Mobile Edge IoT Terminal: Wake, Hold-Up, Rugged Power
← Back to: IoT & Edge Computing
Mobile Edge IoT Terminal is defined by survivability: motion-triggered wake, radio load bursts, and harsh input transients must be handled through a provable power-path, always-on domain control, and brownout-proof sequencing—so the device stays stable and diagnosable in the field. This page focuses on measurable evidence (rails/PG/reset/logs) to turn “random” resets, GNSS dropouts, and short outages into actionable root causes.
accel-wake
always-on domain
supercap hold-up
transient-tolerant power path
brownout-proof sequencing
H2-1 · Scope & Boundary: what this page solves (and what it doesn’t)
Intent
Lock the engineering boundary so the page stays vertical: a mobile edge terminal is defined here by power events, wake domains,
hold-up windows, sequencing, and field evidence—not by RF internals, protocol stacks, or platform/cloud design.
Definition (mobile edge terminal)
- Mobile operating context: handheld/vehicle/field use with unstable input and mechanical motion.
- At least one bursty radio load: cellular or satellite TX bursts create rail droop risk.
- Always-on wake path: accel-wake/RTC/GPIO triggers domain bring-up and safe recovery.
- Ride-through requirement: short hold-up to avoid uncontrolled reset and data loss during dips.
Ownership → deliverables (this page must produce)
- accel-wake wake chain + debounce + false-wake evidence checklist.
- always-on AON power budget table + domain handover timing rules.
- hold-up sizing equation + constraints (ESR/temperature) + validation method.
- transients energy path diagram + top 3 waveforms to capture.
- brownout PG/RESET thresholds + delays + reset-reason logging fields.
Hard boundaries (sibling pages)
- GNSS RF / anti-jamming: only power/clock/enable sensitivity is referenced here → see GNSS Timing / Positioning Module.
- Cellular stacks / carrier certification: only TX burst power stress is referenced here → see LTE-M / NB-IoT / RedCap Terminal.
- OTA / PKI / attestation: only “safe power-down & log evidence” is referenced here → see Secure OTA Module / Edge Security Probe.
Evidence rule (mechanical audit)
- Every conclusion must map to power, timing, reset, wake, or logs.
- Any deep dive that requires RF or protocol internals is out of scope by design.
- Minimum evidence set: VIN(t), Vsys(t), key rails PG/RESET, radio status/log, reset reason.
Practical readout: When a terminal “randomly resets” in the field, the fastest path is not guessing firmware—it is proving
whether the event is under-energy (dip), over-energy (spike), or fast-coupled (EFT/ESD), then checking if sequencing and logging
convert that event into a controlled, observable behavior.
Figure F1 — Boundary map: what belongs to this page
Central ownership (blue) vs sibling topics (gray). Focus stays on power, wake, sequencing, and evidence.
ALT: Boundary map showing owned topics (wake domains, hold-up, transients, brownout, evidence) and out-of-scope sibling areas (GNSS RF, cellular stacks, OTA PKI, gateways).
H2-2 · Use-Case → Power Events: the terminal’s power event spectrum
Intent
Convert “mobile scenarios” into a measurable event spectrum. Every later design choice must map back to an event type,
a success criterion, and a minimal evidence set.
Input sources (why they are untrusted)
- Vehicle 12/24 V: dips (crank), spikes (dump), hot-plug ringing, wiring inductance.
- Adapters: hot-plug + intermittent contact; quality variance; short dropouts.
- External battery pack: internal resistance + temperature drift; connector bounce.
- USB supply: cable drop + insertion dropouts (treated as an input type only).
Event classes (engineering grouping)
- Under-energy input drop • crank • brownout • intermittent contact.
- Over-energy load dump • surge • hot-plug overshoot/ringing.
- Fast-coupled EFT/ESD (very fast edges, coupling paths matter).
- Polarity reverse connection or negative transients (needs direction control).
Success criteria (pass/fail levels)
- L1 No reset: key domains remain up; radios stay stable during the event window.
- L2 Controlled reset: if reset occurs, it is explainable and recoverable via logs and sequencing.
- L3 No data loss: critical transaction completes (log commit / safe stop) within hold-up window.
- L4 Fast recovery: service returns within a defined time after input returns (timing-level only).
Minimum evidence set (top 3 checks)
- Waveforms: VIN(t), Vsys(t), and at least one burst rail (radio rail or main rail).
- Sequencing: PG/RESET timing (including debounce/blanking window).
- Traceability: reset reason + last-known minima + radio status snapshot in logs.
Why both VIN and Vsys matter: VIN describes the external event; Vsys shows how the design buffered or failed to buffer it.
Many “random resets” are actually sequencing/blanking errors where Vsys stayed acceptable but PG/RESET reacted to a short glitch.
| Event | Class | What it looks like (measurable) | Breaks first (typical) | Design levers (this page) | Evidence to capture |
|---|---|---|---|---|---|
| Cold start | Under-energy | Slow ramp; inrush + sequencing race; early droop before rails settle. | Boot loops; radio not ready; log not initialized. | Inrush limit; staged rails; PG/RESET gating; minimum ramp profile. | VIN/Vsys ramp; PG edges; reset reason. |
| Hot-plug | Over-energy | Overshoot + ringing from wiring inductance; fast dV/dt edges. | Protection false trips; latch-up; brownout after overshoot. | Clamp path; input damping; controlled inrush; robust UV/OV limits. | VIN ringing; Iin/limit status; fault flags. |
| Input drop | Under-energy | VIN falls below UV threshold for ms–s; may recover quickly. | Radio drop; uncontrolled resets; incomplete writes. | Hold-up window; controlled shutdown; brownout sequencing; log commit. | VIN/Vsys dip; PG/RESET; last-min log. |
| Crank | Under-energy | Deep dip + longer duration; repeated sag possible. | Repeated resets; radio attach loops; RTC corruption. | UVLO strategy; hold-up vs controlled reset decision; domain prioritization. | VIN profile; reset reason timeline; recovery time. |
| Load dump | Over-energy | High VIN spike; sustained energy; clamp stress. | Front-end overstress; downstream overvoltage; thermal trip. | Energy clamping path; derating; fault reporting; safe-off behavior. | VIN peak; clamp/thermal flags; post-event health log. |
| Reverse | Polarity | Wrong polarity / negative excursion; potential backfeed paths. | Damage; uncontrolled backpowering through IO. | Reverse protection; ideal diode; backfeed blocking; IO protection. | VIN sign; leakage/backfeed current; fault flag. |
| EFT / ESD | Fast-coupled | Very fast spikes; coupling via cable/shield/ground return. | Latch, false reset, sensor upset. | Return path control; clamp placement; reset debounce; observable counters. | RESET glitch; fault counters; rail micro-dip. |
| Brownout | Under-energy | Near-threshold slow sag; metastable states; partial rail collapse. | “Hung” state; corrupted peripherals; non-reproducible behavior. | Brownout-proof sequencing; strict PG/RESET; stateful recovery logging. | PG timing; reset reason; last-known rails. |
| Intermittent contact | Under-energy | Repeated short dropouts (10–200 ms) due to connector bounce. | Data loss; radio detach; repeated wake cycles. | Ride-through hold-up; debounce; transaction boundary design; wake filtering. | VIN bursts; Vsys hold-up; event counters in logs. |
Figure F2 — Event spectrum → success criteria → design levers
Events are grouped by threat type. Each group maps to measurable waveforms and the levers used later (hold-up, transients, sequencing, logging).
