LM4839 datasheet(17/34 Pages) NSC

17 / 34 page

Application Information (Continued)

microprocessor, or a microcontroller. When using a switch,

connect an external 10k

Ω pull-up resistor between the

SHUTDOWN pin and V

DD. Connect the switch between the

SHUTDOWN pin and ground. Select normal amplifier opera-

tion by closing the switch. Opening the switch connects the

SHUTDOWN pin to V

DD through the pull-up resistor, activat-

ing micro-power shutdown. The switch and resistor guaran-

tee 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 control

voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin

with active circuitry eliminates the need for a pull up resistor.

TABLE 1. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation

SHUTDOWN

HP-IN PIN

MUX CHANNEL

SELECT PIN

OPERATIONAL MODE

(MUX INPUT CHANNEL #)

Logic Low

Bridged Amplifiers (1)

Logic Low

Logic High

Bridged Amplifiers (2)

Logic Low

Logic High

Logic Low

Single-Ended Amplifiers (1)

Logic Low

Logic High

Single-Ended Amplifiers (2)

Logic High

Micro-Power Shutdown

MUTE FUNCTION

The LM4839 mutes the amplifier and DOCK outputs when

DD is applied to pin 5, the MUTE pin. Even while muted, the

LM4839 will amplify a system alert (beep) signal whose

magnitude satisfies the BEEP DETECT circuitry. Applying

0V to the MUTE pin returns the LM4839 to normal, unmated

operation. Prevent unanticipated mute behavior by connect-

ing the MUTE pin to V

DD or ground. Do not let the mute pin

float.

HP SENSE FUNCTION ( Head Phone In )

Applying a voltage between 4V and V

DD to the LM4839’s

HP-IN headphone control pin turns off the amps that drive

the left out ’+’ and right out ’+’ pins. ( Pins 15 and 20 on the

MT/MTE & 12 and 25 on the LQ ). This action mutes a

bridged-connected load. Quiescent current consumption is

reduced when the IC is in this single-ended mode.

Figure 2 shows the implementation of the LM4839’s head-

phone control function. With no headphones connected to

the headphone jack, the R1-R2 voltage divider sets the

voltage applied to the HP Sense pin at approximately 50mV.

This 50mV puts the LM4839 into bridged mode operation.

The output coupling capacitor blocks the amplifier’s half

supply DC voltage, protecting the headphones.

The HP-IN threshold is set at 4V. While the LM4839 operates

in bridged mode, the DC potential across the load is essen-

tially 0V. Therefore, even in an ideal situation, the output

swing cannot cause a false single-ended trigger. Connecting

headphones to the headphone jack disconnects the head-

phone jack contact pin from R2 and allows R1 to pull the HP

Sense pin up to V

DD through R4. This enables the head-

phone function, turns off both of the ’+’ output amplifiers and

mutes the bridged speaker. The amplifier then drives the

headphones, whose impedance is in parallel with resistors

R2 and R3. These resistors have negligible effect on the

LM4839’s output drive capability since the typical impedance

of headphones is 32

Ω.

Figure 2 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 ring should each carry one of

the two stereo output signals, whereas the sleeve should

carry the ground return. A headphone jack with one control

pin contact is sufficient to drive the HP-IN pin when connect-

ing headphones.

A microprocessor or a switch can replace the headphone

jack contact pin. When a microprocessor or switch applies a

voltage greater than 4V to the HP-IN pin, a bridge-connected

speaker is muted and the single ended output amplifiers A1

and A2 will drive a pair of headphones.

BASS BOOST FUNCTION

The Bass Boost Function can be toggled by changing the

logic at the Bass Boost Select pin. A logic low will switch the

power amplifiers to bass boost mode. In bass boost mode,

the low frequency gain of the ampflifier is set by the external

CBS capacitor in Figure 1. Where as a logic high sets the

amplifiers to unity gain.

In some cases, a designer may want to improve the low

frequency response of the bridged amplifier or incorporate a

bass boost feature. This bass boost can be useful in systems

where speakers are housed in small enclosures. If the de-

signer wishes to dsiable the bass boost feature, pin 19 (

MT/MTE packages ) can be tied to V

DD.

DS200134-4

FIGURE 2. Headphone Sensing Circuit (MT/MTE

Pinout)

LM4839 Datasheet(PDF) 17 Page - National Semiconductor (TI)

LM4839 Datasheet(HTML) 17 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Datasheet Download

Link URL