Infineon XMC Series, XMC4000, XMC1000 Application Manual
Microcontrollers
XMC4000/1000
Microcontroller Series
for Industrial Applications
Application Guide
V1.0 2015-01
Introduction to Digital Power
Conversion
Edition 2015-01
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2015 Infineon Technologies AG
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Introduction to Digital Power Conversion
Revision History
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V1.0, 2015-01
XMC4000/1000 Family
Revision History
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Introduction to Digital Power Conversion
XMC4000/1000 Family
Table of Contents
Table of Contents
1 About this document ......................................................................................................................... 6
1.1 Scope and Purpose .............................................................................................................................. 6
1.2 Intendend Audience ............................................................................................................................. 6
2 Comparison of Power Conversion Methods ................................................................................... 7
2.1 What is Power Conversion ................................................................................................................... 7
2.2 Why Power Conversion ........................................................................................................................ 7
2.3 Methods of Power Conversion ............................................................................................................. 7
2.3.1 Linear Mode Power Conversion ..................................................................................................... 7
2.3.2 Switch Mode Power Conversion .................................................................................................... 9
2.3.2.1 Analog Switch Mode Controllers ............................................................................................. 11
2.3.2.2 Digital Switch Mode Controllers .............................................................................................. 11
2.3.2.3 ASIC controller versus MCU / DSP / DSC controllers ............................................................ 12
2.4 Infineon XMC-families for Switch Mode Power Control ..................................................................... 13
2.4.1 Power Conversion Oriented Peripheral Features ........................................................................ 14
2.4.1.1 Sensing ................................................................................................................................... 14
2.4.1.2 Stability and Software ............................................................................................................. 14
2.4.1.3 Modulation .............................................................................................................................. 14
2.4.1.4 PWM Generation .................................................................................................................... 15
3 Converter Topologies ...................................................................................................................... 16
3.1 Buck ................................................................................................................................................... 17
3.2 Boost .................................................................................................................................................. 18
3.3 PFC .................................................................................................................................................... 19
3.4 Phase-Shift Full-Bridge (PSFB) ......................................................................................................... 21
3.5 LLC (Inductor-Inductor-Capacitor) ..................................................................................................... 22
3.6 Generic Digital Power Converter ........................................................................................................ 23
4 PWM Generation............................................................................................................................... 24
4.1 Single Channel ................................................................................................................................... 24
4.2 Single Channel with Complementary Outputs ................................................................................... 24
4.3 Dual Channel with Complementary Outputs with Dead-Time, using CCU8 ...................................... 25
4.4 Dual Channel with Complementary Outputs with Dead-Time, using CCU4 ...................................... 25
4.5 ON/OFF Control ................................................................................................................................. 27
4.6 Fixed ON-Time (FOT) ........................................................................................................................ 27
4.7 Fixed ON-Time with Frequency Limit Control .................................................................................... 28
4.8 Fixed Off-Time (FOFFT) .................................................................................................................... 31
4.9 Phase Shift Control ............................................................................................................................ 32
4.10 Fixed Phase-Shift ............................................................................................................................... 32
4.10.1 Center Aligned Mode ................................................................................................................... 32
4.10.2 Edge Aligned Mode ...................................................................................................................... 33
4.10.3 Interleave ..................................................................................................................................... 34
4.11 Variable Phase-Shift .......................................................................................................................... 35
4.11.1 Power Conversion Control Example ............................................................................................ 37
4.11.2 Zero-Voltage Switching (ZVS) Control ......................................................................................... 38
4.12 Adding High Resolution Channel (HRC) – HRPWM .......................................................................... 39
4.12.1 PWM Dead-Time Compensation ................................................................................................. 40
4.13 Half-Bridge LLC Control using ½ CCU4............................................................................................. 41
4.14 Half-Bridge LLC Control - Synchronous Rectification using CCU4 ................................................... 42
4.15 Full-Bridge LLC Control Using HRC – Synchronous Rectification ..................................................... 43
