AN55662 Migrating from STK14C88-3 to CY14B256LA Author: Ravi Prakash Associated Project: No Associated Part Family: STK14C88-3, CY14B256LA Software Version: N/A Related Application Notes: None AN55662 provides details for migrating from the STK14C88-3 nvSRAM part to CY14B256LA part in applications. This application note also lists the parameter differences between the parts and the design considerations for migration when converting applications to CY14B256LA. Introduction Feature Set Cypress CY14B256LA is a 3 V, 256 Kbit (32 K x 8) nvSRAM in 0.13 micron technology. This part with a few performance enhancements is functionally equivalent to STK14C88-3 in 0.8 micron technology but with a few differences in parameters. This application note highlights the differences between the STK14C88-3 and the CY14B256LA and the parameters of significance that must be considered while migrating. Overview The following tables compare the features and parameters of the two parts. As shown in Table 1, the 256 Kbit nvSRAM is available in x8 configuration. Table 1. Part Number Description Description Original Part Number Replacement Part Number 32 K x 8 STK14C88-3 CY14B256LA Speed STORE Cycles Data Retention STK14C88-3 35 ns 45 ns 1,000,000 100 years at 55 °C CY14B256LA 25 ns 45 ns 1,000,000 20 years at 85 °C Operating Temperature Range While STK14C88-3 is available in both commercial and industrial temperature ranges, CY14B256LA is offered only in the industrial temperature range. Table 3. Operating Temperature Range Comparison Operating Temperature Range Commercial (0 to 70 °C) Industrial (–40 to 85 °C) STK14C88-3 CY14B256LA Available Not Available Available Available Feature Set Packages Both the parts share the same overall feature set and are available in the operation speed bins give in Table 2. CY14B256LA is pin compatible with STK14C88-3 and is available in the packages and pin configurations as follows. Table 2. Feature Set Comparison Table 4. Packages Comparison Feature Set AutoStore Software STORE Hardware STORE Software RECALL AutoStore Inhibit AutoStore Enable/Disable Preventing STORE on the fly www.cypress.com STK14C88-3 Available Available Available Available Available CY14B256LA Available Available Available Available Not Available Not Available Available Available Not Available Package STK14C88-3 CY14B256LA 32-pin SOIC Available Available 32-pin PDIP Available Not Available 48-pin SSOP Not Available Available 44-pin TSOPII Not Available Available Document No. 001-55662 Rev. *E 1 Migrating from STK14C88-3 to CY14B256LA Parameters The CY14B256LA is a pin compatible replacement for STK14C88-3 and requires minimum changes in the application board in most applications. However, the differences in parameters should be considered before replacing one part with the other. Table 5 lists the differences in parameters between STK14C88-3 and CY14B256LA. Table 5. Parameter Comparison Parameter Description Speed STK14C88-3 CY14B256LA Min Max Min Max - 3.0 3.6 2.7 3.6 25 ns - - - 70 35 ns - 52 - - 45 ns - 44 - 52 - 3 - 10 Unit DC Parameters VCC Power Supply ICC1 Average VCC Current ICC2 Average VCC Current during STORE - ICC3 Average VCC Current at tRC = 200 ns, VCC typ, 25 °C - ICC4 Average VCAP Current during AutoStore Cycle - - 2 ISB1 Average VCC Standby Current (Standby, Cycling Input) 35 ns - 19 45 ns - 17 ISB VCC Standby Current - - 1 VIH Input High Voltage - 2.2 9 (typ) 5 Not specified - VOH Output HIGH Voltage - - VOL Output LOW Voltage - - 0.4 (IOUT = 8 mA) VCAP Storage Capacitor - mA mA 5 2 2.4 (IOUT = -4 mA) mA mA 35 (typ) - V mA V - 2.4 (IOUT = -2 mA) V - 0.4 (IOUT = 4 mA) V 54 to 264 61 to 180 µF AC Switching Parameters tOHA Output Hold After Address Change - 5 - 3 - ns tLZCE Chip Enable to Output Active - 5 - 3 - ns tLZWE Output Active After End of Write - 5 - 3 - ns AutoStore / Power-Up RECALL Parameters tHRECALL Power-Up RECALL Duration - - 0.55 - 20 ms tSTORE STORE Cycle Duration - - 10 - 8 ms tVSBL Low Voltage Trigger (VSWITCH) to - - 300 - 25 ns tRESET Low Voltage Reset Level - - 2.4 tSWITCH Low Voltage Trigger Level - 2.7 2.95 tDELAY Time Allowed to Complete SRAM Cycle - 1,000 low