LM4834-MS

Manufacturer Part NumberLM4834-MS
ManufacturerNational Semiconductor
LM4834-MS datasheet
 


Specifications of LM4834-MS

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Application Information
BEEP IN FUNCTION
The Beep In pin (pin 14) is a mono input, for system beeps,
that is mixed into the left and right input. This Beep In pin will
allow an input signal to pass through to the Sum Out and
Line/HP output pins. The minimum potential for the input of
the Beep In signal is 300mV. Beep in signals less than
300mV
will not pass through to the output. The beep in
P-P
circuitry provides left-right signal isolation to prevent
crosstalk at the summed input. As shown in the Fig. 2, it is
required that a resistor and capacitor is placed in series with
the Beep In pin and the node tied to V
resistor. The recommended value for the input resistor is
between 120kΩ to 10kΩ and the input capacitor is between
.22Fµ and .47µF. The input resistor can be changed to vary
the amplitude of the beep in signal. Higher values of the
input resistor will reduce the amplifier gain and attenuate the
beep in signal. In cases where system beeps are required
when the system is in a suspended mode, the LM4834 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
LM4834 contains a shutdown pin to externally turn off the
bias circuitry. The LM4834 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
, the LM4834 supply current draw will be mini-
DD
mized. While the device will be disabled with shutdown pin
voltages less than V
, the idle current may be greater than
DD
the typical value of 0.6 µA.The shutdown pin should not be
floated, since this may result in an unwanted shutdown
condition.
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 so-
lution is to use a single-pole, single-throw switch in conjuc-
tion 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 LM4834. This scheme prevents
the shutdown pin from floating.
MODE FUNCTION
The LM4834 was designed to operate in two modes. In
mode 0 (lineout mode),where the mode pin (pin 17) is given
a logic level low, the attenuation at the Line/HP outputs are
fixed at a gain of 1.4. In mode 1 (headphone mode), where
the mode pin is given a logic level high, the attenuation of the
Line/HP outputs is controlled through the DC voltage at pin
22. The signal levels of the Left and Right Sum Out pins are
always controlled by the DC potential at pin 22 regardless of
the mode of the IC. In mode 0, pin 5 and pin 24 are line out
drivers. In mode 1, pin 5 and pin 24 are headphone drivers.
MUTE FUNCTION
By placing a logic level high on the mute pin (pin 15), the
Right and Left Sum Out pins will be muted. If the LM4834 is
in the headphone mode, the HP/Line out pins as well as the
Sum Out pins are muted. The mute pin must not be floated.
HP SENSE FUNCTION
The LM4834 possesses a headphone sense pin (pin 16) 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 LM4834’s head-
phone control function using a single-supply.The voltage
divider of R1, R2, R4, and R5 sets the voltage at the HP
sense pin (pin 16) to be approximately 50 mV when there are
no headphones plugged into the system. This logic-low volt-
age at the HP sense pin enables bridged power amplifier.
Resistor R4 limits the amount of current flowing out of the HP
sense pin when the voltage at that pin goes below ground
through a 100kΩ
DD
resulting from the music coming from the headphone ampli-
fier. Resistor R1, R4, and R5 form a resistor divider that
prevents false triggering of the HP sense pin when the
voltage at the output swings near the rail, since V
2.5V.
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, R2, R4, and R5. Resistor R1 then pulls up the HP sense
pin, enabling the headphone function and disabling the
bridged amplifier. The headphone amplifier then drives the
headphones, whoseimpedance is in parallel with resistor R2
and R3. Also shown in Figure 3 are the electrical connec-
tions 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
to provide
DD
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 LM4834 can be used to drive both a bridged 8Ω internal
speaker and a pair of 32Ω speakers without using the HP
sense pin. In this case the HP sense is controlled by a
microprocessor or a switch.
DC VOLUME CONTROL
The DC voltage at the DC Volume Control pin (pin 22)
determines the attenuation of the Sum Out and Line/HP
amplifiers. If the DC potential of pin 22 is at 4V the internal
11
IH
FIGURE 3. Headphone Input Circuit
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