ALT: Diagram grouping mobile terminal power events (under-energy, over-energy, fast-coupled, polarity) and mapping them to success criteria and design levers (hold-up, transient path, UV/OV, PG/RESET, logging).
H2-3 · Reference Architecture: minimal partition (Always-on vs Active vs Radios)
Intent
Convert “a pile of modules” into controllable power domains and a measurable sequencing timeline.
This domain model is reused by hold-up, accel-wake, and brownout/PG/RESET policies.
Domain model (three domains)
- Always-on (AON) RTC / AON controller or small MCU • accel wake • power monitor • minimal log storage.
- Active compute main MCU/SoC • memory • peripherals • application tasks (treated as load & state machine).
- Radios GNSS + cellular/satellite modem as boundary blocks: power / clock / enable / status only.
Who “manages power” (responsibility boundary)
- PMIC / Power tree: rail sequencing, PG generation, UV/OV decisions, fault flags, rail isolation.
- AON controller: wake arbitration, domain bring-up order, TX inhibit decisions under droop risk, evidence snapshots.
- Main SoC/MCU: controlled degrade (reduce load), transaction boundary (log commit), explainable recovery after reset.
Domain failure policy (designed behavior)
- AON must outlive others: it preserves reset reason + last minima + event counter.
- Radios are sacrificial first: if droop risk is detected, disable TX / power-cycle radio rail before the system rail collapses.
- Active compute is controlled: if a reset is inevitable, it becomes controlled reset with logs—not a silent crash.
Measurable sequencing (no protocol deep dive)
- wake_req (WAKE_INT) → rails_on (AON_PG / SYS_PG) → clocks_stable (CLK_OK/LOCK) → modem_on (RADIO_PG/READY) → service_ready (status snapshot).
- Each stage must have at least one observable pin/flag so “random reset” can be turned into a traceable timeline.
Key rule: “Power management” is not firmware heroics. It is a layered loop:
hardware protection → domain sequencing (PMIC + AON) → controlled policy (SoC) inside the hold-up window.
Figure F3 — Minimal domain architecture & responsibility boundary
Three domains, three controllers, and the minimal evidence lines (WAKE / PG-RESET / STATUS-LOG). Text is intentionally minimal for mobile readability.
ALT: Block diagram partitioning a mobile edge IoT terminal into Always-on, Active Compute, and Radios domains, showing PMIC sequencing, AON arbitration, and minimal evidence lines (WAKE, PG/RESET, STATUS/LOG).
H2-4 · Radio Integration Boundary: GNSS + cellular/satellite interface surfaces
Intent
Treat radios as boundary blocks. Only the integration surfaces are covered: power rails, clock boundary,
control (EN/RESET/READY), and coexistence/layout principles, plus the evidence recipe that links TX bursts to rail droop.
The 4 integration surfaces
- Power rails avg/peak/TX burst + startup inrush + allowed droop window.
- Clock TCXO/XTAL sharing boundary + “clock stable before TX” sequencing.
- Control EN/RESET/READY timing + AON-gated TX inhibit under droop risk.
- Coexistence isolation/return-path principles (no matching-network deep dive).
Typical failure chain (what to prove)
- MODEM TX burst → rail droop on Vradio or Vsys → GNSS unlock or system brownout/reset.
- Sat/cellular mode switching → transient current step → droop/glitch if sequencing or damping is weak.
Correlation recipe (fast root-cause)
- Trigger: TX_IND rising edge (or equivalent burst indicator).
- Waveforms: capture Vsys(t) + Vradio(t) on the same timebase; note droop amplitude and duration.
- Status: GNSS LOCK / MODEM READY + reset reason snapshot; check alignment with the droop window.
Minimum observable pins/flags
- MODEM: TX_IND, READY/STATUS, EN, RESET.
- GNSS: LOCK/STATUS, EN, (optional) CLK_OK/LOCK boundary flag.
- System: PG/RESET, fault flag from power tree, reset reason register.
Non-negotiable rule: if a “reset” cannot be correlated to a measured droop window (Vsys/Vradio) and a state snapshot (TX_IND/LOCK/reset reason),
it remains an unbounded problem. This page exists to bound it with evidence.
| Radio block | Avg current | Peak / TX burst | Startup inrush | Allowed droop window | Evidence method |
|---|---|---|---|---|---|
| GNSS | datasheet + steady-state measurement | short peaks during acquisition (verify) | power-on transient (verify) | max droop + max duration before unlock | Vrail + LOCK flag on same timeline |
| Cellular modem | idle/attach average (measure) | TX burst peak (must capture) | inrush during rail ramp (capture) | max droop + duration before brownout/reset | trigger on TX_IND; log reset reason |
| Satellite modem | standby average (measure) | TX step + burst duration (capture) | mode-switch transient (capture) | droop window vs service interruption | Vrail + status snapshot + event counter |
Figure F4 — Radio integration interface map (power / clock / control / evidence)
Boundary view only: radios are black boxes; integration focuses on rails, clock boundary, control timing, and the evidence loop.
