AN6068 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM Author: Shivendra Singh Associated Project: No Associated Part Family: CY14x104NA Software Version: None Related Application Notes: AN43593 To get the latest version of this application note, or the associated project file, please visit http://www.cypress.com/go/AN6068. AN6068 discusses the key pinout differences between the Everspin 4-Mbit (256K x 16) MRAM and the Cypress 4-Mbit (256K x 16) nvSRAM devices. These differences should be taken into consideration when designing a PCB to use either MRAM or the high performance nvSRAM on the same footprint as true alternate source part number on the same bill of materials (BOM). Introduction Cypress offers the highest performance and most reliable nonvolatile RAM products available with its nvSRAM product line. The nvSRAM technology combines the performance characteristics of a high-speed SRAM with that of a nonvolatile memory. A similar nonvolatile solution is the Magnetoresistive RAM (MRAM) from Everspin in which magnetic polarization is used to store information. This application note discusses designing applications hardware with the option to use either MRAM or nvSRAM on the same socket without any hardware redesign. The nvSRAM requires a storage capacitor (VCAP) to execute AutoStore. The VCAP pin on the nvSRAM package corresponds to either a DC (Do Not Connect) or a NC (No Connect) pin on the MRAM part depending upon package type. The MRAM recommends that NC or DC pins can be left either floating or tied to VSS. Therefore the storage capacitor for nvSRAM can remain connected when nvSRAM or MRAM are interchangeably used. ������ pin to monitor the device The nvSRAM also has a HSB ������ pin on the status or to initiate a hardware store. The HSB nvSRAM package corresponds to a NC (No Connect) pin on the MRAM package. This allows using MRAM and nvSRAM interchangeably on the same footprint. In this case the NC pin corresponding to ������ HSB can be either left floating or can be connected to the VCC. www.cypress.com Additional on-demand nonvolatile features of nvSRAM such as hardware initiated STORE through a hardware pin ������) or software initiated STORE and RECALL through (HSB soft sequences and so on, are specific to the nvSRAM device and need not be considered while migrating from MRAM to nvSRAM. However, an application can integrate these additional features of nvSRAM to enhance their application performance and flexibility. Refer to the Cypress nvSRAM datasheets for using additional nvSRAM features in your applications. Replacing MRAM with Cypress nvSRAM This section highlights pin and package differences between the Cypress nvSRAM and the MRAM devices for 4-Mbit (256K x 16) in 44-pin TSOP-II (Thin Small Outline Package - Type II) and 48-ball FBGA (Fine Pitch Ball Grid Array) package options respectively. This section also discusses about necessary design considerations which will enable you to create a common PCB footprint for using either nvSRAM or MRAM on the same footprint. Replacing 44 TSOP-II Package Option Figure 1 shows an example of replacing 4-Mbit (x16) MRAM by the 4-Mbit (x16) nvSRAM in a 44-pin TSOP-II package option on the same 44 pad PCB footprint. The dimensions of the 44-pin TSOP-II package of MRAM and nvSRAM devices are identical and shown in Table 1. Document No. 001-16633 Rev. *D 1 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM Table 1. 44-pin TSOP II Package Comparison Package Dimensions MRAM (Typ in mm) The nvSRAM 44-pin TSOP-II pinout is similar to that of the MRAM 44-pin TSOP-II pinout except for the pin 28, which is designated as a DC (Do Not Connect) pin on the MRAM, whereas it is the VCAP pin on the nvSRAM. By creating a footprint option for connecting an appropriate capacitor for nvSRAM VCAP, the MRAM can be easily replaced by the nvSRAM, or the nvSRAM replaced by the MRAM, without any modification to the board. Refer Figure 3 for the nvSRAM VCAP connection. nvSRAM (Typ in mm) Length 18.4 18.4 Width 10.16 10.16 Height 1.2 1.2 Pitch 0.8 0.8 Figure 1. MRAM and nvSRAM 44-pin TSOP II Package Comparison A0 1 44 A17 A0 1 44 A17 A1 2 43 A16 A1 2 43 A16 A2 3 42 A15 A2 3 42 A15 A3 4 41 OE