4990WXYZ データシートの表示（PDF） - Unspecified

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4990WXYZ

2W Audio Power Amplifier with Selectable Shutdown

Unspecified 

Application Information

Shutdown Control

Shutdown circuitry is employed to switch off the amplifier bias in order to reduce power consumption. The circuit contains

two input pins: a shutdown mode pin (SD Mode) and shutdown pin with selectable input level. This allows the user to

implement high- or low-switch commands to control the shutdown circuit. Normally, the SD mode pin is permanently tied to

VDD or GND, with the shutdown pin controlling the shutdown function. When the SD mode is calibrated to VDD, the

device’s shutdown mode is set at its high switch position. On the other hand, if SD mode is set to GND, the low switch

setting will trigger the device to shut down. To avoid unwanted status changes, the shutdown pin should be tied to a definite

voltage.

In many applications, the output signal from a microcontroller is used to control the shutdown circuitry, which provides a

quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction with an external resistor

(pull-up or pull-down, depending on shutdown mode selection). This scheme guarantees that the shutdown pin will not float,

thus preventing unwanted status changes.

Selection of External Components

The external components used play an important factor in affecting amplifier performance, with the proper selection

enabling more efficient system functions. The AUD4990 should be used in low gain configurations to minimize THD+N

values, and maximize the signal-to-noise ratio. Besides gain, another major consideration in system performance is the

closed loop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of external components.

The input coupling capacitor forms a first-order, high-pass filter that limits low frequency response, and should be chosen

based on the required frequency response. In many cases the speakers used in portable systems, whether internal or

external, have little ability to reproduce signals below 100Hz to 150Hz. Thus, using a large input capacitor may not increase

actual system performance.

Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value, as it will

determine how fast the chip turns on.

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