Not Applicable V - 2.65 V - 25 ns 1.9 V VHDIS Output Disable Voltage - Not specified - tLZHSB To Output Active Time - Not specified - 5 µs tHHHD High Active Time - Not specified - 500 ns Software Controlled STORE/RECALL Cycle Parameters tHA Address Hold Time - 20 0 ns tRECALL RECALL Duration - - 20 - 200 µs Hardware STORE Cycle Parameters tHLBL LOW to STORE Busy - - 300 - 25 (tDELAY) ns tDHSB To Output Active Time - - 700 - 25 ns www.cypress.com Document No. 001-55662 Rev. *E 2 Migrating from STK14C88-3 to CY14B256LA Critical Considerations The impact of the differences in CY14B256LA with respect to the STK14C88-3 in existing applications are discussed in this section. System designers are recommended to review the detailed datasheets when migrating to the new part. DC Parameters The power supply design in most applications with STK14C88-3 would require no changes when replacing the nvSRAM with the CY14B256LA in spite of the higher values in the operating / higher standby current. The critical parameters to consider are the VCAP and the VSWITCH. VCAP While most of the differences do not impact the application, the difference in VCAP is a critical consideration while converting from the older rev parts. VCAP is the capacitor, that provides the required charge for AutoStore to complete NV store of the SRAM data during power down. The required capacitor range is different for the two parts. Table 6. VCAP Comparison Description STK14C88-3 CY14B256LA VCAP 54 µF to 264 µF 61 µF to 180 µF Therefore, in any existing application which uses a capacitor value outside the overlapping range (61 µF to 180 µF) the impact of capacitor dimensions needs to be considered while changing to the new capacitor. be in tristate as long as the controller. is held LOW by the AC Switching Parameters There are a few minor differences in switching parameters between the CY14B256LA and the STK14C88-3, as listed in the Table 5. However, these differences do not impact most applications. For replacing 35 ns speed parts, choose the 25 ns speed parts as replacement (since 35 ns speed grade is not available in the CY14B256LA). AutoStore/Power-Up RECALL Parameters tHRECALL The power-up RECALL is much different in the CY14B256LA compared to the STK14C88-3 because of architecture differences. Table 8. tHRECALL Comparison Description STK14C88-3 CY14B256LA tHRECALL 550 µs 20 ms This difference is not likely to affect applications since the initialization of the controller on the board happens at the same time. However, this should be taken into consideration when replacing the STK14C88-3 with CY14B256LA. Software Controlled STORE/RECALL Cycle Parameters Note The capacitor range is the absolute value of the capacitor, net of tolerence. The Software cycle parameter tRECALL is different in CY14B256LA as described in the following section. VSWITCH tRECALL The STK14C88-3 operates from 3 V while the CY14B256LA operates from 2.7 V. Hence the VSWITCH levels are different. Software RECALL time (tRECALL) is higher in CY14B256LA. Table 7. VCC, VSWITCH Comparison Description STK14C88-3 CY14B256LA VCC 3.0 V to 3.6 V 2.7 V to 3.6 V VSWITCH 2.7 V to 2.95 V <2.65 V Table 9. tRECALL Comparison Description STK14C88-3 CY14B256LA tRECALL 20 µs 200 µs This difference could require firmware change in the existing application to increase the controller wait state when software RECALL is initiated. The difference in levels do not affect most applications except where the controller has operating range from 3.0 V and above. In such applications, if CY14B256LA is used to replace STK14C88-3, at voltage levels below 3 V, the controller could be tristated and hence CY14B256LA could write invalid data into the SRAM. This is because the CY14B256LA would be active up to 2.7 V. In such application, it is necessary that the controller issues a reset when the VCC crosses below 3 V and remains LOW as long as the controller is inactive. This would initiate a Hardware STORE in the CY14B256LA and the nvSRAM outputs would www.cypress.com Document No. 001-55662 Rev. *E 3 Migrating from STK14C88-3 to CY14B256LA Software Sequence AutoStore Inhibit The CY14B256LA