SS54 Guide

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The datasheet confirms MDD’s SS54 is an SMA device, but this library entry’s package property says SMC; I’ll flag that conflict prominently without changing the part. I’ve also verified the current and thermal limits, including why the 5 A rating does not guarantee continuous operation on a small PCB.
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2/2 Write and check the seven-section cited application guide in project files.

Verify MDD SS54 ratings, polarity, package, and alternatives from primary sources.

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"SS54 Guide" completed.

flux

Created the SS54 Application and Usage Guide in project files, covering all seven requested sections with citations, practical wiring, thermal guidance, alternatives, and sourcing details.
Important: The manufacturer specifies SMA, but this library entry’s package property says SMC; footprint compatibility remains unverified. The next priority is to inspect the footprint against the manufacturer drawing before using the part on a PCB.
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SS54 Application and Usage Guide
The MDD SS54 (LCSC C22452) is a 5 A, 40 V Schottky rectifier. Its most common engineering use case is as a catch or freewheeling diode in power converters, where it provides a current path when the switching device turns off.
Library metadata warning: MDD specifies an SMA (DO-214AC) package, while this Flux project currently carries an SMC_L6.9-W5.9-LS7.9-RD package property. Footprint compatibility of this library entry is not verified; confirm the land pattern against the manufacturer drawing before PCB release.
1. Quick Specifications

Table

ParameterManufacturer rating / characteristicClassificationEngineering operating guidance
Repetitive peak reverse voltage, VRRM40 V Absolute maximumKeep normal reverse voltage comfortably below 40 V and include switch-node ringing, cable transients, and tolerance in the margin.
RMS reverse voltage, VRMS28 V Absolute maximumUse only when the applied waveform and RMS interpretation are appropriate; do not substitute this for a transient check.
DC blocking voltage, VDC40 V Absolute maximumSelect a higher-voltage diode if worst-case steady-state plus transients can approach 40 V.
Average rectified forward current, IAV5.0 A Absolute maximum under stated test conditionsThere is no universal safe continuous current: calculate diode duty cycle and losses, then validate junction temperature on the actual PCB. For the datasheet's 60 Hz half-wave test context, capacitive loads require a 20% current derating; do not generalize that rule to every switcher.
Non-repetitive surge current, IFSM120 A for one 8.3 ms half-sine wave, superimposed on rated load, JEDEC method Absolute maximum, non-repetitiveDo not treat 120 A as repetitive pulse capability; separately evaluate pulse width, repetition rate, starting temperature, and thermal recovery.
Forward voltage, VF0.55 V maximum at 5 A Maximum electrical characteristic, not typicalEstimate first-pass conduction loss as Pcond ≈ IF(avg) × VF; 5 A × 0.55 V = 2.75 W is an illustrative worst-case-point calculation, not a guaranteed loss at every current or temperature.
Reverse leakage, IR1 mA maximum at 25 °C and 50 mA maximum at 100 °C, at rated blocking voltage Maximum electrical characteristicInclude hot leakage in standby-current and thermal budgets, especially near the 40 V limit.
Junction capacitance, CJ500 pF typical at 1 MHz and 4 V reverse bias Typical characteristicAccount for switching loss and ringing in high-frequency converters; actual capacitance varies with bias.
Junction-to-ambient thermal resistance, RθJA60 °C/W typical with 2 × 2 in (5 × 5 cm) copper pad areas Typical, test-board dependentDo not assume 60 °C/W on a compact layout. At 2.75 W it implies an illustrative 165 °C rise, showing why copper area, airflow, duty cycle, and temperature testing matter.
Junction temperature, TJ−55 °C to +125 °C Absolute operating rangeDesign for margin below 125 °C at worst-case ambient, input, load, and component tolerance.
Storage temperature, TSTG−55 °C to +150 °C Absolute storage rangeThis is not the allowable powered junction-temperature range.
Package / polaritySMA, JEDEC DO-214AC; cathode identified by a band Manufacturer package identificationVerify the physical package and land pattern before PCB release because the project metadata currently says SMC. Individual land dimensions and pitch were not verified in this guide.
2. Pinout & Connections
The device has two terminals and no standardized connector pitch. The Flux symbol convention is pin 1 = K and pin 2 = A; the manufacturer documentation identifies polarity by the cathode band rather than a numbered pinout.

