Application Guide - XMC1000 - PCB Design Guidelines

XMC1000
Microcontroller Series
for Industrial Applications
De vice Gu ide
 PCB Layout Guideline for XMC1x00 microcontroller
De vice Gu ide
V1.0 2013-08
Microcontrollers
Edition 2013-08
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2013 Infineon Technologies AG
All Rights Reserved.
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Device Guide
XMC1000 Family
Revision History
Revision History
Page or Item
Subjects (major changes since previous revision)
V1.0, 2013-08
Trademarks of Infineon Technologies AG
AURIX™, C166™, CanPAK™, CIPOS™, CIPURSE™, EconoPACK™, CoolMOS™, CoolSET™,
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IsoPACK™, MIPAQ™, ModSTACK™, my-d™, NovalithIC™, OptiMOS™, ORIGA™, PRIMARION™,
PrimePACK™, PrimeSTACK™, PRO-SIL™, PROFET™, RASIC™, ReverSave™, SatRIC™,
SIEGET™, SINDRION™, SIPMOS™, SmartLEWIS™, SOLID FLASH™, TEMPFET™, thinQ!™,
TRENCHSTOP™, TriCore™.
Other Trademarks
Advance Design System™ (ADS) of Agilent Technologies, AMBA™, ARM™, MULTI-ICE™, KEIL™,
PRIMECELL™, REALVIEW™, THUMB™, µVision™ of ARM Limited, UK. AUTOSAR™ is licensed by
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Consortium. HYPERTERMINAL™ of Hilgraeve Incorporated. IEC™ of Commission Electrotechnique
Internationale. IrDA™ of Infrared Data Association Corporation. ISO™ of INTERNATIONAL
ORGANIZATION FOR STANDARDIZATION. MATLAB™ of MathWorks, Inc. MAXIM™ of Maxim
Integrated Products, Inc. MICROTEC™, NUCLEUS™ of Mentor Graphics Corporation. Mifare™ of
NXP. MIPI™ of MIPI Alliance, Inc. MIPS™ of MIPS Technologies, Inc., USA. muRata™ of MURATA
MANUFACTURING CO., MICROWAVE OFFICE™ (MWO) of Applied Wave Research Inc.,
OmniVision™ of OmniVision Technologies, Inc. Openwave™ Openwave Systems Inc. RED HAT™
Red Hat, Inc. RFMD™ RF Micro Devices, Inc. SIRIUS™ of Sirius Satellite Radio Inc. SOLARIS™ of
Sun Microsystems, Inc. SPANSION™ of Spansion LLC Ltd. Symbian™ of Symbian Software Limited.
TAIYO YUDEN™ of Taiyo Yuden Co. TEAKLITE™ of CEVA, Inc. TEKTRONIX™ of Tektronix Inc.
TOKO™ of TOKO KABUSHIKI KAISHA TA. UNIX™ of X/Open Company Limited. VERILOG™,
PALLADIUM™ of Cadence Design Systems, Inc. VLYNQ™ of Texas Instruments Incorporated.
VXWORKS™, WIND RIVER™ of WIND RIVER SYSTEMS, INC. ZETEX™ of Diodes Zetex Limited.
Last Trademarks Update 2011-02-24
Device Guide
XMC1000 Family
Table of Contents
Table of Contents
1
1.1
Overview ............................................................................................................................................. 6
Optimized ADC performance ............................................................................................................... 6
2
2.1
2.1.1
2.1.2
2.1.3
2.2
Power Supply De-coupling and Improved ADC Performance ....................................................... 7
PCB layouts for TSSOP-38 package ................................................................................................... 7
ADC and a general GPIO application .................................................................................................. 7
ADC and LED Touch Sense application .............................................................................................. 8
ADC and Motor or Power Conversion Application ............................................................................... 8
PCB layouts for TSSOP-28 and TSSOP-16 packages ........................................................................ 9
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XMC1000 Family
Overview
PCB Layout Guideline
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Device Guide
XMC1000 Family
Overview
1
Overview
This application note discusses product specific recommendations and guidelines for the XMC1000
family of products from Infineon, specifically in reference to optimizing ADC performance.
