■ Key criteria engineers should consider when selecting the right gate driver IC for their application

The half-bridge topology is widely used for power conversion in a variety of commercial and industrial applications. The gate driver IC is the heart of this switch mode configuration, and its main function is to receive a pulse-width modulated (PWM) signal and provide a clean, level-shifted signal to the MOSFET power switches so that the high-side and low-side MOSFETs can operate with optimum efficiency and high stability.

This article explores the key criteria engineers must consider when selecting the right gate driver IC for their application. In addition to the required voltage and current ratings, we will explore the importance of high common-mode transient immunity (CMTI) and the need for variable dead time. In high-voltage power systems, some use cases require the ability to electrically isolate the gate driver IC from the MOSFET, and this floating ground method is described along with a simple reference design.

■ Minimizing loss during power conversion

Power conversion is a key function in almost every electronic device design today. Ideally, any conversion from one DC voltage to another, say 9 V to 24 V, should be as efficient as possible with minimal losses. To accommodate different voltage, current requirements, and power densities, a variety of circuit architectures, or topologies, are available for a variety of applications. For DC-DC power conversion, these include buck, boost, buck-boost, half-bridge, and full-bridge topologies. Another consideration is whether the output needs to be electrically isolated from the input voltage, which leads to the distinction between non-isolated and isolated conversion methods.

For high-voltage, high-current applications such as motor control and solar inverters, half-bridge and full-bridge DC-DC conversion techniques are commonly used.

■ Half-bridge power conversion

The half-bridge configuration uses a switch-mode method to increase or decrease the DC input voltage. This method uses two switching devices, typically MOSFETs or insulated gate bipolar transistors (IGBTs), to switch the input voltage either through a transformer (isolated mode) or directly to the load (non-isolated mode). The gate driver IC receives a pulse-width modulated (PWM) signal from the controller IC. This IC amplifies and shifts the signal to the level necessary to quickly turn the MOSFET power switches (high side and low side) on or off, thereby minimizing power loss and improving converter efficiency. Selecting the right gate driver IC for an application depends on factors such as the converter topology used, voltage, current ratings, and switching frequency. Selecting a gate driver with accurate and efficient switching characteristics is essential to achieving optimal conversion efficiency.

■ Gate Driver IC Selection

When selecting a gate driver IC, engineers must consider several key criteria, some of which may vary depending on the application. For example, in a solar energy conversion application, the gate driver must be capable of handling a wide range of input voltage and power requirements.

- High-side voltage: Depending on the application, the high-side MOSFET may need to accept the full supply voltage, so the gate driver must be able to handle this with a sufficiently high level of safety margin.

- Common-mode transient immunity (CMTI): It is important to select a gate driver with high transient immunity characteristics to protect the control section connected to low power from noise generated by power switches that switch at high speeds in high-voltage systems.

- Peak Drive Current: For high-power designs, the gate driver must supply high peak current to the MOSFET to quickly charge and discharge the gate capacitance.

- Dead Time: To avoid shoot-through in the MOSFET when both the high and low sides of the MOSFET are conducting simultaneously, it is an important characteristic of all half-bridge circuits to establish a short dead-time period between the high and low side switching. For dual-channel gate driver ICs that drive half-bridge circuits with a single IC, it is recommended to select a gate driver with variable dead time to achieve optimal efficiency. Some gate drivers have a built-in default dead time to prevent shoot-through.

■ Half-bridge driver with floating ground and variable dead time

The LTC7063 is one of the half-bridge gate drivers suitable for a wide range of high voltage and high current applications. The LTC7063 is suitable for a variety of industrial, automotive and telecommunications power systems. This device is a high voltage gate driver designed to drive N-channel MOSFETs in a half-bridge configuration with input supply voltages up to 140V. This IC provides powerful capabilities to rapidly charge and discharge the large gate capacitances typically associated with high voltage MOSFETs. It also features adaptive shoot-through protection that monitors the voltage of the switching node and controls the driver output to prevent the MOSFETs from conducting simultaneously. This important feature helps to block the possibility of shoot-through current and improve power efficiency.

