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DDR4 SDRAM FAQs

DDR4 SDRAM(12)
What newer power saving features does DDR4 provide compared to DDR3?

DDR4 added several new power saving features over DDR3, including:

1. Lower power pseudo-open drain drivers for the DQ pins

2. Optional ODT Input Buffer Disable Mode For Power-Down feature

3. Optional Maximum Power Saving Mode feature

4. Optional Command Address Latency (CAL)

What new features does DDR4 have that DDR3 did not have?

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 are DDR4 devices manufactured?

DDR4 is produced in Micron fabs around the world, including Virginia, Japan, 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?

Not exactly.  DDR4 still uses VTT mid-point termination on the data bus for good signal quality, however it uses pseudo open-drain drivers for less switching current compared to full push-pull drivers.

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 that were present in earlier versions of DDR SDRAM including DDR3. Providing this voltage externally allows 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 8n-bit prefetch used by DDR3; thus, BL8 is still supported.

Did DDR4 finally add boundary-scan or JTAG support?

DDR4 now has a Connectivity test mode to simplify testing with a boundary scan enabled controller. Designed to work with a boundary scan device, CT mode is supported in all Micron ×4, ×8, and ×16 devices (Though JEDEC requires only for x16). CT model allows a boundary scan device to load and read a pattern from a DDR4 in CT mode. DDR4 does not directly support IEEE 1149.1.

Does DDR4 support DLL Disable Mode or DLL-off Mode for slower clock rates?

Yes, DDR4 supports DLL-off Mode similar to DLL Disable Mode in DDR3, up to 125 MHz