The logic and internal voltage reference circuits are powered by the AVDD voltage supply. The VDD1 is the internal level translator power supply. AVDD and VDD1 are connected to the same voltage as the VDD2. This voltage rail on the
demoboard is called VNF and is referenced to VNN. It should be between 9 – 12V. The voltage should be selected according to the size of the power MOSFETs, gate threshold, and PWM frequency of the class-D amplifier.

The post MD7120 Class-D Audio Amplifier Design appeared first on Amplifier Circuit Design.

This is the circuit design of Class-D power audio amplifier using IC MD7120 as MOSFET driver. The MD7120 used to drive four N- channel MOSFET Transistors that operate on both sides of the H-bridge switches. It consists of controller Logic circuits, level translators, two bootstrap powered high-side Gate drivers, two VDD powered low-side Gate drivers, and over current protection circuits (without using a current-sensing resistor). The over current protection thresholds for both the high and low side are separately resistor-programmable.

The MD7120 is designed to drive 3.0A, fast switching MOSFETs with well-matched input to output propagation delay between the high-side and the low-side, as well as from channel A to channel B. The circuit uses the direct-coupling method in its internal level translators, from logic inputs to the gates of the N-channel power MOSFETs.

The MD7120 input logic voltage can be set to any voltage between 1.8 and 5.0V by connecting the EN pin H logic voltage level at the same level as the switching control inputs. The internal EN pin circuit will compute the logic threshold when it is high and disable the output when it is low. The MD7120 is packaged in a low inductance, thermally-resistant, 32-Lead, 7.00×7.00mm QFN package. With a proper PCB heatsink, the IC power dissipation is about 3.5W.

The high-side power MOSFET drains can be connected to a high voltage power supply, while the bottom N-channel MOSFET source is grounded if it is connected to a single high voltage power supply. In that case, digital audio signal processor IC outputs can be directly connected to the MD7120 input with ground-reference level with no level shifter required. However, then the speaker or the single channel output reference cannot be connected to ground.

Download the Application Note of this circuit design here:

MD7120 Class-D Audio Amplifier Design

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