The DS3644 is a secure supervisor with 1024 bytes of SRAM for the secure storage of sensitive data and the physical tamper-sensing response functions required in cryptographic processors and data security equipment.

One of the DS3644's primary features is the on-chip nonimprinting memory, consisting of eight 128-byte banks incorporating a high-speed, direct-wired clearing function. The 1KB memory is constantly complemented in the background to prevent memory imprinting of data. The DS3644 architecture allows the user to clear selective banks of the memory based upon specified tamper events. In the event of a qualified tamper event, the desired bank(s) of memory are rapidly cleared and a negative bias can be applied to erase external memory.

The DS3644 includes a seconds counter, watchdog timer, CPU supervisor, nonvolatile (NV) SRAM controller, and on-chip temperature sensor. In the event of a primary power failure, an external battery source is automatically switched in to keep the memory, time, and tamper-detection circuitry active. The DS3644 provides low-leakage, tamper-detection inputs for interface to external sensors, interlocks, and antitamper meshes. The DS3644 also invokes a tamper event on absolute temperature, if the temperature rate-of-change exceeds programmed limits, or if the crystal oscillator frequency falls outside a specified window. The tamper event is latched and timestamped for fault-recovery purposes.

Access to the timer, tamper monitoring, memory, and device configuration is conducted through an I2C-compatible interface. The DS3644 is assembled in a Pb-free, 7mm x 7mm x 0.8mm CSBGA package.

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Memory

• 1024-Byte Nonimprinting Memory with High-Speed Erase
• 64 Bytes General-Purpose RAM (Not Cleared)
• External SRAM Control and Optional Tamper-Event Erasure
• Segmented Tamper-Detection Memory Hierarchy with Programmable Tamper-Event Sources