Texas Instruments LM48861TMBD Evaluation Board LM48861TMBD/NOPB LM48861TMBD/NOPB Ficha De Dados
Códigos do produto
LM48861TMBD/NOPB
AUDIO
INPUT
COM
COMMON MODE SENSE
EQUIVALENT CIRCUIT
SNAS450B – JUNE 2008 – REVISED MAY 2013
APPLICATION INFORMATION
GENERAL AMPLIFIER FUNCTION
The LM48861 headphone amplifier features TI’s ground referenced architecture that eliminates the large DC-
blocking capacitors required at the outputs of traditional headphone amplifiers. A low-noise inverting charge
pump creates a negative supply (CPV
blocking capacitors required at the outputs of traditional headphone amplifiers. A low-noise inverting charge
pump creates a negative supply (CPV
SS
) from the positive supply voltage (V
DD
). The headphone amplifiers
operate from these bipolar supplies, with the amplifier outputs biased about GND, instead of a nominal DC
voltage (typically V
voltage (typically V
DD
/2), like traditional amplifiers. Because there is no DC component to the headphone output
signals, the large DC-blocking capacitors (typically 220
μ
F) are not necessary, conserving board space and
system cost, while improving frequency response.
COMMON MODE SENSE
The LM48861 features a ground (common mode) sensing feature. In noisy applications, or where the headphone
jack is used as a line out to other devices, noise pick up and ground imbalance can degrade audio quality. The
LM48861 COM input senses and corrects any noise at the headphone return, or any ground imbalance between
the headphone return and device ground, improving audio reproduction. Connect COM directly to the headphone
return terminal of the headphone jack
jack is used as a line out to other devices, noise pick up and ground imbalance can degrade audio quality. The
LM48861 COM input senses and corrects any noise at the headphone return, or any ground imbalance between
the headphone return and device ground, improving audio reproduction. Connect COM directly to the headphone
return terminal of the headphone jack
. No additional external components are required. Connect COM
to GND if the common-mode sense feature is not in use.
Figure 17.
MICRO POWER SHUTDOWN
The voltage applied to the shutdown (SHDN) pin controls the LM48861’s shutdown function. Activate micro-
power shutdown by applying a logic-low voltage to the SHDN pin. When active, the LM48861’s micro-power
shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V
(max) for a logic-low level, and 1.4V (min) for a logic-high level. The low 0.1
power shutdown by applying a logic-low voltage to the SHDN pin. When active, the LM48861’s micro-power
shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V
(max) for a logic-low level, and 1.4V (min) for a logic-high level. The low 0.1
μ
A (typ) shutdown current is
achieved by applying a voltage that is as near as ground as possible to the SHDN pin. A voltage that is higher
than ground may increase the shutdown current.
than ground may increase the shutdown current.
There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw
switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100k
switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100k
Ω
pull-up resistor
between the SHDN pin and GND. Connect the switch between the SHDN pin and V
DD
. Select normal amplifier
operation by closing the switch. Opening the switch connects the SHDN pin to ground, activating micro-power
shutdown. The switch and resistor ensure that the SHDN pin will not float. This prevents unwanted state
changes. In a system with a microprocessor or microcontroller, use a digital output to apply the control voltage to
the SHDN pin. Driving the SHDN pin with active circuitry eliminates the pull-up resistor.
shutdown. The switch and resistor ensure that the SHDN pin will not float. This prevents unwanted state
changes. In a system with a microprocessor or microcontroller, use a digital output to apply the control voltage to
the SHDN pin. Driving the SHDN pin with active circuitry eliminates the pull-up resistor.
POWER DISSIPATION
Power dissipation is a major concern when using any power amplifier, especially one in mobile devices. In the
LM48861, the power dissipation comes from the charge pump and two operational amplifiers. Refer to the
LM48861, the power dissipation comes from the charge pump and two operational amplifiers. Refer to the
Power Dissipation vs Output Power curve in the
section of the
datasheet to find the power dissipation associated the output power level of the LM48861. The power dissipation
should not exceed the maximum power dissipation point of the DSBGA package given in
should not exceed the maximum power dissipation point of the DSBGA package given in
.
P
DMAX
= (T
JMAX
- T
A
) / (
θ
JA
)
(1)
Copyright © 2008–2013, Texas Instruments Incorporated
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