ALT: Interface map treating GNSS, cellular modem, and satellite blocks as boundary radios with power rails, clock boundary, EN/RESET/READY control, and an evidence loop linking TX_IND to rail droop and GNSS lock/reset behavior.
H2-5 · Accel-Wake & Always-on Domain: why “sleeping well” is harder than “running fast”
Intent
Build a provable wake chain: accel interrupt → AON arbitration → rail sequencing → host handover.
Make sleep current a measurable budget and turn “false wakes” into a debuggable decision tree.
Wake chain (measurable state machine)
- Wake source: accel motion trigger raises WAKE_INT (count + timestamp).
- AON arbitration: AON confirms (window + debounce), applies cooldown if noisy, then asserts WAKE_REQ.
- Rails on: PMIC brings up rails in order; AON_PG then SYS_PG must be stable before clocks/radios.
- Host handover: main MCU/SoC reads wake reason + minima snapshot and commits a short log record.
Debounce & false-wake control (integration level)
- Threshold + duration: treat motion as “event in a window”, not a single edge.
- Two-stage wake: INT → AON confirm → rails_on (prevents random bumps from powering the whole system).
- Cooldown window: repeated triggers within a short period enter a hold-off state to protect battery/hold-up budget.
Recommended bring-up order (protect power margin)
- 1) record wake reason in AON → 2) stabilize Vsys and PG → 3) ensure clocks stable → 4) boot active compute → 5) enable radios.
- Default rule: radio TX stays inhibited until Vsys margin is confirmed; avoid burst loads during early ramp.
Sleep current budget (bucket model)
- Power-tree IQ PMIC quiescent + monitoring.
- AON rail IQ LDO/buck quiescent + references.
- Sensor standby accel standby + interrupt logic.
- Retention/RTC timekeeping + minimal retention.
- Leakage & pulls ESD structures, pull-ups, dividers, cap leakage.
Evidence first: a wake is “valid” only if the timeline can be reconstructed:
WAKE_INT count/timestamp + AON state + PG stability + (optional) TX inhibit status + a short host log record.
| Bucket | Target | Measured | ΔI method | Typical evidence |
|---|---|---|---|---|
| Power-tree IQ | set a hard budget | record in µA/mA | disable monitor / isolate branch | Vsys steady + fault flags stable |
| AON rail IQ | minimize always-on rails | record per rail | remove jumper / gate rail | AON_PG stable; no wake loops |
| Sensor standby | choose low standby sensors | record with sensor enabled | force sensor standby / detach | WAKE_INT count drops to baseline |
| Retention/RTC | only keep what is needed | record after retention on | disable retention blocks | RTC ticks; wake reason persists |
| Leakage & pulls | audit pins/dividers | record after pull changes | remove pull / change divider | I_sleep improves without wake errors |
False-wake debug tree (symptom → evidence → first action)
- Symptom: wakes at rest → Evidence: WAKE_INT high count → Action: raise threshold / extend confirm window / add cooldown.
- Symptom: wake leads to rapid drain → Evidence: RADIO_EN early + burst indicators → Action: delay radio enable; enforce TX inhibit until PG stable.
- Symptom: wake loops or immediate reset → Evidence: SYS_PG oscillation + reset reason = brownout → Action: tighten PG debounce; verify hold-up & rail ramp margins.
Figure F5 — Accel-wake chain & AON budget (boundary view)
Wake chain, AON arbitration states, and the sleep-current “bucket” budget. Text is minimal for mobile readability.
ALT: Diagram of the accel-wake chain (WAKE_INT → AON confirm/cooldown → rail bring-up with PG/CLK_OK → host log handover) plus a sleep-current budget bucket model.
H2-6 · Supercap Hold-Up: turn “no power loss” into a provable energy budget
Intent
Size hold-up with a minimal, usable model and validate it with a step-cut test:
energy window, efficiency, ESR droop, and precharge that does not fight input transients.
Hold-up targets (three practical types)
- Endurance sustain operation for N seconds (no reset, service maintained).
- Transaction complete one commit/report or controlled shutdown (log consistency is the pass criteria).
- Momentary ride through 10–200 ms contact bounce (no unexplained reset).
Minimal sizing model (usable, not long)
- Cap energy: E = 1/2 · C · (Vhi² − Vlo²)
- Load energy: Eload ≈ Pload · thold / η
- Capacity: C ≥ 2·Eload / (Vhi² − Vlo²)
- Key definition: Vlo is the lowest voltage where PG/RESET policy still guarantees the intended outcome (transaction or ride-through).
Constraints that break hold-up (must be budgeted)
- ESR droop: ΔV = Ipeak · ESR can instantly cross Vlo during bursts. Radios should be shed first under droop risk.
- Low temperature: effective C drops and ESR rises; size for worst-case temperature or define a degrade mode.
- Precharge/inrush: uncontrolled charging looks like a short and can trigger brownout during hot-plug or intermittent contact.
Precharge strategy (does not fight input events)
- Rule 1: stabilize Vsys first, then allow cap charging with current limit.
- Rule 2: cap charge can be paused by AON during droop risk windows (hot-plug/bounce).
- Rule 3: defer high-burst behavior until cap and rails are in a stable state (TX inhibit gating).
Validation requirement: hold-up is “real” only if a step-cut test reproduces the expected
Vsys(t) window and the device state proves it (PG/RESET order + short log consistency).
| Target type | t_hold | P_load | Vhi / Vlo | η | C (result) | ESR / ΔV budget | Validation evidence |
|---|---|---|---|---|---|---|---|
| Endurance | seconds | average during hold-up | allowed energy window | path eff. | computed C_min | limit droop vs Vlo | Vsys(t) + PG stable + service continues |
| Transaction | ms–s | peak/avg during commit | Vlo set by commit safety | path eff. | computed C_min | budget for I_peak | log consistent + reset reason explainable |
| Momentary | 10–200 ms | instantaneous load | tight droop window | path eff. | computed C_min | ESR dominates | no unexplained reset across contact bounce |
Figure F6 — Hold-up energy budget & validation loop
Energy window (Vhi→Vlo), ESR droop, controlled precharge, and a step-cut validation loop with PG/RESET and log evidence.
