lm48823tlx National Semiconductor Corporation, lm48823tlx Datasheet - Page 13

• Manufacturer Part Number: lm48823tlx
• Description: Mono, Bridge-tied Load, Ceramic Speaker Driver With I2c Volume Control And Reset
• Manufacturer: National Semiconductor Corporation

SHUTDOWN FUNCTION
The LM48823 features a low-power shutdown mode that dis-
ables the device, lowering the quiescent current to 0.01µA.
Set bits B1 (ENABLE_A) and B2 (ENABLE_B) to 0 to disable
the amplifiers and charge pump. Set both ENABLE_A and
ENABLE_B to 1 for normal operation. Shutdown mode does
not clear the I
to its previous volume setting. To clear the I
remove power from the device, or toggle RESET (see RE-
SET section).
RESET
The LM48823 features an active low reset input. Driving RE-
SET low clears the I
(-70dB) and both ENABLE_A and ENABLE_B are set to 0,
disabling the device. While RESET is low, the LM48823 ig-
nores any I
driven high, the LM48823 remains in shutdown mode with the
volume set to -70dB. Re-enable the device by writing to the
I
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 device as possible. Place a 1µF ceramic
capacitor from V
be added as required.
Bypass Capacitor Selection
The BYPASS capacitor, C
jection and output offset. For best results, use a capacitor of
identical value to the input coupling capacitors
Charge Pump Capacitor Selection
Use low ESR ceramic capacitors (less than 100mΩ) for opti-
mum performance.
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
2
C register.
2
C data. After the device is reset, and RESET is
2
C register. When re-enabled, the device returns
DD
2
to GND. Additional bulk capacitance may
C register. Volume control is set to 00000
BYPASS
, improves PSRR, noise re-
2
C register, either
13
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 Hold 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 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 LM48823. The input
capacitors create a high-pass filter with the input resistors
R
tion (1) below.
Where the value of R
tics Table.
High pass filtering the audio signal helps protect the speakers.
When the LM48823 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.
IN
. The -3dB point of the high pass filter is found using Equa-
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
IN
(Hz)
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