L4952TS NSC [National Semiconductor], L4952TS Datasheet - Page 13

• Manufacturer Part Number: L4952TS
• Description: 3.1W Stereo-SE Audio Power Amplifier with DC Volume Control
• Manufacturer: NSC [National Semiconductor]

Application Information
power dissipation is a function of output power, higher am-
bient temperatures are allowed as output power or duty
cycle decreases.
If the result of Equation (1) is greater than that of Equation
(2), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further,
ensure that speakers rated at a nominal 4Ω do not fall below
3Ω. If these measures are insufficient, a heat sink can be
added to reduce θ
additional copper area around the package, with connec-
tions to the ground pins, supply pin and amplifier output pins.
Refer to the Typical Performance Characteristics curves
for power dissipation information at lower output power lev-
els.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding
the voltage applied to any pin, with respect to ground, as
listed in the Absolute Maximum Ratings section.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a voltage regulator typi-
cally use a 10µF in parallel with a 0.1µF filter capacitors to
stabilize the regulator’s output, reduce noise on the supply
line, and improve the supply’s transient response. However,
their presence does not eliminate the need for a local 10µF
tantalum bypass capacitance connected between the
LM4952’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation. Keep the length of leads and traces that connect
capacitors between the LM4952’s power supply pin and
ground as short as possible.
BYPASS PIN BYPASSING
Connecting a 4.7µF capacitor, C
PASS pin and ground improves the internal bias voltage’s
stability and improves the amplifier’s PSRR. The PSRR im-
provements increase as the bypass pin capacitor value in-
creases. Too large, however, increases turn-on time. The
selection of bypass capacitor values, especially C
depends on desired PSRR requirements, click and pop per-
formance (as explained in the section, SELECTING EXTER-
NAL COMPONENTS), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4952 features an active-low micro-power shutdown
mode. When active, the LM4952’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the
supply current. The low 55µA typical shutdown current is
achieved by applying a voltage to the SHUTDOWN pin that
is as near to GND as possible. A voltage that is greater than
GND may increase the shutdown current.
There are a few methods to control the micro-power shut-
down. These include using a single-pole, single-throw switch
(SPST), a microprocessor, or a microcontroller. Figure 3
shows a simple switch-based circuit that can be used to
control the LM4952’s shutdown fucntion. Select normal am-
plifier operation by closing the switch. Opening the switch
applies GND to the SHUTDOWN pin, activating micro-power
shutdown. The switch and resistor guarantee that the SHUT-
DOWN pin will not float. This prevents unwanted state
JA
. The heat sink can be created using
BYPASS
, between the BY-
(Continued)
BYPASS
,
13
changes. In a system with a microprocessor or a microcon-
troller, use a digital output to apply the active-state voltage to
the SHUTDOWN pin.
DC VOLUME CONTROL
The LM4952 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the DC VOL
input pin.
The LM4952 volume control consists of 31 steps that are
individually selected by a variable DC voltage level on the
volume control pin. As shown in Figure 4, the range of the
steps, controlled by the DC voltage, is 20dB to -46dB.
The gain levels are 1dB/step from 20dB to 14dB, 2dB/step
from 14dB to -16dB, 3dB/step from -16dB to -27dB, 4dB/step
from -27db to -31dB, 5dB/step from -31dB to -46dB.
Like all volume controls, the LM4952’s internal volume con-
trol is set while listening to an amplified signal that is applied
to an external speaker. The actual voltage applied to the DC
VOL input pin is a result of the volume a listener desires. As
such, the volume control is designed for use in a feedback
system that includes human ears and preferences. This
feedback system operates quite well without the need for
accurate gain. The user simply sets the volume to the de-
sired level as determined by their ear, without regard to the
actual DC voltage that produces the volume. Therefore, the
accuracy of the volume control is not critical, as long as
volume changes monotonically and step size is small
enough to reach a desired volume that is not too loud or too
FIGURE 3. Simple switch and voltage divider
FIGURE 4. Volume control response
generates shutdown control signal
200809H3
200809F5
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