XC 87 x an d XC8 5 x Fa mil y Or derl y P owe r -u p o f XC8 7 x a nd XC 85 x De vices AP08125 Applic atio n N ote V1.0, 2013-04 Mic rocon t rolle rs Edition 2013-04 Published by Infineon Technologies AG 81726 Munich, Germany © 2013 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. INFINEON TECHNOLOGIES HEREBY DISCLAIMS ANY AND ALL WARRANTIES AND LIABILITIES OF ANY KIND (INCLUDING WITHOUT LIMITATION WARRANTIES OF NON-INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS OF ANY THIRD PARTY) WITH RESPECT TO ANY AND ALL INFORMATION GIVEN IN THIS APPLICATION NOTE. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. For information on the types in question, please contact the nearest Infineon Technologies Office. Infineon Technologies components may be used in life-support devices or systems only with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. Orderly Power-up of XC87x and XC85x Devices AP08125 Trademarks of Infineon Technologies AG AURIX™, C166™, CanPAK™, CIPOS™, CIPURSE™, EconoPACK™, CoolMOS™, CoolSET™, CORECONTROL™, CROSSAVE™, DAVE™, DI-POL™, EasyPIM™, EconoBRIDGE™, EconoDUAL™, EconoPIM™, EconoPACK™, EiceDRIVER™, eupec™, FCOS™, HITFET™, HybridPACK™, I²RF™, ISOFACE™, IsoPACK™, MIPAQ™, ModSTACK™, my-d™, NovalithIC™, OptiMOS™, ORIGA™, POWERCODE™; 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 AUTOSAR development partnership. Bluetooth™ of Bluetooth SIG Inc. CAT-iq™ of DECT Forum. COLOSSUS™, FirstGPS™ of Trimble Navigation Ltd. EMV™ of EMVCo, LLC (Visa Holdings Inc.). EPCOS™ of Epcos AG. FLEXGO™ of Microsoft Corporation. FlexRay™ is licensed by FlexRay 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. 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 2011-11-11 Application Note 3 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Revision History Revision History: V1.0, 2013-04 Previous Version: none Page Subjects (major changes since last revision) We Listen to Your Comments Is there any information in this document that you feel is wrong, unclear or missing? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: [email protected] Application Note 4 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Table of Contents Table of Contents Revision History .................................................................................................................................................... 4 Table of Contents .................................................................................................................................................. 5 1 Overview ............................................................................................................................................. 6 2 2.1 2.2 Pre-Condition for Orderly Start-up ................................................................................................... 6 Why Any Pin < 0.3V ? .......................................................................................................................... 8 Example of Good and Bad Practice ..................................................................................................... 9 Application Note 5 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Overview 1 Overview This Application note explains the pre-conditions that need to be satisfied before a microcontroller from the XC87x and XC85x family of products can be powered up reliably. The following points need to be taken into consideration: Voltage level of VDDP before power-up Risetime of VDDP Voltage levels at any pin prior to power-up RESET delay with reference to VDDP These basic requirements are mandatory for ensuring orderly start-up of the microcontroller and are explained by way of examples. These are guidelines with specific reference to XC87x family of devices, but are also examples of good practice in any microcontroller based design. These examples are not exhaustive and an application developer may use his or her own methods as long as the pre-conditions can be met. By not satisfying those conditions, reliable start-up can not be guaranteed. 2 Pre-Condition for Orderly Start-up Note: All pins should be 0V, or at least below 0.3V, but the most important pins are VDDP and RESET. Figure 1 Start-up Conditions Application Note 6 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Pre-Condition for Orderly Start-up RESET needs to stay below 0.4V until the VDDC pin reaches 2.25V, then RESET can follow VDDP. A simple and inexpensive way to achieve this is by adding a capacitor to the RESET pin. An internal pull-up resistor then charges this capacitor (Figure 2). The pull-up is anything between 64K and 186K. The following formula can be used to calculate the required capacitor: Where: − Vc is the voltage at the capacitor and therefore at the RESET pin − V is VDDP − R is the internal resistor − C is the external capacitor − t is the time taken to get VDDC to 2.25V An external pull-up resistor can also be added if required, to reduce the time constant of RC. Example Given that: V=5V Pull-up is 64K Capacitor is 220nF How long does it take for Vc to reach 0.4V? Measure the slope of VDDC risetime and compare with the result. Is this long enough delay to allow VDDC to reach 2.25V? we want to know ‘t’ Using 220nF = 14.08mS RC = 64K x 0.4=5 = 08 = 92 = 92) = 0.083 = 17 ms -> in this time VDDC needs to get to 2.25V Application Note 7 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Pre-Condition for Orderly Start-up 2.1 Why Any Pin < 0.3V ? Microcontrollers usually have some form of ESD protection on all pins, often in the form of two diodes as illustrated in Figure 2. If there is any voltage above 0.3V, this then leaks into VDDP via the diode from Pin to VDDP. It is actually possible to un-intentionally power up a microcontroller in this way. Therefore it is a basic requirement to ensure that all pins are below 0.3V when the device is powered off. Figure 3 shows an example of both good and bad practice. VDDP RESET Pin ESD Protection Figure 2 Internal pull-up XC87x ESD Protection and RESET Pull-up Application Note 8 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Pre-Condition for Orderly Start-up 2.2 Example of Good and Bad Practice The normal situation, where power is applied to the application and it stays on for a long period, is not a problem providing that all inputs to the device are kept within the VDDP limits. An example scenario is pictured in Figure 3 (‘Bad Practice’) and Figure 4 (‘Good Practice’), where there is an external voltage regulator and where the microcontroller needs to be switched off. In Figure 3 a sense input needs to detect a switch closure on the 12V side of the external voltage regulator. At times the microcontroller needs to be switched off by applying a control signal to transistor T2, which in turn switches T1 on and off. When the microcontroller is powered off, it can be seen that at GPIO1 voltage can be leaking into the device via the potential divider between 12V and GND when the switch is open. This is not a desired effect and should be avoided. The situation in Figure 4 at GPIO2 is different. In that example a transistor isolates GPIO from the 12V. The resistor is used to effectively sense the presence (or not) of VDDP at GPIO2, depending on the switch state. This arrangement ensures that at all times GPIO2 will not have any voltages leaking into the device when the microcontroller is powered off. 12VDC 5VDC T1 Voltage Regulator T2 ON/OFF VDDP GPIO1 RESET XC87x Figure 3 An Example of ‘Bad Practice’ Application Note 9 V1.0, 2013-04 Orderly Power-up of XC87x and XC85x Devices AP08125 Pre-Condition for Orderly Start-up 12VDC 5VDC T1 Voltage Regulator T2 ON/OFF VDDP RESET GPIO2 Figure 4 XC87x An Example of ‘Good Practice’ Application Note 10 V1.0, 2013-04 w w w . i n f i n e o n . c o m Published by Infineon Technologies AG