Preliminary FM24W256 256Kb Wide Voltage Serial F-RAM Features 256K bit Ferroelectric Nonvolatile RAM Organized as 32,768 x 8 bits High Endurance 100 Trillion (1014) Read/Writes 38 year Data Retention (@ +75ºC) NoDelay™ Writes Advanced High-Reliability Ferroelectric Process Fast Two-wire Serial Interface Up to 1 MHz maximum bus frequency Direct hardware replacement for EEPROM Supports legacy timing for 100 kHz & 400 kHz Description Low Power Operation Wide Voltage Operation 2.7V-5.5V 100 A Active Current (100 kHz) 15 A Standby Current (typ.) Industry Standard Configuration Industrial Temperature -40 C to +85 C 8-pin “Green”/RoHS SOIC Packages Pin Configuration The FM24W256 is a 256-kilobit nonvolatile memory employing an advanced ferroelectric process. A ferroelectric random access memory or F-RAM is nonvolatile and performs reads and writes like a RAM. It provides reliable data retention for 10 years while eliminating the complexities, overhead, and system level reliability problems caused by EEPROM and other nonvolatile memories. A0 A1 A2 1 8 2 7 3 6 VSS 4 5 The FM24W256 performs write operations at bus speed. No write delays are incurred. Data is written to the memory array immediately after it has been successfully transferred to the device. The next bus cycle may commence immediately without the need for data polling. In addition, the product offers substantial write endurance compared with other nonvolatile memories. The FM24W256 is capable of supporting 1014 read/write cycles, or 100 million times more write cycles than EEPROM. Pin Names A0-A2 SDA SCL WP VSS VDD These capabilities make the FM24W256 ideal for nonvolatile memory applications requiring frequent or rapid writes. Examples range from data collection where the number of write cycles may be critical, to demanding industrial controls where the long write time of EEPROM can cause data loss. The combination of features allows more frequent data writing with less overhead for the system. The FM24W256 provides substantial benefits to users of serial EEPROM, yet these benefits are available in a hardware drop-in replacement. The FM24W256 is available in industry standard 8-pin SOIC package using a familiar two-wire protocol. It is guaranteed over an industrial temperature range of -40°C to +85°C. This is a product that has fixed target specifications but are subject to change pending characterization results. Rev. 1.3 July 2011 VDD WP SCL SDA Function Device Select Address Serial Data/Address Serial Clock Write Protect Ground Supply Voltage Ordering Information FM24W256-G FM24W256-GTR FM24W256-EG* FM24W256-EGTR* 8-pin “Green”/RoHS SOIC 8-pin “Green”/RoHS SOIC, Tape & Reel 8-pin “Green”/RoHS EIAJ SOIC 8-pin “Green”/RoHS EIAJ SOIC, Tape & Reel * Not Recommended for New Designs Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000 http://www.ramtron.com Page 1 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Address Latch Counter 4,096 x 64 FRAM Array 8 SDA Serial to Parallel Converter Data Latch SCL WP Control Logic A0-A2 Figure 1. Block Diagram Pin Description Pin Name A0-A2 Type Input SDA I/O SCL Input WP Input VDD VSS Rev. 1.3 July 2011 Supply Supply Pin Description Device Select Address 0-2: These pins are used to select one of up to 8 devices of the same type on the same two-wire bus. To select the device, the address value on the three pins must match the corresponding bits contained in the slave address. The address pins are pulled down internally. Serial Data/Address: This is a bi-directional pin for the two-wire interface. It is open-drain and is intended to be wire-OR’d with other devices on the two-wire bus. The input buffer incorporates a Schmitt trigger for noise immunity and the output driver includes slope control for falling edges. A pull-up resistor is required. Serial Clock: The serial clock pin for the two-wire interface. Data is clocked out of the part on the falling edge, and into the device on the rising edge. The SCL input also incorporates a Schmitt trigger input for noise immunity. Write Protect: When tied to VDD, addresses in the entire memory map will be writeprotected. When WP is connected to ground, all addresses