Microcontrollers (MCUs) with battery-backed SRAM (NVRAM) have found wide acceptance in embedded applications. However, battery-backed SRAM brings with it power management issues that designers can do without.




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SRAM Replacement



EMRAM as SRAM Replacement


EMRAM is a fast memory (cycle time <70ns), is nonvolatile and has unlimited write / read endurance. It is in effect RAM and nonvolatile storage in the same device, and is perfect for data logging operations and in-system programmability.

Because of this unique combination, EMRAM is a perfect choice as external NVRAM to a MCU. In addition, designers will realize significant cost savings by moving from a complex solution to a simple one-chip solution.

Battery backed SRAM issues

Electro-static discharge (ESD) and electrical noise can enter a system and lead to out-of-tolerance voltage spikes. Another source of voltage spikes is the power supply. Many simple voltage regulators are notorious for generating voltage spikes as they power up. The departure from CMOS boundaries comes from both ends: spikes above Vcc or below Vss. These spikes will lead to either hard failure (silicon damage) or soft error (memory corruption).

Negative voltage spikes, for example, leads to one or more parasitic diodes inside the device becoming forward biased. This will cause the device to consume a large amount of current, and may cause a latch up. In general, the only way to remove CMOS latch-up is disconnecting power to the device.

Should excessive current draw not be terminated, irreversible damage to the MCU may occur. As this is simultaneously draining power away from the battery backed SRAM, it may cause the voltage to drop below the minimum needed to maintain the memory, leading to soft errors.

Current solutions may involve using Schottky diodes to protect the I/O pins of a MCU. At higher temperature, a Schottky diode’s reverse leakage will load the I/O line, making it difficult for the device to drive a logic 1. These are all sub-optimal solutions that take up board space and design resources.

EMRAM the simple solution

Employing EMRAM removes the need for a battery as well as the associated protection schemes required to safeguard the performance of the MCU and memory.

In applications where space is at a premium, EMRAM comes in low profile packages that is absent from a battery-backed SRAM solution.

With a simple 1-chip solution, designers can realize significant cost saving with EMRAM.


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