're just changing the load turning it off and it's the regulating
to 3.3 volts so seems that we have an active controller that controls the
voltage to a constant level overload how well it really works
our controller what did eventual performance is and our bandwidth the
transient response that obviously requires a little bit of more thorough
analysis and for that purpose we have a network analyzer which is connected to
that kit so I will just remove these blocks again give it a look the load
module back in
and the software which is currently running on that kit and that kit is
identical so this is exactly the same basic p-card mode control we have just
generated so when we are now letting this board run then we have on this side
our network lies analyzers running and it's continuously measuring the loop so
the way we do this is that we have a tiny resistor on top of our output
voltage divider so voltage dividers at the output I have usually resistors in
the kilo ohm range and we put a tiny 10 ohm resistor on top of this high
resistance and then we use a injection transformer so this is a one-to-one
current transformer and that is connected to the signal generator within
our OD analyzer so this frequency now is applied to the primary winding is
injecting a current that current is then showing up in on the secondary side and
is injecting an error signal in that Tang ohm resistor on top of our voltage
divider so this artificial error signal is now traveling through the voltage
divider entering our feedback loop that's their amplifier the area fire
starts to respond to that error signal and is injecting this error into our
modulator and so our PWM starts to be to modulate against that error that is
showing up at the feedback input and so our output voltage starts to change so
the network analyzer now looks at the signal that has been injected on one
side and then looks at the output of the power supply on the other side of the
Tarin ohm resistor and just measures the sinusoidal response of the system and
measures the difference in amplitude which gives us the game and the phase
shift which gives us the face and plotted as a bode plot
and the port button allows us to do stability analysis where we can measure
it across our frequency the slope of the gain at the crossover frequency the face
at the point where in the game hit zero and the value of the gain when the face
hits the minus hundred eighty degree sole point of instability so the
so-called gain margin so then with phase margin gain margin in Kosova frequency
we now have all the parameters that determine the total bandwidth and
performance basic performance parameter instability of our power supply so
before we have a closer look at the measurement let's briefly revisit what
we are actually going to measure so this is a block diagram of our system
consisting of the power plant which is the transfer function G of s in the S
domain and then we have the second transfer function which is our
compensator H H of s in the S plane so our feedback in our system is closed
with a voltage divider and this feedback signal is then fed into the compensator
and the compensator and is and comparing just into a reference and the difference
is then applied by our modulator to the plant and that changes when we change
the duty cycle for example the optical burst goes up or down and any transients
that might hit the system from outside or no transients or from the input will
then be compensated by our control system so to make sure that this system
is stable we have to have a look at the total transfer function of this entire
block from input to output and this is the gain the closed-loop gain so g
closed-loop equals the plant gain over 1 plus the plant gain times the
compensator gain so when we look at this term and one thing becomes obvious that
thing is always stable as long as G of s times H of s is different than minus one
because imagine when this tends to go to minus 1 then we have 1 plus minus 1 this
goes to what 0 so the gain of the system will go to infinity which means that the
system is coding getting out of control and the gain becomes infinite and the
game the system is gone and will most probably blow up in our case so this is
why we call this G of s times H of s equals minus 1 is the sole point of
instability so in any other condition the system is de facto stable and only
in that point it becomes uncontrollable so when we are making a stability
analysis the whole stability analysis is now about how far are we away from the
sole point of instability so and this is the so-called open loop gain within the
closed loop system so while the system is operating a closed loop we are only
having a look at the open loop gain of the system so now when we have a closer
look at the bode plot so what you are seeing here is a continuous measurement
of the open loop gain and closed loop system so this term of open loop in a
closed loop system comes from the open loop component that looks for how far
away are we from the sole point of instability which is the point when the
system hits a phase lag of - degrees so in this region the system
should not be able to respond to any transient in any reasonable form so we
need to have a large negative gain in that region the bode measurement is as
always when we look at the face there's always one kind of misleading thing
about the scale of the face and this is the minus 180 degree line is actually a
serum at 0 degree phase in that ball plot the reason for that is that the
small signal model defines that monitored minus 180 degrees at the
reference of the system however the measurement now is done at the output of
