AN2014 Application note How a designer can make the most of STMicroelectronics serial EEPROMs Introduction Electrically Erasable and PROgrammable Memory (EEPROM) devices are standard products used for the non-volatile storage of data parameters, with a fine-granularity. This application note describes most of the internal architecture and related functionality of the STMicroelectronics EEPROM, such as the storage mechanism, interface circuits, optimal settings of hardware, software and data management. With these guidelines, an application designer gains a better understanding of the device’s operation and can profit from these recommendations to significantly improve the reliability of the application. February 2015 DocID10701 Rev 10 1/65 www.st.com AN2014 Contents Contents 1 EEPROM cell and memory array architecture . 7 1.1 Floating gate operation within an EEPROM cell . 7 1.1.1 Reading the value stored in a memory cell . 9 1.1.2 Writing a new value to the memory cell . 9 1.1.3 Cycling limit of EEPROM cells . 12 1.2 Electrical architecture of ST serial EEPROM arrays . 13 1.2.1 Memory array architecture . 13 1.2.2 Decoding architecture . 14 1.2.3 Intrinsic electrical stress induced by programming . 14 2 Choosing a suitable EEPROM for your application . 16 2.1 Choosing a memory type suited to the task to be performed . 16 2.2 Choosing an appropriate memory interface . 16 2.3 Choosing an appropriate supply voltage and temperature range . 17 3 Recommendations to improve EEPROM reliability . 18 3.1 Electrostatic discharges (ESD) . 18 3.1.1 What is ESD? . 18 3.1.2 How to prevent ESD? . 18 3.1.3 ST EEPROM ESD protection . 18 3.2 Electrical overstress and latchup . 19 3.2.1 What are EOS and latchup? . 19 3.2.2 How to prevent EOS and latchup events . 19 3.2.3 ST EEPROM latchup protection . 20 3.3 Power supply considerations . 20 3.3.1 Power-up and power-on-reset sequence . 21 3.3.2 Stabilized power supply voltage . 22 3.3.3 Absolute maximum ratings . 22 4 Hardware considerations . 23 4.1 I2C family (M24xxx devices) . 23 4.1.1 Chip enable (E0, E1, E2) . 23 4.1.2 Serial data (SDA) . 24 4.1.3 Serial clock (SCL) . 25 DocID10701 Rev 10 2/65 4 Contents AN2014 4.1.4 Write control (WC) . 26 4.1.5 Recommended I2C EEPROM connections . 27 4.2 SPI family (M95xxx devices) . 29 4.2.1 Chip Select (S) . 29 4.2.2 Write Protect (W) . 29 4.2.3 Serial Data input (D) and Serial Clock (C) . 30 4.2.4 Hold (HOLD) . 30 4.2.5 Serial Data output (Q) . 31 4.2.6 Recommended SPI EEPROM connections . 31 4.3 MICROWIRE® family (M93Cxxx and M93Sxxx devices) . 33 4.3.1 Chip Select (S) . 33 4.3.2 Serial Data (D) and Serial Clock (C) . 33 4.3.3 Organization Select (ORG) . 34 4.3.4 Serial Data output (Q) . 34 4.3.5 Don’t use (DU) . 34 4.3.6 Recommended MICROWIRE EEPROM connections . 35 4.4 PCB Layout considerations . 36 4.4.1 Cross coupling . 36 4.4.2 Noise and disturbances on power supply lines . 36 5 Software considerations . 37 5.1 EEPROM electrical parameters . 37 5.2 Optimal Write control . 37 5.2.1 Page mode . 37 5.2.2 Data polling . 38 5.3 Write protection . 41 5.3.1 Software write protection . 41 5.3.2 Hardware write protection . 42 5.4 Data integrity . 43 5.4.1 The checksum . 43 5.4.2 Data redundancy . 43 5.4.3 Checksum and data redundancy . 44 5.4.4 Extra redundancy . 44 5.5 Cycling endurance and data retention . 45 5.5.1 Cycling and data retention qualification procedures . 45 5.5.2 Optimal cycling with ECC . 45 3/65 DocID10701 Rev 10 AN2014 Contents 5.5.3 Cycling and temperature dependence . 46 5.5.4 Defining the application cycling strategy . 47 5.5.5 Overall number of write cycles . 48 6 Power supply loss and application reset . 49 6.1 Application reset . 49 6.1.1 I2C family . 49 6.1.2 SPI family . 51 6.1.3 MICROWIRE family . 52 6.2 Power supply loss . 53 6.2.1 Hardware recommendations . 53 6.2.2 Supply voltage energy tank capacitor . 53 6.2.3 Interruption of an EEPROM request . 54 6.3 Robust software and default operating mode . 58 7 Operating conditions . 59 7.1 Temperature . 59 7.2 Humidity and chemical vapors . 59 7.3 Mechanical stress . 59 8 Conclusions . 60 9 References . 61 10 Revision history . 62 DocID10701 Rev 10 4/65 4 AN2014 List of tables List of tables Table 1. Three serial bus protocols . 17 Table 2. ESD generation . 18 Table 3. Typical POR threshold values . ..