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
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
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.