LM4830N National Semiconductor, LM4830N Datasheet - Page 10

• Manufacturer Part Number: LM4830N
• Description: IC AMP AUDIO PWR 2W MONO 24DIP
• Manufacturer: National Semiconductor
• Type: Class ABr

Specifications of LM4830N

• Output Type: 1-Channel (Mono) with Mono Headphones
• Max Output Power X Channels @ Load: 2W x 1 @ 4 Ohm; 100mW x 1 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Microphone, Shutdown, Thermal Protection, Volume Control
• Mounting Type: Through Hole
• Package / Case: 24-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM4830N

www.national.com
Application Information
ground return lines should not be tied together with AC input
reference ground return lines. In addition, the layout of these
ground lines should be physically located as far as reason-
ably possible from each other so that large signal coupling
cannot occur. To further exemplify this point, the outputs and
output load returns for the power amplifier, which have volts
of signal on them, should be physically isolated from the sen-
sitive inputs and AC input ground returns associated with the
preamp. It is easy for large signals to couple into the sensi-
tive low voltage microphone preamp inputs.
0 — Logic Low (0V)
1 — Logic High (5V)
X — Don’t Care
NC — No Change
DIGITAL ATTENUATION CONTROL
The Load (LD) pin, pin 9, has two modes of operation. When
this input pin is a logic high, 5V, the power amp’s attenuation
control is in “transparent mode” where the voltages on bits
D0–D3 will cause the appropriate attenuation level to be
latched and decoded within the IC. For normal attenuation,
pin 9 should be at 5V. When the LD input pin is a logic low,
0V, the power amp’s attenuation control is “locked-out” so
that any change in the input bits will not cause a subsequent
change in the amp’s attenuation level.
The attenuation level is preset to −16 dB when the IC is first
powered up, assuming that LD is a logic low until the IC is
fully biased up.
To provide the best click and pop performance when chang-
ing attenuation levels, each step should be utilized. If a
mute-type function is desired, it is recommended that each
of the attenuation steps be “ramped through” quicker than
the normal attenuation ramp.
To ensure that attenuation steps are flawless when data is
transitioning with load, refer to the timing diagram for proper
setup and hold times.
Pin
LD
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
TABLE 1. 4-Bit Attenuation Control
msb: lsb
Input Bits
D3–D0
XXXX
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Attenuation
Level (dB)
NC
−10 dB
−12 dB
−14 dB
−16 dB
−18 dB
−20 dB
−22 dB
−24 dB
−26 dB
−28 dB
−30 dB
−2 dB
−4 dB
−6 dB
−8 dB
0 dB
(Continued)
Gain (dB)
Amplifier
Bridge
NC
−10 dB
−12 dB
−14 dB
−16 dB
−18 dB
−20 dB
−22 dB
−24 dB
−2 dB
−4 dB
−6 dB
−8 dB
6 dB
4 dB
2 dB
0 dB
10
SELECTION OF EXTERNAL CAPACITORS
The IC’s low frequency power supply rejection can be im-
proved by using a larger bypass capacitor, C
this capacitor value, the THD performance at low frequen-
cies will also be improved. For cost sensitive designs, 0.1 µF
is recommended, however, for best performance at least 1
µF should be used.
The selection of the microphone input coupling capacitors
should be based on desired low frequency coupling. Since
the input resistance for those inputs is around 20 k , the
coupling cap should be 0.47 µF for 17 Hz coupling or 0.047
µF for 170 Hz coupling.
Similarly, the selection of the power amplifier input coupling
capacitors should be based on an input resistance of 40 k ,
so for flatband 20 Hz reproduction, 0.47 µF caps or larger
should be used.
VOICE-BAND DESIGN
The preamp on this IC is intended to be used for microphone
amplification. Depending upon the frequency response of
the microphone, the preamplifier’s response can be config-
ured to fit the microphone. Simple capacitors can be used to
bandwidth limit the frequency response of the preamplifier
and improve the system’s performance. Once the gain of the
preamp is chosen, the values for the resistors and capacitors
can be selected based upon desired cutoff frequencies using
the equations below.
As an example, lets assume that the desired closed-loop
gain is 40 dB and the desired voice-band is 300 Hz to 3 kHz.
Using Equation 4, we choose R
The desired value in dB is equal to 20 log (A
ing for C
k , and R
i
COMPUTER APPLICATION CIRCUIT
The LM4830 can also be used to drive both an internal sys-
tem speaker and stereo headphones simultaneously, as
shown in Figure 2 . The internally configured unity-gain buffer
requires the preamp to also be set up in an inverting
unity-gain fashion to maintain proper signal phase between
channels for the stereo headphone amplifier. The unity-gain
configured circuit also requires that the AC input signal dy-
namic range be properly conditioned for the 2.5 V
swing.
Please refer to the Typical Performance Characteristics
curves for THD+N vs P
and buffer.
SHUTDOWN FUNCTION
In order to reduce current consumption while not in use, the
LM4830 contains a shutdown pin to externally turn off the
IC’s bias circuitry. This shutdown feature turns the IC off
when a logic high is placed on the shutdown pin. The trigger
point between a logic low and logic high is typically
half-supply. Quiescent current consumption will depend
upon the value of this voltage. It is best for this voltage to be
forced to V
The shutdown feature reduces quiescent supply current con-
sumption from a typical 11 mA to under 2 µA for the whole IC.
= 0.53 µF.
f
and C
i
= 1 k
DD
to obtain the guaranteed shutdown current.
i
using flp = 3 kHz, fhp = 300 Hz, R
we get the following: C
A
fhp = 1/(2 R
flp = 1/(2 R
VCL
O
and frequency of the MIC preamp
= 1 + R
f
= 100 k
f
f
C
i
C
/R
f
i
)
)
i
f
VCL
= 530 pF and C
b
and R
. By increasing
). Then, solv-
i
PK
= 1 k .
f
= 100
signal
(4)
(5)
(6)