ALT: Diagram showing a supercap hold-up power path with controlled precharge, an energy-window sizing model (Vhi to Vlo), key constraints (ESR, temperature, inrush), and a step-cut validation loop using Vsys(t), PG/RESET order, and log consistency.
H2-7 · Transient-Tolerant Power Entry: make “protection” an energy-path design
Intent
Map each mobile power event to a clear energy outcome: clamp, limit, disconnect, or ride-through.
Prove robustness with VIN/Vsys/Iin waveforms and protection fault/limit flags.
Modular power entry (by responsibility)
- Direction & isolation: reverse protection + ideal diode (prevents backfeed, enforces current direction).
- Clamp & withstand: TVS/clamp paths limit peak voltage within downstream safe margin.
- Inrush & hot-plug control: controlled dV/dt + current limiting to tame harness L and input C ringing.
- UV ride-through boundary: UVLO + policy decides when to ride-through, degrade, or disconnect (no “mystery states”).
Event → countermeasure (energy outcome)
- Load dump: clamp energy + ensure downstream withstand/derating; confirm VIN peak stays inside margin.
- Crank / deep UV: ride-through via hold-up and degrade ladder; tune UVLO boundary to avoid reset loops.
- Hot-plug: limit inrush + damp ringing; avoid Vsys dip caused by Iin spikes.
- EFT/ESD: shunt via return path + placement; verify PG/RESET does not chatter and flags stay explainable.
Evidence & observability (pass/fail is measurable)
- VIN(t): event amplitude, duration, and ringing (what actually hits the connector).
- Vsys(t): system bus stability and threshold crossings (what the electronics live on).
- Iin(t) or limit state: inrush peaks and limiter engagement (whether “limit” truly happens).
- Fault/limit flags: protection IC status that matches the waveform (no silent failures).
Boundary (what this section stops at)
Focus is on functional blocks, energy outcomes, and measurement points. Certification procedures and standard clause walkthroughs are intentionally out of scope.
| Event | Primary risk | Energy outcome | First protection focus | Must-capture evidence |
|---|---|---|---|---|
| Load dump / OV | Downstream overstress, thermal overload | Clamp + withstand margin | TVS/clamp path, downstream derating, OV disconnect threshold | VIN peak/width, Vsys max, fault flags |
| Crank / UV | Brownout resets, radio bursts collapse Vsys | Ride-through or controlled degrade | UVLO boundary, TX inhibit policy, hold-up window definition | Vsys_min, PG/RESET timeline, radio state |
| Hot-plug | Inrush surge, ringing, false trips | Limit + damp | Hot-swap limiter, input C strategy, damping/π placement | Iin peak, Vsys dip, limit_active flag |
| EFT / ESD | Coupled spikes into sensitive nodes | Shunt + return control | Return path, clamp placement, isolation boundary where used | PG chatter check, reset reason, fault flags |
Design rule: each protection block must be justified by an event and validated by waveforms.
If a block cannot be tied to VIN/Vsys/Iin + a status flag, it becomes “invisible” in field debugging.
Figure F3 — Power-entry energy path & measurement points
A modular front-end showing clamp/limit/disconnect/ride-through boundaries and where VIN/Vsys/Iin and flags should be observed.
ALT: Block diagram of a transient-tolerant power entry showing reverse protection, hot-swap inrush limiting, TVS clamp branch, filtering, Vsys bus, and the required measurement probes (VIN/Vsys/Iin) plus protection status flags.
H2-8 · Brownout-Proof Sequencing: PG, RESET, and a deterministic degrade ladder
Intent
Prevent “random resets” and “silent hangs” by turning brownout into a controlled state machine:
PG gating, blanking/debounce, degrade order, and traceable reset reasons.
PG/RESET principles (what gates reset vs what only monitors)
- Hard gating rails: must participate in RESET gating because instability corrupts state or data (core bus, compute, critical memory rails).
- Soft monitor rails: degraded performance is acceptable; they should log faults without triggering chatter resets.
- Rule: fewer hard gates, but with stronger debounce; more monitors, but with explicit logging.
Blanking & debounce (stop glitch resets)
- Blanking window: ignore PG changes during known transition windows (hot-plug ramp, rail switching, controlled boot stages).
- Debounce: require stability for a minimum time before declaring PG valid/invalid (filters spikes and ringing).
- Rule: hard gating rails use stricter debounce; soft monitors can log transient anomalies without forcing RESET.
Degrade ladder under brownout (protect bus → data → recovery)
- Stage 1: reduce burst loads first (TX inhibit, delay radio enable) to stabilize Vsys.
- Stage 2: reduce compute/write risk (slow down, suspend risky writes) to protect consistency.
- Stage 3: controlled reset/shutdown when Vsys remains below boundary (avoid “mystery states”).
Traceable reset reason (minimum log fields)
- reset_reason from MCU/PMIC/SoC classification.
- Vsys_min minimum observed during the event window.
- PG_timeline compressed rail PG/RESET order evidence.
- radio_state TX inhibit / burst indicators.
- temperature for explaining margin shifts (ESR/C at low temp).
| Rail (type) | Role | Threshold concept | Blanking | Debounce | Action on violation | Evidence to log |
|---|---|---|---|---|---|---|
| VSYS / main bus | Hard gating | below safe Vlo boundary | during known ramp | strict (no spikes) | Stage ladder; controlled reset if persistent | Vsys_min, PG_timeline, reset_reason |
| Compute core | Hard gating | PG must be stable | boot transitions | strict | block boot / safe reset | PG_timeline, reset_reason |
| Critical memory | Hard gating | write-safe boundary | write windows | strict | stop writes; mark transaction state | log consistent + Vsys_min |
| Radio rails | Soft monitor | burst-safe margin | attach/enable window | moderate | TX inhibit; delay enable; log only | radio_state, Vsys_min |
| Peripherals | Soft monitor | functional threshold | switching events | loose | log fault; avoid reset chatter | PG_timeline, temperature |
Pass criteria: brownout events must produce deterministic outcomes.
Either the system remains stable via Stage 1/2 actions, or it enters a controlled reset with a complete evidence record (no “silent hang”).