may be written. This pin is pulled down internally. Supply Voltage: 2.7V to 5.5V Ground Page 2 of 14 FM24W256 - 256Kb Wide Voltage I2C F-RAM Overview Two-wire Interface The FM24W256 is a serial F-RAM memory. The memory array is logically organized as a 32,768 x 8 bit memory array and is accessed using an industry standard two-wire interface. Functional operation of the F-RAM is similar to serial EEPROMs. The major difference between the FM24W256 and a serial EEPROM with the same pinout relates to its superior write performance. The FM24W256 employs a bi-directional two-wire bus protocol using few pins or board space. Figure 2 illustrates a typical system configuration using the FM24W256 in a microcontroller-based system. The industry standard two-wire bus is familiar to many users but is described in this section. Memory Architecture When accessing the FM24W256, the user addresses 32,768 locations each with 8 data bits. These data bits are shifted serially. The 32,768 addresses are accessed using the two-wire protocol, which includes a slave address (to distinguish other non-memory devices), and a 2-byte address. Only the lower 15 bits are used by the decoder for accessing the memory. The upper most address bit should be set to 0 for compatibility with higher density devices in the future. The access time for memory operation is essentially zero beyond the time needed for the serial protocol. That is, the memory is read or written at the speed of the two-wire bus. Unlike an EEPROM, it is not necessary to poll the device for a ready condition since writes occur at bus speed. That is, by the time a new bus transaction can be shifted into the part, a write operation will be complete. This is explained in more detail in the interface section below. Users expect several obvious system benefits from the FM24W256 due to its fast write cycle and high endurance as compared with EEPROM. However there are less obvious benefits as well. For example in a high noise environment, the fast-write operation is less susceptible to corruption than an EEPROM since it is completed quickly. By contrast, an EEPROM requiring milliseconds to write is vulnerable to noise during much of the cycle. By convention, any device that is sending data onto the bus is the transmitter while the target device for this data is the receiver. The device that is controlling the bus is the master. The master is responsible for generating the clock signal for all operations. Any device on the bus that is being controlled is a slave. The FM24W256 always is a slave device. The bus protocol is controlled by transition states in the SDA and SCL signals. There are four conditions including start, stop, data bit, or acknowledge. Figure 3 illustrates the signal conditions that specify the four states. Detailed timing diagrams are in the electrical specifications. VDD Rmin = 1.1 Kohm Rmax = tR/Cbus Microcontroller SDA SCL SDA SCL FM24W256 FM24W256 A0 A1 A2 A0 A1 A2 Figure 2. Typical System Configuration Note that it is the user’s responsibility to ensure that VDD is within datasheet tolerances to prevent incorrect operation. Rev. 1.3 July 2011 Page 3 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM SCL SDA 7 Stop (Master) Start (Master) 6 Data bits (Transmitter) 0 Data bit Acknowledge (Transmitter) (Receiver) Figure 3. Data Transfer Protocol Stop Condition A stop condition is indicated when the bus master drives SDA from low to high while the SCL signal is high. All operations using the FM24W256 should end with a stop condition. If an operation is in progress when a stop is asserted, the operation will be aborted. The master must have control of SDA (not a memory read) in order to assert a stop condition. Start Condition A start condition is indicated when the bus master drives SDA from high to low while the SCL signal is high. All commands should be preceded by a start condition. An operation in progress can be aborted by asserting a start condition at any time. Aborting an operation using the start condition will ready the FM24W256 for a new operation. If during operation the power supply drops below the specified VDD minimum, the system should