NCP4308DDR2G - 35V Synchronous Rectifier Controller | onsemi
MPN: NCP4308DDR2G ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.8493 | $0.85 |
| 10 | $0.8493 | $8.49 |
| 100 | $0.8493 | $84.93 |
| 500 | $0.8493 | $424.65 |
| 1,000 | $0.8493 | $849.30 |
NCP4308DDR2G Overview
A synchronous rectifier controller is a power-management semiconductor that drives an external MOSFET on the secondary side of an isolated or non-isolated switching converter. By replacing diode conduction with low-loss MOSFET switching, it can reduce power loss during output-current transfer. The NCP4308 family belongs to the secondary-side controller, power-management IC, and switch-mode power-supply hierarchy.
Key features include externally adjustable minimum off-time and on-time blanking periods, operation across discontinuous-conduction, continuous-conduction, and quasi-resonant flyback modes, and a 1 MHz switching-frequency capability. The controller is designed to provide reliable and low-noise operation of the synchronous-rectifier system while allowing the power stage to be tailored to the transformer, MOSFET, and PCB layout.
The NCP4308 architecture coordinates gate timing with the secondary-side waveform. The adjustable timing features help prevent premature MOSFET turn-on or turn-off during ringing and transition intervals. Designers must still validate the timing window against the actual transformer reset behavior, MOSFET gate charge, leakage current, and operating frequency rather than treating the timing values as universal constants.
Typical uses include AC-DC adapters, offline power supplies, flyback converters, quasi-resonant flyback converters, LLC converters, USB power supplies, and industrial power modules. In each case, the controller is paired with external synchronous-rectifier MOSFETs rather than acting as the primary-side converter controller.
A key design consideration is maintaining adequate separation between the controller and high-current secondary-side switching nodes. Use the manufacturer’s recommended layout, minimize gate-loop area, place timing components close to their pins, and verify dead time, ringing, and cross-conduction behavior with an oscilloscope across the full input and load range.
Drop-in alternatives for NCP4308DDR2G — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
NCP4308AMTTWG
✅ Drop-In📋 Reference alternative (not in catalog)
NCP4308DDR2G Maximum Ratings & Electrical Characteristics
| Product Type | Secondary-side synchronous rectifier controller |
| Operating Voltage Range | 4 V to 35 V |
| Switching Frequency | 1 MHz |
| Current Rating | 8 A |
| Quiescent Current | 2 mA |
| Propagation Delay | 12 ns |
| Minimum Off-Time | 50 ns |
| Adjustable On-Time Blanking | 245 ns |
| Input Voltage Minimum | 4 V |
| Input Voltage Maximum | 35 V |
| Operating Temperature Range | -40 °C to +125 °C |
| Supported Operating Modes | DCM, CCM, and quasi-resonant flyback |
| Supported Power-Supply Topologies | Flyback, quasi-resonant flyback, and LLC |
| Package | SOIC-8 |
| Mounting Type | Surface mount |
| Moisture Sensitivity Level | MSL3 |
| RoHS Status | Compliant |
NCP4308DDR2G soic-8 Pin Configuration Guide
Pin configuration for NCP4308DDR2G (soic-8 package). This power device features gate, drain, and source terminals. For non-polarized packages, refer to the manufacturer datasheet for exact pin 1 orientation and footprint details. Common applications include power supply design, motor driving, and load switching.
No detailed pinout data available for NCP4308DDR2G.
Refer to the datasheet for full pin configuration.
Typical Applications
NCP4308DDR2G is suitable for 6 applications: AC-DC Flyback Adapter, Quasi-Resonant Flyback Converter, LLC Resonant Power Supply, USB Power Adapter, Industrial Power Module, Low-Voltage DC/DC Output Stage.
AC-DC Flyback Adapter
The NCP4308DDR2G fits the secondary side of an offline flyback adapter where a controller replaces a rectifier diode with externally controlled MOSFETs. Its 4 V to 35 V range covers a broad secondary-bias domain, while adjustable minimum off-time and on-time blanking help separate gate commands from switching-node ringing. The 1 MHz controller capability supports compact high-frequency designs, although the actual primary frequency is set elsewhere. Engineers should size the MOSFETs for the transformer current, verify dead time in DCM, CCM, and quasi-resonant transitions, and inspect efficiency at light and full load.
Recommended
Quasi-Resonant Flyback Converter
The NCP4308DDR2G is suited to quasi-resonant flyback converters because the verified family data identifies QR operation and adjustable blanking functions. Resonance can produce low-voltage and high-voltage intervals around the secondary waveform, so controlled MOSFET conduction must avoid false turn-on during ringing. Use the adjustable timing inputs to account for transformer leakage and MOSFET package characteristics. A useful design check is to capture gate-to-source voltage, drain voltage, and secondary current at startup, resonance transitions, and full load.