A3 4 41 G A4 5 40 UB A4 5 40 BHE E 6 39 LB CE 6 39 BLE DQL0 7 38 DQU15 DQ0 7 38 DQ15 DQL1 8 37 DQU14 DQ1 8 37 DQ14 DQL2 9 36 DQU13 DQ2 9 36 DQ13 DQL3 10 35 DQU12 DQ3 10 VDD 11 34 VSS VCC 11 VSS 12 33 VDD VSS DQL4 13 32 DQU11 DQL5 14 31 DQU10 DQL6 15 30 DQL7 16 W 17 MRAM 44- pin TSOP II (x16) 35 DQ12 34 VSS 12 33 VCC DQ4 13 32 DQ11 DQ5 14 31 DQ10 DQU9 DQ6 15 30 DQ9 29 DQU8 DQ7 16 29 DQ8 28 DC WE 17 28 VCAP 18 27 A14 44- pin TSOP II (x16) A5 18 27 A14 A5 A6 19 26 A13 A6 19 26 A13 A7 20 25 A12 A7 20 25 A12 A8 21 24 A11 A8 21 24 A11 A9 22 23 A10 A9 22 23 A10 Replacing 48-ball FBGA Package Option Figure 2 shows an example of replacing 4-Mbit (x16) MRAM by a 4-Mbit (x16) nvSRAM in a 48-ball FBGA package option on the same 48 pad PCB footprint. The dimensions of 48-ball FBGA package of MRAM and nvSRAM devices differ in their length, width, and height. However the pitch of the 48-ball FBGA package remains identical which makes it possible to create a drop in replacement footprint for both package options. In this case, the package keep-out area on the PCB should be maintained such that either nvSRAM or MRAM 48-ball FBGA package can be mounted easily without obstructing other components on the PCB. The comparison of 48-ball FBGA package dimension for MRAM and nvSRAM are shown in Table 2. www.cypress.com nvSRAM Table 2. 48-ball FBGA Package Comparison Package Dimensions MRAM (Typ in mm) nvSRAM (Typ in mm) Length 8 10 Width 8 6 Height 1.35 1.2 Pitch 0.75 0.75 Document No. 001-16633 Rev. *D 2 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM The nvSRAM pinout is similar to that of the MRAM except for the three balls E3, G2, and H6 which are either designated as a DC (Do Not Connect) or NC (No Connect) pin for the MRAM. Whereas E3, G2, and H6 are the VCAP, ������), and NC pin for the nvSRAM respectively. By (HSB creating a footprint option for connecting an appropriate capacitor for nvSRAM VCAP, the MRAM can be easily replaced by the nvSRAM, or the nvSRAM replaced by the MRAM, without any modification to the board. The nvSRAM ������ HSB pin is pulled to HIGH internally by a weak pull up resistor (~100 KΩ). Therefore, if the nvSRAM ������) pin functionality is not used in the design, the (HSB ������) (HSB pin can be left as floating (NC). There is no restriction for nvSRAM NC pin connection. The nvSRAM NC pin can be biased to any logic level (HIGH or LOW) or can be left as floating (NC) in the design. Refer to Figure 3 for the ������) connection. nvSRAM VCAP and (HSB Figure 2. MRAM and nvSRAM 48-ball FBGA Package Comparison MRAM 48-ball FBGA (x16) nvSRAM 48-ball FBGA (x16) 1 2 3 4 5 6 LB G A0 A1 A2 NC DQU8 UB A3 A4 E DQU9 DQU10 A5 A6 VSS DQU11 A17 VDD DQU12 DQU14 1 2 3 4 5 6 A BLE OE A0 A1 A2 NC A DQL0 B DQ8 BHE A3 A4 CE DQ0 B DQL1 DQL2 C DQ9 DQ10 A5 A6 DQ1 DQ2 C A7 DQL3 VDD D VSS DQ11 A17 A7 DQ3 VCC D NC A16 DQL4 VSS E VCC DQ12 VCAP A16 DQ4 VSS E DQU13 A14 A15 DQL5 DQL6 F DQ14 DQ13 A14 A15 DQ5 DQ6 F DQU15 NC A12 A13 W DQL7 G DQ15 HSB A12 A13 WE DQ7 G NC A8 A9 A10 A11 DC H NC A8 A9 A10 A11 NC H Figure 3. nvSRAM VCAP and ������ HSB Connection VCC 10K Ohm Note 1 Pull up (Optional) HSB nvSRAM To Controller I/O (Optional) VCAP C Note 2 ������ can be left floating (or NC) if its functionality is not used in the design. It is recommended to Note 1: The nvSRAM HSB ������ pin if this pin is connected to a controller I/O for its control. connect an external pull-up resistor of 4.7KΩ-10KΩ on the HSB Note 2: The capacitor (C) on the nvSRAM VCAP pin can be specified as DNI (Do Not Install) in the BOM while using MRAM instead of nvSRAM on the same footprint. The capacitor (C) should be installed when using the nvSRAM. Refer AN43593 for selecting an appropriate VCAP. www.cypress.com Document No. 001-16633 Rev. *D 3 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM Other System Design Considerations The nvSRAM’s power circuitry is robustly designed to maintain its data integrity across all types of power supply ramp rates or brown out conditions which can be observed in a system setup. The nvSRAM does not put any condition on its power-up and power-down behavior. The follow on sections explain nvSRAM behavior during power-up and power-down cycles. Power