calc.engineer

power supply decoupling

power_supply_decoupling

Select bypass and bulk decoupling capacitors for IC power supply pins. Computes the target PDN (Power Distribution Network) impedance from supply current, voltage, and allowable ripple using Z_target = V_ripple / I_total. Recommends a ceramic bypass capacitor (high-frequency decoupling, placed closest to IC pins) and a bulk capacitor (low-frequency decoupling, near the regulator). Calculates the ceramic cap's self-resonant frequency assuming typical lead inductance, and checks whether ESR-induced ripple stays within limits. Essential for digital, analog, and mixed-signal PCB design. Chain with lc_resonance to verify the decoupling capacitor's resonant behavior, or with trace_width to size the power trace.

Input Schema

TableJSON Schema

Name	Required	Description
`num_ics`	No	Number of identical ICs sharing this supply rail. Scales the total current demand.
`esr_mohm`	No	Equivalent series resistance (ESR) of the ceramic bypass capacitor in milliohms. Typical MLCC: 5-20 mohm.
`max_ripple_mv`	No	Maximum allowable supply ripple in millivolts (mV). Typical: 50 mV for digital, 10 mV for analog/RF.
`supply_voltage_v`	Yes	Supply voltage in volts (V). Common values: 1.8, 2.5, 3.3, 5.0, 12.0.
`supply_current_ma`	Yes	IC supply current draw in milliamps (mA). Use the maximum or typical from the datasheet.
`switching_freq_mhz`	No	Primary switching or clock frequency of the IC in MHz. Determines the target impedance frequency range.

Output Schema

TableJSON Schema

Name	Required	Description
`bulk_cap_uf`	Yes	Recommended bulk capacitor value in microfarads (uF). Placed near the voltage regulator for low-frequency decoupling.
`bulk_cap_value`	Yes	Nearest standard bulk capacitor value with unit (e.g. '10 uF', '47 uF').
`ceramic_cap_uf`	Yes	Recommended ceramic bypass capacitor value in microfarads (uF). Placed closest to IC pins.
`bypass_adequate`	Yes	Whether the ESR-induced ripple is within the specified max_ripple_mv limit.
`ripple_at_esr_mv`	Yes	Estimated ripple voltage due to ESR at the switching frequency: V = I_peak * ESR.
`total_current_ma`	Yes	Total supply current for all ICs on this rail.
`ceramic_cap_value`	Yes	Nearest standard E12 capacitor value with unit (e.g. '100 nF', '1 uF').
`target_impedance_ohm`	Yes	Target supply impedance at the switching frequency: Z_target = V_ripple / I_total. The decoupling network must keep PDN impedance below this value.
`self_resonant_freq_mhz`	Yes	Self-resonant frequency of the recommended ceramic capacitor assuming 0.5 nH lead inductance. Above this frequency, the capacitor becomes inductive.

TDQS

A4.9/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations exist, so the description must fully disclose behavior. It explains the computation steps: target PDN impedance, ceramic and bulk capacitor recommendation, self-resonant frequency calculation, and ESR ripple check. This gives the agent a clear understanding of internal operations and safety (non-destructive calculator).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise with no wasted sentences, front-loading the purpose. However, the single-paragraph structure could be improved for AI readability (e.g., bullet points). Still, it is efficient and informative.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The output schema exists, so return values need not be explained. The description covers all relevant aspects: target impedance calculation, capacitor type recommendations, frequency analysis, and ripple check. It is complete for a decoupling selection tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

All 6 parameters have schema descriptions (100% coverage), but the description adds extra context: it defines the Z_target formula linking supply_current_ma, supply_voltage_v, and max_ripple_mv; explains num_ics scales current; gives typical ESR values; and clarifies switching_freq_mhz role. This goes beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Select bypass and bulk decoupling capacitors for IC power supply pins.' It provides a specific verb+resource and differentiates from siblings by mentioning chaining with lc_resonance and trace_width.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit usage guidelines are given: 'Essential for digital, analog, and mixed-signal PCB design.' It also advises chaining with related tools (lc_resonance, trace_width) for further verification or sizing, providing clear context and alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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TDQS

A3.9/5.0

Disambiguation4/5

Despite 89 tools, each has a clearly distinct purpose with detailed descriptions that often reference related tools. Overlap exists (e.g., multiple LoRa/RF tools), but the descriptions are sufficient to distinguish them. Some confusion possible among similar-sounding tools like attenuator_pi and attenuator_tee, but the descriptions explicitly compare them.

Naming Consistency4/5

Consistent underscore-separated lowercase naming. Most tools follow a verb_noun pattern (e.g., capacitor_charge, wire_gauge) or noun_noun (power_cost). Minor inconsistencies such as 'bmi_calculator' vs 'solar_sizing' but overall predictable.

Tool Count2/5

89 tools is far too many for a single MCP server. This scope is more appropriate for multiple specialized servers. The sheer number will slow agent selection and increase cognitive load, reducing coherence.

Completeness3/5

Covers many domains (RF, solar, PCB, networking, math, etc.) but lacks depth in some areas (e.g., no three-phase power, no airflow calculations). Some domains have comprehensive coverage (LoRa/Meshtastic), but others feel incomplete for the tool count.

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