16 POWER SEMICONDUCTORS www.littelfuse.com Issue 2 2024 Power Electronics Europe www.power-mag.com design effort and space usage. When a pchannel MOSFET serves as the HS switch in this configuration, as shown in Figure 3b, it can significantly simplify the driver design. The designer could remove the charge pump to drive the HS switch, and the MCU can easily control the p-channel MOSFET through a simple level shifter. This approach reduces design effort and part count, resulting in a cost-efficient design that utilizes space efficiently. Reverse Polarity Protection Reverse polarity protection is a system safety measure to prevent potential fire hazards and damage in case of a reversed power source connection. Figure 4a depicts the reverse polarity protection implemented using a p-channel power MOSFET. When the battery is correctly connected, the intrinsic body diode conducts until the MOSFET channel is activated. In the event of a reverse connection of the battery, the body diode is reverse-biased, with the gate and source at the same potential, thereby turning off the p-channel MOSFET. A Zener diode clamps the gate voltage of the p-channel MOSFET, safeguarding it in case of excessively high voltage levels. Load Switching Load switches connect or disconnect a voltage rail to a specific load, offering a costeffective and straightforward way for a system to manage power efficiently. Figure 4b illustrates a circuit using a p-channel power MOSFET for a load switch. This circuit is driven by a logic enable (EN) signal to control the p-channel load switch via a smallsignal n-channel MOSFET Q1. When EN is low, Q1 is off, and the p-channel gate is pulled up to VBAT. Conversely, when EN is high, Q1 activates, grounding the p-channel gate, and turning on the load switch. If VBAT exceeds the p-channel MOSFET’s threshold voltage, it can turn on when EN is high, eliminating the need for an additional voltage source to bias the gate, which is necessary for n-channel MOSFETs. The series resistor is needed to limit the current, and a Zener Diode is required in order to clamp the gate voltage to a maximum value. DC-DC Synchronous Buck and Boost Converters In low-power DC-DC converters like the synchronous buck converter in Figure 5a, using a p-channel device as the HS switch simplifies the circuit and saves space, eliminating the need for external gate driving circuitry. It also reduces the bill-ofmaterials (BOM), leading to cost efficiency. Similarly, a P-channel device can replace a diode with low forward voltage as an output synchronous rectifier in synchronous boost converters, as seen in Figure 5b. This approach improves the converter efficiency due to the improved figure-of-merit (FoM = RDS(on) * Qg) of the p-channel MOSFET. P-Channel MOSFETs in Low-Voltage Applications As today’s low-voltage (LV) applications advance, the Littelfuse p-channel MOSFETs continue proving their versatility in meeting the evolving needs of tomorrow’s power electronics. Employing p-channel MOSFETs enables designers to provide simplified, highly reliable, and optimized circuit design in advanced automotive and industrial applications. Electronics design engineers must evaluate the trade-off between RDS(on) and Qg when selecting a pchannel MOSFET to achieve optimal performance for specific applications. This article is co-authored by Sachin Shridhar Paradkar, Raymon Zhou, and José Padilla of Littelfuse, Inc. Figure 4. Using p-channel power MOSFET for a) reverse polarity protection and b) load switching. Figure 5. Using complementary MOSFETs for low power a) synchronous buck and b) synchronous boost converter. To receive your own copy of Power Electronics Europe subscribe today at: www.power-mag.com
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