issue a start condition prior to performing another operation. Data/Address Transfer All data transfers (including addresses) take place while the SCL signal is high. Except under the two conditions described above, the SDA signal should not change while SCL is high. Acknowledge The acknowledge takes place after the 8th data bit has been transferred in any transaction. During this state the transmitter should release the SDA bus to allow the receiver to drive it. The receiver drives the SDA signal low to acknowledge receipt of the byte. If the receiver does not drive SDA low, the condition is a no-acknowledge and the operation is aborted. Second and most common, the receiver does not acknowledge to deliberately end an operation. For example, during a read operation, the FM24W256 will continue to place data onto the bus as long as the receiver sends acknowledges (and clocks). When a read operation is complete and no more data is needed, the receiver must not acknowledge the last byte. If the receiver acknowledges the last byte, this will cause the FM24W256 to attempt to drive the bus on the next clock while the master is sending a new command such as stop. Slave Address The first byte that the FM24W256 expects after a start condition is the slave address. As shown in Figure 4, the slave address contains the device type, the device select address bits, and a bit that specifies if the transaction is a read or a write. Bits 7-4 are the device type and should be set to 1010b for the FM24W256. These bits allow other types of function types to reside on the 2-wire bus within an identical address range. Bits 3-1 are the address select bits. They must match the corresponding value on the external address pins to select the device. Up to eight FM24W256s can reside on the same two-wire bus by assigning a different address to each. Bit 0 is the read/write bit. R/W=1 indicates a read operation and R/W=0 indicates a write operation. The receiver would fail to acknowledge for two distinct reasons. First is that a byte transfer fails. In this case, the no-acknowledge ceases the current operation so that the part can be addressed again. This allows the last byte to be recovered in the event of a communication error. Rev. 1.3 July 2011 Page 4 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Memory Operation Device Select Slave ID 1 0 1 0 A2 A1 A0 R/W 7 6 5 4 3 2 1 0 Figure 4. Slave Address Addressing Overview After the FM24W256 (as receiver) acknowledges the slave address, the master can place the memory address on the bus for a write operation. The address requires two bytes. The first is the MSB. Since the device uses only 15 address bits, the value of the upper bit is “don’t care”. Following the MSB is the LSB with the remaining eight address bits. The address value is latched internally. Each access causes the latched address value to be incremented automatically. The current address is the value that is held in the latch -- either a newly written value or the address following the last access. The current address will be held for as long as power remains or until a new value is written. Reads always use the current address. A random read address can be loaded by beginning a write operation as explained below. After transmission of each data byte, just prior to the acknowledge, the FM24W256 increments the internal address latch. This allows the next sequential byte to be accessed with no additional addressing. After the last address (7FFFh) is reached, the address latch will roll over to 0000h. There is no limit to the number of bytes that can be accessed with a single read or write operation. Data Transfer After the address information has been transmitted, data transfer between the bus master and the FM24W256 can begin. For a read operation the FM24W256 will place 8 data bits on the bus then wait for an acknowledge from the master. If the acknowledge occurs, the FM24W256 will transfer the next sequential byte. If the acknowledge is not sent, the FM24W256 will end the read operation. For a write operation, the FM24W256 will accept 8 data bits from the master then send an acknowledge. All data transfer occurs