Power dissipation and heat generation in MOSFETsare critical considerationsin high-frequency switching since excess heat impacts system reliability and lifespan. Moreover, MOSFETs often exhibit high on-resistance, resulting in conduction losses and lower efficiency. These limitations pose significant obstacles in the design of power-efficient, compact devices, hence the need for advanced MOSFET solutions.
P-channel vs. N-channel
The primary difference between P-channel and N-channel MOSFETs lies in the type of charge carriersthat constitute the currentflow. The mobility of holes (the charge carriers in P-channel MOSFETs) is lower than that of electrons (the charge carriers in N-channel MOSFETs).This results in P-channel MOSFETs having higher on-resistances and lower current capabilities compared to N-channel MOSFETs of similar size and construction.
In terms of switching operations, P-channel MOSFETs typically used for high-side switching are turned on by applying a negative voltage to the gate relativeto the source. Conversely, N-channel MOSFETs adopted for low-side switching require a positive gate-source voltage to turn on. Despite slower switching speeds compared to N-channel devices, P-channel types offer the convenienceof driving the gate with a lower voltage in high-side configurations. This is advantageous in applications where circuit complexity and voltage levels make N-channel high-side drive impractical without additional circuitry.
Complementary use
Complementary P-channel and N-channel MOSFETuse is beneficial in power management circuits such as H-bridges for motor control— P-channel MOSFETs are used in high-side and N-channel types in low-side switches. This complementary action enables bi-directional control.
Figure 1 compares Nch+Nch (two N-channel) and Nch+Pch (N-channel and P-channel) architectures using pre- drivers for motor control.
The bootstrap circuit uses an Nch+Nch configuration to provide the higher voltage needed for the gate drive of the high-side N-channel MOSFET. It requires an external diode and capacitor, which increases component count and circuit complexity. Similarly, the charge pump circuit, also in an Nch+Nch setup, needs two external capacitors to provide high voltage. The result is a more complex circuit that can introduce additional system noise.
In contrast, a Nch+Pch configuration needs no additional components asthe P-channel MOSFETcan be driven at a lower voltage, simplifying gate drive requirements. This reduction in component count lowers cost and minimizes PCB area. Moreover, the Nch+Pch configuration produces lower switching noise, and fewer components reduce failure risks and decrease parasitic inductance and capacitance.
ROHM’s next-genP-channel MOSFETsROHM has developed a broad range of low on-resistance, 12-48V input P-channel MOSFETs. Using ROHM’s proven architecture, these products achieve the lowest RON per unit area in their class. Quality is also improved by optimizing the device structure to mitigate electric field concentration. As a result, both high reliability and low RON (which are typicallyin a trade-off relationship)are achieved. Key benefits include the following:
High Current Capabilityand Reduced RON:ROHM’s P-channel MOSFETs deliver high current capability coupled with low RON (up to 62% lower than conventional MOSFETs), allowing miniaturization without compromising performance. Lower RON translates to reduced conduction losses, making these MOSFETs suitable fora variety of applications.
Energy efficiency: Industry- leading low on-resistance and optimized gate characteristics allow ROHM’s P-channel MOSFETs to reduce switching losses, improving overall system efficiency. Thisis especially important in applications with stringent energy requirements.
Improved thermal performance: ROHM P-channel MOSFETs exhibit improved thermal performance due totheir lower RON and heat dissipating DFN packaging. This mitigates the risk of overheating, extending reliability and lifespan.
Reduced complexity and cost: ROHM P-channel MOSFETs can be driven at a lower voltage than N-channel types, simplifying gate drive requirements and avoiding extra circuitry. Their small form factor lowers material costs while minimizingthe need for additional thermal management. Furthermore, the increased reliability and lifespanof devices incorporating these MOSFETs can help reduce maintenance and replacement costs.
Applications
These devices target a wide range of applications, including the following:
EV charging: ROHM P-channel MOSFETs provide efficient, reliable, and safe switching capabilities for electric vehicle charging. They deliver simplified gatedriver and protection features in a compact form factor.As a load switch, the MOSFET is responsible for controlling the connection and disconnection of the load (EV battery) to the power source. P-channel MOSFETs have the inherent ability to be driven by lower gate voltages in relation to the source, simplifying gate drive circuitry and reducing power consumption.
In the high side configuration, the MOSFET—placed between the power source and load—Is used to switch the power flow on and off. Here, P-channel MOSFETs are beneficial since complex gate-driver circuits—often required by N-channel MOSFETs—are unnecessary.
Industrial AC/DC converters: ROHM MOSFETs help maintain isolation between different voltage domains— essential for safety and noise reduction. Devices are offered in compact packages, suiting densely-populated PCBs in industrial converters.
When used in the high side, the sourceis connected to a positive voltage, andthe MOSFET turns off if the polarity is reversed, preventing circuit damage. The device can be driven directly from a control IC without the need for a charge pumpor voltage higher than the supply voltage that is required for N-channel MOSFETs in high side configurations. ROHM’s P-channel MOSFETs are designed to offer low on-resistance, which translates to lower conduction losses in the On state, improving converter efficiency. In load switch applications, the load canbe turned on or off without complex circuitry, and it can be controlled by logic level voltages directly from an MCU.
Consumer electronics: In appliances, ROHM P-channel MOSFETs enable efficient power management and integration with MCUs. Unlike N-channel types, P-channel MOSFETs can be turned on ata lower gate voltage, simplifying gate drive circuitry and reducing component count.
In load switching applications—in a washing machine, for example—ROHM’s P-channel MOSFETs are used to control the power to specific parts of the machinesuch as the drum or water pump. This contributes to modular system design and saves power when certain machine functions are idle. If a fault situation occurs, these products disconnect load and supply, preventing damage.
High side switches also control the power flow, and the fast-switching speeds of ROHM’s P-channel MOSFETs enable the precise control necessary for temperature regulation, water levels etc. Moreover, their low on-resistance ensures minimal power loss and heat generation. In the washing machine example, ROHM MOSFETs are used on the high side of the H-bridge to control the direction and speed of the motor.