Recommended
LLC Resonant Power Supply
The NCP4308DDR2G can support secondary-side synchronous rectification in LLC converters, a topology explicitly listed by onsemi. LLC operation can have resonant current and transition intervals that differ substantially from conventional PWM, making adjustable blanking important. The controller’s 1 MHz capability and 4 V to 35 V operating range provide useful design bounds, but transformer turns ratio and MOSFET selection determine whether synchronous operation is efficient. Validate light-load behavior, burst or intermittent operation if used, and gate overlap before production.
Recommended
USB Power Adapter
The NCP4308DDR2G can be used in a secondary rectifier stage of a USB power adapter when low-voltage conduction loss is important. Replacing a Schottky or other rectifier with controlled MOSFETs can improve efficiency, but USB adapters may also use USB-PD or multi-output control functions that are not part of this IC. The synchronous rectifier must be coordinated with the converter’s secondary waveform and timing. Use low-inductance gate routing and verify cable transients, load steps, standby behavior, and fault shutdown at the adapter level.
Recommended
Industrial Power Module
The NCP4308DDR2G is appropriate for an industrial power module that needs a dedicated secondary-side synchronous-rectifier controller across multiple input or output conditions. Its listed operating-temperature range of -40 °C to +125 °C is relevant to industrial environments, although the external MOSFETs, transformer, magnetics, and enclosure determine the actual thermal margin. The 2 mA quiescent current can help with auxiliary-power budgeting. Validate the controller across worst-case line, load, temperature, and startup conditions rather than relying on nominal specifications.
Recommended
Low-Voltage DC/DC Output Stage
The NCP4308DDR2G can be evaluated in a low-voltage DC/DC output stage when the secondary rectifier current is substantial and diode loss becomes important. The controller’s synchronous operation may reduce rectification loss, but the benefit depends on MOSFET RDS(on), gate-drive overhead, body-diode behavior, and timing losses. Because the IC is a secondary-side controller, it must be paired with an appropriate transformer or converter arrangement. Measure efficiency at several loads and compare against a diode solution before committing the design.
Recommended
Engineering reference data for NCP4308DDR2G — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | NCP4308AMTTWG |
|---|---|---|
| Product Type | Secondary-side synchronous rectifier controller | NCP4308-family controller; exact product type details not supplied |
| Package | SOIC-8 | WDFN-8; package compatibility not confirmed |
| Brand | onsemi | onsemi |
Key Differentiators
- Supports flyback, quasi-resonant flyback, and LLC secondary rectification (vs NCP4308AMTTWG)
- Adjustable blanking supports flexible MOSFET package and layout options (vs NCP4308AMTTWG)
- Broad operating range for secondary bias (vs NCP4308AMTTWG)
- SOIC-8 package is confirmed for the DDR2G ordering code (vs NCP4308AMTTWG)
Design Notes
Keep the NCP4308DDR2G, its timing components, and the MOSFET gate-drive traces close together. Minimize gate-loop area and route the gate and source-return paths as a compact pair. Place supply bypassing at the controller pins and keep the controller ground connection away from the high-current secondary switching loop. Validate the physical layout against the onsemi datasheet recommendations before production.
Do not select the NCP4308DDR2G by its 8 A capability without checking the complete power stage. Transformer current, MOSFET RDS(on), body-diode behavior, gate charge, thermal rise, and layout inductance determine realistic output capability. Also verify that the adjustable blanking timing does not overlap the intended secondary conduction interval; incorrect timing can increase loss or create cross-conduction.
The controller IC is not the main thermal element in most designs; the synchronous MOSFETs and transformer usually dominate heat generation. Estimate MOSFET conduction loss from RDS(on), RMS current, and duty ratio, then include switching and body-diode loss where applicable. Provide copper area, thermal vias, and adequate package airflow according to the MOSFET datasheet and enclosure temperature.
Synchronous rectification can reduce diode loss but may increase high-frequency EMI when MOSFET gate transitions are fast or rings on the switching node. Use the smallest practical gate resistance, maintain short gate loops, and inspect drain-to-source ringing with a low-inductance probe. Adjust blanking and switching timing only after confirming that EMI and efficiency measurements use comparable test conditions.
Compliance Information
RoHS compliance is identified in the verified JLCPCB listing. The supplied data does not independently verify REACH, AEC-Q100, lead-free, halogen-free, or conflict-minerals status.