MSB (most significant bit) first. The FM24W256 is designed to operate in a manner very similar to other 2-wire interface memory products. The major differences result from the higher performance write capability of F-RAM technology. These improvements result in some differences between the FM24W256 and a similar configuration EEPROM during writes. The complete operation for both writes and reads is explained below. Write Operation All writes begin with a slave address, then a memory address. The bus master indicates a write operation by setting the LSB of the slave address to a 0. After addressing, the bus master sends each byte of data to the memory and the memory generates an acknowledge condition. Any number of sequential bytes may be written. If the end of the address range is reached internally, the address counter will wrap from 7FFFh to 0000h. Unlike other nonvolatile memory technologies, there is no effective write delay with F-RAM. Since the read and write access times of the underlying memory are the same, the user experiences no delay through the bus. The entire memory cycle occurs in less time than a single bus clock. Therefore, any operation including read or write can occur immediately following a write. Acknowledge polling, a technique used with EEPROMs to determine if a write is complete is unnecessary and will always return a ready condition. Internally, an actual memory write occurs after the 8th data bit is transferred. It will be complete before the acknowledge is sent. Therefore, if the user desires to abort a write without altering the memory contents, this should be done using start or stop condition prior to the 8th data bit. The FM24W256 uses no page buffering. The memory array can be write protected using the WP pin. Setting the WP pin to a high condition (VDD) will write-protect all addresses. The FM24W256 will not acknowledge data bytes that are written to protected addresses. In addition, the address counter will not increment if writes are attempted to these addresses. Setting WP to a low state (VSS) will deactivate this feature. WP is pulled down internally. Figures 5 and 6 below illustrate a single-byte and multiple-byte write cycles. Rev. 1.3 July 2011 Page 5 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Start By Master S Stop Address & Data Slave Address 0 A X Address MSB By FM24W256 A Address LSB A Data Byte A P Acknowledge Figure 5. Single Byte Write Start S By FM24W256 Stop Address & Data By Master Slave Address 0 A X Address MSB A Address LSB A Data Byte A Data Byte A P Acknowledge Figure 6. Multiple Byte Write Read Operation There are two basic types of read operations. They are current address read and selective address read. In a current address read, the FM24W256 uses the internal address latch to supply the address. In a selective read, the user performs a procedure to set the address to a specific value. Current Address & Sequential Read As mentioned above the FM24W256 uses an internal latch to supply the address for a read operation. A current address read uses the existing value in the address latch as a starting place for the read operation. The system reads from the address immediately following that of the last operation. To perform a current address read, the bus master supplies a slave address with the LSB set to 1. This indicates that a read operation is requested. After receiving the complete slave address, the FM24W256 will begin shifting out data from the current address on the next clock. The current address is the value held in the internal address latch. Beginning with the current address, the bus master can read any number of bytes. Thus, a sequential read is simply a current address read with multiple byte transfers. After each byte the internal address counter will be incremented. Each time the bus master acknowledges a byte, this indicates that the FM24W256 should read out the next sequential byte. Rev. 1.3 July 2011 There are four ways to properly terminate a read operation. Failing to properly terminate the read will most likely create a bus contention as the FM24W256 attempts to read out additional data onto the bus. The four valid methods are: 1. 