4.16 Full-Bridge LLC Control – Synchronous Rectification Using HRC ..................................................... 44
5 Sensing ............................................................................................................................................. 46
5.1 Analog Signal Sensing ....................................................................................................................... 46
5.1.1 Level Crossing Detection, Fast Compare mode .......................................................................... 46
5.1.2 PWM with Fast Compare mode Hysteretic Switching ................................................................. 47
5.1.3 Peak Control Using Fast Compare mode .................................................................................... 48
5.1.4 ZCD Control Using Fast Compare mode ..................................................................................... 49
Application Guide 4 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Table of Contents
5.2 Over Voltage and Over Current Protection (OVP / OCP) .................................................................. 50
6 Modulation ........................................................................................................................................ 51
6.1 Voltage Control (VC) .......................................................................................................................... 52
6.1.1 Timing Scheme ............................................................................................................................ 53
6.2 Current Control ................................................................................................................................... 55
6.2.1 Average Current Control (ACC) ................................................................................................... 55
6.2.2 Average Current Control, Edge-Aligned Scheme ........................................................................ 56
6.2.3 Discontinuous to Continuous Current Recovery by Timer-Load ................................................. 58
6.2.4 ACC Center Aligned Scheme ...................................................................................................... 59
6.3 Peak Current Control (PCC) .............................................................................................................. 60
6.3.1 PCC Timing Scheme.................................................................................................................... 62
6.4 Blanking, Filtering and Clamping ....................................................................................................... 63
6.5 Slope Compensation .......................................................................................................................... 64
6.5.1 A Necessity in Fixed Frequency PCC .......................................................................................... 64
6.5.2 Fast Average Current Mode PCC ................................................................................................ 65
6.5.3 VIN independent Average Current mode ...................................................................................... 66
6.5.4 Slope Compensation Conditions – PCC ...................................................................................... 67
6.5.5 Slope Compensation Conditions: PCC ‘Stable Area’ examples .................................................. 70
6.5.6 Without Slope Compensation, Fixed-ON-Time (FOT) ZCD Control ............................................ 71
6.5.7 Without Slope Compensation, Fixed-OFF-Time (FOFFT) PCC .................................................. 71
6.6 CCM, CRM (CrCM) and DCM ............................................................................................................ 72
6.7 CRM: PFC using Fixed-On-Time (FOT)............................................................................................. 74
6.8 CCM / (DCM): PFC using Fixed-Off-Time (FOFFT) .......................................................................... 75
6.9 CCM: PFC example using Average Current Mode Control ............................................................... 76
7 Control Loops ................................................................................................................................... 77
7.1 Using CSG (HRPWM) with an Internal Comparator and Slope Generator........................................ 77
7.2 Using embedded ACMP and external Slope Compensation Ramp .................................................. 78
7.3 Using FADC Compare Mode; Slope Compensation Add-On ............................................................ 81
7.4 Open Loop Gain Stabilization (Frequency Compensation)................................................................ 83
7.4.1 Open Loop Gain Voltage Mode ................................................................................................... 84
7.4.2 Open Loop Gain Bode Plot, Voltage Mode Stabilization ............................................................. 85
7.4.3 Open Loop Gain Current Mode w/ Slope Compensation ............................................................ 86
7.4.4 Open Loop Gain Bode Plot, Current Mode Stabilization ............................................................. 87
8 Application Software ....................................................................................................................... 88
8.1 Advanced Algorithms / User software IP for Power Conversion ........................................................ 88
8.2 Multi-stage, multi-functional, multi-tasking control by a single controller ........................................... 88
8.3 Safety ................................................................................................................................................. 89
8.4 Communication capabilities ............................................................................................................... 89
8.5 Data logging / Firmware updates ....................................................................................................... 89
8.6 Human Machine Interface .................................................................................................................. 89
8.7 Digital Switch Mode Control by New Feed-Forward Techniques ...................................................... 90
8.8 Non-linear Slope Compensation ........................................................................................................ 90
Application Guide 5 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
About this document
1 About this document
1.1 Scope and Purpose
This document aims to stimulate and challenge accepted solutions in the field of power applications
with digital control, by revisiting the basics of electric energy transfer and creating a summarized
picture of what can be achieved today with a weighted mix of embedded dedicated peripherals and
computing power.
1.2 Intendend Audience
The information is intended for persons in charge or executive position, with a diverse background in
the subject – as well as to people with deeply rooted experience in the field, such as power supply
designers, for which we want to show the possibilities XMC families can offer.
