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How Much Power Will a Low-Power SDRAM Save You?

Author: Marc Greenberg, Director Technical Marketing

[image] Marc Greenberg

Introduction:
There are two types of DRAM chips commonly used in embedded systems. PC DRAM chips are the DDR1, DDR2 or DDR3 parts that are used in almost all PCs and servers. Low-Power DRAM chips are the LPDDR1 and LPDDR2 parts used most often in cellphones and portable applications.

PC DRAM often is the lowest cost DRAM memory and often finds its way into consumer products, even though in many cases it's not technically ideal for that purpose.

Low-Power DRAM is often a better technical fit for embedded-type applications and a requirement for low-power applications, however, Low-Power DRAM often comes at a higher cost than PC DRAM. Although LPDDR2 has recently been introduced into the marketplace, the mainstream Low-Power DRAM today is LPDDR1 and it has been 6 years since its introduction. The standard voltage of DDR3 and new low-voltage variants of PC DRAM even offer lower voltage operation than LPDDR1. One of the questions I am often asked is, could you be better off with PC DRAM for low-power embedded applications?

First Principle:
In this article, let's look at the supply voltage of the different memory types. Reducing supply voltage is one of the surest ways of reducing power consumption, as Power (P) is the product of Current (I) and Voltage (V), (P=I*V). In fact if we take the gross assumption that the losses in a memory can be modeled as resistive (R) losses, and since I=V/R, then Power is proportional to V²/R.

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