Texas Instruments LM48861TMBD Evaluation Board LM48861TMBD/NOPB LM48861TMBD/NOPB Ficha De Dados
Códigos do produto
LM48861TMBD/NOPB
SNAS450B – JUNE 2008 – REVISED MAY 2013
For the LM48861TM DSBGA package,
θ
JA
= 70°C/W. T
JMAX
= 150°C, and T
A
is the ambient temperature of the
system surroundings.
PROPER SELECTION OF EXTERNAL COMPONENTS
Power Supply Bypassing/Filtering
Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass
capacitors as close to the supply pins as possible. Place a 1
capacitors as close to the supply pins as possible. Place a 1
μ
F ceramic capacitor from V
DD
to GND. Additional
bulk capacitance may be added as required.
Charge Pump Capacitor Selection
Use low ESR ceramic capacitors (less than 100m
Ω
) for optimum performance.
Charge Pump Flying Capacitor (C5)
The flying capacitor (C5) affects the load regulation and output impedance of the charge pump. A C5 value that
is too low results in a loss of current drive, leading to a loss of amplifier headroom. A higher valued C5 improves
load regulation and lowers charge pump output impedance to an extent. Above 2.2
is too low results in a loss of current drive, leading to a loss of amplifier headroom. A higher valued C5 improves
load regulation and lowers charge pump output impedance to an extent. Above 2.2
μ
F, the R
DS(ON)
of the charge
pump switches and the ESR of C5 and C6 dominate the output impedance. A lower value capacitor can be used
in systems with low maximum output power requirements.
in systems with low maximum output power requirements.
Charge Pump Hold Capacitor (C6)
The value and ESR of the hold capacitor (C6) directly affects the ripple on CPV
SS
. Increasing the value of C6
reduces output ripple. Decreasing the ESR of C6 reduces both output ripple and charge pump output impedance.
A lower value capacitor can be used in systems with low maximum output power requirements.
A lower value capacitor can be used in systems with low maximum output power requirements.
Power Supply Bypassing /Filtering
Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass
capacitors as close to the device as possible. Typical applications employ a voltage regulator with 10µF and
0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing
of the LM48861 supply pins. A 1µF capacitor is recommended.
capacitors as close to the device as possible. Typical applications employ a voltage regulator with 10µF and
0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing
of the LM48861 supply pins. A 1µF capacitor is recommended.
Input Capacitor Selection
The LM48861 requires input coupling capacitors. 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 LM48861.
The input capacitors create a high-pass filter with the input resistors R
eliminating any conflict between the DC component of the audio source and the bias voltage of the LM48861.
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
•
the value of R
IN
is selected based on the gain-setting resistor selection.
(2)
In relation to
, R
IN
= R1 = R2, C
IN
= C1 = C2.
The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers
can not reproduce, and may even be damaged by low frequencies. High-pass filtering the audio signal helps
protect the speakers. When the LM48861 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.
can not reproduce, and may even be damaged by low frequencies. High-pass filtering the audio signal helps
protect the speakers. When the LM48861 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.
10
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