LM49450SQ/NOPB National Semiconductor, LM49450SQ/NOPB Datasheet - Page 23

• Manufacturer Part Number: LM49450SQ/NOPB
• Description: IC AUDIO SUBSYSTEM 2.5W D 32LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class Dr

Specifications of LM49450SQ/NOPB

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 2.5W x 2 @ 4 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: 3D, DAC, Depop, I²C, I²S, Mute, Short-Circuit and Thermal Protection, Shutdown, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 32-LLP
• Amplifier Class: D
• No. Of Channels: 2
• Output Power: 1.2W
• Supply Voltage Range: 2.7V To 5.5V
• Load Impedance: 8ohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: LLP
• Rohs Compliant: Yes
• For Use With: LM49450SQEVAL - BOARD EVAL FOR LM49450
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM49450SQ; LM49450SQ; LM49450SQTR

Fixed Frequency Mode
The LM49450 features two modulation schemes, a fixed fre-
quency mode and a spread spectrum mode. Select the fixed
frequency mode by setting the SS bit (B3) in the Mode Control
Register (0x00h) to 0. In fixed frequency mode, the speaker
amplifier outputs switch at a constant 300kHz. The output
spectrum in fixed frequency mode consists of the fundamen-
tal and its associated harmonics (see Typical Performance
Characteristics).
Spread Spectrum
The logic selectable spread spectrum mode eliminates the
need for output filters, ferrite beads or chokes. In spread
spectrum mode, the switching frequency varies randomly by
30% about a 300kHz center frequency, reducing the wide-
band spectral content, improving EMI emissions 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 of the LM49450 spreads that energy over a larger
bandwidth (see Typical Performance Characteristics). The
cycle-to-cycle variation of the switching period does not affect
the audio reproduction, efficiency, or PSRR. Set the SS bit
(B3) in the Mode Control Register (0x00h) to 1 to select
spread spectrum mode.
Headphone Amplifier
The LM49450 headphone amplifiers feature National’s
ground referenced architecture that eliminates the large DC-
blocking capacitors required at the outputs of traditional head-
phone amplifiers. A low-noise inverting charge pump creates
a negative supply (HPV
(CPV
lar supplies, with the amplifier outputs biased about GND,
instead of a nominal DC voltage (typically V
tional amplifiers. Because there is no DC component to the
headphone output signals, the large DC-blocking capacitors
(typically 220µF) are not necessary, conserving board space
and system cost, while improving frequency response.
Power Supplies
The LM49450 uses different power supplies for each portion
of the device, allowing for the optimum combination of head-
room, power dissipation and noise immunity. The analog
input, and gain (volume control) stages for both speaker and
headphones are powered from V
stage is powered from LSV
charge pump are powered from HPV
supplies allow the class D amplifiers to operate from a higher
voltage, maximizing headroom, while the headphones oper-
ate from a lower voltage, improving power dissipation, as well
as minimizing switching noise coupling between the speaker
and headphone amplifiers. The digital portion of the device is
powered from DV
DAC. IOV
to interface with lower voltage digital controllers.
National's 3D Enhancement
The LM49450 digital audio path features National’s 3D en-
hancement that widens or narrows the perceived soundstage
of a stereo audio signal. The 3D enhancement either increas-
es or decreases the apparent stereo channel separation,
improving audio reproduction whenever the placement of
both left and right speakers is not ideal.
The LM49450 3D function is controlled through the I
face. The headphone and speakers have independent 3D
controls, allowing each signal path to have its own individual
DD
). The headphone amplifiers operate from these bipo-
DD
powers the I
DD
, including the 3D processing core and
SS
2
) from the positive supply voltage
DD
S and I
. The headphone amplifiers and
2
C, allowing the LM49450
DD
DD
. The speaker output
. The separate power
DD
/2), like tradi-
2
C inter-
23
3D configuration. The LM49450 3D features two effect
modes, a narrow effect that decreases the channel separa-
tion, making the speakers sound closer together, and a wide
effect that makes the speakers sound farther apart. Because
the narrow effect mode adds a portion of the left and right
signals together, a selectable 6dB attenuation mode is pro-
vided to maintain a constant output amplitude when the nar-
row effect mode is active without changing the volume level.
The high pass 3dB roll off frequency, 3D gain (amount chan-
nel mixing), and narrow/wide effect selection is done through
registers 0x05h (headphone) and 0x06h (speaker. See the
Headphone 3D Configuration Register and Loudspeaker 3D
Control Register sections for more information.
Headphone Sense
The LM49450 features a headphone sense input (HPS) that
monitors the headphone jack and configures the device de-
pending on the presence of a headphone. When the HPS pin
is low, indicating that a headphone is not present, the
LM49450 speaker amplifiers are active and the headphone
amplifiers are disabled. When the HPS pin is high, indicating
that a headphone is present, the headphone amplifiers are
active while the speaker amplifiers are disabled.
Volume Control
The LM49450 features two separate 32-step volume controls,
one for the speaker channels and one for the headphone
channels. This allows for the gain of the headphone and
speakers to be set independently of each other.
FIGURE 8. HPS Connection
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