Figure F4 — Brownout sequencing & evidence loop
A controlled state machine: Vsys droop → PG debounce/blanking → degrade ladder → controlled reset, with mandatory log evidence.
ALT: Diagram showing a Vsys droop event, PG blanking and debounce logic preventing glitch resets, a three-stage degrade ladder (TX inhibit, slow/stop writes, controlled reset), and mandatory log evidence fields for traceable reset reasons.
H2-9 · Field Failure Modes Map: symptoms → evidence → root-cause routing
Intent
Replace guesswork with the shortest evidence chain. Use the same 3-step template everywhere:
Waveforms → Pins/Flags → Logs, then route to power, sequencing, or margin causes.
3-evidence priority template (copy/paste)
- Evidence #1 — Waveforms: VIN(t), VSYS(t), IIN(t) (or limiter state) + PG/RESET on the same capture.
- Evidence #2 — Pins/Flags: TX indicator, enable/reset pins, lock indicators, fault/limit flags (align behavior with droops).
- Evidence #3 — Logs: reset_reason, Vsys_min, PG_timeline, radio_state, temperature (minimum set for replayability).
Routing rules (fast split, no RF/protocol deep dive)
- If VSYS dips near the symptom window → start with burst-load + energy-path checks (inrush/limit/hold-up).
- If VSYS is stable but behavior fails → check enable/clock/reset ordering and debounce/blanking.
- If failures correlate with temperature → check margin shifts (ESR/C/UVLO boundary concepts) and record Vsys_min statistics.
- If “hang without reset” → suspect PG/RESET policy gaps or latched fault states; prove with flags + missing reset_reason.
| Symptom | Shortest evidence chain (what to capture first) | High-probability root-cause routing | Next verification action (minimum change) |
|---|---|---|---|
| A) Motion wake → GNSS takes too long to fix |
Waveforms: VSYS + GNSS rail + PG/RESET during wake window Pins: GNSS enable/reset/lock + TX indicator (time-aligned) Logs: wake_reason, Vsys_min, radio_state, temperature |
Power window GNSS rail not stable Sequencing clock/enable released too early Burst coupling TX droop causes unlock |
Gate TX until VSYS stable or GNSS ready; delay GNSS enable to prove sequencing window hypothesis. |
| B) Cellular reporting → random reboot |
Waveforms: TX indicator + VSYS + modem rail + PG/RESET (same capture) Flags: limit_active / fault_flag time-aligned Logs: reset_reason + Vsys_min histogram |
Burst current transient droop beyond boundary PG chatter debounce too weak → glitch reset Policy gap no TX inhibit / no degrade ladder |
A/B test: enable TX inhibit / power-limit before burst; tighten PG debounce to separate droop vs glitch reset. |
| C) Works at room temp; fails at low temp |
Waveforms: VSYS droop + recovery under identical load steps (cold vs room) Pins: precharge complete / hold-up ready state (if available) Logs: temperature + reset_reason correlation |
Margin shift higher ESR / lower effective C Source impedance input droops more at cold UV boundary UVLO threshold/behavior shifts |
Compare success rate with “precharge done” vs “not done”; adjust ride-through boundary and confirm with Vsys_min statistics. |
| D) Hot-plug → occasional hang (no reset) |
Waveforms: VIN ringing + VSYS + PG/RESET at hot-plug edge Flags: latched fault/limit states (persistent flags after event) Logs: missing/unclear reset_reason is evidence itself |
Policy gap should reset but didn’t (blanking/debounce mismatch) Latched fault protection state not handled by recovery logic Order gap rails recover but modules not re-initialized deterministically |
Force controlled recovery on fault flags (or on PG timeline anomalies); verify hang disappears and evidence becomes consistent. |
Field rule: if the first capture does not include VSYS + PG/RESET + one behavior indicator, it is usually not actionable.
Always align symptom time with waveforms before interpreting logs.
Figure F5 — 3-step evidence funnel and symptom routing
A reusable field workflow: collect waveforms first, align pins/flags next, then confirm with logs; route to the most likely root-cause class.
ALT: Evidence funnel and symptom routing map showing a three-step workflow (waveforms, pins/flags, logs) and four common field symptoms with quick root-cause splits and minimum-change verification actions.
H2-10 · Validation Plan: turn the design into a deliverable test checklist
Intent
Prove mobile robustness with measurable pass/fail. Each test must define:
injection → observe → pass/fail → records to keep.
Radio activity is treated only as a power stress workload, not a protocol KPI.
Layered validation (what is proven at each layer)
- Layer 1 — Power event injection: drop, dip, surge, hot-plug, intermittent contact (energy-path validation).
- Layer 2 — Sequencing & reset policy: PG gating, blanking, debounce, controlled recovery (no mystery states).
- Layer 3 — Wake & sleep: false-wake rate, sleep current breakdown, deterministic wake handoff.
- Layer 4 — Radio power stress: burst loads via TX indicator/workload triggers; verify degrade ladder behavior.
Recommended tools/fixtures (brief)
- Oscilloscope (multi-channel) for VSYS + PG/RESET + TX indicator alignment.
- Programmable supply / event injector for dips/surges; electronic load for steps/bursts.
- Harness-L simulation (series inductance equivalent) to reproduce hot-plug ringing and inrush.
- Temperature chamber / cold plate to capture Vsys_min statistics across temperature.
Pass/fail writing rules (measurable, repeatable)
- Waveform criteria: VSYS must stay within window, or degrade ladder must trigger deterministically.
- Timing criteria: PG stable before RESET release; glitches do not cause resets (debounce works).
- Behavior criteria: Stage order is consistent (TX inhibit → stop risky writes → controlled reset).
