LX1701CLQ MICROSEMI [Microsemi Corporation], LX1701CLQ Datasheet - Page 7

• Manufacturer Part Number: LX1701CLQ
• Description: 2W Filterless Mono Class-D Audio Amplifier
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2004
Rev. 1.0a, 2004-07-09
G
power amplifier. It offers high performance (THD+N is
just 0.1% at 2W), high efficiency (>85% at 1.2W), and best
in class EMI radiation (just 20dBuV/m).
signal path is completely differential to minimize common-
mode noise pickup. The inputs may be driven single-ended
or differentially and they may be direct or AC coupled. The
LX1701 may be operated with just a single decoupling
capacitor.
F
The LX1701 output stage is configured as a full H-bridge
push-pull driver. The speaker must be driven differentially
from the OUTP and OUTN pins. Each side of the speaker
is driven by a 200KHz switching signal that transitions
between Vdd and GND. With zero input voltage, the duty
cycle at each output is around 50% and the signals are in-
phase with each other. In this case, there is basically no
differential voltage across the speaker.
signal goes positive, the duty cycle at OUTP increases
above 50% and the duty cycle at OUTN decreases below
50%. This causes a net positive current to flow into the
speaker. A negative input voltage causes the OUTN duty
cycle to increase and the OUTP duty cycle to decrease
which causes a net negative current to flow into the
speaker. The differential voltage across the speaker has a
fundamental frequency of twice the 200KHz switching
frequency. The speaker itself serves as the low pass filter
which then recreates the audio signal.
modulation can be described as driving +Vdd, -Vdd, and
0V across the speaker which is why it is referred to as 3-
Level modulation.
Classical, 2-Level modulation drives either +Vdd or –Vdd
across the speaker at all times. This scheme requires an L-
C filter between the amplifier’s outputs and the speaker in
order to keep the output current low.
ILTERLESS
ENERAL
The LX1701 is a filterless, low-EMI, class-D audio
TM
D
ESCRIPTION
3-L
EVEL
11861 Western Avenue, Garden Grove CA. 92841 714-898-8121, FAX [phone]
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F U N C T I O N A L D E S C R I P T I O N
When the input
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AND
With 3-Level modulation, the carrier frequency drives a
full amplitude common-mode signal to the speaker wires.
This can cause high EMI radiation. One way to combat
this would be to filter the outputs with L-C filters or ferrite
beads located close to the amplifier. In the LX1701, the
output stage has been carefully designed to minimize EMI
radiation so that these types of filters are not required.
Slew rate limiting is used to keep the outputs from
switching too quickly. Active overshoot clamping is used
to minimize the inductive overshoot which occurs at each
transition. These two techniques allow the LX1701 to
easily meet FCC standards for radiated emissions when
driving up to 3 meters of speaker wire.
A
An internal DC servo loop senses the output differential
voltage and feeds it back to the error amplifier through a
low pass filter. The corner frequency of this filter can be
set at 20Hz or 300Hz via a control pin. This allows the
LX1701 to reject signals below these frequencies. Since
this is an active control loop, it does not have the same
dynamic range as a purely passive solution (such as an
input AC-coupling capacitor). The dynamic range of the
offset cancellation loop is a function of the selected gain
and high pass corner frequency. In applications where the
input offset may be higher than the DC offset cancellation
range, AC-coupling capacitors should be used.
D
AND
The fully differential signal path uses delta-sigma
techniques and multiple feedback loops to provide high
performance and low distortion. This is all fully-integrated
to eliminate the need for any external feedback
components or filters. The gain can be selected to be either
8 or 14dB by a control pin. The differential signal path
and internal voltage boosters allow for wide dynamic
range. In fact, the LX1701 can be operated from supplies
as low as 1.8V and as high as 6V. The output power will
be limited by the available supply voltage.
thermal sensing circuit shuts down the outputs and forces
the TOVL output pin high when the junction temperature
exceeds about 150degC to provide thermal overload
protection.
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2W Filterless Mono Class-D Audio Amplifier
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LX1701
IMITING
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