LM4819MX National Semiconductor, LM4819MX Datasheet - Page 10

• Manufacturer Part Number: LM4819MX
• Description: IC AMP AUDIO PWR .35W MONO 8SOIC
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4819MX

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 350mW x 1 @ 16 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Features: Depop, Differential Inputs, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LM4819MXTR

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Application Information
There are a few ways to activate micro-power shutdown.
These included using a single-pole, single-throw switch, a
microcontroller, or a microprocessor. When using a switch,
connect an external 10k to 100k pull-up resistor between
the SHUTDOWN pin and V
the SHUTDOWN pin and ground. Select normal amplifier
operation by closing the switch. Opening the switch con-
nects the shutdown pin to V
activating micro-power shutdown. The switch and resistor
guarantee that the SHUTDOWN pin will not float. This pre-
vents unwanted state changes. In a system with a micropro-
cessor or a microcontroller, use a digital output to apply the
control voltage to the SHUTDOWN pin. Driving the SHUT-
DOWN pin with active circuitry eliminates the pull-up resistor
PROPER SELECTION OF EXTERNAL COMPONENTS
Optimizing the LM4819’s performance requires properly se-
lecting external components. Though the LM4819 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4819 is unity gain stable, giving the designer maxi-
mum design flexibility. The gain should be set to no more
than a given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain demands input signals
with greater voltage swings to achieve maximum output
power. Fortunately, many signal sources such as audio CO-
DECs have outputs of 1V
Audio Power Amplifier Design section for more informa-
tion on selecting the proper gain.
Another important consideration is the amplifier’s close-loop
bandwidth. To a large extent, the bandwidth is dictated by
the choice of external components shown in Figure 1 . The
input coupling capacitor, C
that limits low frequency response. This value should be
chosen based on needed frequency response for a few
distinct reasons discussed below
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (C
capacitor can be expensive and may compromise space
efficiency in portable designs. In many cases the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with limited frequency response reap little
improvement by using a large input capacitor.
Besides affecting system cost and size, C
the LM4819’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quies-
cent state. The magnitude of the pop is directly proportional
to the input capacitor’s value. Higher value capacitors need
more time to reach a quiescent DC voltage (usually 1/2 V
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
R
than necessary to meet the desired -3dB frequency can
minimize pops.
As shown in Figure 1 , the input resistor (R
capacitor, C
that is found using Equation (5).
F
. Thus, selecting an input capacitor value that is no higher
i
produce a -3dB high pass filter cutoff frequency
RMS
i
, forms a first order high pass filter
DD
DD
(2.83V
. Connect the switch between
through the pull-up resistor,
i
in Figure 1 ). A high value
P-P
). Please refer to the
(Continued)
i
has an effect on
i
) and the input
DD
)
10
As an example when using a speaker with a low frequency
limit of 150Hz, C
C
efficiency, full range speaker whose response extends down
to 20Hz.
Besides optimizing the input capacitor value, the bypass
capacitor value, C
pass capacitor’s value is the most critical to minimizing
turn-on pops because it determines how fast the LM4819
turns on. The slower the LM4819’s outputs ramp to their
quiescent DC voltage (nominally 1/2V
turn-on pop. While the device will function properly (no os-
cillations or motorboating), with C
device will be much more susceptible to turn-on clicks and
pops. Thus, a value of C
recommended in all but the most cost sensitive designs.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to the value of C
connected to the BYPASS pin. Since C
fast the LM4819 settles to quiescent operation, its value is
critical when minimizing turn-on pops. The slower the
LM4819’s outputs ramp to their quiescent DC voltage (nomi-
nally 1/2V
equal to 1.0µF along with a small value of C
0.1µF to 0.39µF) produces a click-less and pop-less shut-
down function. As discussed above, choosing C
than necessary for the desired bandwidth helps minimize
clicks and pops.
Optimizing Click and Pop Reduction Performance
The LM4819 contains circuitry that minimizes turn-on and
shutdown transients or ’clicks and pops’. For this discussion,
turn on refers to either applying the power or supply voltage
or when the shutdown mode is deactivated. While the power
supply is ramping to it’s final value, the LM4819’s internal
amplifiers are configured as unity gain buffers. An internal
current source charges the voltage of the bypass capacitor,
C
manner. Ideally, the input and outputs track the voltage
charging on the bypass capacitor. The gain of the internal
amplifiers remains unity until the bypass capacitor is fully
charged to 1/2V
capacitor is stable, the device becomes fully operational.
Although the BYPASS pin current cannot be modified,
changing the size of the bypass capacitor, C
device’s turn-on time and magnitude of ’clicks and pops’.
Increasing the value of C
pops. However, this presents a tradeoff: as the size of C
increases, the turn-on time (Ton) increases. There is a linear
relationship between the size of C
Below are some typical turn-on times for various values of
C
i
B
B
, connected to the BYPASS pin in a controlled, linear
:
shown in Figure 1 allows the LM4819 to drive a high
DD
), the smaller the turn-on pop. Choosing C
i
DD
, using Equation (5) is 0.063µF. The 0.39µF
f
B
. As soon as the voltage on the bypass
-3dB
requires careful consideration. The by-
0.01µF
0.22µF
0.47µF
C
0.1µF
1.0µF
B
= 1/(2 R
B
B
reduces the magnitude of turn-on
equal to or greater than 1.0µF is
i
C
T
200ms
440ms
940ms
i
) (Hz)
B
B
ON
20ms
and the turn on time.
less than 1.0µF, the
2S
DD
B
), the smaller the
B
determines how
i
, the capacitor
(in the range of
B
, alters the
i
no larger
(5)
B
B