typical value. Increased THD may also be observed with

voltages less than V

mode.

The LM4666 has an internal resistor connected between

GND and Shutdown pins. The purpose of this resistor is to

eliminate any unwanted state changes when the Shutdown

pin is floating. The LM4666 will enter the shutdown state

when the Shutdown pin is left floating or if not floating, when

the shutdown voltage has crossed the threshold. To mini-

mize the supply current while in the shutdown state, the

Shutdown pin should be driven to GND or left floating. If the

Shutdown pin is not driven to GND, the amount of additional

resistor current due to the internal shutdown resistor can be

found by Equation (1) below.

(V

Ω

(1)

With only a 0.5V difference, an additional 8.3µA of current

will be drawn while in the shutdown state.

GAIN SELECTION FUNCTION

The LM4666 has fixed selectable gain to minimize external

components, increase flexibility and simplify design. For a

differential gain of 6dB, the Gain Select pin should be per-

manently connected to V

For a differential gain of 12dB, the Gain Select pin should be

permanently connected to GND or driven to a logic low level.

The gain of the LM4666 can be switched while the amplifier

is in PLAY mode driving a load with a signal without damage

to the IC. The voltage on the Gain Select pin should be

switched quickly between GND (logic low) and V

high) to eliminate any possible audible artifacts from appear-

ing at the output. For typical threshold voltages for the Gain

Select function, refer to the Gain Threshold Voltages graph

in the Typical Performance Characteristics section.

www.national.com

11