Table

Pin NumberPin NameDescriptionBest Practice
1K (Cathode)Banded terminal; connects toward the more-positive side in ordinary forward conduction. Confirm the band orientation on the received component and match it to PCB silkscreen and assembly drawings. In a buck catch-diode circuit, connect K to SW.
2A (Anode)Unbanded terminal; conventional current enters here during forward conduction.In a buck catch-diode circuit, connect A to power ground using a short, low-inductance path. For series reverse-polarity protection, connect VIN to A and protected VIN to K.
3. Standard Application Circuit
Asynchronous buck-converter catch diode
Text
Switch: VIN → SW
Inductor L: SW → VOUT
SS54: K (cathode) → SW; A (anode) → GND
CIN: VIN → GND
COUT: VOUT → GND
Connect the SS54 anode to power ground and cathode to the SW node. Place CIN from VIN to power ground near the switch, and place COUT from VOUT to ground near the inductor/load return. Inductor and capacitor values are selected from the converter/controller requirements; there is no universal capacitor or inductor value for the SS54.
For an ideal continuous-conduction-mode buck converter, use ID(avg) ≈ IOUT × (1 − D) and ID(peak) ≈ IOUT + ΔIL/2 as first-pass engineering estimates. Check average current, peak current, startup/fault surge, reverse voltage including ringing, and temperature; estimate conduction loss with Pcond ≈ ID(avg) × VF, then add reverse-leakage and switching-related losses where significant.
A simpler reverse-polarity connection is VIN → A | SS54 | K → protected VIN; no mandatory series resistor is inherent to that topology. Its trade-off is the diode's forward-voltage drop and power dissipation during normal operation.
4. PCB Layout & Routing Guidelines
  • Keep the high-di/dt commutation loop—switch, SS54, and input bypass capacitor—as physically small as practical; place the diode next to the switch and power-ground return.
  • Use wide copper pours sized from copper weight, allowable temperature rise, current waveform, and manufacturing constraints; avoid narrow neck-downs and high-current thermal-relief spokes at the diode pads.
  • Control SW-node copper area: make it large enough for current and heat, but no larger than necessary because it is electrically noisy. Prefer heat spreading on quieter anode/ground copper where the topology allows.
  • Place controller and power-stage bypass capacitors at their relevant current loops, not merely somewhere on the same net, and keep sensitive feedback or analog traces away from SW.
  • Verify the manufacturer SMA drawing and the actual library footprint before fabrication. This guide did not verify pad dimensions, and the project's SMC package property conflicts with the manufacturer SMA identification.
5. Common Pitfalls / Things to Watch Out For
  1. Treating 5 A as a guaranteed continuous PCB current. The rating depends on stated conditions, while the reference 60 °C/W value uses very large copper pad areas; calculate loss and validate junction temperature on the real board.
  2. Using the wrong footprint or polarity. The manufacturer specifies SMA (DO-214AC) with a cathode band, but this library project presently reports an SMC package property; verify the land pattern, body size, band marking, and pin mapping before release.
6. Popular Alternatives & Equivalents

Table

PartVerified characteristicsCompatibility
Diodes Incorporated B540C-13-F5 A, 40 V Schottky rectifier ; VF is 0.475 V typical and 0.55 V maximum at 5 A and 25 °C .Functional electrical alternative, not a footprint drop-in. It uses an SMC package and is supplied 3000 per reel. Confirm polarity, footprint, thermal behavior, and purchasing suffix.
Diodes Incorporated B550C5 A, 50 V member of the same B520C–B560C Schottky series. Higher-voltage functional alternative, not a footprint drop-in. It is an SMC-series device, so do not place it on an SMA land pattern without a documented footprint change. No Flux library part was verified for this exact ordering code.
Even when voltage and current ratings match, an alternative is not automatically equivalent. Compare package/land pattern, VF across temperature and current, leakage at hot, capacitance, surge conditions, thermal test conditions, qualification level, and tape/reel suffix.
7. Sourcing & Purchasing Guide

Table

AttributeDetails
Primary DistributorsLCSC lists MDD SS54 as C22452 in SMA packaging. DigiKey publishes an MDD SS54 ordering-variant document, but exact suffix, stock, distributor authorization, and package identity must be confirmed at purchase time.
Packaging OptionsMDD's product page lists 5000 pieces per reel. Distributor-cut quantities or alternate reels may exist; do not confuse the manufacturer full-reel quantity with distributor MOQ.
Standard MOQLCSC listed MOQ 10 pieces with order multiples of 10 when checked on 2026-10-06. MOQ and availability can change without notice. MDD's 5000-piece reel quantity is packaging, not necessarily the distributor MOQ.
Sourcing AdvicePrefer the manufacturer or manufacturer-franchised distributors when reliability matters; verify authorization rather than assuming it. Non-authorized marketplaces carry increased counterfeit and re-marked-stock risk. Match manufacturer, MPN, package, polarity marking, and ordering suffix; inspect incoming reels and retain lot traceability. Before production, resolve the SMA-versus-SMC project metadata mismatch and compare the actual footprint to the manufacturer's package drawing.
Sources

  • 1. Quick Specifications

  • 2. Pinout & Connections

  • 3. Standard Application Circuit

  • Asynchronous buck-converter catch diode

  • 4. PCB Layout & Routing Guidelines

  • 5. Common Pitfalls / Things to Watch Out For

  • 6. Popular Alternatives & Equivalents

  • 7. Sourcing & Purchasing Guide

  • Sources