Choosing Between nvSRAM and F-RAM™

[Anonymous]

What are the considerations to determine whether choosing between an nvSRAM or an F-RAM™?

Interface standards, density, power consumption, throughput, and endurance are the major considerations while choosing between Infineon's nonvolatile devices: nvSRAM or F-RAM.

Infineon's nonvolatile products are available with parallel, SPI, I²C, and ONFI interfaces.

1. Parallel: Some controllers have parallel interfaces (asynchronous memory interfaces) to use peripheral devices Infineon's parallel nvSRAMs and F-RAMs can be used with controllers that have an asynchronous SRAM interface.

Table 1. Parallel nvSRAMs and F-RAMs                 

Item	nvSRAM (Parallel)	F-RAM (Parallel)
Density range	64 Kbit to 16 Mbit	64 Kbit to 4 Mbit
Speed range	20 ns to 55 ns	55 ns to 70 ns
Operating current (typ)	70 mA	12 mA
Standby current (max)	5 mA	150 µA

2. SPI: SPI is a 4-wire communication interface. Most of the controllers will have this interface. SPI nvSRAMs and F-RAMs are recommended to use with such controllers.

Table 2. SPI nvSRAMs and F-RAMs                                                                         

Item	nvSRAM (SPI)	F-RAM (SPI)
Density range	64 Kbit to 1 Mbit	4 Kbit to 2 Mbit
Speed range	Up to 40 MHz	Up to 40 MHz
Operating current (typ)	10 mA	3 mA
Standby current (max)	5 mA	150 µA

3. I²C: I²C is a 2-wire communication interface. Most of the controllers will have this interface. I²C nvSRAMs and F-RAMs are recommended for use with such controllers.
  

Table 3. I²C nvSRAMs and F-RAMs                      

Item	nvSRAM (I2C)	F-RAM (I2C)
Density range	64 Kbit to 1 Mbit	4 Kbit to 1 Mbit
Speed range	Up to 3.4 MHz	Up to 3.4 MHz
Operating current (typ)	1 mA	1 mA
Standby current (max)	250 µA	150 µA

4. ONFI 1.0 (Open NAND Flash Interface): Some RAID controllers have ONFI-compliant controllers. Infineon's ONFI nvSRAMs can be interfaced with such controllers.
  
The power consumption of F-RAMs is much less than that of nvSRAMs. Tables 1, 2, and 3 provide a comparison of operating current and standby current between nvSRAMs and F-RAMs.
  
The throughput comparison of Infineon parallel and serial nvSRAM is given in the below table,
  
Table 4. Throughput Comparison Between Parallel and Serial nvSRAMs (1 Mbit)                                               

nvSRAM (Parallel)	nvSRAM (I2C)	nvSRAM (SPI)
400 Mbits/s	3.4 Mbits/s	40 Mbits/s

Table 5. Throughput Comparison Between Parallel and Serial F-RAMs (1 Mbit)                                                        

F-RAM (Parallel)	F-RAM (I2C)	F-RAM (SPI)
88 Mbits/s	3.4 Mbits/s	40 Mbits/s

As seen from this table, parallel nvSRAMs have the highest throughput compared to serial nvSRAMs and F-RAMs.

Both nvSRAMs and F-RAMs provide similar performances in terms of endurance. All writes to nvSRAMs are carried out through the SRAM memory and do not use up any endurance cycles of nvSRAMs. Endurance of F-RAMs is 100 trillion (10¹⁴) accesses (read or write operations). Even though F-RAMs have finite endurance, it will take a long time to reach the end of life of the part in terms of endurance. For example, an F-RAM operating at 40 MHz with 73,520 endurance cycles per second will take 43.1 years to use all the endurance cycles.

Parallel nvSRAMs are recommended for use in applications that require a high throughput. On the other hand, serial F-RAMs are recommended for use in applications that have low power requirements. Tradeoff among throughput, power consumption, and number of devices connected to a single controller will determine the interface type.

NOTE: nvSRAMs need an external capacitor to perform nonvolatile store and recall operations.