SHIKUES MOSFET 65W PD Fast Charging Solution

SHIKUES SKG108N10AD: Addressing Five Fast Charging Design Challenges Through Synchronous Rectification

Delivering 65W while shrinking the enclosure creates a demanding design balance: substantial output-side current must be handled within very limited thermal space. In PD fast chargers, efficiency, temperature rise and power density are closely linked. Losses in the rectification stage can affect overall efficiency and increase localized thermal stress.

Illustrative fast charging circuit boards.

As controllers become more highly integrated, matching the external power devices remains equally important. How can a synchronous rectifier MOSFET be selected to balance conduction loss, gate-drive voltage, off-state stress and a compact layout?

The SHIKUES 65W PD solution uses the SKG108N10AD as its synchronous rectifier MOSFET. Its 100V rating, milliohm-level on-resistance, specifications at two gate-drive voltages and PDFN5×6 package provide a device-level approach to these design challenges.

Figure 1 | SHIKUES 65W PD synchronous rectification solution: matching the SKG108N10AD to loss, drive, voltage stress and thermal requirements.

Solution Architecture: Highly Integrated Control with External Synchronous Rectification

The SHIKUES 65W PD solution pairs the SC3107C controller with an external synchronous rectifier MOSFET. The SC3107C integrates the GaN switch, primary-side control, synchronous rectification control and protocol control into a single package, helping reduce the external circuitry needed to coordinate separate controllers. The external synchronous rectifier preserves flexibility in voltage rating, on-resistance and package selection.

The advantage of this architecture is to use highly integrated control to simplify the system, then optimize key loss mechanisms with a well-matched power device. The SKG108N10AD is used for output-side synchronous rectification. Its gate connects to SRG, its drain connects to the SRD sensing branch through a 51Ω resistor, and a series RC snubber comprising 1nF and 10Ω is connected between drain and source.

Control, sensing and the power device work together to enable synchronous rectification. The device's value lies both in its specifications and in how those specifications meet the actual circuit requirements.

Figure 2 | Functional architecture of the solution.

Figure 3 | Full SHIKUES 65W PD schematic, including the input, main power and control circuit, synchronous rectifier, interface and bulk capacitor modules.

Challenge 1: Rectification Loss Increases Thermal Stress in a Confined Space

Challenge

The fast charger's output stage handles pulsed current. Conduction loss in the synchronous rectifier MOSFET is proportional to the square of the RMS current. As current increases, even a difference of a few milliohms deserves attention in the loss budget. Focusing only on output power can overlook the rectifier's own heat generation.

Solution: Optimize the rectification path with milliohm-level on-resistance.

At VGS=10V, ID=40A and TJ=25°C, the SKG108N10AD has a typical on-resistance of 4.8mΩ and a maximum of 5.2mΩ. With adequate gate drive and appropriate control timing, this low-resistance channel provides a direct basis for reducing rectification conduction loss.

Using Pcond≈ISR,rms²×RDS(on), an RMS channel current of 6A over the full switching cycle and an on-resistance of 5.2mΩ give an estimated conduction loss of 0.187W.

Reducing conduction loss in the rectification stage helps lower the device's thermal load and supports the overall thermal design. Use the actual RMS channel current and account for gate voltage and temperature; average output current cannot be substituted directly.

Figure 4 | Calculated I²R curves using the two maximum room-temperature on-resistance values. Switching, body-diode and external-circuit losses are excluded.

Challenge 2: Will Low On-Resistance Be Achieved with the Actual Gate Drive?

Challenge

MOSFET on-resistance depends on gate-to-source voltage. Using only the 10V specification when the actual gate-drive voltage is lower may produce an overly optimistic loss estimate. Threshold voltage is also not a criterion for full enhancement.

Solution: Explicit specifications at 4.5V and 10V support gate-drive matching.

In addition to a maximum of 5.2mΩ at a 10V gate drive, the SKG108N10AD is specified at VGS=4.5V、ID=20A、TJ=25℃ with 7.0mΩ typical and 8.5mΩ maximum on-resistance.

These two specifications help engineers assess conduction performance at the actual VGS. For the SHIKUES 65W PD solution, use the SRG drive and the gate-to-source waveform measured at the device pins to select the appropriate on-resistance for loss calculations.

This turns the general benefit of low on-resistance into a specification tied to a defined drive condition.

Figure 5 | Key SKG108N10AD specifications, with the corresponding conditions for on-resistance, gate charge and thermal parameters.

Challenge 3: Why Does Rectifier Voltage Rating Matter at a Low Output Voltage?

Challenge

The off-state voltage across a flyback secondary rectifier is not simply the output voltage. The primary voltage reflected through the turns ratio, transformer leakage inductance and circuit parasitics all affect drain-to-source voltage and switching spikes. Selecting a voltage rating from the output voltage alone does not fully account for device stress.

