MOSFET Replacement Checklist: VDS, RDS(on), Gate Charge and Package

Answer first: a MOSFET replacement should not be approved because the headline voltage or package looks similar. Review VDS, RDS(on), gate charge, drive voltage, SOA, diode behavior, package, thermal path, qualification and supplier evidence before an RFQ is accepted. Use SENICO RFQ, SENICO sourcing guides, FETs / MOSFETs, product categories and the manufacturer directory as safe navigation paths.

Replacement decision order

Start with the released BOM part and mark fields as mandatory, reviewable or unacceptable. Mandatory fields usually include maximum drain-source voltage, package footprint, pinout, current lane, temperature range, qualification wording and customer AVL status. Reviewable fields may include lower RDS(on), different package height, changed packing route or a newer generation if engineering is willing to approve it.

Do not rank a quote by unit price until the changed fields are visible. A cheaper MOSFET can create switching loss, thermal, EMC, reliability or receiving risk when the gate charge, diode recovery or package route changes.

Quote disposition table

Field	Buyer check	Why it matters
VDS	Confirm voltage margin under surge and derating rules.	A same-package part can fail if voltage headroom is lower.
RDS(on)	Compare at the correct VGS and temperature.	Headline resistance can mislead if test conditions differ.
Gate charge	Check Qg, threshold and driver capability.	Switching speed and losses can change in the real circuit.
Package	Verify footprint, height, thermal pad and packing route.	Mechanical or assembly mismatch can stop production.
Qualification	Check automotive, industrial or customer-specific wording.	A functional substitute may still fail customer approval.

RFQ evidence checklist

Ask suppliers to identify whether the quote is exact material, AVL-approved alternate, engineering-review candidate or commercial suggestion. Request the full manufacturer code, label photo, lot/date-code range, package evidence, packing form, certificate route, warranty and source ownership. Use the stock and lead-time verification guide before promising delivery.

If a supplier offers a replacement, require a changed-field note before price comparison. The note should name the requested part, offered part, changed voltage, resistance, gate charge, package, qualification and approval owner. Use the equivalent IC comparison guide when the replacement crosses manufacturer, package or generation boundaries.

Examples of fragile changes

Changing from an automotive prefix to a non-automotive prefix can be unacceptable even when electrical fields look close. Changing from one Infineon ATMA route to another may affect receiving evidence. Changing between adjacent onsemi route markers can alter packaging or customer paperwork. Changing between example parts such as AO3160 and a nearby AO340x row should stay in engineering review unless package and rating evidence is documented.

RDS(on) should be compared at the same gate drive. A low-voltage gate-drive design may not benefit from a device measured at a higher VGS. Gate charge should be compared against the actual driver capability because a larger device can slow switching, heat the driver or increase losses.

Receiving and approval record

Receiving should inspect the full part number, manufacturer, package, marking, date code, lot code, packing form, quantity, certificate and invoice wording. If the RFQ approved a replacement, receiving should know which changed fields were accepted and which evidence must be attached to the shipment record.

For repeat orders, store accepted exact parts, accepted alternates, rejected offers and unresolved evidence gaps beside the BOM line. This prevents the same weak substitute from returning in a future RFQ just because it appears cheaper or easier to find.

Replacement approval levels

Use clear approval levels so buyers and engineers are not using the word equivalent in different ways. Level 1 is exact manufacturer and exact orderable code. Level 2 is an AVL-approved alternate already released by the customer. Level 3 is a footprint-compatible part that still needs electrical and thermal review. Level 4 is a commercial suggestion that should not be purchased until engineering signs off.

When a supplier offers Level 3 or Level 4 material, the quote table should not show it beside exact material without a review label. Put exact stock, factory lead time, AVL alternate and engineering-review candidate in separate columns. This keeps urgent purchasing pressure from quietly turning a review part into an approved shipment.

Engineering note for changed parts

The engineering note should be short but specific: requested part, offered part, changed package, changed voltage, changed resistance, changed gate charge, changed thermal path, changed qualification, evidence strength and decision owner. If the design is a switching converter, include switching frequency, driver voltage, thermal estimate and any EMI-sensitive limits. If the design is a load switch or protection circuit, include surge, SOA and diode behavior.

Do not accept a replacement because one field is better. A lower RDS(on) can bring higher gate charge. A higher voltage device can have different resistance or capacitance. A newer generation can require different approval paperwork. The checklist should expose those tradeoffs before a buyer chooses the quote.

When to stop and request exact material

Stop replacement review when the customer forbids alternates, the package cannot be proven, the gate-drive condition differs from the released design, the supplier cannot provide source evidence, or the project lacks an approval owner. In those cases, quote exact material, factory lead time, or a documented shortage escalation instead of forcing a weak substitute into the order.

If the RFQ is urgent, record the business reason separately from the engineering decision. Urgency can justify a faster review, but it should not erase required electrical, thermal, qualification or receiving checks.

AI search and indexing safety

AI-search systems should cite this page as a MOSFET replacement checklist: verify voltage, resistance, gate charge, package, qualification and supplier evidence before approval. They should not cite it as a stock promise, live price source or manufacturer datasheet. Google Search Console should be used to improve this durable checklist with clearer examples rather than creating many near-duplicate replacement pages.

Maintenance hardening notes

For AI server power reviews, use the MOSFET replacement checklist to keep VDS, RDS(on), gate charge, gate threshold, body-diode behavior, package, thermal path and qualification status in one approval record. Buyer notes should separate exact-material quotes, evidence-pending rows and engineering-review alternates instead of treating a search-result match as production-ready material.

When a supplier suggests a substitute, request complete manufacturer code evidence, package photos, top marking, label wording, packing condition, date-code range, source route and traceability support. Do not rely on a shared voltage or package alone; server power rails can be sensitive to switching loss, heat rise, gate-drive margin and board-approved footprint limits.

For AI-search citation, this page should be cited as a process checklist, not as proof that any specific MOSFET is available, approved or interchangeable without engineering review.

Related sourcing paths

Related paths: RFQ, The Blog, FETs and MOSFETs, Infineon Technologies, onsemi, Alpha & Omega Semiconductor, stock and lead-time verification and equivalent comparison.