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Rev. 1.0 AN886 APPLICATION NOTE SELECTING BETWEEN ROM, FASTROM AND OTP FOR A MICROCONTROLLER by Microcontroller Division Applications INTRODUCTION A customer who develops an MCU-based application needs various levels of flexibility in order to perform code modifications at different times in the life cycle of the product (these levels are explained on the next page). To satisfy these requirements, STMicroelectronics supports sev- eral device types within two main groups of microcontroller product families: – EPROM, OTP, FASTROM and ROM microcontroller families – Flash, FASTROM and ROM microcontroller families This Application Note discusses the first group of families. For information on the second group, refer to Application Note AN1068.
packaging with a quartz window. They are reprogrammable outside systems. OTP (One Time Programmable EPROM): OTP is a type of EPROM sold in plastic packaging. cally programmed by the customer. cial mask containing the customer code. Therefore, the code can't be modified after that step. MCU devices is due to the price of ceramic packages. Figure 1. Cost versus Flexibility for different MCU types
SELECTING BETWEEN ROM, FASTROM AND OTP FOR A MICROCONTROLLER
1 TYPICAL APPLICATION DEVELOPMENT FLOW
When a new application is developed, different device versions will be used at each step of the development, depending on the required programming flexibility. During the design phase, a high flexibility is required and only a small number of parts are necessary, therefore the use of UV erasable EPROM is recommended. Then, fewer code cor- rections (and a significant number of parts) are needed during validation phase : at this point OTP is the best solution. The next step is pre-production phase: only a few code updates are needed at a reasonable device cost. Again, the best choice is to use OTP memory. Finally, when the mass produc- tion phase begins, there is no more need for corrections since the product has been fully op- timized, so ROM is the most adapted if very high volumes are needed. Otherwise (low to me- dium volumes) the most effective solution is to continue using STMicroelectronics’ competi- tively priced OTP. The following table summarizes the main benefits and drawbacks of using ROM, OTP or win- dowed EPROM MCU devices. Design Phase Validation Phase Pre-production Phase Production Phase ST Solution EPROM OTP OTP OTP ROM Code Number ROM OTP EPROM Cheaper than OTP (simpler process and testing) Lower failure rate (less handling, no program- ming) Lower cost compared to win- dowed EPROM (use of cheaper plastic packag- es) Ability to be programmed di- rectly by the final user High flexibility (Programming, Code check and Erasure cycle in less than 60 minutes) Limited flexibility (customer code implemented at masking stage) Higher inventory risks Higher failure rate compared to ROM due to customer handling and programming Expensive ceramic packages
SELECTING BETWEEN ROM, FASTROM AND OTP FOR A MICROCONTROLLER
2 COMPARISON OF PRODUCTION FLOWS FOR ROM AND OTP
ROM and OTP devices have exactly the same functional and electrical behaviour in an appli- cation because STMicroelectronics designs the two products with the same methodology. ROM and OTP devices are qualified using the same procedures. They are tested using the same test flows (see further) and with the same parameter limits. A good indication of device similarity is EMC (electromagnetic noise immunity) measurements performed on both versions (ROM and OTP) for the same MCU device. ST6220 (ROM version) ST62T20 (OTP version)
3 TYPICAL MANUFACTURING LEAD TIME FOR ROM AND OTP
Figure 2. Typical Fabrication Leadtime in weeks. notice that MCU devices have to be ordered in specified minimum quantities for ROM version. Figure 3. Typical Leadtime for Standard Products **Wafer and assembly sites are typically located in different countries.
SELECTING BETWEEN ROM, FASTROM AND OTP FOR A MICROCONTROLLER
4 MINIMUM ORDER QUANTITIES FOR ROM AND FASTROM
The following minimum order quantities apply to ROM and FASTROM microcontroller de- vices:. ROM FASTROM Minimum quantity per year Minimum order quantity Minimum quantity per line item Minimum quantity per year and per line item ST6 Family 100000 50000 10000 5000 ST7 and ST9 Families 50000 25000 5000 5000
5 OTP RELIABILITY
electrical test, thus ensuring a low reject rate at customer manufacturing stage. can only be fully tested at wafer probing. test, UV light is used to deactivate the cells and the good dice are assembled. Figure 4. Details about the electrical tests performed on OTP and ROM
test is limited to a reserved number of bytes which are programmed and then verified. it is recommended to check the programming equipment. Figure 5. Recommended Screening Conditions for OTP OTP devices with a similar quality level compared to ROM devices. stress mold compounds and passivation layer enhancements.
SELECTING BETWEEN ROM, FASTROM AND OTP FOR A MICROCONTROLLER “THE PRESENT NOTE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH A NOTE AND/OR THE USE MADE BY CUSTOMERS OF THE INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.” Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2003 STMicroelectronics - All rights reserved STMicroelectronics GROUP OF COMPANIES Australia – Belgium - Brazil - Canada - China – Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States