K4A8G085WC-BCTD Samsung 8Gb DDR4 SDRAM

Ordering scope. The TD designation is DDR4-2666, with the guide’s nominal1333 MHz clock and19-19-19 ordering designation. C denotes the commercial0 to85 °C option. Use the complete BCTD code in the BOM and RFQ.

Native timing. At DDR4-2666, normal reads use CL19 and CWL14 or18 with0.750 ≤ tCK(avg) <0.833ns. tAA14.25–18ns; tRCD/tRP ≥14.25ns; tRAS ≥32ns and ≤9 × tREFI; tRC ≥46.25ns. Use the documented DLL-on normal timing mode; optional reduced-latency and reserved settings are not assumed. Satisfy both CL and CWL period limits and the manufacturer rounding rules.

x8 timing and modes. For this x8/1KB-page configuration, tRRD_S ≥max(4nCK,3ns), tRRD_L ≥max(4nCK,4.9ns), and tFAW ≥max(20nCK,21ns). With supported read DBI enabled, CL22 applies at this native rate and tAA limits increase by3nCK. Common limits: tWR ≥15ns, tRTP ≥max(4nCK,7.5ns), tWTR_S ≥max(2nCK,2.5ns), and tWTR_L ≥max(4nCK,7.5ns). With CRC and data mask both enabled on x8, add max(5nCK,3.75ns) to the corresponding tWR/tWTR_S/tWTR_L limits.

Supply conditions. VDD and VDDQ each operate at1.14–1.26V, nominal1.2V; VDDQ must be ≤VDD and track VDD. AC characterization ties the rails and DC bandwidth is limited to20MHz. Keep the rails within300mV, VREFCA ≤0.6 × VDDQ (≤300mV when both rails are below500mV), and VPP ≥VDD/VDDQ. VPP is2.5V nominal,2.375–2.750V operating. Absolute-maximum ratings are stress limits.

Case temperature and refresh. Normal TC is0 to85°C, measured at the top center of the case. The conditional extended band is85<TC≤95°C: double refresh frequency to tREFI3.9µs instead of7.8µs. For self-refresh above85°C, manual extended-temperature mode MR2 A6=0 and A7=1 is mandatory; the document notes IDD6 can rise around10–20%. The8Gb refresh recovery minima are tRFC1=350ns, tRFC2=260ns and tRFC4=160ns for their corresponding refresh-command modes.

Supplemental timing basis. The additional limits below use the DRAM-device timing tables in Samsung’s 8Gb C-die RDIMM Rev.1.5 (Feb2019), Table59. Its component composition explicitly includes the K4A8G045WC-BCTD and K4A8G085WC-BCTD ordering combinations. Registering-clock-driver and module-board parameters are excluded; the original Rev.1.31 component datasheet remains the primary package and electrical reference.

Command/address timing. At DDR4-2666, tIS(base) ≥55ps at AC90 and tIH(base) ≥80ps at DC65; tIS/tIH at VREF are each ≥145ps. AC thresholds are VREFCA ±90mV and DC thresholds VREFCA ±65mV. These base values use1V/ns single-ended input slew and2V/ns differential clock slew. Add the applicable ΔtIS/ΔtIH derating from section19.3/Table64; use its stated interpolation and valid-transition rules rather than treating the base values as unconditional system limits.

DRAM data window. The DDR4-2666 tDVWd minimum is0.64UI per DRAM device and tDVWp minimum0.72UI per pin, with DBI off. UI is tCK(avg).min/2. Apply the manufacturer’s clock-jitter derating, RONNOM=34Ω and50Ω load-to-VDDQ reference conditions in notes17,18,39,49; these are device reference limits, not a board timing budget.

DLL and mode-register timing. Use tMRD ≥8nCK and tMOD ≥max(24nCK,15ns). For the supplemented operating envelope use DLL locking time ≥1024nCK from the later Table59; the original Rev.1.31 lists854nCK. The longer bound satisfies both published lower-bound requirements and is retained explicitly rather than presented as an undocumented reissue of the original component datasheet. tXSDLL follows tDLLK; tXPR ≥max(5nCK,tRFC(min)+10ns) and tXS ≥tRFC(min)+10ns.

Gear-down transitions. For a supported gear-down configuration, tXPR_GEAR follows tXPR; tXS_GEAR follows tXS; tSYNC_GEAR ≥tMOD+4tCK; tCMD_GEAR ≥tMOD. Apply the even-clock requirement in note27 to the referenced timings. Gear-down setup and hold are each ≥2nCK. The native CL19 timings above describe normal operation; do not carry them into a different mode without a supported CL/CWL configuration.

MPSM and preamble scope. tMPED and tCKMPE follow tMOD(min)+tCPDED(min), with tCPDED ≥4nCK. tCKMPX follows tCKSRX ≥max(5nCK,10ns); tXMP follows tXS; tXMPDLL follows tXMP(min)+tXSDLL(min). tMPX_S follows the applicable tIS(min)+tIH(min); tMPX_HH follows tXP ≥max(4nCK,6ns). tMPX_LH is12ns minimum and actual-system tXMP−10ns maximum under note51. The newer table marks tDQSS2 N/A, so no numeric value is invented for that parameter; its2tCK write-preamble settings remain governed by the manufacturer’s separate mode conditions.

Manufacturer declaration: Samsung’s March2025 RoHS declaration covers its Memory products placed on the EU market by Samsung and its subsidiaries, subject to its stated scope, concentration limits and exemptions. This is a component-level declaration, not a certificate for a supplied lot.

Manufacturer sources: Samsung DDR4 Product Guide · May 2018 · Samsung 8Gb C-die x4/x8 Datasheet · Rev. 1.31 · Samsung 8Gb C-die RDIMM Datasheet · Rev.1.5 · DRAM-device timing tables · Samsung EU RoHS declaration · March 2025