TDA8902J digital power amplifier circuit schematic

TDA8902J digital power discharge principle diagram: Figure 3 is the TDA8902J digital power discharge principle diagram. In the figure, Rosc is the timing element that determines the oscillation frequency. Rosc can be calculated according to 3×10/fs. The value range in the parameter table is 100kHz 500kHz, and the recommended value is 300kHz. From this, it can be calculated that Rosc is 10kO.

C3 is the grounding capacitor of the feedback circuit, and the feedback resistor is already made inside the IC chip. The two together form a first-order low-pass feedback circuit, which has a negative feedback effect on signals below the switching frequency. The capacitance shown in the figure is the relative value when fS=300kHz. Since C6 and C7 are used as bootstrap capacitors externally, the switching frequency MOSFET in the PWM function block is connected in a half-bridge form. The protection circuit has overvoltage protection, output overcurrent protection and thermal shutdown functions, which is safe to use.

This circuit also has auxiliary functions such as mute/standby. The standby function uses an external control signal to shut down the internal oscillator, cut off the power supply current when there is no signal, and reduce the standby current to 3mA. The functional control of the standby sound pressure in three states is achieved by inputting three different voltages to pin (17). Another key component in the circuit is the passive low-pass filter L1, Cl2 and L2, Cll. Their values ​​are determined according to the speaker impedance, the highest required passing frequency fc and the circuit Q value requirements. Here L1=100 UH, C10=0,39 UF, RL:8R, it can be calculated that fc=l/27c(LC)/2=24khz, Q=RLC/L=0,03. If RL-5fl, fc remains unchanged, the Q value will become 0.02. Generally, the smaller the Q value, the more stable the circuit; Q value equals 0,04 is called the flattest response