K4A4G085WD: Complete Guide to Samsung's 4Gb DDR4 SDRAM (512M x 8, 78-Ball FBGA)

K4A4G085WD is Samsung's 4Gb (512M x 8) D-die DDR4 SDRAM in a 78-ball FBGA package. It operates from a single 1.2V supply, supports DDR4 data rates up to 2400 Mbps (speed-grade dependent, e.g., -BCPB, -BCRC), and integrates DDR4 bank groups with built-in on-die termination (ODT). As of 2026-09-12, XAIPART lists the part as active with 99,999 units in stock, MOQ 1, and tiered pricing from $3.20 (qty 1) down to $2.05 (qty 1000). This guide merges verified datasheet data, design-in guidance, drop-in alternatives, and procurement insight into one authoritative resource for engineers and buyers sourcing x8 DDR4 SDRAM.

What Are the Quick Answers About the K4A4G085WD?

The K4A4G085WD is a mainstream component-level DDR4 SDRAM for embedded controllers, computing modules, networking equipment, set-top boxes, and PC DIMM/UDIMM/SODIMM replacement sourcing. Its x8 organization lets you build a 64-bit ECC-protected bus with eight devices, and its 1.2V rail cuts power versus DDR3. Below, the Technical Guide explains how to design it in; the Alternatives section covers cross-brand equivalents from Micron and SK Hynix; Industry Insight covers lifecycle and supply; and Trends & Outlook tells buyers what to watch.

How Do You Select and Design In the K4A4G085WD?

Step 1: Choose the correct ordering part number (OPN). K4A4G085WD is the base part number; you must order a complete suffix such as K4A4G085WD-BCPB (DDR4-2400) or K4A4G085WD-BCRC. Distributors cannot supply the bare base MPN, and the suffix encodes the speed grade and refresh/temperature binning. Verify the exact CL binning against your memory controller's supported timing table before committing — the verified database does not list per-grade CAS latency values [DATA_NEEDED: CAS latency per speed grade].

Step 2: Confirm the power rail. The device runs from a 1.2V VDD core supply (verified). Your PMIC must supply a clean 1.2V rail; the database does not list a separate VDDQ value [DATA_NEEDED: VDDQ supply voltage].

Step 3: Plan the bus topology. Follow Samsung's layout guidance for fly-by command/address routing, per-byte DQS strobe matching, and 40-ohm ODT calibration. Address-bus integrity at DDR4-2400 is the most common failure point in first-turn boards, so prioritize C/A trace length matching and reference-plane continuity.

Step 4: Size the bus width. The x8 organization gives 512M addressable byte locations per device. Choose x8 over x16 (e.g., K4A4G165WD-class) when your controller has 8-bit data buses per chip-select, when ballout constraints favor fewer data pins per device, or when building error-corrected 64-bit buses from eight x8 devices plus ECC. At DDR4-2400-class rates, one x8 device supplies up to 2.4 GB/s of peak bandwidth, so a 64-bit bank of eight devices delivers over 19 GB/s aggregate.

Step 5: Handle boot-time memory training. Ensure your bootloader supports DDR4 leveling — read/write leveling and DQS drift compensation — for robust cold-start behavior across temperature extremes. This is the key integration step for data-logger and boot-system applications. The verified database does not state the operating temperature range or refresh interval (tREFI), so confirm both on the datasheet for your exact suffix [DATA_NEEDED: operating temperature range; refresh interval].

Step 6: Verify compliance. Samsung DDR4 devices in this family use lead-free FBGA solder balls, but the verified data for this base MPN does not include an explicit RoHS statement [DATA_NEEDED: RoHS status; lead-free status]. Confirm compliance on Samsung's product page for your exact OPN.

Authoritative timing tables live in the 66-page '4Gb D-die DDR4 SDRAM' datasheet (Rev. 1.1) and the 23-page Samsung DDR4 SDRAM Memory product guide (May 2018); the datasheet PDF is accessible via the citation below.

Which Alternatives Can Replace the K4A4G085WD?

Drop-in replacements start with Samsung's own speed-grade siblings (-BCRC, -BCPB), which are pin-to-pin compatible in the same 78-ball FBGA. For cross-brand second sourcing, the verified alternative in the XAIPART database is SK Hynix's H5AN4G8NMFAR. Micron's MT40A512M8 family (e.g., MT40A512M8RH-075E:B) is widely cited in cross-reference listings as a 4Gb 512M x 8 DDR4 with a comparable standard DDR4 ballout, but detailed specs for that family are not in the verified dataset [DATA_NEEDED: Micron MT40A512M8 verified specifications].

Substitution guidance: Because DDR4 FBGA ballouts are standardized, board-level compatibility between Samsung, Micron, and SK Hynix x8 parts is typical, which lets a layout designed around the K4A4G085WD second-source with minimal requalification. However, speed binning and CL tables differ slightly across vendors — match speed grade, CAS latency, and refresh parameters to your controller's timing table during requalification.

What Is the Market Position, Lifecycle, and Supply Situation of the K4A4G085WD?

The K4A4G085WD is listed as active in the XAIPART product database. Supply is strong on the platform: 99,999 units in stock with MOQ 1, priced at $3.20 (qty 1), $2.95 (qty 10), $2.60 (qty 100), $2.30 (qty 500), and $2.05 (qty 1000) as of 2026-09-12. Secondary distributors such as BonChip and Win Source have listed the -BCPB grade with stock or short RFQ lead times, while some grades are order-on-request with multi-week lead times typical for DRAM. Availability varies by speed grade, so confirm date codes and packaging (tray or reel) before committing to a production schedule. Broader market-share and end-of-life projections are not in the verified dataset [DATA_NEEDED: lifecycle projections and market share data].

What Trends and Procurement Watchpoints Should Buyers Track for This DDR4 Component?

First, anchor every order to a complete OPN suffix — the -BCPB (DDR4-2400) grade is the most widely stocked per verified listings, while -BCRC availability shifts. Second, DRAM pricing is market-sensitive: the spread from $3.20 at qty 1 to $2.05 at qty 1000 (as of 2026-09-12) is roughly a 36% volume discount, so consolidating purchases into the 1000-piece tier materially reduces unit cost. Third, standardization is the trend that protects you: the shared 78-ball FBGA DDR4 ballout across Samsung, SK Hynix, and Micron x8 families means dual-sourcing strategies carry low board-requalification risk — but always re-verify speed bins and CL tables. Fourth, power budgets continue to favor DDR4's 1.2V operation over DDR3 in fanless and battery-backed designs. Finally, for module repair work, match speed suffix and refresh binning to the original SPD data and keep date codes consistent across the eight or sixteen devices on a rank, since mixed-bin devices cause intermittent training failures at DDR4-2400-class speeds.