lm48310sd National Semiconductor Corporation, lm48310sd Datasheet - Page 11

• Manufacturer Part Number: lm48310sd
• Description: Ultra-low Emi, Filterless, 2.6w, Mono, Class D Audio Power Amplifier With E2s
• Manufacturer: National Semiconductor Corporation

Application Information
GENERAL AMPLIFIER FUNCTION
The LM48310 mono Class D audio power amplifier features
a filterless modulation scheme that reduces external compo-
nent count, conserving board space and reducing system
cost. With no signal applied, the outputs (V
switch between V
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 the input signal applied, the duty cycle (pulse width) of
the LM48310 outputs changes. For increasing output voltage,
the duty cycle of V
V
verse occurs. The difference between the two pulse widths
yields the differential output voltage.
ENHANCED EMISSIONS SUPPRESSION SYSTEM (E
The LM48310 features National’s patent-pending E
that reduces EMI, while maintaining high quality audio repro-
duction and efficiency. The E
nizable oscillator with selectable spread spectrum, and
advanced edge rate control (ERC). The LM48310 ERC great-
ly reduces the high frequency components of the output
square waves by controlling the output rise and fall times,
slowing the transitions to reduce RF emissions, while maxi-
mizing THD+N and efficiency performance. The overall result
of the E
FCC Class B radiated emissions standards with 20in of twist-
ed pair cable, with excellent 0.03% THD+N and high 88%
efficiency.
FIXED FREQUENCY MODE (SYNC_IN = GND)
The LM48310 features two modulations schemes, a fixed fre-
quency mode and a spread spectrum mode. Select the fixed
frequency mode by setting SYNC_IN = GND. In fixed fre-
quency mode, the amplifier output switch at a constant
300kHz. In fixed frequency mode, the output spectrum con-
sists of the fundamental and its associated harmonics (see
Typical Performance Characteristics).
SPREAD SPECTRUM MODE (SYNC_IN = V
The logic selectable spread spectrum mode eliminates the
need for output filters, ferrite beads or chokes. In spread
OUTB
decreases. For decreasing output voltages, the con-
2
S system is a filterless Class D amplifier that passes
DD
OUTA
and GND with a 50% duty cycle, in
increases, while the duty cycle of
2
S system features a synchro-
OUTA
DD
)
and V
2
S system
OUTB
2
S)
)
11
spectrum mode, the switching frequency varies randomly by
30% about a 300kHz center frequency, reducing the wide-
band spectral contend, 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 LM48310 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 SYNC_IN =
V
EXTERNAL CLOCK MODE (SYNC_IN = CLOCK)
Connecting a clock signal to SYNC_IN synchronizes the
LM48310 oscillator to an external clock, moving the output
spectral components out of a sensitive frequency band, and
minimizing audible beat frequencies when multiple LM48310s
are used in a single system. The LM48310 accepts an exter-
nal clock frequency between 200kHz and 1MHz. The
LM48310 can be synchronized to a spread spectrum clock,
allowing multiple LM48310s to be synchronized in spread
spectrum mode (see SYNC_OUT section).
SYNC_OUT
SYNC_OUT is a clock output for synchronizing external de-
vices. The SYNC_OUT signal is identical in frequency and
duty cycle of the amplifier’s switching frequency. When the
LM48310 is in fixed frequency mode, SYNC_OUT is a fixed,
300kHz clock. When the LM48310 is in spread spectrum
mode, SYNC_OUT is an identical spread spectrum clock.
When the LM48310 is driven by an external clock,
SYNC_OUT is identical to the external clock. If unused, leave
SYNC_OUT floating.
Multiple LM48310s can be synchronized to a single clock. In
Figure 2, device U1 is the master, providing a spread spec-
trum clock to the slave device (U2). This configuration syn-
chronizes the switching frequencies of the two devices,
eliminating
SYNC_OUT has no audio content, there is minimal THD+N
degredation or crosstalk between the devices, Figure 3-5.
DD
for spread spectrum mode.
any
audible
beat
frequencies.
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