has been designed to be compatible with the CY14B256L/STK14C88-3 in the software sequence modes. Hence, the same Software STORE and RECALL address sequences in CY14B256L/STK14C88-3 works in CY14B256LA, requiring no firmware change. However, there is a difference in the required state of / during the software sequence reads as explained further. The STK14C88-3 has the AutoStore Inhibit feature and the CY14B256LA has AutoStore Disable mode. These two provide the same result of AutoStore disable but are done by different means – hardware in STK14C88-3 and software in CY14B256LA. In the CY14B256L/STK14C88-3 while software sequence must be clocked with / controlled reads it is not necessary that / be low for the sequence to be valid. That is, it is not necessary that the read is a real read with / held LOW. But, in the CY14B256LA the software sequence may be clocked with controlled reads or controlled reads. This means that while in the STK14C88-3 / state was immaterial, in the CY14B25LA , needs to be LOW for a valid software sequence read. It does not matter if goes LOW first or goes LOW first but the read is valid for software sequence only when both and have gone LOW. In both the STK14C88-3 and CY14B256LA must be kept HIGH for all the six read sequences. In effect, this difference will affect applications where software sequence reads are done with / held HIGH. Firmware change will be required to take LOW when using the new part CY14B256LA. Applications where software sequence reads are performed with / LOW do not require any change. Hardware STORE Cycle Parameters The Hardware STORE parameters are improved in the CY14B256LA. The improvements are listed under the Details of Improvement section. No changes are required in applications. www.cypress.com To disable AutoStore in STK14C88-3, the power is connected to the VCAP pin and the VCC pin is grounded (or left open). This cannot be done in CY14B256LA. For proper operation of the device, in CY14B256LA, power is connected to the VCC pin only. However, AutoStore disable is more easily done through simple software sequence. Therefore, if the STK14C88-3 is replaced in an application where AutoStore has been disabled, then the layout has to be modified to connect the power to the VCC pin and a software sequence has to be used to disable AutoStore function followed by a Software STORE, the first time the board is powered up. Preventing STORE In the STK14C88-3, STORE function can be disabled on the fly by holding pin HIGH at the onset of STORE with a driver capable of sourcing 30 mA at a VOH of at least 2.2 V. This feature is not available in the CY14B256LA parts. In the CY14B256LA, a STORE initiated by any means, cannot be disabled on the fly. Data Retention The Data Retention in the CY14B256LA part is improved from the older technology part. The CY14B256LA has data retention of 20 years at 85 °C against the STK14C88-3 data retention of 100 years at 55 °C. This translates to over four times improvement in data retention at the same temperatures. Document No. 001-55662 Rev. *E 4 Migrating from STK14C88-3 to CY14B256LA Details of Improvement Hardware STORE Related Improvements pin (Hardware STORE Busy Indication/Hardware STORE Initiation) The pin of the nvSRAM is an open drain I/O pin used to indicate or initiate a STORE operation. When a STORE operation is in progress, nvSRAM pulls the pin low to indicate that the device is busy and cannot be accessed for read/write operation. During normal operation, the pin can be pulled low to initiate a Hardware STORE operation. As shown in Table 5, several timing parameters related to the pin input and output have changed from STK14C88-3 to CY14B256LA. All of these changes are improvements from the original part specification and should be considered as added benefits in your system while migrating to the new part number. tDELAY If a write latch is set and the pin is pulled low, STK14C88-3 enables 1 µs time for write operations to complete before STORE operation begins and reads and writes are inhibited. This potentially enables inadvertent data to be written to the nvSRAM during the tDELAY duration. Note