The LTC7063's high-side and low-side MOSFET drivers are both floating, allowing up to 10V of ground offset between the IC and output ground. This floating architecture makes the driver outputs more robust and less sensitive to ground offset, noise and transients. This floating ground feature makes the LTC7063 an excellent choice for remote MOSFET control applications and high voltage, high current switched capacitor converters.

Safety and protection features of the LTC7063 include thermal shutdown, input undervoltage and overvoltage lockout circuits, and undervoltage lockout circuits on both the high side and low side MOSFET drivers. These features ensure long-term reliability and robustness for all half-bridge applications.

For efficient heat transfer, this gate driver is offered in a thermally enhanced exposed pad package.

■ LTC7063-based step-down converter application with remote load

Figure 1 shows a 2:1 step-down converter design with a remote load using the LTC7063. The converter operates from an input supply of up to 80 V and supplies ½ VIN to a load of up to 5 A. The PWM pin receives a 3-state logic signal from an external controller. When the PWM signal rises above the rising threshold, the gate of the high-side MOSFET is driven high. The low-side MOSFET is driven complementarily to the high-side MOSFET. The hysteresis between the rising and falling thresholds of the input signal eliminates false triggering of the MOSFETs. Both the high-side and low-side MOSFETs are low during the hysteresis portion of the input signal. When the enable (EN) pin is high, both the high-gate (TG) and low-gate (BG) outputs respond to the input PWM signal, and when the EN pin is driven low, both the TG and BG outputs are low.


Bootstrapping the BST-SW and BGVCC-BGRTN supplies allows efficient high-side and low-side driver operation without additional isolated supply voltages, reducing both cost and board component count. This control waveform and average output voltage results can be seen in Figure 2.


The dead time between TG and BG is short, and the dead time between BG/TG can be increased by adding a resistor between the DT pin and ground. Shorting the dead time (DT) pin to ground creates a default dead time of 32 ns for this transition, and floating the DT pin increases the dead time up to 250 ns. This variable dead time feature ensures more robust shoot-through protection for high-voltage applications.

To achieve high efficiency, it is important to minimize switching losses. The 1.5Ω pull-up resistor and 0.8Ω pull-down resistor on the high-side and low-side MOSFET drivers turn the switches on and off quickly, preventing any cross-conduction current, thus improving efficiency. Figures 3 and 4 show the switching transition between turn-on and turn-off, along with the dead time.



The Fault (FLT) pin is an open-drain output and is internally pulled low when the junction temperature of the LTC7063 reaches 180°C. This pin also goes low whenever the VCC supply voltage is less than 5.3 V or greater than 14.6 V. For the application shown in Figure 1, a fault condition is triggered when the BGVCC-BGRTN and BST-SW float voltages are less than 3.3 V and the FLT pin goes low. When all faults have cleared, the FLT pin is pulled high via an external resistor after a 100μs delay.

Table 1 shows several members of the LTC706x family that have similar features to the LTC7063.


■ LTC7063, Fast Switching and High Efficiency in High Voltage and High Current DC-DC Applications

The LTC7063 is a high voltage N-channel half-bridge gate driver and a member of the LTC706x family. The device’s unique dual floating ground architecture provides efficient driver outputs for ground offset and remote load applications, while providing high noise immunity. Adaptive shoot-through protection and variable dead-time functionality eliminate any potential shoot-through current, and powerful MOSFET drivers minimize power loss by enabling fast switching and high efficiency in high-voltage, high-current DC-DC applications.


※ About the author
Srikesh Pulluri joined Analog Devices in 2023 as a Product Applications Engineer, working in the Industrial Power Systems team on power solutions including half-bridge gate drivers and 4-switch buck-boost topologies. He holds a bachelor’s degree in electrical engineering from Osmania University, India, and an master’s degree in electrical engineering from the University of Colorado, Boulder.