Application Guide 6 V1.0, 2015-01
Introduction to Digital Power Conversion
Category
Type
General Purpose
DC / DC
DC-to-DC converter
Regulator / Stabilizer / Voltage Adapter
AC / DC
AC-to-DC converter
Rectifier / Mains Power Supply Unit (PSU)
DC / AC
AC-to-DC converter
Inverter
AC / AC
AC-to-AC converter
Transformer / Variable frequency Converter
XMC4000/1000 Family
Comparison of Power Conversion Methods
2 Comparison of Power Conversion Methods
2.1 What is Power Conversion
Power conversion is the conversion of electric energy from one form to another. As long as it does not
concern electro-mechanic equivalent energy that consumes energy (e.g. motors) or produces energy
(e.g. generators), then it is about pure power transfer, in any form, from the following categories:
Table 1 Power conversion categories
2.2 Why Power Conversion
According to the global environmental context, each case of electric energy transfer between an
energy source and an energy consuming unit, should consume as little energy as possible to perform
the task by optimal adaption. This is generally unachievable without some form of power conversion.
2.3 Methods of Power Conversion
There are two significantly different ways to convert a DC supply voltage to another DC voltage:
Linear Power Conversion
Switch Mode Power Conversion
When Switch Mode is chosen (e.g. for High Power) the next choice is between:
Analog (discrete) control
Digital (ASIC/MCU/DSP) control
2.3.1 Linear Mode Power Conversion
A Linear DC/DC Converter output/input voltage ratio is < 1 and the output/input current ratio is < 1, so
there is always a significant power loss.
Linear voltage regulators meet such demands as ‘Easy-to-Use’, Accuracy, Low Cost and EMC. They
are therefore the “best-choice” in low power / low current DC-converters.
Application Guide 7 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
Figure 1 Linear DC/DC Conversion
Passive Linear Conversion
Passive conversion means that there are no control components involved in the process that are
capable of changing the conversion properties in any way; i.e. the steady state input-to-output transfer
function is not adjustable in runtime. The consequence of this is Load dependent output voltage.
Active Linear Conversion
By “active” conversion we mean that there are components involved that are capable of influencing
the conversion activity; i.e. there is at least one semiconductor capable of controlling the conversion
by at least one additional input signal. This might be to stabilize the output to a reference level for
example.
Application Guide 8 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.3.2 Switch Mode Power Conversion
A Switch Mode DC/DC Converter output/input voltage ratio can be any value, including a negative
value. That property is not covered by any Linear Voltage Converter, so most power conversion usecases can be solved by Switch Mode, especially in the area of high power, where efficiency and formfactor are vital.
Figure 2 Switch Mode DC/DC Conversion
Switch mode conversion is always an “active” conversion, in the sense there has to be active, working
semiconductors in the input-to-output transfer path. The presence of at least one winded component,
such as an inductor, is also essential.
Application Guide 9 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
Switch Mode Power Conversion Principle – Compared to Linear Mode
In switch mode voltage conversion, portions of energy, divided by switching in time lengths (T1 or T2),
are transferred from a voltage source to an inductor (L) current as magnetic energy, cyclic in periods
(T). During the rest of each period (T), the energy is moved into a capacitor (C), for the output voltage.
This principle is true for any DC/DC converter topology.
Interesting similarities with linear conversion can be seen in the output/input voltage ratios, when
replacing ‘R’ with ‘T’. This comparison is true as long as the magnetic energy of the inductor is never
emptied before the end of each period (T); i.e. Continuous Conduction Mode (CCM) is assumed.
Figure 3 Power Conversion Principles and Similarities - Demo Model
Power Loss Comparison
The voltage drop (V
) in linear mode is maintained by a resistor (R) and constant current, causing
1 – V2
active power loss.
The voltage (V
) in switch mode is reactive by self-inductance (L) during rising or falling current in
1 – V2
the switch time intervals (T1 or T2) respectively, resulting (ideally) in no power loss.
