Infineon Technologies STK12C68-SF45I

Overview

STK12C68-SF45I from Cypress Semiconductor is a 64 Kbit (8 K × 8) nonvolatile SRAM with QuantumTrap technology, delivering 45 ns access time, AutoStore on power-down using a 68 µF VCAP capacitor, and unlimited SRAM read/write cycles. It operates at single 5 V ±10%, supports software/hardware STORE/RECALL, and is used in industrial control systems requiring persistent memory without battery backup.

For engineers reviewing the STK12C68-SF45I datasheet, STK12C68-SF45I pinout, STK12C68-SF45I application, or STK12C68-SF45I equivalent, key selection criteria include AutoStore timing behavior, HSB-controlled hardware store latency, VCAP capacitor sizing requirements, and compatibility with legacy 28-pin SOIC-based 5 V memory interfaces.

Technical Context

The STK12C68-SF45I integrates parallel SRAM and QuantumTrap nonvolatile cells per bit, enabling simultaneous STORE/RECALL of all 8,192 bytes. Its architecture decouples volatile operation from nonvolatile persistence: SRAM provides standard fast random access, while QuantumTrap retains data for 100 years with 1 million STORE endurance.

STORE is triggered automatically at power-down (when VCC drops below VSWITCH), via HSB pin assertion, or by six-address software sequence; RECALL occurs at power-up or via software sequence. During STORE/RECALL, SRAM I/O is disabled, and HSB asserts open-drain LOW to signal busy state - critical for system-level power sequencing coordination.

Key Specifications

Pinout & Package

STK12C68-SF45I uses a 28-pin SOIC (330 mil width) package with standard 5 V parallel memory pinout. Pin spacing and footprint match JEDEC MS-012AC, enabling drop-in replacement in legacy 28-pin socketed designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar nonvolatile SRAM applications.

Compared with STK12C68-SF35I, the -SF45I trades 10 ns speed for broader noise margin and lower dynamic power; versus FM1808-40-SG, it offers proven industrial reliability and simpler power-loss handling at the cost of density and voltage flexibility.

Availability

STK12C68-SF45I is available at Aetrix Electronics and suitable for industrial PLCs, medical instrumentation, and telecom timing modules requiring stable component supply with guaranteed long-term obsolescence management.

Supply support for STK12C68-SF45I includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Cypress Semiconductor (now part of Infineon Technologies) is a U.S.-based semiconductor company specializing in memory, microcontrollers, and programmable logic solutions for industrial and automotive markets.

The STK12C68 belongs to Cypress's nvSRAM product line, designed specifically to replace battery-backed SRAM in mission-critical systems where maintenance-free, long-life nonvolatility is mandatory.

FAQ

What is the minimum VCAP capacitor value required for reliable AutoStore operation?

The STK12C68-SF45I requires a minimum 68 µF capacitor on the VCAP pin, rated at 6 V with ±20% tolerance. This value ensures sufficient stored energy to complete the full 10 ms STORE cycle when VCC drops below VSWITCH (~3.6 V). Using less capacitance risks incomplete STORE and data loss; larger values (up to 220 µF) extend hold-up time but increase board area and cost.

Can STK12C68-SF45I operate in a 3.3 V system?

No. The STK12C68-SF45I is specified only for 5.0 V ±10% operation (4.5–5.5 V). It lacks 3.3 V logic compatibility, internal level shifters, or dual-voltage support. Attempting to power it from 3.3 V will result in functional failure, undefined STORE/RECALL behavior, and potential damage due to improper internal charge pump operation.

How does the HSB pin function during a software-initiated STORE?

During software-initiated STORE, the HSB pin is actively driven LOW by the STK12C68-SF45I to indicate busy status - identical to hardware or AutoStore modes. The pin remains LOW for the full tSTORE duration (~10 ms), providing external systems a hardware-synchronized signal to gate further memory accesses or initiate fail-safe shutdown sequences.

Is STK12C68-SF45I still recommended for new designs?

No - Cypress explicitly marks the STK12C68 family as "Not Recommended for New Designs" in its official documentation (Rev. *H, Nov 2014). While fully supported for existing production and repair, designers should evaluate Infineon's newer nvSRAM families (e.g., CY14B108QN) for new projects to ensure long-term supply and enhanced features like extended temperature range and improved ESD robustness.