The XMC1000 products are built on a low pin count 32-bit microcontroller. The minimum number of
available supply pins with this microcontroller means that special care needs to be taken with the
layout of these products. The correct board layout will help to achieve the best ADC performance and
EMC behavior.
The XMC1000 microcontroller has two internal oscillators (DCO1 and DCO2).
 DCO1 has a clock output of 64MHz, and is used to generate the main clock, MCLK and fast
peripheral clock, PCLK.
 DCO2 is used to generate the standby clock running at 32.768kHz, and does not require an
external oscillator.
The document should be read in conjunction with the Infineon PCB Design Guidelines for
Microcontrollers (AP24026), which gives general design rule information for PCB design.
1.1
Optimized ADC performance
The TSSOP-16 and TSSOP-28 package of the XMC1000 microcontroller has just two supply pins
(VDDP / VDD and VSSP / VSS) to which all internal modules are connected. These are the
embedded voltage regulator, the port pins, the ADC module and the oscillators in the XMC1000
microcontroller.
The performance of the ADC and the robustness of the oscillator will be reduced, if power supply
noise or pin activity noise are not properly de-coupled. For the TSSOP-38 package, there are four
supply pins. The VDDP / VDD and VSSP / VSS pins are dedicated to power the ADC module while
VDDP and VSSP pins are used to power the rest of the internal modules.
Proper de-coupling can be achieved by separating the ground traces in analog and digital groups. A
star point connection should be considered at the pad of the VSSP / VSS pin of the TSSOP-16 and
TSSOP-28 package. The ADC reference voltage is connected to the VDDP / VDD pin. Hence, supply
noise directly influences the ADC performance.
ADC analog ground can be disturbed by noise injection from neighboring active pins driving high
frequency signals from I2C, PWM or the LED and Touch Sense unit. Good PCB layout will reduce the
capacitance between those traces to a minimum.
This application note includes layout recommendations for optimized ADC performance.
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XMC1000 Family
Power Supply De-coupling and Improved ADC Performance
2
Power Supply De-coupling and Improved ADC Performance
There are two reasons why microcontrollers can cause noise at the power supply. Firstly the
synchronous clocked logic functions lead to peak current at the MCU clock frequency. Secondly,
pulse pattern and clock output at any port pin will draw current at the pulse pattern’s frequency. Decoupling capacitors are intended to buffer the charge needed to feed the required current pulses.
Noise at the power supply lines might also disturb the microcontroller. This noise can be filtered by
the same de-coupling capacitor.
The figures in this section show the recommended PCB layout for different applications using
TSSOP-38, TSSOP-28 and TSSOP-16 packages of the XMC1000 microcontroller.
2.1
PCB layouts for TSSOP-38 package
Note that for each of the following layout examples, C1 should be at least 100nF and C2 also at least
100nF. Capacitors with low ESR (type X7R for example) are recommended.
2.1.1
ADC and a general GPIO application
If the intended application is primarily for ADC measurement and some simple general purpose
input/output toggling, then the following PCB layout is recommended.
Figure 1
PCB layout for ADC and general GPIO application using TSSOP-38 package
Normally, there is a low drop-out voltage regulator to step down the input voltage to the operating
voltage of the XMC1000 microcontroller. The electrolytic capacitor C4 at the output of the voltage
regulator acts as a low pass filter and reduces the ripple voltage of VDDP. C3 is the decoupling
capacitor for filtering of high frequency noise.
C1 acts as decoupling capacitor for ADC circuitry. C2 acts as the decoupling capacitor for the digital
circuitry of the XMC1000 microcontroller. Any additional connection will bypass the decoupling
capacitor C1 and C2 and will therefore reduce their effectiveness.