Application Guide 10 V1.0, 2015-01
Introduction to Digital Power Conversion
Positive properties
Negative properties
Fast
Do not adapt to new conditions during run-time
Well known
Sensitivity of parasitic effects and ageing
Simple IPs
Limited range of topologies
Standard discreet components
Narrow input / load range with efficiency
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.3.2.1 Analog Switch Mode Controllers
Traditional Analog Controllers have a significant BOM (Bill of Materials) list of OpAmps, comparators,
filters, and so on. They cover just a limited range of topologies and do not adapt autonomously to
condition changes in run-time. Form factor can be poor and reusability is limited, but they are fast and
well known.
Table 2 Properties of Analog Controllers
2.3.2.2 Digital Switch Mode Controllers
Digital controllers are flexible, with a wide load / input range, and sophisticated reactions to condition
changes during run-time through multi-control loops. They are reconfigurable by software and can
connect to a network / HMI. A smart system can predict ageing or process variations, enabling
scalability and portability of IPs.
Digital Controllers – Positive properties
Cost is higher and complexity is higher too, but there are many positive properties:
Highest efficiency over wide load and input range
Sophisticated start-up algorithms
Overload condition reactions
Auto-switch between power modes (CCMCRMDCMBurst)
Programmable / configurable by software
Multiple control loops are possible
Correct real-time performance
Prediction of system behavior
Reduction of parasitic effects
Scalable for wider ranges
IPs are easily portable: lowhigh end
Fast time to market
Sophisticated reactions to events
Communication and HMI feature
Application Guide 11 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.3.2.3 ASIC controller versus MCU / DSP / DSC controllers
Here we outline some of the guiding properties to be considered, for the type of controller to choose
when selecting for High-end versus Low-end.
ASIC
ASIC controllers offer gate drivers and fixed optimized solutions at the lowest possible cost. They are
easy to use and they fit Low-end switch mode converters very well.
However, on the downside, they only handle known changes in load and input conditions during runtime, and reusability is limited because they are a customized solution.
Positive properties:
Custom design for known conditions
Fixed and optimized settings
Lowest possible cost
Easy to use
Embedded gate drivers
Form factor
MCU / DSP / DSC
An MCU, DSP or DSC controller brings a platform approach, a smart system with high computation
capability, and embedded power conversion orientated peripherals.
Condition changes are handled in run-time, ensuring the highest efficiency and correct real-time
performance. These features mean that the MCU, DSP or DSC solution is particularly suited to Highend power converters.
Positive properties:
Platform approach (Reuse, Extend)
When highest efficiency is required
Mixed power mode capability
Variable load / inputs
Programmable dwith software IP
Flexible communication
Application Guide 12 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.4 Infineon XMC-families for Switch Mode Power Control
The Infineon XMC power conversion oriented devices offer flexible 3-level control architectures, for
sense-compute-modulate-and-drive of any power converter topology.
Advanced analog and digital peripherals interact on events in real-time via a hardware matrix,
supported by DMA, Software, DSP (Digital Signal Processing) or over a network.
Figure 4 The Power Conversion Oriented XMC Devices 3-Level Architecture Control Loop
The XMC series for power control meets the performance challenges and demands of today’s
embedded control applications. The high performance, real-time capability is achieved with an ARMCortex architecture, with or without DSP, and a Floating Point Unit (FPU).
Application Guide 13 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.4.1 Power Conversion Oriented Peripheral Features
Here we highlight features of the XMC-family embedded peripherals that are essential for the
significant tasks required in power conversion control loops.
2.4.1.1 Sensing
Analog values are monitored, or detected upon crossing level limits, via Versatile Analog-to-Digital
Converter (VADC) channels (featuring fast compare mode), or by Analog Comparator (ACMP/CSG).
These units are interconnected with events via hardware action providers, or softwre routines via
interrupts.
The functionality of the ADCs includes:
Automatic scheduling of complex conversion sequences with priority for time-critical conversions
Synchronous sampling of up to 4 signals / Independent result registers, selectable for 8/10/12 bits
Sampling rates up to 2MHz / Flexible data rate reduction / FIR/IIR filter with selectable coefficients
Adjustable conversion speed and sampling timing
4 independent converters with up to 8 inputs w/ channel wise selectable reference voltage source
2.4.1.2 Stability and Software
An important property of conversion control loops is the frequency response of the duty-cycle-tooutput-voltage transfer function. Stabilization is provided via softwre actions in the open loop gain
paths, using DSP operations on discrete time variables, maintained by sampling at rates triggered by
a CCU (Capture and Compare Unit).
