Diodes Incorporated Releases New MOSFET Driver for Synchronous Rectification

February 10, 2020 by Gary Elinoff

The APR348 supports secondary-side output voltages up to 20 V in QR, CCM, and DCM flyback modes.

The APR348 from Diodes Incorporated is designed to drive external MOSFETs in a wide range of secondary-side synchronous-rectifier applications. It is applicable to both high-side and low-side implementations.



The APR348 MOSFET driver. Image used courtesy of Diodes Incorporated

The highly integrated nature of this secondary-side MOSFET driver means that engineers will need few additional components for their designs.

The APR348 is aimed at 5 V to 20 V power converters used in a wide variety of portable, consumer, and home automation devices. It will also serve in USB power delivery (PD) and rapid charging applications.


What is Synchronous Rectification?

Synchronous rectification, also known as active rectification, is aimed at increasing the efficiency of rectification. It does so by eschewing diodes and substituting actively-controlled switches, such as MOSFETs. A MOSFET's turn-on time is determined by monitoring its drain-to-source voltage.


Typical applications circuit for APR348

The APR348 will serve in both high-side and low-side. Image used courtesy of Diodes Incorporated


Semiconductor diodes all feature unavoidable voltage drops in the range of a volt or so. MOSFETs, on the other hand, behave as resistances. When conducting, that resistance, RDS(ON), is very low, which can result in a far lower voltage drop and less wasted power.


APR348 Capabilities

The APR348 can support continuous mode (CCM), discontinuous conduction mode (DCM), or quasi-resonant flyback (QR) modes. Operations are based on a MOSFET's on-time control technology, which allows fast turn-on and turn-off delay. This also serves to reduce power losses and to maintain safe operating conditions while requiring few external components or circuitry.

The maximum VCC is 28 V.


Block diagram of APR348

APR348 block diagram. Image used courtesy of Diodes Incorporated


The minimum turn-on period is set via a featured blanking period. The blanking period limits the effects of voltage ringing, thereby improving performance. Typical turn-on delay time and turn-off propagation delay times are 30 ns and 25 ns, respectively.

The APR348 features a light load (LL) mode, which allows for cycles to be skipped when there is either no output load or only a light load. Because of this important capability, the unit can consume lower standby power at no load. In addition, high-side switching does not require an additional transformer winding, further minimizing the bill of materials cost.

The unit also features under-voltage lockout (UVLO) protection.


Physical Considerations

The APR348 has an operating temperature range of -40℃ to +85℃. The unit is completely lead-free and is fully RoHS compliant. As a “green” device, it is also halogen- and antimony-free.

For automotive applications, the device has been AEC-Q100 qualified and PAPP approved. It can also be manufactured in IATF16949:2016-certified facilities.

The APR348 is available in SOT26 (Type CJ) package with maximum dimensions of 3.02 mm by 2.95 mm.


Around the Industry

Power efficiency is a vital aspect of today’s product design, and Diodes Incorporated has a lot of competition in this highly-active field.

The LT8309 from Analog Devices is a secondary-side synchronous rectifier driver that supports VCC's ranging from 4.5 V to 40 V. The unit features a 26 ns turn-off propagation delay.

ON Semiconductor offers the NCP81178, a secondary-side synchronous rectifier driver designed for isolated power converters. Its VIN/VCC range is from 4.5 V to 14 V. The unit features a 12 ns rise time and a 10 ns fall time with a VCC of 6 V.