DDR5 PMIC on-DIMM: Power Rails, Protection, and IC Selection

Keep Vref quiet and time-aligned to VDDQ. Generate Vref from VDDQ with a low-noise divider and RC filter, route with a dedicated return/Kelvin sense, and avoid crossing noisy splits. During bring-up, ensure Vref follows VDDQ within the spec window (per JEDEC).

• Place RC close to the receiver pins; shortest loop and isolated return.
• Limit scope bandwidth for ripple measurements; probe at the load.
• Log Vref vs VDDQ timing on power-up and power-down.

See also: #rails, #pi, #layout, #sequence.

Meet ΔV and recovery during training/initialization. VPP (~1.8 V) powers the wordline pump; verify droop and settling under burst load patterns and across temperature. Use DDR-like current pulses and compare against spec windows (per JEDEC/datasheet).

• Exercise burst read/write scripts; capture ΔV and t_settle.
• A/B test local decoupling and routing options.
• Record PG events and fault logs during stress.

See also: #rails, #validation.

Design to a target PDN impedance. Define Z_target=ΔV/I_step per rail, then place bulk at the entry, distribute mid-band caps to clusters, and put high-freq caps at pins in tiny packages to minimize loop inductance.

• Spread values/ESL to avoid sharp multi-resonance dips.
• Use damping only where necessary to flatten peaks.
• Validate in both frequency (VNA) and time domain (step load).

See also: #pi, #rails.

Rail oscillation around the valid window causes chatter. Add PG debounce, confirm window thresholds, and check that compensation/decoupling keeps the rail stable through load steps. Merge per-rail PG with proper timing before asserting system PG.

• Scope rails and PG on the same timeline; add timing markers.
• Inspect return paths and plane slots under high-di/dt loops.
• Correlate with PMBus status and last-fault registers.

See also: #sequence, #protections, #layout.

SW flux, detoured returns, and shared impedance. Large switch copper near references, slots under loops, and long common returns inject ripple and spikes. Close loops locally, fence edges with stitching vias, and isolate Vref routing.

• Use near-field probes around SW and inductors.
• Reduce loop area; avoid crossing splits; add via fences.
• Apply RC at Vref and evaluate snubbers on SW if needed.

See also: #layout, #pi.

Cover the worst-case I_step and edge rates you expect. Build burst patterns (duty/pulse/idle) that bracket system behavior; measure ΔV, t_settle, and ripple with bandwidth-limited probing at the load.

• Parametric sweep of amplitude and repetition rate.
• Run across cold/room/hot to reveal compensation margins.
• Log PG/FLT for correlation with droop events.

See also: #validation, #rails.

Loss → heat; heat → higher loss. Conduction and switching losses raise PMIC temperature, which can further reduce efficiency and provoke protection/derating. Spread heat with via-in-pad/stitching and backside copper; log power vs temperature.

• Correlate I²R + switching estimates with IR/thermocouples.
• Check airflow and DIMM stacking scenarios.
• Apply derating policy; monitor OTP/PG behavior.

See also: #thermal, #validation.

Track inputs, per-rail V/I, temperature, and states. Poll Vin/Iin, V/I for VDD/VDDQ/VPP, PMIC temperature, PG/FLT bits, and fault logs. Use ~10–100 ms during run, accelerate when anomalies are detected.

• Timestamped logs with cause codes and counters.
• Snapshot around events (pre/post buffers).
• Export CSV for matrix scoring.

See also: #protections, #validation.

Match to fault profile and thermal goals. Hiccup limits average power under shorts; latch-off avoids oscillatory stress; foldback helps large startup caps; constant-current gives predictable soak tests with careful thermal design.

• Record recovery behavior and last-fault reason.
• Verify connector/device ratings under repeated faults.
• Document policy in the bring-up checklist.

See also: #protections, #sequence.

They can share input but need independent regulation/feedback. Avoid cross-coupling by isolating compensation, providing per-rail decoupling, and validating that simultaneous switching does not violate windows.

• Scope both rails under mixed bursts.
• Place decoupling at each domain’s pins.
• Confirm Vref relation to VDDQ remains valid.

See also: #rails, #pi, #layout.

Yes—treat it as a small but sensitive 1.8 V rail. Keep it quiet, verify its sequencing relative to the PG chain, and ensure down-time ordering prevents unintended resets or false reads of SPD/thermal sensors.

• Local decoupling and short routing.
• Check power-cycle behavior with logging.
• Confirm host restart policies.

See also: #powertree, #sequence.

Oversized SW copper, detoured returns, and leaky edges. Shrink high-di/dt loops, add input π/CM filtering, consider RC snubber at SW, and stitch edges with via fences to contain fringing fields.

• Scan with near-field probes to localize sources.
• Move Vref/VTT away from inductors and SW nodes.
• Re-route to avoid plane slots under loops.

See also: #layout, #thermal.

Fix geometry before piling capacitance. Shorten loops and place high-freq caps at pins; then diversify values/ESL and add light damping where needed. Re-verify in time and frequency domains.

• Prioritize proximity and return integrity.
• Stagger values to smooth multi-resonance.
• Confirm stability margins after edits.

See also: #pi.

Write a state machine and log everything. Detect UVLO/OVP/OCP events, protect rails, record fault cause/temperature/counters, then retry per policy or latch off. Validate Vref/VDDQ ordering throughout.

• Document retry cadence and limits.
• Confirm PG timing on re-entry.
• Store last-fault for post-mortem.

See also: #sequence, #protections.

Use a rail×condition matrix with thresholds. Score ΔV, t_settle, ripple, temperature rise, and PG/FLT events across cold/room/hot, burst, and endurance. Keep timestamped telemetry for traceability.

• Define margins for “Warn” to catch drift.
• Automate CSV export and lot summaries.
• Gate release on matrix pass rate.

See also: #validation.