Up When the nvSRAM VCC power supply crosses an internal threshold (VSWITCH) level, the device starts boot-up sequence followed by memory RECALL, which recalls user data from its nonvolatile memory cell to SRAM and becomes ready for the access. The nvSRAM takes maximum 20 ms (tHRECALL) to complete its boot-up sequence before the controller can access the part. The nvSRAM’s I/Os remains disabled during tHRECALL time therefore none of the I/Os require tracking to the power supply during power-up as in the case of MRAM. The � and W � ) to track the MRAM requires its control signals (E power supply during power-up and must be held high for a 2 ms start-up period after the power supply reaches the MRAM minimum operating voltage (VDD min). The nvSRAM recommends a 4.7 kΩ - 10 kΩ pull-up �����) control line to avoid any resistor on its write enable (WE unwanted write in case if controller is still booting-up and its I/Os remain tri-stated or floating while nvSRAM becomes ready after its boot-up cycle. This issue is also applicable to MRAM if the device is not write-protected properly in case of floating controller I/Os. Data corruption due to unwanted write in MRAM is permanent and irreversible, whereas it is reversible in case of nvSRAM. The nvSRAM retains a copy of the most recently stored user data in its nonvolatile memory which is recalled to the SRAM portion of the memory cell during power-up recall, therefore the host controller can easily recover the original data by executing software RECALL and replace the corrupted SRAM data with correct user data. www.cypress.com Power Down When the nvSRAM VCC power supply falls below (VSWITCH) threshold, the device initiates the AutoStore operation internally using stored charge on the small capacitor connected to its VCAP pin. When the nvSRAM loses VCC power when a write cycle has been initiated and is still in progress, the write cycle will be allowed to complete before data transfer from the SRAM portion of the cells to nonvolatile elements begins. This ensures that the last data word successfully written to the nvSRAM is saved during AutoStore. Once an AutoStore cycle starts in the nvSRAM, the I/Os are disabled and internal circuitry automatically switches from VCC power to the VCAP power source. Summary Cypress nvSRAM’s pinout is similar to the MRAM pinout except for the VCAP pin which is typically a no connect (NC) pin in MRAM. Customers using a MRAM can easily migrate to nvSRAM by designing a provision on the PCB to connect a capacitor on the VCAP pin. The capacitor can be left in place when MRAM is used on the board with no influence on the MRAM. Including VCAP allows nvSRAM and MRAM to be used as alternate sources in applications requiring NVRAM performance. The remainders of the pins provide identical functionalities for both MRAM and nvSRAM. About the Author Name: Shivendra Singh Title: Applications Engineer Principal Document No. 001-16633 Rev. *D 4 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM Document History Document Title: Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM - AN6068 Document Number: 001-16633 Revision ECN Orig. of Change Submission Date ** 1200303 ZSK 06/29/2007 *A 3125574 ZSK 01/02/2011 *B 3756324 ZSK 09/27/2012 Description of Change Obtain spec# for note to be added to spec system. This note had no technical updates. Kindly replace existing .pdf file on http://www.cypress.com. Updated Introduction. Updated in new template. Added section “Other System Design Considerations”. Updated Summary. Updated template. Updated Abstract to include 4-Mbit specific description. *C 3908795 ZSK 02/20/2013 Added package dimension tables (Table 1 and Table 2). Included 48-ball FBGA package option. Update the title to “Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM”. *D 4677354 www.cypress.com KAHA 03/03/2015 Updated the document as per new template. Corrected Figure 1. Document No. 001-16633 Rev. *D 5 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM Worldwide Sales and Design Support Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find the office closest to you, visit us at Cypress Locations. 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