2.4.1.3 Modulation
The steady state duty-cycle-to-output-voltage transfer function is controlled by sense-modulate-drive
algorithms in hardware, with some optional add -on attributes, including (but not limited to):
Fixed-Frequency (FF)
Fixed-On-Time (FOT)
Fixed-Off-Time (FOFFT)
Conduction Mode Switching
Comparator & Slope Generation (CSG)
Blanking
Clamping
Filtering
XMC modulation modes
Voltage Mode Control (VC)
Average Current Mode Control (ACC)
Peak Current Mode Control (PCC)
Valley Current Mode Control (VCC)
Zero Crossing Detection Mode (ZCD)
The XMC peripherals handle modulation dynamically, with mode-switch on changed conditions in runtime (on load variation for example). A set of resources can be exchanged “on-the-fly” by a Mode-Bit.
Application Guide 14 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Comparison of Power Conversion Methods
2.4.1.4 PWM Generation
The XMC CAPCOM Units (CCU4 or CCU8) timer slices can be regarded as “timer-cells” that can
cooperate and fit together like “puzzle pieces” to form matrices of sophisticated and compound timing
functions. These can interact for certain function request events and event profile conditions.
Theoretically, any on-chip module can be considered to act on a slice via one of (up to 3) inputs. A
flexible library of modular timing control applications (PWM “Apps”) can be created and then be
reused across projects.
The XMC single and multi-channel PWM drive capabilities include:
Global Synchronization
− to ensure a fully synchronized start with any combination of CAPCOM units
PWM
− by Symmetric / Asymmetric Modulation (Edge-Aligned or Center-Aligned)
− with Active / Passive Output Level Control / Trap Handling Protocol in hardware
− with Dithering (4 bits)
− by Status Events (by Compare or Period-Control)
− by external Set/Clear (by various conditional Start/Stop functions, which can be combined with
Status Events)
− by Matrix Interactions (on specific function request events and event profile conditions)
Examples
Peak, Valley or Hysteretic On-Off PWM
Fixed-On-TIme (FOT) PWM
Fixed-Off-TIme (FOFFT) PWM
Phase-Shift / Fixed Phase-Shift (Interleave) PWM
Half Bridge (HB) control with optional Synchronous-Rectification (SR)
Full Bridge (FB) control (w/ SR)
HB / FB Drive of LLC Resonance Converters
HRPWM Attributes
High Resolution Control (HRC) Insertion – down to 150 ps accuracy:
- HRC can handle switch frequencies up to 5 MHz with 10 bit resolution PWM
- Highly Accurate Low-Load Scenario Control
- Converter Efficiency Improvement: Each HRC can operate with two set of resources
Dead Time Insertion, with “On-the-Fly” optimization during run-time.
Application Guide 15 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3 Converter Topologies
The fundamental power converter topologies that we focus on in this document are:
Buck (“Step-Down”) (Section 3.1)
− Conventional
− Interleaved
− Synchronous
− Inverted
Boost (“Step-Up”) (Section 3.2)
− Conventional
− Interleaved
− Synchronous
− Inverted (Buck-Boost)
PFC (”Power-Factor-Correction” (Section 3.3)
− Conventional Boost PFC
− Interleaved Boost PFC
− Bridgeless Boost PFC
− Totem-Pole Bridgeless PFC
PSFB (“Phase-Shift-Full-Bridge”) (Section 3.4)
− (Principle Scheme)
LLC (”L-L-C-resonant”) (Section 3.5)
− (Principle Scheme)
The Generic Digital Power Converter (Section 3.6)
Application Guide 16 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.1 Buck
A Buck converter can only generate lower output average voltage (V
) than the input voltage (VIN),
OUT
and is therefore also referred to as a “Step-Down” converter.
The DC/DC conversion is non-isolating, in the sense that there is a common ground between input
and output. Some improved versions exist:
Figure 5 Buck
Interleaved Buck Converter
When reduced ripple and smaller components are required, especially in high-voltage applications,
then a realistic approach is to interleave the output currents from a multiphase Buck converter stage.
