Datasheet

LM4853
SNAS155E –JANUARY 2002–REVISED MAY 2013 www.ti.com
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry. This
provides a quick, smooth shutdown transition. Another solution is to use a single-pole, single-throw switch in
conjunction 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, the external pull-up resistor, R
PU2
will disable the
LM4853. This scheme ensures that the SHUTDOWN pin will not float, thus preventing unwanted state changes.
HP-IN FUNCTION
The LM4853 features a headphone control pin, HP-IN, that enables the switching between BTL and SE modes.
A logic-low to HP-IN activates the BTL mode, while a logic-high activates the SE mode.
Figure 39 shows the implementation of the LM4853's headphone control. The voltage divider formed by R
PU1
and
R
D1
sets the voltage at HP-IN to be approximately 50mV with no headphones plugged into the system. This
logic-low voltage at the HP-IN pin enables the BTL mode
When a set of headphones is plugged into the system, the headphone jack's contact pin is disconnected from the
signal pin. This also interrupts the voltage divider set up by the resistors R
PU1
and R
D1
. Resistor R
PU1
applies V
DD
to the HP-IN pin, switching the LM4853 out of BTL mode and into SE mode. The amplifier then drives the
headphones, whose impedance is in parallel with resistors R
D1
and R
D2
. Resistors R
D1
and R
D2
have negligible
effect on the output drive capability since the typical impedance of headphones is 32Ω.
Figure 39. Headphone Control Circuit
Also shown in Figure 39 are the electrical connections for the headphone jack and plug. A 3-wire plug consists of
a Tip, Ring, and Sleave, where the Tip and Ring are audio signal conductors and the Sleave is the common
ground return. One control pin for each headphone jack is sufficient to indicate to the control inputs that a user
has inserted a plug into the jack and that the headphone mode of operation is desired.
To ensure smooth transition from BTL to SE operation, it is important to connect HP-IN and R
PU1
to the control
pin on the Right Output of the headphone jack. The control pin on the Left Output of the headphone jack should
be left open. Connecting the node between the HP-IN and R
PU1
to the Left Output control pin may cause
unwanted state changes to the HP-IN pin.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical for optimum
device and system performance. While the LM4853 is tolerant to a variety of external component combinations,
consideration must be given to the external component values that maximize overall system quality.
The LM4853's unity-gain stability allows a designer to maximize system performance. The LM4853's gain should
be set no higher than necessary for any given application. A low gain configuration maximizes signal-to-noise
performance and minimizes THD+N. However, a low gain configuration also requires large input signals to obtain
a given output power. Input signals equal to or greater than 1V
RMS
are available from sources such as audio
codecs. Please refer to the section, AUDIO POWER AMPLIFIER DESIGN, for a more complete explanation of
proper gain selection.
14 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM4853