- Evidence criteria: logs include reset_reason + Vsys_min + PG_timeline for every failure or recovery.
| Test ID | Condition | Injection / workload | Observe | Pass / Fail (measurable) | Records to keep |
|---|---|---|---|---|---|
| L1-1 | Input dip / crank-like | Program VIN dip profile; repeat with identical load | VIN/VSYS + PG/RESET + IIN | VSYS window maintained or deterministic degrade ladder + controlled reset | Waveform screenshot + Vsys_min + reset_reason |
| L1-2 | Hot-plug | Hot-plug with harness-L simulation; vary input C | VIN ringing, IIN peak, limit_active | IIN peak is limited; VSYS dip does not cause glitch resets | VIN/IIN capture + limit_active timeline |
| L1-3 | Surge / load dump-like | Apply controlled surge; verify clamp/OV policy boundary | VIN peak, VSYS max, fault flags | VIN peak stays within margin; fault/flags are explainable and recover | VIN/VSYS screenshot + fault_flag log |
| L2-1 | PG/RESET glitch immunity | Inject short disturbances and ringing events | PG, RESET, VSYS | No reset on short PG glitches (debounce works); reset only on persistent violations | PG/RESET capture + PG_timeline |
| L2-2 | Latched fault recovery | Trigger a protection fault; verify recovery path | fault_flag persistence, recovery sequence | Recovery is deterministic; no “hang without reset_reason” | Flag trace + reset_reason evidence |
| L3-1 | Sleep current breakdown | Measure sleep current with staged isolation/jumpers | Total sleep current + domain-level deltas | Budget matches target; biggest contributors identified | Current breakdown sheet + temperature note |
| L3-2 | False wake rate | Motion profile replay (or vibration table); count wakes | wake_reason, wake counter | False wake rate below limit; wakes are attributable | Wake counter log + configuration snapshot |
| L4-1 | TX burst power stress | Enable burst workload; align TX indicator to captures | TX ind, VSYS droop, radio rail | Stage 1 action prevents unsafe droop; no random reboot | TX-aligned waveform + radio_state log |
| L4-2 | Worst-case combined stress | Low temp + burst + input dip (stacked margins) | VSYS_min statistics, reset_reason distribution | Outcomes remain deterministic; evidence complete for every fail/recover | Vsys_min histogram + reset_reason summary |
Deliverable standard: every failed run must still be a “good data point”:
a waveform capture aligned to the symptom window and a complete minimal log set for replayability.
Figure F6 — Validation pyramid and deliverables
A four-layer validation plan with clear observability outputs: waveforms, flags, logs, and a copy-ready checklist.
ALT: Validation pyramid diagram showing four layers (power events, sequencing/reset, wake/sleep, radio power stress), required observability artifacts (waveforms, flags, logs), and deliverables (checklist, waveform pack, log fields with pass/fail notes).
H2-11 — Design Checklist & IC Direction (with MPN examples)
Core idea: Mobile edge terminals fail most often inside power-event and state-transition windows. This section converts event-driven constraints into procurement-ready specs: what must be tolerated, what must be observable, and what must be testable.
11.1 Procurement-first checklist (Event → Spec → Evidence → Test)
Use the same 4-line template for every subsystem: events to survive, capabilities required, evidence points to capture, and the minimum validation action that proves it.
Power Entry Protection (reverse / OV-UV / inrush / surge)
- Events: hot-plug ringing, intermittent contact, reverse connection, surge/overvoltage bursts, EFT/ESD coupling.
- Must-have capabilities: adjustable current limit / inrush control, predictable fault behavior (latch/auto-retry), reverse blocking, OV/UV thresholds, fault telemetry pin.
- Evidence points: VIN(t)VSYS(t)IIN or ILIM stateFAULT flagPG/RESET
- Minimum test: hot-plug with harness inductance + inrush limit enabled; log VSYS_min and confirm “no-limbo” behavior (either clean reset or controlled degrade).
eFuse/hot-swap:
TPS2660
Surge stopper: LTC4368
Ideal diode: LM74700-Q1
Ideal diode: LTC4359
Regulators / Rails (wide-input buck + low-IQ AON LDO)
- Events: brownout and fast input dips, cold start, low-temperature drift, radio TX pulse loading.
- Must-have capabilities: wide VIN buck for 5V/3.3V, clean startup sequencing, fast transient response, low-IQ AON supply, rail-level enable control for domain gating.
- Evidence points: rail PG timing (or supervisor output), VSYS_min statistic, reset reason register, optional ADC taps on key rails.
- Minimum test: replay the same dip profile at room/cold; compare reset-reason distribution and VSYS_min distribution (proves “predictable” behavior).
Wide-input buck:
LM53635-Q1
AON LDO: TPS7A02
Supercap Hold-up & Health (precharge / energy window / ESR)
- Events: 10–200 ms contact dropouts, “transaction hold-up” (finish write/report), short ride-through windows.
- Must-have capabilities: controlled precharge (input-friendly), defined VHI/VLO window aligned to UVLO/PG policy, optional ESR/capacitance monitoring for low-temp aging drift.
- Evidence points: VSYS(t) droop curve, cap stack voltage, “power-fail” marker, log integrity after cut.
- Minimum test: step power removal; confirm rail drop order + log consistency (no partial writes / corrupted state).
Supercap backup:
LTC3351
Accel-Wake + Always-on Domain (threshold / debounce / handoff)
- Events: false wake, vibration bursts, threshold drift, “wake while rails are unstable”.
- Must-have capabilities: motion threshold + debounce configurability, ultra-low standby current, deterministic handoff: wake_req → rails_on → clocks_stable → radio_enable.
- Evidence points: wake_reason, AON current, wake-to-ready timestamp, “radio enable” vs PG alignment.
- Minimum test: false-wake rate under a fixed motion profile + sleep-current breakdown (segment-by-segment isolation).
ULP accel:
BMA400
Micropower accel: ADXL362
Diagnostics & Evidence Package (flags / ADC / logs)
- Goal: make “field failures” diagnosable without guessing.
- Must-have capabilities: readable fault flags, at least one “VSYS_min” capture mechanism, reset reason, minimal event log fields.
- Minimum log fields (recommendation): reset_reason, VSYS_min, PG timeline marker, radio_state marker, temperature.
- Minimum test: every injected event must produce an evidence bundle (waveform + flags + log line); otherwise the test is not deliverable.
