Verified calculation capability

Heatsink Thermal Resistance Calculation Capability

Junction temperature from effective θJA or θJC+θCS+θSA, or required heatsink θSA,max = (Tj,max−Ta)/P − θJC − θCS. · Electrical · Thermal

Capability ID electrical.thermal.heatsink_rth · version 1.1.0

Open calculator REST API MCP Evidence Evidence JSON CVP Manifest Review policy

Model

Effective θJA

Effective θJA: Tj = Ta + P · θJA
Heatsink stack: Tj = Ta + P · (θJC + θCS + θSA)
Required heatsink: θSA,max = (Tj,max − Ta)/P − θJC − θCS

Solve modes: junction effective ja · junction heatsink stack · required heatsink sa · rise · rth

Inputs / Outputs

Canonical symbols for this capability. Agent schemas remain the contract.

Symbol	Quantity	Unit	Role
`Ta`	Ambient temperature (°C)	°C	input / output
`P`	Device power dissipation converted to heat (W). ≥ 0 on rise models; > 0 when solving θSA.	W	input / output
`Rth_JA`	Effective / application junction-to-ambient thermal resistance (°C/W ≡ K/W)	—	input / output
`Rth_JC`	Junction-to-case thermal resistance (°C/W)	—	input / output
`Rth_CS`	Case-to-sink / TIM interface thermal resistance (°C/W). 0 means the interface is neglected.	—	input / output
`Rth_SA`	Sink-to-ambient thermal resistance (°C/W) — the heatsink. Input on stack mode; output as Rth_SA_required on required mode.	—	input / output
`Tj_max`	Required on required_heatsink_sa. Optional on rise models for thermal margin.	°C	input / output
`thermal_path`	JA = effective θJA; JC+CS+SA = explicit heatsink stack; required_SA = solved θSA,max. Not interchangeable models.	—	output
`Rth_C_per`	Headline resistance: θJA or θtotal on rise models; θSA,max on required_heatsink_sa	W	output
`Rth_total`	—	—	output
`Rth_total_max`	(Tj,max−Ta)/P in required mode	—	output
`Rth_SA_required`	—	—	output
`dT`	—	°C	output
`dT_JC`	—	°C	output
`dT_CS`	—	°C	output
`dT_SA`	—	°C	output
`Tj`	—	°C	output
`margin`	—	°C	output

Assumptions / Validity

Declared scope for this capability. Do not use it outside this domain.

Assumptions

Steady-state lumped thermal resistance
Rθ constant (not Zth(t))
θJA is an effective / application value, not a JEDEC-board package constant
θJC+θCS+θSA is a single series path; parallel PCB/package paths are ignored
P is device dissipation converted to heat

Example

One numerical check. The calculator page holds worked steps and FAQ.

Ta=25, P=10, Tj_max=150, θJC=1.5, θCS=0.5 → θSA,max=10.5

Open this example in the calculator

Trust

CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance. Computational verification is defined by CVP. Supplemental domain review (internal) and named expert review are defined by the Review policy and do not by themselves determine CVP conformance.

CVP: CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Assurance: Engineering
Declared partition coverage: PASS · 4/4 declared partitions (ja, stack, required-sa, invalid-domain)
Calculation version: 1.1.0
Verification: 17/17 calculation tests · 4/4 legacy golden · 5/5 legacy boundary · 8/8 legacy property
Production surface contract: 4/4
Versions: Calculation 1.1.0 · CVP protocol 1.0.0-proposed
CVP identity: 3/3 property · digest e84796291008
Reference: O1 model · O2 expected_values · O2 numerical_behavior
Interfaces: PASS · UI (SSR) / REST / MCP
ui-ssr is query-result HTML, not a live browser session.
CVP suite: 4/4 golden · 8/8 CVP boundary · 9/9 invalid · 3/3 property · 3/3 metamorphic · 2/2 round-trip · 3/3 cross-interface · 1/1 cross-calculator · 4/4 CVP contract
Supplemental domain review: Internal · Pass · electrical-engineer
Named expert review: Not performed
Version lock: Supported (409 VERSION_MISMATCH)
Artifact consistency: Build verified · 1.1.0 (workspace artifacts agree)
Review-policy tier: Internally reviewed — catalog token internally_reviewed; supplemental; not CVP status

This calculator CURRENT · Public schema 1.1.0 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓

Call this capability

Human page, REST, and MCP share the same engine and calculation_version. Build verified hashes workspace artifacts only. After deploy, attest:production GETs canonical URLs twice — the public/cached view an Agent actually hits, and origin — including every /capabilities/{id} HTML page. Public Capability HTML version must match catalog before production attestation passes. Live Trust rows above fetch /.well-known/calculatorx-production-attestation.json and the output schema const. Build hashes: release integrity. That proves currently published page / engine / schema / evidence / MCP agree — not that a historical version is independently immutable. Reference Calculation Standard — Production surface contract 4/4.

Tool id: heatsink-rth
Engine: heatsink-rth
REST: POST /api/v1/calc/heatsink-rth
MCP: execute_calculation with capability_id: "electrical.thermal.heatsink_rth"
Agent input schema: Canonical (MCP / Agent)
Output schema: JSON Schema (latest)
Versioned input schema: Immutable pin (1.1.0)
Versioned output schema: Immutable pin (1.1.0)

Operations

Declared calculation modes for this capability.

junction_effective_ja
junction_heatsink_stack
required_heatsink_sa

References

Human-readable sources plus CVP reference evidence classes.

Sources

JEDEC JESD51 series — Integrated Circuits Thermal Measurement Method — Junction-to-ambient and junction-to-case thermal metrics on specified test boards
Analog Devices — Practical Design Techniques for Power and Thermal Management — Section 8, Fig. 8.50 — junction → case → case-to-sink → sink-to-ambient
Texas Instruments SPRA953 — Semiconductor and IC Package Thermal Metrics — RθJA, RθJC, and application dependence of junction-to-ambient metrics
Analog Devices — Thermal Characterization of IC Packages — θCA is case-to-ambient (all case-to-ambient paths); θJA = θJC + θCA

Reference evidence classes: O1 model · O2 expected_values · O2 numerical_behavior

Try with an agent

Inspect this capability via same-origin MCP, then call execute_calculation.

curl -sS -X POST 'https://www.calculatorx.com/mcp' \
  -H 'Content-Type: application/json' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: tools/call' \
  -H 'Mcp-Name: inspect_capability' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"inspect_capability","arguments":{"capability_id":"electrical.thermal.heatsink_rth"}}}'

Inspect the trust tier and required assurance level before execution. Pin calculation_version (1.1.0) when reproducibility matters. Full protocol notes: MCP docs.