2. 3. 4. The bus master issues a no-acknowledge in the 9th clock cycle and a stop in the 10th clock cycle. This is illustrated in the diagrams below. This is preferred. The bus master issues a no-acknowledge in the 9th clock cycle and a start in the 10th. The bus master issues a stop in the 9th clock cycle. The bus master issues a start in the 9th clock cycle. If the internal address reaches 7FFFh, it will wrap around to 0000h on the next read cycle. Figures 7 and 8 below show the proper operation for current address reads. Selective (Random) Read There is a simple technique that allows a user to select a random address location as the starting point for a read operation. This involves using the first three bytes of a write operation to set the internal address followed by subsequent read operations. To perform a selective read, the bus master sends out the slave address with the LSB set to 0. This specifies a write operation. According to the write protocol, the bus master then sends the address bytes that are Page 6 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM loaded into the internal address latch. After the FM24W256 acknowledges the address, the bus master issues a start condition. This simultaneously aborts the write operation and allows the read Start By Master command to be issued with the slave address LSB set to a “1”. The operation is now a current address read. No Acknowledge Address Stop S Slave Address By FM24W256 1 A Data Byte Acknowledge 1 P Data Figure 7. Current Address Read By Master Start Address No Acknowledge Acknowledge Stop S Slave Address By FM24W256 1 A Data Byte A Acknowledge Data Byte 1 P Data Figure 8. Sequential Read Start Address By Master Start No Acknowledge Address Stop S By FM24W256 Slave Address 0 A X Address MSB A Address LSB A S Slave Address Acknowledge 1 A Data Byte 1 P Data Figure 9. Selective (Random) Read Rev. 1.3 July 2011 Page 7 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Electrical Specifications Absolute Maximum Ratings Symbol Description VDD Power Supply Voltage with respect to VSS VIN Voltage on any pin with respect to VSS TSTG TLEAD VESD Storage Temperature Lead Temperature (Soldering, 10 seconds) Electrostatic Discharge Voltage - Human Body Model (AEC-Q100-002 Rev. E) - Charged Device Model (AEC-Q100-011 Rev. B) - Machine Model (AEC-Q100-003 Rev. E) Package Moisture Sensitivity Level Ratings -1.0V to +7.0V -1.0V to +7.0V and VIN < VDD+1.0V * -55C to +125C 260 C 3.5kV 1.25kV 200V MSL-1 (SOIC) MSL-2 (EIAJ) * Exception: The “VIN < VDD+1.0V” restriction does not apply to the SCL and SDA inputs. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only, and the functional operation of the device at these or any other conditions above those listed in the operational section of this specification is not implied. Exposure to absolute maximum ratings conditions for extended periods may affect device reliability. DC Operating Conditions (TA = -40 C to + 85 C, VDD =2.7V to 5.5V unless otherwise specified) Symbol Parameter Min Typ Max Units VDD Main Power Supply 2.7 3.3 5.5 V IDD VDD Supply Current @ SCL = 100 kHz 100 A @ SCL = 400 kHz 200 A @ SCL = 1 MHz 400 A ISB Standby Current 15 30 A ILI Input Leakage Current ±1 A ILO Output Leakage Current ±1 A VIL Input Low Voltage -0.3 0.3*VDD V VIH Input High Voltage 0.7*VDD VDD + 0.3 V VOL Output Low Voltage @ IOL = 3.0 mA 0.4 V RIN Address Input Resistance (WP, A2-A0) For VIN = VIL (max) 40 K For VIN = VIH (min) 4 M Notes 1 2 3 3 4 Notes 1. SCL toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V. 2. SCL = SDA = VDD. All inputs VSS or VDD. Stop command issued. 