with the DC volume control. However the gain of the outputs

can be configured by adjusting the feedback and input resis-

tors for the input op-amp. The input op-amp is in an inverting

configuration where the gain is:

R

Note that by adjusting the gain of the input op-amp the over-

all gain of the output amplifiers are also affected. Although

the single ended outputs of the output amplifiers can be used

to drive line level outputs, it is recommended to use Pins 9

and 13 to achieve better performance.

MUX CONTROL

The LM4836 contains two pairs of inputs. The Mux Contol

pin controls wihch set of inputs are selected. Left In 1 and

Right In 1 are selected when Pin 2 is given a logic level low.

Left In 2 and Right In 2 are selected whenever a logic level

high is placed on Pin 2.

BEEP DETECT FUNCTION

The Beep Detect pin (pin 11) is a mono input that detects the

presence of a beep signal. When a signal greater than

2.5V

P-P

(or 1/2 V

cuitry will enable the bridged amplifiers. Beep in signals less

than 2.5V

cuitry. When triggered, the Beep Detect circuitry will enable

the bridged amplifiers regardless of the state of the Mute,

Volume Control, or HP sense pins. The Beep Detect pin will

not pass the beep signal to the output. As shown in the Fig.

2, a 200k

Ω resistor is placed in series with the input capaci-

tor. This 200k

Ω resistor can be changed to vary the ampli-

tude of the beep in signal. Higher values of the resistor will

reduce the amplifier gain and attenuate the beep in signal.

These resistors are required in order for the beep signal to

pass to the output. In cases where system beeps are re-

quired when the system is in a suspended mode, the

LM4836 must be brought out of shutdown before the beep in

signal is input.

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the

LM4836 contains a shutdown pin to externally turn off the

bias circuitry. The LM4836 will shutdown when a logic high is

placed on the shutdown pin. The trigger point between a

logic low and logic high level is typically half supply. It is best

to switch between ground and the supply V

maximum device performance. By switching the shutdown

pin to V

mized. While the device will be disabled with shutdown pin

voltages less than V

the typical value of 0.2 µA.The shutdown pin should not be

floated, since this may result in an undetermined state.

In many applications, a microcontroller or microprocessor

output is used to control the shutdown circuitry which pro-

vides a quick, smooth transition into shutdown. Another solu-

tion is to use a single-pole, single-throw switch in conjuction

with an external pull-up resistor. When the switch is

closed,the shutdown pin is connected to ground and enables

the amplifier. If the switch is open, then the external pull-up

resistor will shutdown the LM4836. This scheme prevents

the shutdown pin from floating.

MUTE FUNCTION

By placing a logic level high on the mute pin (pin5), the out-

puts of the amplifiers and pins 9 and 13 will be muted. The

beep in signal will be output even if the LM4836 is muted.

The mute pin must not be floated.

HP SENSE FUNCTION

The LM4836 possesses a headphone sense pin (pin 21) that

mutes the bridged amplifier, when given a logic high, so that

headphone or line out operation can occur while the bridged

connected load will be muted.

Figure 3 shows the implementation of the LM4836’s head-

phone control function using a single-supply. The voltage di-

vider of R1 and R2 set the voltage at the HP sense pin (pin

21) to be approximately 50 mV when there are no head-

phones plugged into the system. This logic-low voltage at

the HP sense pin enables the bridged power amplifiers. Re-

sistor R4 limits the amount of current flowing out of the HP

sense pin when the voltage at that pin goes below ground re-

sulting from the music coming from the headphone amplifier.

Since the threshold of the HP sense pin is set at 4V ( or 80%

V

When a set of headphones are plugged into the system, the

contact pin of the headphone jack is disconnected from the

signal pin, interrupting the voltage divider set up by resistors

R1 and R2. Resistor R1 then pulls up the HP sense pin, en-

abling the headphone function and disabling the bridged am-

plifier. The headphone amplifier then drives the headphones,

whose impedance is in parallel with resistor R2 and R3. Also

shown in

Figure 3 are the electrical connections for the

headphone jack and plug. A 3-wire plug consists of a Tip,

Ring and Sleeve, where the Tip and Ring are signal carrying

conductors and the Sleeve is the common ground return.

One control pin contact for each headphone jack is sufficient

to indicate that the user has inserted a plug into a jack and

that another mode of operation is desired.

The LM4836 can be used to drive both a bridged 8

Ω internal

speaker and a pair of 32

Ω speakers without using the HP

sense circuit. In this case the HP sense is controlled by a mi-

croprocessor or a switch.

DS101088-4

FIGURE 3. Headphone Sensing Circuit

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