For example a 2-phase Buck converter controlled by fixed 180o phase-shifted PWM from an XMC
CCU4/8
Synchronous Buck Converter
When reduced power conversion loss is required, the rectifying diode D may be replaced by an active
switch that can offer a lower voltage drop. In such a solution the rectification will be synchronously
invoked by a signal that is complementary to the control signal, from a CC8 timer or CC4 timer pair.
Inverted Buck Converter
When a simplified current measurement is required, then an Inverted Buck controller is an alternative,
assuming common ground between input and output voltage is not necessary. By sensing the voltage
over a resistor (R) to ground, the inductor current (IL) can be monitored by a VADC or ACMP.
Application Guide 17 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.2 Boost
A Boost converter is non-isolating and can only generate a higher output average voltage than the
input supply voltage. It is therefore called a “Step-Up” converter.
There is one exception to note however. The Inverted Buck-Boost converter theoretically generates
an output voltage from 0 to minus infinity.
Figure 6 Boost
Interleaved Boost Converter
Similar to the Buck converter, i.e. the ripple will be reduced and smaller components can be used, by
having interleaved output currents from a multiphase Boost converter stage – here by a 2-phase
Boost converter that is controlled by fixed 180o phase-shifted PWM from an XMC CCU4/-8.
Synchronous Boost Converter
A synchronous Boost works similar to a synchronous Buck – however, this variant of improvement is
not often used, since reduced power conversion loss by replacing the rectifying diode D by an active
switch is not very significant in the high voltage range – where this topology more frequently appears.
Application Guide 18 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.3 PFC
Abstract
The Power Factor (PF) is defined as the transfer ratio of real power [Watt] to apparent power [VA]:
PF = Real Power / Apparent Power [Watt / VA]
The Power-Factor-Correction (PFC) purpose is (according to the environmental context) to achieve:
Real Power = Apparent Power
i.e.:
PF = 1
PFC Rectifier
A PFC rectifier accomplishes “PF = 1” by phase correct rectification of the mains AC voltage – so that
the current conduction angle becomes fully 180o in both half periods – phase correct to the mains AC
voltage – i.e. without any parasitic or reactive signal components reflected back into the mains lines:
See Figure 7.
In principle, the mains is rectified into a sinusoidal half-wave rippling DC voltage. In turn it is converted
to a ripple-free DC output voltage by a Boost PFC – e.g. by Fixed-On-Time inductor current (IL) mode
control. (Each Off-Time interval lasts till the current (IL) falls back to Zero-Crossing-Detection, ZCD.)
Since all tOn pulses are fixed, the I
L(PEAK)
and I
L(AVERAGE)
envelopes will follow the |VAC(t)| in proportion.
Figure 7 Boost Power-Factor-Correction (PFC) – E.g. in Fixed On-Time Current Mode Control
Application Guide 19 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
PFC Variants
There are different types of PFC circuits, which mix a balance of complexity versus performance.
Here we show just some of the basic topologies. These can be mixed into more sophisticated, multiphased, interleaved, full-bridgeless PFCs by Synchronous rectification.
Figure 8 PFC Types such as – Conventional – Bridge Interleave – Bridgeless – Totem pole
PFC Performance
High Power Factor (PF) and low Total Harmonic Distortion (THD) are directly related, so the basic
circuits can be listed in performance order, as follows:
Conventional Boost PFC
− Low cost BOM solution.
Interleaved Boost PFC (High Power)
− Even though there still is a diode bridge, the continuous interleaved current offers the advantage
of using smaller components.
Bridgeless/Totem-Pole Bridgeless PFC (High Power)
− The diode bridge is replaced by a MOSFET semi-bridge / half-bridge Totem-Pole rectifier.
Bridgeless Interleaved PFC (High power)
− (Not shown) Enables use of successive expansion of multi-phase bridgeless interleaved boost
PFC.
Application Guide 20 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.4 Phase-Shift Full-Bridge (PSFB)
The PSFB is a Phase-Shift-Full-Bridge DC/DC converter. Power is transferred in a Phase-Shift (PS)
via a Full-Bridge (FB), a transformer, a rectifier and filter. The PSFB is an isolating converter.
Figure 9 PSFB Principle
PSFB power conversion stages
Stage one
− Split the DC rail input voltage (V
) into two Phase-Shifted pulse streams (PhA , PhB) according
IN
to the Full-Bridge control signals.
