Extended case study

Signoff review: ESD path completeness, latch-up risk flags, isolation waiver backlog regressed after a change touching ESD & Isolation.

Background

Team had prior closure; latest integration run shows instability concentrated in one operating condition.

Symptoms observed

• ESD path completeness, latch-up risk flags, isolation waiver backlog degradation

• Cross-team disagreement on root cause

• Directed tests pass but system scenario fails

Investigation timeline

1. Hour 0: freeze data tags, firmware build, and environmental conditions

2. Hour 1: diff boundary assumptions and handoff revisions

3. Hour 2: isolate first failing mode and trigger sequence

4. Hour 3: correlate waveform/log/report evidence

5. Hour 4: classify root cause and ownership

6. Hour 5: apply bounded fix

7. Hour 6: execute full regression and issue signoff memo

Root cause

Root cause tied to ESD & Isolation: ESD and isolation structures create safe discharge and domain separation paths so transients do not propagate into sensitive digital flops or analog macros.

Fix and validation

• Bounded RTL/config/layout correction

• Re-run ESD deck summary, isolation review memo, foundry waiver log

• Full cross-domain regression matrix

Lessons learned

• Tag everything

• Mechanism before commands

• No signoff without owner agreement

CASE STUDY — ESD & Isolation
baseline metric / regressed metric / post-fix metric

Sequence under stress

AMS BOUNDARY SEQUENCE — ESD & Isolation

analog macro -> wrapper / boundary cell -> synchronizer or sampler -> digital consumer
      |                 |                         |                     |
  analog assumptions    legal voltage/state       clock/reset contract   protocol/data validity

metric under watch: ESD path completeness, latch-up risk flags, isolation waiver backlog

AMS deep dive

Boundary assumptions must be explicit, versioned, and testable.

Concept diagram

BOUNDARY CONTRACT FLOW

analog intent -> boundary implementation -> digital wrapper -> signed review

Metric graph

BOUNDARY RISK MIX

missing boundary cells    ███████
stale handoff assumptions ██████
silent mode changes       ████

Reports and artifacts

• boundary-cell coverage

• isolation/ESD review

• handoff contract checklist

• integration waiver log

Mini case study

Noise bursts traced to missing isolation clamp on one low-power transition mode.

Debug branches

• Validate boundary-cell insertion

• Diff handoff assumptions

• Reproduce with tagged mode sequence

Senior review question

Ask: what boundary condition proves this topic is actually closed?

Key takeaways

• State boundary, mode, and evidence tag with every claim.

• Always align analog, digital, and physical owners before signoff decisions.

Common pitfalls

• Fixing averages while tails still fail.

• Skipping package/supply evidence in jitter or SerDes issues.

• Shipping with waivers that lack owner and expiration criteria.

Principal AMS review addendum

ESD and isolation structures create safe discharge and domain separation paths so transients do not propagate into sensitive digital flops or analog macros.

Metric: ESD path completeness, latch-up risk flags, isolation waiver backlog