Supervisor/reset:
TPS3899
AON MCU: STM32U0
AON MCU: MSP430FR
11.2 Buyer-friendly spec sheet (Must-have / Bonus / Risk flags)
This table is written for procurement and cross-functional reviews. Every “Risk flag” maps to an expensive field symptom (random resets, GNSS lock loss, wake limbo, low-temp failures).
| Subsystem | Must-have (no compromise) | Bonus (reduces debug cost) | Risk flags (ask before buying) |
|---|---|---|---|
| Power entry | reverse ILIM/inrush OV/UV fault flag predictable retry/latch behavior | IMON/telemetry programmable thresholds/delays, fast fault reporting to MCU | “fault = only one pin”, unclear auto-retry, no defined inrush control (hot-plug ringing), unknown behavior at negative input |
| Regulators/PMIC | wide VIN stable startup, deterministic enable control for domains, transient robustness to TX pulses | low-IQ AON rail monitoring hooks, clean “degrade-first” options (radio-first shed) | no clear sequencing story, poor dip behavior (brownout limbo), low-temp drift not characterized |
| Supercap hold-up | precharge defined VHI/VLO window, consistent UVLO alignment, no corruption on cut | ESR/health capacitance/ESR readback, alarms for “cap aging / low-temp” | precharge fights hot-plug, no window definition (math ≠ usable), unverified low-temp capacitance/ESR drift |
| Accel-wake/AON | threshold debounce handoff ultra-low standby current, deterministic wake-to-ready order | false-wake counters, timestamped wake reason, flexible interrupt routing | noisy wake thresholds, no debounce controls, wake triggers while rails are unstable |
| Supervisor/Logs | reset gating programmable delay/debounce, reset_reason + VSYS_min capture | multi-point ADC taps, event counters, simple “evidence bundle” export | reset only tied to one rail, no record of min voltage, failures reproduced but not diagnosable |
Procurement rule of thumb: if a supplier cannot explain (1) fault behavior, (2) brownout behavior, and (3) observability hooks,
the integration risk remains high even if headline specs look good.
11.3 IC direction (example MPNs — non-exhaustive, equivalents OK)
The parts below are example material numbers to anchor procurement and schematic discussions. Final selection must pass the event-spectrum validation plan and evidence requirements.
-
Power entry protection (eFuse / surge stopper / reverse blocking)
Typical capability keywords: wide VIN, adjustable ILIM/inrush, OV/UV thresholds, reverse input protection, FAULT/IMON.
Example MPNs:TPS2660,LTC4368 -
Ideal diode / OR-ing (low loss reverse protection, multi-source)
Capability keywords: ideal diode control, reverse current blocking, fast switchover, low IQ.
Example MPNs:LM74700-Q1,LTC4359 -
Wide-input buck regulators (12V/24V front rails → 5V/3.3V)
Capability keywords: wide VIN, fast transient response, robust dip behavior, enable control for domain gating.
Example MPNs:LM53635-Q1 -
Always-on LDO (AON rail for RTC/AON MCU/wake sensor)
Capability keywords: ultra-low IQ, clean enable behavior, stable at light loads, low-temp operation.
Example MPNs:TPS7A02 -
Supercap backup/charger (precharge + boost-backup + optional health)
Capability keywords: controlled precharge, CC/CV charge, reverse boost to VSYS, stack monitoring, alarms.
Example MPNs:LTC3351 -
Supervisor / reset manager (brownout-proof gating)
Capability keywords: programmable threshold, reset delay, debounce/blanking, ultra-low supply current.
Example MPNs:TPS3899 -
Motion wake accelerometer (wake-on-motion, false-wake control)
Capability keywords: configurable threshold + debounce, ultra-low standby, clear interrupt behavior.
Example MPNs:BMA400,ADXL362 -
Always-on controller / ULP MCU (handoff + evidence logging hooks)
Capability keywords: ultra-low-power modes, RTC/backup domain, deterministic wake orchestration, log timestamping.
Example MPNs:STM32U0,MSP430FR
How to avoid “hard-ad” tone while keeping conversion value: keep every part number tied to a measurable requirement
(event, waveform, flag, log field, pass/fail test). Do not list brands without the corresponding procurement question and evidence point.
Figure F7 — Checklist → Evidence Points → IC Direction (example MPN anchors)
Request a Quote
H2-12 — FAQs (evidence-first, no guessing)
Each answer stays inside this page boundary: power events, wake domains, rail/PG/reset sequencing, supercap hold-up, and the minimum evidence needed for field diagnosis. Wireless protocol and RF implementation details are intentionally excluded.
FAQs ×12
1After motion-wake, power jumps but functions look normal. What most often prevents “return to sleep”?
Most cases are an always-on or peripheral domain that never returns to standby, an interrupt storm that keeps re-waking the system, or a “safe mode” entered after brownout. Prove it before touching software.
- Capture: AON rail current steps (sleep→wake→idle), wake/IRQ counter trend, domain enable/clock-enable snapshot.
- Split: if current never drops → domain not gated; if counters keep rising → false triggers; if reset/brownout markers exist → recovery mode.
Mapped chapters: H2-5 (Accel-wake & AON domain), H2-8 (brownout behavior).
2Same PCB, different accelerometer → false-wake rate increases. Check threshold, noise, or mounting first?
Check configuration equivalence first: ODR/filtering, threshold, and debounce defaults differ widely. Then verify noise/bandwidth (more noise → more threshold crossings). Mounting orientation and mechanical coupling comes last and must be A/B tested.
- Capture: config diff table, raw acceleration histogram/over-threshold counts, fixed motion profile false-wake statistics.
- Split: config mismatch → fix settings; same settings but higher crossings → sensor noise/bandwidth; only changes with mounting → mechanical coupling.
Mapped chapters: H2-5 (threshold/debounce, wake chain).
3Cellular reporting causes random resets. What three waveforms/states prove “power droop” vs “software”?
Use correlation: a radio load marker aligned to a rail droop aligned to reset reason/time. Average supply numbers are not evidence; only minimum voltage and timing are.
- Capture: modem TX/load marker, VSYS + critical rail Vmin droop shape, reset_reason + timestamped log line.
- Split: TX↔droop↔reset aligned → power-path/transient issue; TX without droop → reset gating/PG issue; droop without reset → margin exists but may break other rails.
Mapped chapters: H2-4 (radio power interface), H2-9 (symptom→evidence flow).
4GNSS occasionally loses lock while “average power looks stable”. What transient/coexistence issues dominate, and how to prove them?
Lock loss usually correlates with short rail dips/ripple bursts, clock-supply disturbance, or coexistence timing when a high-load radio turns on. Prove correlation using time-aligned markers, not RF speculation.