Stage two
− A transformer, which is fed onto its primary coil (n
) with the phase difference voltage (PhA ,
p
PhB). This difference voltage will be transformed with a ratio (ns : np) to two secondary coils (ns ,
ns).
Stage three
− A “step-down” converter configuration with two diodes (D
positive levels of the two secondary voltages respectively into a PWM pulse stream. These
PWM pulses have a duty cycle that corresponds to the phase shift |Ph
, DB) that rectify and interleave the
A
o
Ao – PhB
|, and will be
filtered via the inductor (L) into the output capacitor (C), and result as an output voltage (V
− The PSFB total voltage conversion ratio (V
ratio (ns : np) times the phase-shift |Ph
Ao – PhB
/ VIN) is proportional to the transformer winding-
OUT
o
|:
V
/ VIN = (ns : np) * |Ph
OUT
Ao – PhB
o
| / 180
o
OUT
).
Application Guide 21 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.5 LLC (Inductor-Inductor-Capacitor)
The LLC converter is a series resonant converter. Power is transferred in a sinusoidal manner, so the
switching devices are softly commutated by ZVS (Zero-Voltage-Switching) and without capacitive
loss. A transformer takes part in the process, making the LLC an isolating converter.
Figure 10 LLC Principle – Using Half-Bridge Control
Performance
A resonant converter enables high voltage and faster switching, which allows for smaller components
thanks to the reduced switching losses.
An LLC converter, with two inductors (Lr ,Lm) and a capacitor (Cr), is superior to all other types of
resonant converters, especially with respect to a wide load range.
Properties
The LLC inductor Lm shunts the transformer primary coil when the impedance becomes infinite:
If there is no diode current, the resonant tank will become “(L
If there is diode current, the tank is “L
“. Therefore open load can be handled. The power
rCr
r +Lm)Cr
“
transfer is tuned by frequency or PWM.
Application Guide 22 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
Converter Topologies
3.6 Generic Digital Power Converter
There is a mutual property of all DC/DC power converters: Energy from an input power source is
periodically stored as magnetic energy in the air-gap of inductors (L), and converted into certain
output power voltage-current pairs via some rectifier-and-capacitor (C) filter configuration.
Because of this property, the essential components and control loops for Switch Mode DC/DC power
converters can be described by a “Generic DC/DC Converter” that is representative for all topologies
of this type.
Figure 11 The Generic Switch Mode DC/DC Converter.
Key Attributes
Generic hardware protocol
Flexible Drive and Sense Interfaces for Feed-Back Loop Control of Voltage and Current Transfers
Modular Loop Control by Event Interconnection Paths between XMC Embedded Unit Functions
Global Start and Synchronization Features
Application Guide 23 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
PWM Generation
4 PWM Generation
4.1 Single Channel
The PWM duty cycle range is 0 – 100% for all available combinations of alignments, count and
in/output modes.
Status bit ST can be set to 1 or 0 by timer compare or period events, or by external events (even if
stopped timer).
An output can be set active high or low (and with Dead-Time in CC8).
Figure 12 PWM – Single Channel
4.2 Single Channel with Complementary Outputs
A single channel (Ch1/-2) of a CC8y timer slice can output a complementary PWM signal pair in any
alignment mode. It may include Dead-Time Insertion of individual rise-/fall times, as well as accurate
active level settings for 1 or 2 half-bridges. The Trap input coordinates shut-down in correct real-time.
Figure 13 PWM – Single Channel Half-Bridge Drive
Application Guide 24 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
PWM Generation
4.3 Dual Channel with Complementary Outputs with Dead-Time, using CCU8
By using both channels (Ch1 and Ch2) in a CC8y timer slice, it is possible to output a dual pair of
complementary PWM signals to target 1 or 2 full-bridges.
Dead-Time insertion of individual rise-/fall times can be provided independently, as well as accurate
output active level settings and trap care.
Figure 14 PWM – Dual Channel Full-Bridge Drive
4.4 Dual Channel with Complementary Outputs with Dead-Time, using CCU4
A ‘sea’ of individual ‘timer-cells’
The timer slices of all CCUs can be regarded as a ‘sea’ of individual ‘timer-cells’ that are
interconnectable to act upon each other’s event requests, and accomplish dedicated and compound
timing functions.
