lm4702

Description: The graph illustrates the measured temperature rise above ambient for a typical range of power supply voltages. The upper two plot lines represent scenarios without a heatsink: one with the LM4702 mounted above the PCB, as is standard, and the other with the LM4702 mounted below the PCB, which experiences reduced cooling due to air convection. Beyond approximately 45 Volts, the chip begins to overheat. The GND pin should be directly connected to the "star earth" point. Additional connections to the "star earth" include the central 0V point of the power supply, the common output of the speaker, the Zobel network, the power supply bypass capacitors, and the low-level "clean earth" point used for the input signal and feedback network. The "clean earth" point is isolated from large currents circulating through the "star earth" by either a thin PCB track or a low-value resistor.

The schematic described involves a temperature-sensitive application utilizing the LM4702 integrated circuit, which is a high-performance audio amplifier. The temperature rise above ambient is a critical parameter that must be monitored, particularly as the power supply voltage approaches 45 Volts. In configurations without a heatsink, the thermal management becomes vital, as the LM4702 can reach unsafe operating temperatures, especially when mounted below the PCB where airflow is limited.

The grounding strategy employed utilizes a "star earth" configuration, which minimizes ground loop issues and ensures stable operation of the circuit. The GND pin's direct connection to the "star earth" point helps maintain a common reference potential for all components, which is essential for signal integrity and noise reduction.

Connections to the "star earth" include the central 0V point of the power supply, which serves as the reference for the entire circuit, as well as the common output of the speaker. This arrangement ensures that all components share a common ground, reducing the potential for interference and improving overall performance.

The Zobel network, which is typically used to stabilize the amplifier's frequency response and prevent oscillations, is also connected to the star ground. The power supply bypass capacitors are crucial for filtering high-frequency noise from the supply voltage, further enhancing the stability and performance of the amplifier.

The low-level "clean earth" point is particularly important for the input signal and feedback network. By isolating this point from the high currents that circulate through the "star earth," the design minimizes the risk of introducing noise into sensitive signal paths. This isolation can be achieved through the use of a thin PCB track or a low-value resistor, both of which limit the impact of ground potential fluctuations on the clean earth point.

In summary, the described circuit emphasizes the importance of thermal management and grounding strategies in high-performance audio applications. Proper implementation of these elements is crucial for maintaining the reliability and performance of the LM4702 amplifier under varying operational conditions.The following graph shows the measured temperature rise above ambient for a typical range of power supply voltages. The upper two plot lines are for no heatsink, with the LM4702 mounted above the PCB (as it normally would be) and mounted below the PCB (which has reduced cooling by air convection).

Beyond about 45 Volts the chip begins to get too h ot. The GND pin should be directly connected to the "star earth" point. Other connections to the "star earth" are the central 0V point of power supply, the speaker output common, the Zobel network, the power supply bypass capacitors, and the low level "clean earth" point which is used for the input signal and feedback network. The "clean earth" point is isolated by a thin PCB track or a low value resistor from the large currents which circulate through the "star earth" point.