LM4914’s supply pins and ground. Do not substitute a ce-

ramic capacitor for the tantalum. Doing so may cause oscil-

lation.

Keep the length of leads and traces that connect capacitors

between the LM4914’s power supply pin and ground as

short as possible. Connecting a 0.47µF capacitor, C

tween the BYPASS pin and ground improves the internal

bias voltage’s stability and improves the amplifier’s PSRR.

The PSRR improvements increase as the bypass pin ca-

pacitor value increases. Too large, however, increases

turn-on time and can compromise the amplifier’s click and

pop performance. The selection of bypass capacitor values,

especially C

click and pop performance (as explained in the section,

Proper Selection of External Components), system cost, and

size constraints.

MICRO-POWER SHUTDOWN

The LM4914 features an active-low micro-power shutdown

mode. When active, the LM4914’s micro-power shutdown

feature turns off the amplifier’s bias circuitry, reducing the

supply current. The logic threshold is typically V

low 0.03µA typical shutdown current is achieved by applying

a voltage to the SHUTDOWN pin that is as near to GND as

possible. A voltage that is greater than GND may increase

the shutdown current.

There are a few methods to control the micro-power shut-

down. These include using a single-pole, single-throw switch

(SPST), a microprocessor, or a microcontroller. When using

a switch, connect a 100k

Ω pull-up resistor between the

SHUTDOWN pin and V

SHUTDOWN pin and GND. Select normal amplifier opera-

tion by opening the switch. Closing the switch applies GND

to the SHUTDOWN pin, activating micro-power shutdown.

The switch and resistor guarantee that the SHUTDOWN pin

will not float. This prevents unwanted state changes. In a

system with a microprocessor or a microcontroller, use a

digital output to apply the active-state voltage to the SHUT-

DOWN pin.

HEADPHONE (SINGLE-ENDED) AMPLIFIER

OPERATION

BTL/SE [Mono (BTL)/Stereo (SE)] Function

Applying a voltage greater than 0.9V

BTL/SE headphone control pin switches the amplifier’s op-

eration from mono BTL to stereo SE. Applying a voltage less

than 0.55V

pin switches the amplifier’s operation from stereo SE to

mono BTL.

Figure 3 shows how to control the LM4914’s headphone

function using four external resistors and a dual-switch ste-

reo headphone jack. External resistors R4 - R6 provide the

control voltages that are applied through the upper head-

phone jack switch. R6 and R7 provide a DC return path for

the SE coupling capacitors.

With no headphones connected to the headphone jack, the

R5-R6 voltage divider sets the voltage applied to the BTL/SE

pin (pin 7) at approximately 50mV (comfortably below the

0.55V

select the signal applied to the MONO-IN input and places

the LM4914 in mono BTL operation. When stereo SE opera-

tion is desired, both headphone jack switches are opened

with a headphone plug. Opening the lower one allows R5 to

apply V

inputs to the stereo signal. Opening the lower one breaks the

connection between AMP4’s output and the BTL speaker,

muting it. The output coupling capacitors block the amplifi-

er’s half supply DC voltage, protecting the headphones from

the V

Figure 3 also shows the suggested headphone jack electri-

cal connections. The jack is designed to mate with a three-

wire plug. The plug’s tip and adjacent ring should carry the

left and right channel stereo signals, respectively. The sleeve

furthest from the tip should carry the ground return. The

Switchcraft 35RAPC4BH3 five-terminal headphone jack

200634A1

FIGURE 3. Headphone Operation and BTL - SE Mode Switching

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