rite Latch: hen a write operation is done, a ‘write latch’ is set internally. hen is pulled low, nvSRAM checks this write latch before initiating a STORE. This is done to prevent any unnecessary loss of endurance cycles. In CY14B256LA, the tDELAY parameter enables only one write cycle time for any ongoing write to complete after pin is pulled low. This improvement provides better security from inadvertent write operations. Also, if pin is pulled low externally for a minimum of tPHSB time on CY14B256LA, the output driver of pin pulls the pin low only indicating a STORE operation within 25 ns (tDELAY). This parameter for low to STORE busy is not specified in the STK14C88-3. (See Figure 1 and Figure 2). LOW when write latch not set: If no writes are performed since the last STORE/RECALL operation, STORE operation does not start when is pulled low. However, the pin is still internally pulled low for 1 us (tDELAY) time in the STK14C88-3 device. CY14B256LA device does not pull the pin low internally if write latch is not set. This improvement prevents the possibility of being in an infinite loop when pins of two nvSRAM devices are ganged. Figure 1. STK14C88-3: AC Parameters Related to Figure 2. CY14B256LA: AC Parameters Related to Write Latch Set www.cypress.com Write Latch Not Set Document No. 001-55662 Rev. *E 5 Migrating from STK14C88-3 to CY14B256LA Power-Up Recall Related Improvements Additional parameters are specified in CY14B256LA such as Output Disable Voltage (VHDIS), To Output Active Time (tLZHSB), and High Active Time (tHHHD), which helps in system design. See the Figure 3 and Figure 4 for the definition of the additional specs in power-up. Also, note that remains low until the end of the power-up in the new part. This would guard against the system inadvertently thinking the part has completed the boot up prior to real completion. Figure 3. STK14C88-3: Power-Up Recall Figure 4. CY14B256LA: Power-Up Recall www.cypress.com Document No. 001-55662 Rev. *E 6 Migrating from STK14C88-3 to CY14B256LA Summary The application note discusses the differences between CY14B256LA in the latest 0.13 micron technology and STK14C88-3 in the 0.8 micron technology. Several parameters related to and power-up have improved/ specified in the new device enabling faster device response, greater data security, and ease of design. application board in most applications. Applications where STK14C88-3 is in AutoStore inhibit mode would require layout changes, and also, it is not possible to prevent STORE on the fly in the CY14B256LA. The value of VCAP in the existing design needs to be considered while replacing the part. CY14B256LA is pin compatible with STK14C88-3 and can replace the STK14C88-3 device with minimum changes in www.cypress.com Document No. 001-55662 Rev. *E 7 Migrating from STK14C88-3 to CY14B256LA Document History Document Title: Migrating from STK14C88-3 to CY14B256LA – AN55662 Document Number: 001-55662 Revision ECN Orig. of Change Submission Date Description of Change ** 2773126 PSR 10/01/09 New Spec. *A 3016464 PSR 09/27/10 Updated Introduction in page 1. Added a feature, Preventing STORE on the fly, to Table 2 and added a paragraph under Critical Consideration indicating this feature difference. Changed STORE cycles of CY14B256LA in Table 2 to 1,000,000 and deleted the STORE cycles paragraph under Critical Consideration since the parts are identical in this. Updated Summary in page 7. *B 3376003 GVCH 09/19/2011 Added requirement differences in Software Sequence section in page 3, 4 *C 3618997 PSR 06/05/2012 Updated document to match with current Cypress template. hanged title from “ onverting” to “Migrating” Reworded the Abstract for better understanding. Text and drawing updates for more clarity. No change in technical content. *D 4168635 GVCH 10/21/2013 Obsolete document. *E 4221998 GVCH 12/19/2013 Document reactivated. Updated in new template. www.cypress.com Document No. 001-55662 Rev. *E 8 Migrating from STK14C88-3 to CY14B256LA Worldwide Sales and Design Support ypress 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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