the power supply so feed other side of the island and then we have that phase
lag of 180 degrees throughout the system doesn't really matter it's just if
you're wondering why we're always talking about minus 180 degrees as so
point of instability and here in that scale we look for that point at 0
degrees that's actually the same thing so what that Buddha plot here in an
active measurement is showing you is actually more for more tuned towards
stability analysis then a theoretical description of the system so that is the
only thing that's maybe interesting to keep in mind
so let's perform a measurement so as you see it's running here at the low
frequency range we see a lot of noise and that is the small signal model so
you're achieved best and most accurate results of the transit function when the
signal you're injecting is as small as possible so that it you don't drive some
components like especially the air amplifier into nonlinear regions at its
margin of its total input reading range so this is why we always try to keep
that injected error signal as small as possible
and at low frequencies this is getting tricky for the measurement equipment to
see the variation of the sinusoidal curve that is so small that the noise
floor starts to have a large influence on the measurement result so this is why
we see in that low frequency range it's always very noisy so luckily that
measurement tool we're using here the Buddhahood home that has a feature that
allows us to shape the gain of our input stage so that we can increase the gain
to reduce the noise but as you see it is may be good but still not good enough so
we would have to perform many many measurements of exactly the same
operation point and activate an averaging over that period to get rid of
that noise to also achieve a better more accurate result in that region but for
the moment we are not really interested in this local frequency range we are
more interested in the total performance of our feedback loop which is more about
stability so the stability criteria we are now looking for is start with the
crossover frequency of the game so when it does the creating of the game which
is the red line cross zero dB so this is pretty much exactly at 30
kilo Hertz we can make a more precise measurement if we go here into the scale
and say okay please give me the number at zero DB and we see exactly it's at
thirty point one point six kilohertz the other point that's important for its
instability at area is the gain margin which we find when the face which is the
blue line now hits minus one at eighty degrees or in our plot C or the green
line so we do the same I go into that table put zero and the cursor gives me
thanks the number of minus 14 DB which is a sufficient gain margin for a power
bond so when we are let me stop the
measurements to keep it really quiet so knowing we analyze it one of them the
third stability criteria would look fine four would then be the slope of the game
at the crossover point so ideally it should be minus 20 DB per decade so
we're looking into that decade so here we have a point which was very close to
10 DB so that is easy to take and then it should be a linear minus 45 degrees
over minus 20 DB per decade slope and when we draw a line when we imagine the
line that has a slope of minus 20 DB per decade then it would be at minus 10 DB a
ton of kilohertz and the crossover point would right be in the middle of that
slope so we exactly hit that slope of minus 20 DB per decade so it's a
perfectly schoolbook stable system so the last and foremost designers most
important value would then be the phase margin so that is determined to be at
the crossover point so what's the phase lag at the crossover point so we take
that server cursor and we've framed when we reset this to zero again so we find a
phase margin of 60 degrees gain margin of 14 DB add a crossover frequency of 30
kilo Hertz and we are meeting so we have really good stability at the crossover
frequencies of phase margin a margin and the slope at the crossover frequency all
three major stability factors are in a really good region for a real stable
power supply so the bandwidth we have set at 30 kilo Hertz is a little bit is
at many of fifteenth of the switching frequency
which is also a good ratio and which allows us to have enough safety margin
to account for variations in inductor component values capacitor component
values and so forth
so what we have covered today is we saw a short introduction of the CFP
hyperpower starter kit our demo setup the design procedure using our switch
from power supply libraries in the microchip code configurator and finally
how we generate the project we built our pwm controller downloaded into the
device bring it into the system and then measure and analyze it so I hope also
that the measurement results have given you some idea about the performance
level you can expect from the analog peripherals on board of these chips it
is really a straightforward pwm controller as you can expect it to find
on any other ASIC in terms of performance nevertheless have a look at
the data sheets and every further information you can find on the
descriptions below just click on the links follow them and you will find all
the documentation about the board the devices that are imposed by libraries
and further information on generic topics of simulation of switching power
supplies and design practices thank you very much for watching hope to see you
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SMPS Design with the CIP Hybrid Power Starter Kit

205 Folder Collection
Red published on October 31, 2019
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