GreenPAK MOSFET Driving: High-Side, Low-Side, and Bridge Switching

MOSFET switching circuits appear in a wide range of electronic systems, including DC-DC converters, motor drivers, power distribution switches, and actuator controls. These systems commonly use low-side switches, high-side switches, half-bridges, and full H-bridges to regulate power delivery to loads.

Although MOSFETs perform the actual power switching, additional circuitry is usually required to generate control signals and enforce safe switching behavior. In many designs, these functions can be implemented with a small programmable mixed-signal processor that combines configurable digital logic, timing elements, and analog monitoring functions to manage switching control and basic protection.

Programmable Control Logic in MOSFET Switching

Many switching circuits are tailor-made for specific topologies with fixed PWM control, complementary outputs, fault handling, and timing control features. Some designers add flexibility with discrete logic, while others use a microcontroller plus analog support circuitry. There are also some integrated gate drive controllers available, but they are only for a single topology with limited control over other features.

A programmable mixed-signal processor offers gate driving with adaptability, but without the footprint of added parts bolted onto a typical gate drive IC. It can be used as a configurable gate driver that provides control over switching behavior, can be reconfigured for a new topology, and allows additional monitoring and control features.

Typical functions that can be implemented include:

• PWM generation
• Enable and shutdown logic
• Dead-time insertion
• Complementary output generation
• Overcurrent trip logic
• Undervoltage monitoring
• Timed restart or fault latching

Low-Side and High-Side MOSFET Switching

In most applications, switching is performed with a positive gate voltage, which will impact how MOSFETs are hooked up in high-side or low-side switching circuits.

Low-side switching places the MOSFET between the load and ground and is normally used when logic-level gate control is required. A pull-down resistor sets the source-side reference so that VGS will always be positive.

High-side switching places the MOSFET between the supply rail and the load. This configuration holds the source HIGH such that the MOSFET will be OFF when there is no gate voltage signal applied.

In both instances, a programmable mixed-signal processor could generate the control signal for either configuration, as well as implement monitoring features on the load, monitor the supply voltage, and allow for configurable switching and control loop implementation. In many systems, the processor also implements protection features such as overcurrent shutdown or supply monitoring. The processor output may drive the MOSFET gate directly in low-power designs or interface with a gate driver stage in higher current systems.

Low-side switching is usually the simplest solution and is widely used when the load can tolerate switching on the ground return path. When faster switching, higher-current switching, and GaN/SiC is used, low-side with an NMOS is the only option for switching.

Half-Bridge and Full-Bridge Control

Half-bridge brings together low-side and high-side switching into the same leg, i.e., in a push-pull configuration. This is often used when higher currents are needed as it effectively reduces the ON time for each MOSFET and spreads the switching losses across the two components.

Full-bridge uses four MOSFETs (or two half-bridges) driving ON at each instant. These enable distribution of switching stress across two MOSFETs at a time. The full-bridge is often used when high currents are needed or when operating at high voltages (or both), or when bidirectional/polarity-reversing load current is needed.

In DC/DC converters, inverters, actuators, and motor drivers, both topologies require some sense and control mechanism to manage current flow in each leg of the system. The control problem is more complicated because the system must manage direction selection as well as shoot-through prevention in each bridge leg. Only valid conduction states should be allowed, and switching transitions must be sequenced carefully.

A programmable mixed-signal processor can simplify this by implementing the state control logic for the bridge alongside analog sensing for power delivery or other diagnostics needed to understand system reliability. Direction inputs can be filtered and combined with PWM gating so that the correct diagonal pair of MOSFETs is driven while invalid states are blocked.

For H-bridge control, the processor may handle multiple features:

• Forward and reverse state decoding
• PWM gating of the active switch pair
• Dead-time insertion on each leg
• Overcurrent shutdown and retry timing

Protection and Monitoring Functions

One reason mixed-signal processors fit well in switching systems is that they can combine logic and analog control in one component, but with both feature sets being programmable. Many MOSFET stages need at least one or two protective functions, and these can easily be added to a mixed-signal processor without extra circuitry.

Common protection and monitoring functions implemented in a programmable mixed-signal processor include:

• Overcurrent detection from a shunt resistor
• Undervoltage lockout
• Overtemperature input from a sensor or comparator
• Fault latching until reset
• Blanking time to ignore switching transients
• Timed auto-retry or auto-start after a fault

These functions are often just as important as the gate waveform itself. In real hardware, a switching stage that operates correctly during normal conditions but lacks controlled fault response is incomplete.

The benefit of a mixed-signal processor is not just the capacity to customize a gate drive stage for these switching topologies. Custom logic can be instantiated in mixed-signal processor macro cells so that unique features can be implemented. These features would typically necessitate an additional analog-to-digital converter pin and/or more general-purpose input/output pins on the microcontroller. However, with additional general-purpose input/output pins and a customizable analog front end in a mixed-signal processor, these functions can be instantiated directly without adding additional chips or using pins on a microcontroller.

Renesas GreenPAK allows designers to create reconfigurable gate drives featuring integrated sensing, protection, and status functionalities. By combining CPLD-like custom digital logic with fully customizable analog circuitry in one programmable component, GreenPAK enables advanced gate drive control. The Go Configure Software Hub assists designers in configuring logic, customizing the pinout, and developing an integrated analog front-end.

To learn more, take a look at the GreenPAK components and reference examples.

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