A wide-input DC-DC converter must keep the required output within limits across the supply conditions it will actually encounter. For telecom equipment using nominal 24 V or 48 V supplies, compare the complete input envelope, output load and cooling conditions. An exact part number and datasheet revision are the starting point.
Separate normal input from short events
Nominal bus voltage names the system; it does not describe every voltage at the module terminals. Prepare a requirement record covering the normal minimum and maximum, startup conditions and specified disturbances. State the voltage polarity and reference point. Include distribution drop when determining the lowest input the converter will see.
The SynQor PQ30 family page distinguishes continuous and transient input ranges. For a concrete model example, its linked PQ30033EGA20 datasheet, revision C, July 2019 specifies 18–60 V continuous input and an 80 V, 100 ms transient capability. This is an eighth-brick model; use its document only for that model and variant. The duration is part of the rating.
On a narrow screen, scroll the table horizontally. Keyboard users can focus the table and use the arrow keys.
| Requirement | Record | Evidence to request |
|---|---|---|
| Continuous operation | Minimum and maximum terminal voltage | Specified output regulation across that range |
| Startup and recovery | Available supply, ramp and load state | Startup thresholds, hysteresis and startup behavior |
| Transient exposure | Amplitude, duration and event waveform | Exact permitted conditions and required external protection |
| Input current | Worst planned steady load and minimum input | Efficiency at that point plus separate startup requirements |
Write down what the equipment needs to do during each event: maintain output, interrupt and recover, or survive for later restart. These are different acceptance criteria. Have the responsible engineer identify the applicable system specification instead of treating a family-page range as a universal telecom requirement.
Use power to understand low-input current
Fictional steady-state example: a 66 W load supplied at an assumed 90% conversion efficiency needs 66 ÷ 0.90 = 73.33 W at the converter input. At 18 V that is about 4.07 A; at 48 V it is about 1.53 A. Converter dissipation is approximately 7.33 W.
The efficiency is invented and held constant to isolate the voltage effect. Actual efficiency varies with operating point. This arithmetic excludes startup, input-filter behavior and distribution losses; it is an early sizing check.
Compare that steady-state result with the upstream supply and distribution requirements. Keep the input-current calculation separate from output-current capability: amperes at different voltages describe different power levels.
Read the rating together with the cooling conditions
The model datasheet includes output-power derating curves for different ambient temperatures and airflow conditions, as well as application information for remote sense and output trim. Identify the curve that represents the proposed enclosure. Record the airflow direction, neighboring heat sources and measured temperature location before accepting the available output.
Use a comparison line such as “required load at lowest input, highest specified ambient and available airflow,” followed by the supporting figure number. A cooling assumption that cannot be reproduced in the equipment remains an open engineering item. Thermal shutdown is a protective function; normal operation needs its own verified margin.
Close the integration questions
Alongside the voltage and thermal record, ask the supplier to confirm the required isolation classification, control-pin reference, startup into the actual load, external components and mechanical variant. Check the complete system's applicable approvals separately from a component's historical certification.
A useful selection record ends with the exact document revision, each unresolved condition and its planned validation. For broader conversion choices see DC-DC converter evaluation; for a specific step-up/step-down topology see SEPIC converters.
Converter input requirements record
Download the converter input requirements record (plain text). Save a copy and fill it in with your own evidence. Instructions, units, assumptions and the fictional example are included.