LM4836MT National Semiconductor, LM4836MT Datasheet - Page 12

• Manufacturer Part Number: LM4836MT
• Description: Stereo 2W Audio Power Amplifiers with DC Volume Control/ Bass Boost/ and Input Mux
• Manufacturer: National Semiconductor

www.national.com
Application Information
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:
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
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
tor. This 200k
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.
P-P
(or 1/2 V
DD
P-P
, the LM4836 supply current draw will be mini-
resistor is placed in series with the input capaci-
(or 1/2 V
DD
resistor can be changed to vary the ampli-
) is present at pin 11, the Beep Detect cir-
DD
DD
, the idle current may be greater than
R
) will not trigger the Beep Detect cir-
F
/ R
i
= - A
v
(Continued)
DD
to provide
12
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 internal
speaker and a pair of 32
sense circuit. In this case the HP sense is controlled by a mi-
croprocessor or a switch.
DD
), the output swing cannot cause false triggering.
FIGURE 3. Headphone Sensing Circuit
speakers without using the HP
DS101088-4