Event sources and function commands are easily mapped by registers: CC4(8)yINS and
CC4(8)yCMC.
A typical example is a CCU4 Full-Bridge drive with complementary outputs and individual Deadtimes
(see Figure 15).
PWM with Complementary Outputs by Using CCU4 Single-Shot Timers
A complementary PWM output pair can be built from two timer slices (e.g. CC40 and CC41) in singleshot mode. The timers run, one at a time so that when one timer stops after its single-shot, it starts
the other timer with an event request Input Function ‘Start’. This can be mapped via interconnect
settings.
PWM with Dual Complementary Outputs by Using Synchronized Single-Shot Timer Pairs
When adding the other two timer slices of a CCU4 (e.g. CC42 and CC43), Full-Bridge control is
possible. Dead-Time insertion can be added and the ‘channel 1’ and ‘channel 2’ (CC40/41 and
CC42/43) can be synchronized with a Global Start.
PWM with Complementary Outputs Including Dead-Time Insertions
By using a preset compare register to shorten the output width of each single-shot, it is possible to get
individual deadtimes for different switch delays, and enable a Full-Bridge drive capability with a
CCU4.
Note: The pulse width modulating role is performed by period registers – not by compare registers.
Application Guide 25 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
PWM Generation
PWM Duty-Cycle Control by Period Register
PWM modulation (with fixed cycle period target option) is achieved by adding a ∆PR-value and
respectively substracting the same ∆PR-value to the period registers of the PWM channel single-shot
timer pair. Updates are via period shadow registers, by compare-ISR, and are set on shadow
transfers.
Figure 15 PWM – Dual Channel / Complementary Outputs w/ Individual Deadtime
PWM Phase-Shift Control by External Start of Single-Shot Timer Pairs
The coherent update mechanism via shadow transfers can be used to control a certain Phase-Shift
magnitude between the two slice-pairs, in this instance CC40/41 and CC42/43 respectively.
A good example, using just a CCU4 in this concept, is Fixed Phase-Shift Control with Zero-Voltage
Switching (ZVS) (See Figure 27).
Application Guide 26 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
PWM Generation
4.5 ON/OFF Control
Since all the individual ‘timer-cells’ of a CCU can be mapped to act upon virtually any external event
and function request, then theoretically any on-chip module can be considered to control a PWM. For
example, an ADC or comparators can join in the PWM control loops in this way, acting on analog
events. With such configurations, variable frequency and/or PWM pattern control is easily
accomplished.
Figure 16 PWM On/Off Control by External Events
4.6 Fixed ON-Time (FOT)
Fixed-On-Time (FOT) PWM has two essential properties:
1. The FOT Pulse Width is generated by a fixed active output state of a timer, by single-shot mode
for example.
2. The FOT Pulse Rate is controlled by external events; i.e. the timer does not decide pulse density.
Duty-cycle should be monitored for example, to enable feed-back control in the start-up phase.
Figure 17 PWM with Fixed-On-Time (FOT)
Use Case
FOT can be used in a PFC with inductor current ZCD in the control loop (See Figure 18).
Application Guide 27 V1.0, 2015-01
Introduction to Digital Power Conversion
XMC4000/1000 Family
PWM Generation
4.7 Fixed ON-Time with Frequency Limit Control
In power switch control with FOT PWM, it is mandatory to have pulse rate limiting add-ons in the loop,
ensuring a minimum of off-time to be fed back by the conversion process in each FOT start request.
Another extreme is maximum off-time.
Both extremes will require ‘f
timer’ add-ons in the loop.
max–min
Figure 18 FOT Control with Frequency Limits Supervision
The FOT Timer (Slice1)
Assume that this single-shot FOT timer works in a CRM or DCM mode PFC controller. In each switch
cycle the timer waits for a start request in the control loop, after a certain off-time. Then it will switch
on the inductor current for a fixed time, to rise from zero again, on any of the following conditions:
ZCD AND f
An early ZCD event AND before expired f
f
Application Guide 28 V1.0, 2015-01
-period expires AND there was no ZCD event in the meantime // DCM, FOT at ‘Time-Out’
min
-period is due // CRM, FOT density OK
max
-period // DCM, FOT pulse delayed
max
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