[Photo] 18W Class D Monolithic Audio Amplifier TDA7471

18W Class D monolithic audio amplifier TDA7471
2003, Issue 4, Category: Audio Technology

TDA 7481 is an 18W mono class D digital power amplifier produced by ST. This chip can provide 16W peak power output to a 4Î© load at a Â± 18V supply voltage. Its efficiency can reach more than 80%. The main electrical parameters are shown in the table. Show.
The TDA 7481 is packaged in a 15-pin single in-line package. Its pin arrangement and function of each pin are shown in Figure 1. The typical application circuit is shown in Figure 2. R4 and C8 determine the time constant of the oscillation frequency of the oscillating circuit. The recommended value of C8 is 270pF. R4 can be selected according to the formula R4 = 1.4 Ã— 10 (8th power) / fsw (fsw represents the switching frequency). The recommended fsw is 120kHz, so the recommended value for R4 is 12kÎ©.
{5} The external capacitor C4 of the foot is the grounding capacitor of the feedback circuit, and {3} the external capacitor C11 of the foot is a bootstrap capacitor.
The {10} pin is the working mode control terminal. By inputting different control voltages, the TDA 7481 can be switched between "normal" â†’ "standby" â†’ "silent" three modes.
In particular, it should be noted that the parameters of the low-pass filter composed of L1 and C14 at the output end cannot be arbitrarily changed, where fc is usually 30 kHz to 22 kHz (fc = 1 / 2Ï€ LC), and the Q value is 0.7 to 0.53 The effect is the best (Q = RLC / L). If the value of Q is small, the high-frequency response will fall earlier at the high end, but the slope of the decline is small, so the circuit is more stable; the value of Q equals 0.7, the response is flattest , The cutoff frequency point changes most evenly before and after; if the Q value is higher than 0.7, it will cause a large amplitude overshoot of the frequency response at fc, resulting in a dramatic frequency change, so it is not suitable for use.
It should be noted that the {8} foot of TDA 7481 is already connected to the heat sink inside the integrated circuit, so the insulation of the heat sink should be dealt with when using it.

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