LM48557TL/NOPB National Semiconductor, LM48557TL/NOPB Datasheet - Page 16

IC AMP AUDIO PWR MONO AB 16USMD

LM48557TL/NOPB

Manufacturer Part Number
LM48557TL/NOPB
Description
IC AMP AUDIO PWR MONO AB 16USMD
Manufacturer
National Semiconductor
Series
Boomer®r
Type
Class ABr
Datasheet

Specifications of LM48557TL/NOPB

Output Type
1-Channel (Mono)
Voltage - Supply
2.7 V ~ 4.5 V
Features
Depop, Differential Inputs, I²C, Mute, Shutdown, Volume Control
Mounting Type
Surface Mount
Package / Case
16-MicroSMD
Operational Class
Class-AB
Audio Amplifier Output Configuration
1-Channel Mono
Audio Amplifier Function
Speaker
Single Supply Voltage (typ)
Not RequiredV
Dual Supply Voltage (typ)
3V
Power Supply Requirement
Dual
Rail/rail I/o Type
No
Power Supply Rejection Ratio
80dB
Single Supply Voltage (min)
Not RequiredV
Single Supply Voltage (max)
Not RequiredV
Dual Supply Voltage (min)
1.7/2.7V
Dual Supply Voltage (max)
4.5V
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
16
Package Type
uSMD
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Max Output Power X Channels @ Load
-
Lead Free Status / Rohs Status
Compliant
Other names
LM48557TLTR
www.national.com
VOLUME CONTROL
The LM48557 has a 64 step volume control, but only 36 steps
are recommended for use. Use steps 1 through 32 and steps
61 through 64 to set the gain of the device. Accessing steps
33 through 60 results in the repeated gain conditions shown
in Table 6. Steps 33 through 60 are not tested and should not
be used.
SHUTDOWN FUNCTION
The LM48557 features a low-power shutdown mode that dis-
ables the device lowers the quiescent current to 0.01µA. Set
bit B0 (SHDN) of the Mode Control register to 0 to disable the
amplifier and charge pump. Set SHDN to 1 for normal oper-
ation. Shutdown mode does not clear the I
re-enabled, the device returns to its previous volume setting.
To clear the I
or toggle RESET (see RESET section).
RESET
The LM48557 features an active low reset input. Driving RE-
SET low clears the I
000000 (-90dB) and SHDN is set to 0, disabling the device.
While RESET is low, the LM48557 ignores any I
the device is reset, and RESET is driven high, the LM48557
remains in shutdown mode with the volume set to -90dB. Re-
enable the device by writing to the I
MUTE
The LM48557 features a mute mode. Set bit B1 (MUTE) of
the Mode Control register to 1 to mute the device. In mute
mode, the gain is set to -90dB, equivalent to the volume step
1. Set MUTE = 0 to unmute the device. Once unmuted, the
device returns to its previous volume step.
TEST MODE
If enabled, TESTMODE does not affect device performance
under normal operating conditions. Operating above the rec-
ommended supply voltage range with TESTMODE enabled
can result in damage to the device.
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.
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, either remove power from the device,
DD
to GND. Additional bulk capacitance may
2
C register. Volume control is set to
2
C register.
2
C register. When
2
C data. After
16
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 where 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 where 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 LM48557. 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 LM48557 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.
COMMON MODE SENSE
The LM48557 features a common mode sense pin (VCM, pin
A3) that includes additional common mode cancelling circuit-
ry that improves the CMRR. When the volume control is set
at a high gain step such as 48dB, any mismatch in the input
capacitors would degrade CMRR performance significantly.
With the VCM pin connected to the ground of the input source,
it takes the input capacitor mismatches out of the equation
and therefore improves the CMRR. Another advantage with
this feature is that only one input capacitor is needed in the
single-ended configuration as opposed to two well matched
capacitors. See next section for details of different configura-
tions of the LM48857.
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)
(1)

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