Solution: Combine a 100V rating with sensing and an RC network for voltage-stress design.

The SKG108N10AD provides a 100V drain-to-source voltage rating as a basis for evaluating secondary rectifier off-state voltage and spikes. In the SHIKUES 65W PD circuit, the 1nF + 10Ω RC branch across drain and source provides a means of tuning ringing suppression, while the SRD branch provides the associated sensing connection.

Combining device voltage rating, switching sensing and external snubbing supports spike and ringing optimization. The actual voltage margin must still be verified against transformer parameters and VDS waveforms during input changes, startup and load changes.

The combination of a 100V rating and milliohm-level on-resistance allows the SKG108N10AD to address both off-state voltage stress and conduction-loss requirements.

Figure 6 | Redrawn synchronous rectification connections. The 51Ω resistor is in the sensing branch; the 10Ω resistor is in the RC snubber branch.

Figure 7 | Off-state voltage components and verification priorities. The waveform is qualitative, not an oscilloscope measurement.

Challenge 4: How Can Switching Behavior Be Optimized After Conduction Loss Is Reduced?

Challenge

Synchronous rectification involves more than conduction loss. Charging and discharging the gate requires drive energy, and the body diode may conduct briefly during switching transitions. Operating mode and commutation conditions also affect dynamic losses. Comparing RDS(on) alone is insufficient for device selection.

Solution: Use gate-charge and fast-recovery characteristics to assess dynamic matching.

The SKG108N10AD has typical Qg of 62nC and typical Qgd of 20nC, measured at VDD=50V, VGS=10V and ID=40A. These parameters support estimates of controller drive capability and gate-drive power consumption.

The device features a fast-recovery body diode. At IF=40A and di/dt=100A/μs, typical trr is 40ns and typical Qrr is 66nC. These parameters help evaluate commutation behavior and, together with drive timing, support optimization of body-diode conduction intervals and related losses.

For the SHIKUES 65W PD solution, on-resistance, gate charge and diode characteristics together form the basis for device selection.

Figure 8 | Resistive-load switching test arrangement and switching waveforms redrawn from the datasheet. Gate-charge and reverse-recovery parameters use their own test conditions and are not measured directly with the circuit on the left.

Challenge 5: The Device Fits, but Heat Is Difficult to Remove

Challenge

Compact chargers have limited space, so power loops, sensing traces and thermal copper areas must be coordinated. Focusing only on package size while overlooking the complete thermal path makes it difficult to translate low device losses into acceptable temperature rise.

Solution: Combine the PDFN5×6 package with board-level thermal-path design.

The SKG108N10AD uses a PDFN5×6 package with a junction-to-case thermal resistance of RθJC = 1.0°C/W. This compact power package supports pad and copper placement around the synchronous rectification loop. Thermal vias, optimized gate-drive return paths and sensing traces help address both electrical and thermal requirements.

Keep the power loop short, place the snubber close to the relevant switching nodes, and route sensing paths away from interference from high-dv/dt nodes. Because on-resistance increases with junction temperature, the thermal design must also account for temperature-dependent resistance.

Low device on-resistance helps reduce heat generation, while appropriate package and board design help conduct heat away. Together, they provide a more complete approach to compact fast charger design.

Figure 9 | PDFN5×6 pad functions and thermal path. The 1.0°C/W value refers only to junction-to-case thermal resistance, not junction-to-ambient thermal resistance.

Why Choose SKG108N10AD? Match Each Feature to a Design Requirement

The SHIKUES 65W PD solution combines highly integrated control with external synchronous rectification to support system simplification and efficiency optimization. The SKG108N10AD contributes a set of device characteristics matched to the application:

• Rectification loss: 5.2mΩ maximum at a 10V gate drive supports lower channel conduction loss.
• Gate-drive matching: 8.5mΩ maximum at a 4.5V gate drive enables assessment at the actual gate voltage.
• Off-state stress: A 100V rating supports voltage design for secondary-side rectification.
• Dynamic behavior: Defined Qg, Qgd, trr and Qrr parameters support gate-drive and commutation analysis.
• Compact implementation: The PDFN5×6 package supports power-loop layout and complete thermal-path design.

Figure 10 | Build a traceable selection rationale from application requirements to device parameters, circuit matching and verification.

From reducing rectification loss and matching drive and control to managing voltage stress and heat, the SKG108N10AD provides defined device capabilities for the SHIKUES 65W PD fast charging solution. For power designs targeting high efficiency and compact layouts, the key is to connect every parameter to an actual design requirement.

SHIKUES SKG108N10AD: A 100V rating and milliohm-level on-resistance to support synchronous rectification optimization in 65W PD fast chargers.

For further evaluation, refer to the SKG108N10AD datasheet and select the device with reference to actual gate-drive, voltage-stress and temperature-rise conditions.

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