Texas Instruments LM48310SDBD Evaluation Module LM48310SDBD/NOPB LM48310SDBD/NOPB Datenbogen
Produktcode
LM48310SDBD/NOPB
IN+
IN-
C
IN
C
IN
R
INEXT
R
INEXT
R
IN
R
IN
R
F
R
F
SNAS430D – NOVEMBER 2007 – REVISED MAY 2013
AUDIO AMPLIFIER INPUT CAPACITOR SELECTION
Input capacitors may be required for some applications, or when the audio source is single-ended. Input
capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of
the audio source and the bias voltage of the LM48310. The input capacitors create a high-pass filter with the
input resistors R
capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of
the audio source and the bias voltage of the LM48310. The input capacitors create a high-pass filter with the
input resistors R
IN
. The -3dB point of the high pass filter is found using
below.
f = 1 / 2
π
R
IN
C
IN
Where
•
R
IN
is the value of the input resistor given in the
table
(1)
The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers
cannot reproduce, and may even be damaged by low frequencies. High pass filtering the audio signal helps
protect the speakers. When the LM48310 is using a single-ended source, power supply noise on the ground is
seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a
GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors
with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR.
cannot reproduce, and may even be damaged by low frequencies. High pass filtering the audio signal helps
protect the speakers. When the LM48310 is using a single-ended source, power supply noise on the ground is
seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a
GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors
with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR.
AUDIO AMPLIFIER GAIN
The gain of the LM48310 is internally set to 12dB. The gain can be reduced by adding additional input resistance
. In this configuration, the gain of the device is given by:
A
V
= 2 x [R
F
/ (R
INEXT
+ R
IN
)]
Where
•
R
F
is 40k
Ω
•
R
IN
is 20k
Ω
•
R
INEXT
is the value of the additional external resistor
(2)
Figure 31. Reduced Gain Configuration
SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION
The LM48310 is compatible with single-ended sources. When configured for single-ended inputs, input
capacitors must be used to block and DC component at the input of the device.
capacitors must be used to block and DC component at the input of the device.
shows the typical
single-ended applications circuit.
Copyright © 2007–2013, Texas Instruments Incorporated
13
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