LM48822TLEVAL National Semiconductor, LM48822TLEVAL Datasheet - Page 14

• Manufacturer Part Number: LM48822TLEVAL
• Description: BOARD EVAL FOR LM48822TL
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM48822TLEVAL

• Amplifier Type: Class AB
• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 40mW x 2 @ 32 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM48822
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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SHUTDOWN FUNCTION
The LM48822 features three shutdown controls. Bits B6
(SDL) and B1 (SDR) of the MODE CONTROL register control
the left and right channels, respectively. Set the control bits
to 1 to disable the corresponding channel. When SDR = 1 and
SDL = 0, the right channel is disabled, the right and left inputs
are summed and output as a mono signal on the OUTL. When
SDL = 1 and SDR = 0, the left channel is disabled, while only
the right input signal is output on OUTR. Setting both SDL and
SDR = 1 disables both channels, while the charge pump re-
mains active. Bit B6 (SHDN) of the VOLUME CONTROL
register is the global shutdown control for the entire device.
Set SHDN = 1 to disable the entire device; both amplifiers and
charge pump are disabled. Set SHDN = 0 for normal opera-
tion. SHDN = 1 overrides any other shutdown control bit.
MUTE FUNCTION
Set bits B2 (MUTE_LEFT) and B0 (MUTE_RIGHT) of the
MODE CONTROL register to 1 to mute the respective chan-
nels. Set MUTE_LEFT and MUTE_RIGHT to 0 for normal
operation.
SD_BIAS FUNCTION
The LM48822 BIAS is controlled through the I
bit B5 (SD_BIAS) of the MODE CONTROL register to 1 to
enable the LM48822 BIAS. BIAS provides the voltage for both
the amplifiers and the charge pump. When enabled, V
track V
fixed at 3V, limiting the output swing of the device the 6V
Set SD_BIAS = 0 to disable BIAS. Disabling BIAS allows the
amplifier and charge pump to track V
swing; however, a slight degradation in PSSR will occur. Limit
V
PROPER SELECTION OF EXTERNAL COMPONENTS
Power Supply Bypassing/Filtering
Proper power supply bypassing is critical for low noise per-
formance and high PSRR. Place the supply bypass capaci-
tors as close to the supply pins as possible. Place a 1μF
ceramic capacitors from V
itance may be added as required.
Charge Pump Capacitor Selection
Use low ESR ceramic capacitors (less than 100mΩ) for opti-
mum performance.
DD
to 4.2V or less when BIAS is disabled.
DD
for V
DD
< 3V. Once V
DD
to GND. Additional bulk capac-
DD
exceeds 3V, V
DD
FIGURE 7. Single-Ended Input Configuration
, increasing output
2
C interface. Set
BIAS
remains
BIAS
P-P
will
.
14
Charge Pump Flying Capacitor (C1)
The flying capacitor (C1) affects the load regulation and out-
put impedance of the charge pump. A C1 value that is too low
results in a loss of current drive, leading to a loss of amplifier
headroom. A higher valued C1 improves load regulation and
lowers charge pump output impedance to an extent. Above
2.2μF, the R
of C1 and C2 dominate the output impedance. A lower value
capacitor can be used in systems with low maximum output
power requirements.
Charge Pump Flying Capacitor (C2)
The value and ESR of the hold capacitor (C2) directly affects
the ripple on CPV
put ripple. Decreasing the ESR of C2 reduces both output
ripple and charge pump output impedance. A lower value ca-
pacitor can be used in systems with low maximum output
power requirements.
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 LM48822. The input capacitors create a high-
pass filter with the input resistors R
high pass filter is found using
Where the value of R
tics Table.
High pass filtering the audio signal helps protect the speakers.
When the LM48822 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 fre-
quencies, 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 recommend-
ed for impedance matching and improved CMRR and PSRR.
SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION
The LM48822 is compatible with single-ended sources.
ure 7
shows the typical single-ended applications circuit.
DS(ON)
f = 1 / 2
SS
of the charge pump switches and the ESR
. Increasing the value of C2 reduces out-
IN
π
is given in the Electrical Characteris-
R
IN
C
30061056
Equation 1
IN
(Hz)
IN
. The -3dB point of the
below.
Fig-
(1)