LM4811

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R502-560.b



APPLICATION INFORMATION

DIGITAL VOLUME CONTROL

The UTC LM4811 is dual audio power amplifier with digital volume control and shutdown mode function. The

CLOCK pin is drived by an external clock. It’ s gain is controlled by the signals applied to the CLOCK and UP/DN

inputs.

The audio power amplifier’s gain is fixed by the signals, which are applied to the CLOCK and UP/DN inputs. The

gain is controlled by the logic voltage level applied to the UP/DN pin at each rising edge of the clock signal. At each

rising edge of the clock signal, when a logic high voltage level is applying to the UP/DN pin, 3dB is increased, in

verse when a logic low voltage is applying to the UP/DN pin, 3dB is decreased on the contrary. For both the CLOCK

and UP/DN inputs, the trigger point is 1.4V (MIN.) for a logic high level, and 0.4V (MAX.) for a logic low level.

The UTC LM4811 contains16 discrete gain settings varying from +12dB (MAX.) to -33dB (MIN.), amplifier’s gain

is set to a default value of 0dB during power on condition. However, when coming out of shutdown mode, the UTC

LM4811

will revert back to its previous gain setting.

and UP/DN pins should be debounced. This will ensure correct operation of the digital volume control. A

microcontroller or microprocessor output is expected to drive the CLOCK and UP/DN pins.

1

0

0

1

UP/DN

CLOCK

VOLUME

Default

Up

Up

Down

Down

Figure 2. Timing Diagram

POWER SUPPLY BYPASSING

To obtain low noise performance and high power supply rejection, proper supply bypassing is essentially

needed for any power amplifier. Capacitor on both the bypass and power supply pins should be placed closely as

possible. Bypass capacitor value is also critical as it directly affects the device’s half-supply voltage stability and

PSRR. The stability and supply rejection increase as the bypass capacitor’s value increases. In the typical

applications, employing a 5V regulator with 10μF and a 0.1μF bypass capacitors which aid in supply stability. This,

however, is not saving the need for bypassing the supply nodes of the UTC LM4811. The issue of selecting bypass

cost, and size constraints.

SHUTDOWN FUNCTION

The UTC LM4811 contains a bias circuitry shutdown to reduce power consumption while not is use. By applying

a logic high to the SHUTDOWN pin, the shutdown function is active. For a logic high level, the trigger point is 1.4V

(MIN.), and 0.4V (MAX.) for a logic low. For a better shutdown performance, it is best to switch between ground and

0.3μA (TYP.). In either case, the SHUTDOWN pin should be tied to a fixed voltage to avoid undesired state changes.

In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry. This

provides a quick, smooth shutdown transition. Another solution is to use a single-pole, single-throw switch in

conjunction with an external pull-up resistor. When the switch is closed, the SHUTDOWN pin is connected to ground

scheme guarantees that the SHUTDOWN pin will not float, thus preventing undesired state changes.