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DDR4 SDRAM FAQs

DDR4 SDRAM(13)
What are some of the additional power-saving features of DDR4?

Some new power-savings features in DDR4 include pseudo open-drain DQs (for read and write I/O power reduction), data-bit inversion (DBI), and command address latency (CAL).

What is the value of DDR4?

DDR4 has more than 20 new features compared to DDR3, focused on power saving, performance, manufacturability and reliability. These features, coupled with DDR4’s 1.2v core, can provide power savings of 25% compared to standard DDR3. DDR4’s architecture and added performance features offer a substantial performance boost in bandwidth and command scheduling, which can be realized for 100% or better effective bandwidth increase. Premium DDR4 offers over 170% faster max data rates than top-tier DDR3, with speeds as high as 3200MT/s.

Can DDR4 operate at slower DDR3 speeds?

DDR4 is backward compatible as far back as DDR3-1333. For systems that do not need speed increases above DDR3-1333 and DDR3-1600, DDR4 can support these slower bandwidth requirements with substantially lower power requirements.

Where will DDR4 devices be manufactured?

DDR4 will be produced in Micron fabs around the world, including Virginia, Singapore, and Taiwan.

Are there any features on DDR3 that have been eliminated by DDR4?

Not really; however, DDR4 does not require an external VREFDQ, but it does provide an internally generated VREFDQ that requires calibration by the DRAM controller.

Does DDR4 use the same signaling protocol as DDR3?

DDR4 uses the same VTT mid-point termination methodology (SSTL1.5) on the address, command, and control pins as DDR3; however, DDR4 uses VDD termination (POD12) on the data bus due to the use of pseudo open-drain I/Os for improved signal quality and less switching current.

Does DDR4 use the same power sources as DDR3?

No, DDR3 requires VDD and VDDQ equal to 1.5V, VREFCA equal to 0.5 x VDD, and VREFDQ equal to 0.5 x VDDQ, while DDR4 requires VDD and VDDQ equal to 1.2V, VREFCA equal to 0.5 x VDD, and VPP equal to 2.5V.

What is DDR4’s VPP supply, and why does DDR4 have it?

The VPP supply replaces the internal word-line charge pumps. Providing this voltage externally allows the DDR4 to operate at a lower voltage level in a more cost-effective manner rather than providing the internal charge pumps.

Are DDR3 and DDR4 pin-to-pin compatible to each other?

No, the DDR4 ballout is different from the DDR3 ballout. However, DDR4 uses the same package sizes and ball pitch as DDR3.

DDR4 doubled the data rate of DDR3—did the prefetch also double from 8n to 16n?

No, DDR4 kept the 8-bit prefetch used by DDR3; thus, BL8 is still supported.

Did DDR4 finally add boundary-scan or JTAG support?

For x16 devices, yes; DDR4 added a “connectivity test” mode that allows electrical verification of balls after connection to a memory interface.

Are there any new inputs/outputs required to support DDR4?

Yes, seven new inputs/outputs were added: VPP, BG (bank group), DBI_n, ACT_n, PAR, Alert_n, and TEN. However, the ball count increased by only three (73 to 76 balls).

Does DDR4 support DLL off mode for very slow clock rates?

Yes, DDR4 supports DLL-off mode similar to DDR3, up to 125 MHz.