LM49153TMEVAL National Semiconductor, LM49153TMEVAL Datasheet - Page 18

• Manufacturer Part Number: LM49153TMEVAL
• Description: EVAL BOARD LM49153
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM49153TMEVAL

• Amplifier Type: Class D
• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 145mW x 2 @ 16 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM49153
• Lead Free Status / Rohs Status: Lead free by exemption / RoHS compliant by exemption

www.national.com
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM49153 features a differential input stage for the mono
inputs, which offers improved noise rejection compared to a
single-ended input amplifier. Because a differential input am-
plifier amplifies the difference between the two input signals,
any component common to both signals is cancelled. An ad-
ditional benefit of the differential input structure is the possible
elimination of the DC input blocking capacitors. Since the DC
component is common to both inputs, and thus cancelled by
the amplifier, the LM49153 can be used without input coupling
capacitors when configured with a differential input signal.
INPUT MIXER/MULTIPLEXER
The LM49153 includes a comprehensive mixer multiplexer
controlled through the I
lows any input combination to appear on any output of
LM49153. Multiple input paths can be selected simultane-
ously. Under these conditions, the selected inputs are mixed
together and output on the selected channel.
CONTROL) shows how the input signals are mixed together
for each possible input selection.
SHUTDOWN FUNCTION
The LM49153 features the following shutdown controls: Bit
B4 (GAMP_ON) of the SHUTDOWN CONTROL register con-
trols the gain amplifiers. When GAMP_SD = 1, it disables the
gain amplifiers that are not in use. For example, in Modes 1,
4 and 5, the Mono inputs are in use, so the Left and Right
input gain amplifiers are disabled, causing the I
imized. Bit B0 (PWR_ON) of the SHUTDOWN CONTROL
register is the global shutdown control for the entire device.
Set PWR_ON = 0 for normal operation. PWR_ON = 1 over-
rides any other shutdown control bit.
CLASS D AMPLIFIER
he LM49153 features a mono class D audio power amplifier
with a filterless modulation scheme that reduces external
component count, conserving board space and reducing sys-
tem cost. With no signal applied, the outputs (LSOUT+ and
LSOUT-) switch between VDD and GND with 50% duty cycle,
in phase, causing the two outputs to cancel. This cancellation
results in no net voltage across the speaker, thus there is no
current to the load in the idle state.
With an input signal applied, the duty cycle (pulse width) of
the class D output changes. For increasing output voltage, the
duty cycle of LSOUT+ increases, while the duty cycle of
LSOUT- decreases. For decreasing output voltages, the con-
verse occurs. The difference between the two pulse widths
yields the differential output voltage.
ENHANCED EMISSION SUPPRESSION (E
The LM49153 class D amplifier features National’s patent-
pending E
quality audio reproduction and efficiency. The E
features selectable spread spectrum and advanced edge rate
control (ERC). The LM49153 class D ERC greatly reduces
the high frequency components of the output square waves
by controlling the output rise and fall times, slowing the tran-
sitions to reduces RF emissions, while maximizing THD+N
and efficiency performance.
SPREAD SPECTRUM
The selectable spread spectrum mode minimizes the need for
output filters, ferrite beads or chokes. In spread spectrum
mode, the switching frequency varies randomly by 30% about
2
S system that reduces EMI, while maintaining high
2
C interface. The mixer/multiplexer al-
2
Table 5
S)
DD
2
to be min-
S system
(MODE
18
a 300kHz center frequency, reducing the wideband spectral
content, improving EMI emission radiated by the speaker and
associated cables and traces. Where a fixed frequency class
D exhibits large amounts of spectral energy at multiples of the
switching frequency, the spread spectrum architecture
spreads that energy over a larger bandwidth. The cycle-to-
cycle variation of the switching period does not affect the
audio reproduction, efficiency, or PSRR. Set bit B0 (SS_EN)
of the SS CONTROL register to 1 to enable spread spectrum
mode.
GROUND REFERENCE HEADPHONE AMPLIFIER
The LM49153 features a low noise inverting charge pump that
generates an internal negative supply voltage. This allows the
headphone outputs to be biased about GND instead of a
nominal DC voltage, like traditional headphone amplifiers.
Because there is no DC component, the large DC blocking
capacitors (typically 220μF) are not necessary. The coupling
capacitors are replaced by two small ceramic charge pump
capacitors, saving board space and cost. Eliminating the out-
put coupling capacitors also improves low frequency re-
sponse. In traditional headphone amplifiers, the headphone
impedance and the output capacitor from a high-pass filter
that not only blocks the DC component of the output, but also
attenuates low frequencies, impacting the bass response.
Because the LM49153 does not require the output coupling
capacitors, the low frequency response of the device is not
degraded by external components. In addition to eliminating
the output coupling capacitors, the ground referenced output
nearly doubles the available dynamic range of the LM49153
headphone amplifiers when compared to a traditional head-
phone amplifier operating from the same supply voltage.
EARPIECE (EP) BYPASS
When B4 of MODE_CONTROL register is set to 1, earpiece
amplifier is enabled and differential inputs are passed down
to speaker outputs. This in turn disables the class D amplifier.
AUTOMATIC LIMITER CONTROL (ALC)
When enabled, the ALC continuously monitors and adjusts
the gain of the loudspeaker amplifier signal path if necessary.
The ALC serves two functions: voltage limiter/speaker pro-
tection and output clip prevention (No-Clip) with three clip
controls levels. The voltage limiter/speaker protection pre-
vents an output overload condition by maintaining the loud-
speaker output signal below a preset amplitude (See voltage
Limiter section). The No Clip feature monitors the output sig-
nal and maintains audio quality by preventing the loudspeaker
output from exceeding the amplifier’s headroom (see No Clip/
Output Clip Control section). The voltage limiter thresholds,
clip control levels, attack and release times are configured
through the I
VOLTAGE LIMITER
The voltage limiter function of the ALC monitors and prevents
the audio signal from exceeding the voltage limit threshold
(). The voltage limit threshold (V
in the Voltage Limit Threshold Register (see
though the ALC reduces the gain of the speaker path to
maintain the audio signal below the voltage limit threshold, it
is still possible to overdrive the speaker output in which case
loudspeaker output will exceed the voltage limit threshold and
cause clipping on the output, and speaker damage is possi-
ble. Please see the ALC Headroom section for further details.
2
C interface.
TH(VLIM)
) is set by bits B2:B0
Table
6). Al-