3. VIN or VOUT = VSS to VDD. Does not apply to WP, A2-A0 pins. 4. The input pull-down circuit is strong (40K) when the input voltage is below V IL and weak (4M) when the input voltage is above VIH. Rev. 1.3 July 2011 Page 8 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM AC Parameters (TA = -40 C to + 85 C, VDD =2.7V to 5.5V unless otherwise specified) Symbol Parameter Min Max Min Max Min fSCL SCL Clock Frequency 0 100 0 400 0 tLOW Clock Low Period 4.7 1.3 0.6 tHIGH Clock High Period 4.0 0.6 0.4 tAA SCL Low to SDA Data Out Valid 3 0.9 tBUF tHD:STA tSU:STA tHD:DAT tSU:DAT tR tF tSU:STO tDH tSP Bus Free Before New Transmission Start Condition Hold Time Start Condition Setup for Repeated Start Data In Hold Data In Setup Input Rise Time Input Fall Time Stop Condition Setup Data Output Hold (from SCL @ VIL) Noise Suppression Time Constant on SCL, SDA Max 1000 0.55 Units kHz s s s 4.7 4.0 4.7 1.3 0.6 0.6 0.5 0.25 0.25 s s s 0 250 0 100 0 100 300 100 ns ns ns ns s ns 50 ns 1000 300 4.0 0 300 300 0.6 0 50 0.25 0 50 Notes 1 2 2 Notes : All SCL specifications as well as start and stop conditions apply to both read and write operations. 1 The speed-related specifications are guaranteed characteristic points along a continuous curve of operation from DC to 1 MHz. 2 This parameter is periodically sampled and not 100% tested. Capacitance (TA = 25 C, f=1.0 MHz, VDD = 3V) Symbol Parameter Max CI/O Input/Output Capacitance (SDA) 8 CIN Input Capacitance 6 Units pF pF Notes 1 1 Notes 1 This parameter is periodically sampled and not 100% tested. Power Cycle Timing VDD VDD min. tVR tVF tPU tPD SDA,SCL Power Cycle Timing (TA = -40 C to +85 C, VDD = 2.7V to 5.5V unless otherwise specified) Symbol Parameter Min Max tPU Power Up (VDD min) to First Access (Start condition) 10 tPD Last Access (Stop condition) to Power Down (VDD min) 0 tVR VDD Rise Time 30 tVF VDD Fall Time 100 Notes 1. Slope measured at any point on VDD waveform. Rev. 1.3 July 2011 Units Notes ms s s/V s/V 1 1 Page 9 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM AC Test Conditions Input Pulse Levels Input rise and fall times Input and output timing levels Equivalent AC Load Circuit 0.1 VDD to 0.9 VDD 10 ns 0.5 VDD 5.5V 1700 Diagram Notes All start and stop timing parameters apply to both read and write cycles. Clock specifications are identical for read and write cycles. Write timing parameters apply to slave address, word address, and write data bits. Functional relationships are illustrated in the relevant datasheet sections. These diagrams illustrate the timing parameters only. Output 100 pF Read Bus Timing tR ` tF t HIGH t SP t LOW t SP SCL t SU:SDA 1/fSCL t BUF t HD:DAT t SU:DAT SDA Start t DH t AA Stop Start Acknowledge Write Bus Timing t HD:DAT SCL t HD:STA t SU:STO t SU:DAT t AA SDA Start Data Retention Symbol Parameter TDR @ +85ºC @ +80ºC @ +75ºC Rev. 1.3 July 2011 Stop Start Acknowledge Min 10 19 38 Max - Units Years Years Years Notes Page 10 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Mechanical Drawing 8-pin SOIC (JEDEC Standard MS-012 variation AA) Recommended PCB Footprint 7.70 3.90 ±0.10 3.70 6.00 ±0.20 2.00 0.65 1.27 Pin 1 4.90 ±0.10 1.27 0.33 0.51 0.25 0.50 1.35 1.75 0.10 0.25 0.19 0.25 45 0.10 mm 0-8 0.40 1.27 Refer to JEDEC MS-012 for complete dimensions and notes. All dimensions in millimeters. SOIC Package Marking Scheme XXXXXXX-P RLLLLLLL RICYYWW Legend: XXXXXX= part number, P= package type (G=SOIC, EG=EIAJ SOIC) R=rev code, LLLLLLL= lot code RIC=Ramtron Int’l Corp, YY=year, WW=work week Example: FM24W256, “Green” SOIC package, Year 2010, Work Week 37 FM24W256-G A00002G1 RIC1037 Rev. 1.3 July 2011 Page 11 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM 8-pin EIAJ SOIC (Wide Body) Recommended PCB Footprint 9.30 5.28 ±0.10 5.00 8.00 ±0.25 D E D S N E GN M S I 6 -G M 5 E 2 O D 24 W C E R EWe: FM T N a t iv O N O R lt e r n F A 2.15 0.65 1.27 Pin 1 5.23 ±0.10 1.27 0.36 0.50 0.19 0.25 1.78 2.00 0.05 0.25 0.10 mm 0- 8 0.51 0.76 All dimensions in millimeters. EIAJ SOIC Package Marking Scheme XXXXXXX-P RLLLLLLL RIC YYWW Legend: XXXXXX= part number, P= package type (G=SOIC, EG=EIAJ SOIC) R=rev code, LLLLLLL= lot code RIC=Ramtron Int’l Corp, YY=year, WW=work week Example: FM24W256, “Green” EIAJ SOIC package, Year 2010, Work Week 37 FM24W256-EG A00002G1 RIC1037 Rev. 1.3 July 2011 Page 12 of 13 FM24W256 - 256Kb Wide Voltage I2C F-RAM Revision History Revision 1.0 1.1 1.2 1.3 Rev. 1.3 July 2011 Date 11/19/2010 1/17/2011 2/15/2011 7/12/2011 Summary Initial Release Added ESD ratings. Changed VIH (max) to VDD+0.3V. Changed to MSL-2 for EIAJ package. Changed tPU and tVF spec limits. EIAJ package is Not Recommended for New Designs (NRND). Page 13 of 13