- Capture: GNSS lock/status marker, GNSS rail VSYS_min/ripple snapshot, cellular TX/load marker and shared-clock enable events.
- Split: lock loss follows rail dip → power integrity; follows clock enable disturbance → clock boundary; follows TX bursts without rail dip → coupling/timing interaction to investigate at interface level.
Mapped chapters: H2-4 (power/clock/control interface), H2-9 (evidence chain).
5Supercap hold-up: size by “energy” or by “allowed voltage window”? When does ESR become the main problem?
Energy sets how long the load can run, but the usable window is defined by UVLO/PG thresholds. ESR dominates short interruptions and peak loads because it creates an immediate voltage step that can trip resets even if energy is sufficient.
- Capture: VSYS(t) showing initial step + slope, UVLO/PG trigger points, peak load profile during hold-up.
- Split: big immediate drop → ESR-limited; fast decay slope → capacitance/window-limited; trips before window ends → thresholds/sequencing mismatch.
Mapped chapters: H2-6 (energy budget + ESR), H2-8 (PG/RESET thresholds).
6Precharge current set too high vs too low: what field symptoms appear (hot-plug, slow start, protection trips)?
Too high precharge looks like inrush: hot-plug ringing, repeated UV/OV trips, and unstable startups. Too low precharge creates long “not-ready” windows: delayed radio readiness, incomplete cap charge, and shortened hold-up under cold or weak inputs.
- Capture: IIN peak/limit markers, VIN/VSYS ringing envelope, precharge-complete time vs system-ready time.
- Split: trips and ringing → reduce inrush/damp; slow readiness and short hold-up → increase precharge or adjust window policy.
Mapped chapters: H2-6 (precharge), H2-7 (hot-plug dynamics).
7During vehicle crank: decide “ride-through no reset” vs “controlled reboot”? What evidence makes the call?
Choose ride-through only if the workload must remain continuous and its state can remain consistent across dips. Otherwise, controlled reboot is safer when brownout creates limbo states, partial writes, or undefined rail order. The decision must be based on dip distribution and state integrity evidence.
- Capture: crank dip Vmin/duration histogram, reset_reason distribution, transaction/log integrity markers.
- Split: dips shorter than hold-up window → ride-through; dips that cause partial state → controlled reboot + clear sequencing policy.
Mapped chapters: H2-2 (event spectrum), H2-8 (brownout-proof sequencing).
8Load dump / overvoltage: TVS is “large” but failures still occur. Where does energy usually take the wrong path?
Failures often mean the clamp current returns through an unintended path, the clamp is placed too far from the entry node, or the harness L with input C creates overshoot that the clamp cannot control fast enough. The goal is to keep energy at the entry and prevent it from reaching downstream rails.
- Capture: entry-node VIN, downstream VSYS, clamp-node voltage, fault flags (OV/thermal).
- Split: VIN clamps but VSYS overshoots → path/placement issue; VIN overshoots with ringing → harness-L/input-C dynamics; downstream trips first → derating/threshold mismatch.
Mapped chapters: H2-7 (energy path + measurement points).
9PG/RESET is connected, yet “hung without reset” happens. Check debounce, thresholds, or hold circuits first?
Start with debounce/blanking, because short PG glitches can release reset at the wrong time and create half-initialized states. Next check whether the right rails participate in reset gating and whether thresholds match actual droop behavior. Latch/hold circuits are last, after timing evidence is collected.
- Capture: PG/RESET glitch timing, VSYS_min at the event, rail enable states and reset_reason.
- Split: PG glitch present → tune debounce; no glitch but wrong rail order → gating set; repeated faults with no recovery → latch/clear policy.
Mapped chapters: H2-8 (PG/RESET + degrade order), H2-9 (symptom map).
10Low temperature reduces hold-up time. Is it capacitance drop or resistance rise? One experiment to tell?
Use a single cut-power step and inspect two features of VSYS(t): the immediate step and the subsequent slope. A large immediate step indicates ESR rise. A much steeper slope with a similar initial step indicates capacitance loss. Run the same load profile at room and cold and compare these two signatures.
- Capture: VSYS(t) initial ΔV and slope, identical load power profile, UVLO/PG trigger time.
- Split: ΔV dominates → ESR; slope dominates → C; triggers early with both stable → thresholds/window mismatch.
Mapped chapters: H2-6 (ESR vs window), H2-10 (validation method).
11Hot-plug ringing triggers protection falsely. How to distinguish end-capacitance, harness inductance, or TVS dynamics as the main cause?
Change one variable at a time and watch what the ringing frequency and damping do. Harness inductance mainly shifts ringing frequency; end capacitance shifts frequency and stored energy; TVS dynamics changes peak clamp level and damping near the clamp node. This A/B method produces proof without standards deep-dives.
- Capture: VIN ringing frequency + envelope, IIN peak/limit marker, clamp-node peak and downstream VSYS peak.
- Split: frequency shifts with harness → L-dominant; shifts with C → C-dominant; peak changes with TVS → clamp-dominant.
Mapped chapters: H2-7 (hot-plug energy path), H2-10 (repeatable validation).
12Lowest-cost health diagnosis in the field: which log fields are the most valuable to shorten RMA root-cause time?
Prioritize fields that turn “random” failures into a time-aligned evidence bundle: why reset happened, how low voltage dipped, which rails were valid, and what the radios and wake chain were doing. Keep it small (≤8 fields) so it survives power events and is always collected.
- Top fields: reset_reason, VSYS_min, PG timeline marker, radio_state marker (TX/ON/OFF), wake_reason + wake_count, temperature, fault_flags snapshot, event_counter.
- Split: if VSYS_min + PG markers exist → power path; if wake_count spikes → false wakes; if fault_flags dominate → protection behavior.
Mapped chapters: H2-8 (reset/log fields), H2-9 (evidence-first diagnosis).
Evidence priority (always): waveforms (VIN/VSYS/rails) → status pins/flags → logs with timestamps.
This keeps the FAQ answers inside the Mobile Edge IoT Terminal page boundary.
Figure F8 — FAQ “Evidence Ladder”: Waveforms → Pins/Flags → Logs → Decision
