AN-405 Comparing FM31xx and FM3127x/FM31L27x I2C Processor Companion with F-RAM Devices DESCRIPTION The FM31xx and FM3127x/FM31L27x processor companion families are similar in many ways, however there are a few key differences. The original FM31xx family operates over a wide voltage range, 2.7V to 5.5V. The FM3127x and FM31L27x families are split into 5V and 3V versions, respectively. The following table shows the new part numbers and the corresponding densities. Density Original Family New 5V Family New 3V Family 256Kb 64Kb 16Kb 4Kb FM31256-G FM3164-G FM3116-G FM3104-G FM31278-G FM31276-G FM31274-G FM31272-G FM31L278-G FM31L276-G FM31L274-G FM31L272-G The original and new devices are mostly the same. The interface, features, and densities are the same, however, there are a few differences: (1) operating voltage range, (2) trickle charger, and (3) RTC crystal. Register 0Bh, FM31xx Reg Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register 0Bh, FM3127x/FM31L27x Reg Bit 7 Bit 6 Bit 5 (1) The new FM3127x devices operate from 4.0V to 5.5V and requires only one bit to program two VTP trip points, 3.9V and 4.4V. Similarly the new FM31L27x devices operate from 2.7V to 3.6V and also requires only one bit to program two VTP trip points, 2.6V and 2.9V. Register 0Bh is shown above for original and new devices. Note: This is code compatible with the original FM31xx since Bit 1 in the new FM3127x/FM31L27x is ignored. (2) The new devices have a higher trickle charger current for the base setting (FC=0). They also have a new Fast Charge mode (FC=1) that is user-selectable. This Fast Charge mode allows a 0.1F supercap to be fully charged in 15 minutes. Note the VBC bit remains in location Bit 2, Register 0Bh. The FC bit has been added to location Bit 5, Register 0Bh. If the trickle charger is disabled (i.e. VBC=0 and battery used as backup source), then the trickle charger changes are irrelevant. (3) The new families use a 12.5pF crystal, a more commonly available type than the 6pF type. Otherwise there is no change to the RTC. All other specifications have remained the same for the new family of companions. The new families are software backward compatible. The original and new devices are available in the "green"/RoHS package, designated as "-G". http://www.ramtron.com Dec. 2007 Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000 Page 1 of 2 AN405 - Comparing FM31xx and FM3127x/FM31L27x COMPARISON TABLE The differences between the original and new families are summarized below. Operating Voltage Range Voltage Detect Trip Points RTC Crystal Type Trickle Charger (min max range) Dec. 2007 Original Family FM31xx 2.7V to 5.5V New 5V Family FM3127x 4.0 to 5.5V New 3V Family FM31L27x 2.7V to 3.6V 2.6V, 2.9V, 3.9V, 4.4V 3.9V, 4.4V 2.6V, 2.9V 6 pF 12.5 pF 5 - 25 A 50 - 120 A, FC=0 200 - 2500 A, FC=1 Comments Split into 5V and 3V versions. New devices have only one VTP bit in register 0Bh. A more common crystal Added Fast Charge mode (Register 0Bh, bit 5). Increased current on standard setting. Page 2 of 2