The grey areas shown in the figures should be kept clear of any GND connections and GND planes.
Ensure that the decoupling capacitors C1 and C2 are placed as close to the pins as possible.
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XMC1000 Family
Power Supply De-coupling and Improved ADC Performance
For TSSOP-38 package, pin 10 (VDDP / VDD) and pin 26 (VDDP) are connected internally. Similarly,
pin 9 (VSSP / VSS) is connected internally to pin 25 (VSSP). Hence, those pins do not need to
connect externally.
The ADC reference GND connection is intended to be utilized in common mode with the ADC’s input
pins. Any additional connection to pin 9 (VSSP / VSS) in this figure will cause supply noise to be
injected to the ADC’s reference GND.
2.1.2
ADC and LED Touch Sense application
If the board is also to be used for driving an LED, then an additional VDDP copper trace should be routed from
pin10 (VDDP / VDD) to pin26 (VDDP) of the TSSOP-38 package. As additional current needs to be supplied
from the port pin to drive the LEDs, so an additional VDDP copper trace will increase the current carrying
capability of the internal VDDP bonding wire.
Figure 2
2.1.3
PCB layout for ADC and LED Touch Sense application using TSSOP-38 package
ADC and Motor or Power Conversion Application
If the board is to be used for ADC and Motor or Power Conversion applications, where high switching
waveforms will be output from the CCU4 / CCU8 port, then the following PCB layout is recommended:
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XMC1000 Family
Power Supply De-coupling and Improved ADC Performance
Figure 3
PCB layout for ADC and Motor or Power Conversion application using TSSOP-38
package
At the negative terminal of the electrolytic capacitor C4, a star-point ground should be used. A digital
ground trace will run from this star-point ground to VSSP (Pin 25) of the XMC1000 microcontroller.
Another analog ground trace will also run from the negative terminal of C4 to VSSP / VSS (Pin 9) of
the XMC1000 microcontroller. By using this star-point ground configuration, the interference of digital
noise at VSSP (Pin 25) to the analog ground at VSSP / VSS (Pin 9) is minimized.
2.2
PCB layouts for TSSOP-28 and TSSOP-16 packages
In the following layouts, C2 should be set 100nF and capacitors with low ESR (type X7R for example)
are recommended.
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Power Supply De-coupling and Improved ADC Performance
Figure 4
PCB layout for TSSOP-28 package
Figure 5
PCB layout for TSSOP-16 package
For TSSOP-28 and TSSOP-16 packages, there is only 1 pair of VDDP / VDD and VSSP / VSS pins,
so a star-point ground is recommended at de-coupling capacitor C2.
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Power Supply De-coupling and Improved ADC Performance
A star configuration at the VSSP / VSS pin (for the TSSOP-16 and TSSOP-28 packages) is the least
noisy connection for the ADC reference ground. This connection is best coupled to the ADC’s
reference voltage ground potential and is important for minimizing ADC errors.
From the star point ground, digital grounds (e.g. PWM ground, LED/Touch sense ground) and analog
ground (ADC reference ground) are branched out individually to their circuitry.
The noise of the power supply (VDDP / VDD and VSSP / VSS) is filtered by the capacitor C2 in the
TSSOP-28 and TSSOP-16 packages.
It must be ensured that the de-coupling capacitors C2 are placed as close to the pins as possible. It is
also important to connect the power supply GND and VDD only at those traces shown in the figures.
Any additional connection will bypass the de-coupling capacitor C2 and will therefore reduce it’s
effectiveness. The grey areas shown in the figures should be kept clear of any GND connections and
GND planes.
The ADC reference GND connection is intended to be used in common mode with the ADC’s input
pins. Any additional connection to the power supply GND will cause supply noise to be injected to the
ADC’s reference GND. So, if LED/Touch sense ground is required on the application board, please
use the star point ground configuration as shown.
Device Guide
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