MD3203
Filterless 3W Class-D Stereo Audio Amplifier
the second stage’s gain is fixed at 2x. The output
of amplifier 1 serves as the
Ω,minimum R
24dB.
i=18kΩ,so the maximum closed-gain is
Mute Operation
The MUTE pin is an input for controlling the output
state of the MD3203,A logic low on this pin disables
the outputs,and a logic high on this pin enables the
outputs,This pin may be used as quick disable or
Shutdown operation
enableoftheOutputswithoutavolumefade.Quiescent
current is listed in the electrical characteristic
table.Te MUTE pin can be left floating due to the
internal pull-up.
In order to reduce power consumption while not in
use,theMD3203containsshutdowncircuitrytoturnoff
the amplifier’s bias circuitry. This shutdown
feature turns the amplifier off when logic low is
Power supply decoupling
applied to the SHDN pin,By switching the SHDN pin
connected to GND,the MD3203 supply current draw will
be minimized in idle mode,The SHDN pin can be left
floating due to the internal pull-up.
The MD3203 is a high performance CMOS audio amplifier
that requires adequate power supply decoupling to
ensure the output THD and PSRR as low as possible .
Power supply decoupling affects low as possible .
Power supply decoupling affects low frequency
response. Optimum decoupling is achieved by using two
capacitors of different types targeting to different
types of noise on the power supply leads. For higher
frequency transients,spikes,or digital has on the
line,a
good
low
equivalent-series-resistance(ESR)ceramic
capacitor, typically 1.0μF ,works best, placing it
as close as possible to the device VDD terminal.For
filtering lower-frequency noise signals,a large
capacitor of 20 μ F (ceramic) or greater is
recommended,placing it near the audio power
amplifier.
Input Capacitor(Ci)
Large input capacitors are both expensive and space
hungry for portable designs. Clearly,acertain sized
capacitor is needed to couple in low frequencies
without severe attenuation.But in many cases the
speakers used inportable systems,whether internal or
external,have little ability to reproduce signals
below 100Hz to 150Hz,Thus,using a large input
filter with the corner frequency determined by
equation below, fc=1/2TTRiCi in addition to system
cost and size,click and pop performance is affected
by the size of the input coupling capacitor Ci.A
larger input coupling capacitor requires more charge
to reach its quiescent DC voltage(nominall 1/2 VDD).
This charge comes from the internal circuit via the
feedback and is apt to create pops upon device
enable.Thus,by minimizing the capacitor size based
onnecessarylowfrequencyresponse,turn-onpopscan
be minimized.
capacitor
performance .In this case,input capacitor(Ci)and
inputresistance(R)oftheamplifierformahigh-pass
may
not
increase
actual
system
i
Analog Reference Bypass Capacitor(CBYP
)
The analog Reference Bypass Capacitor(CBYP)is the most
critical capacitor and serves several important
functions.During start-up or recovery from shutdown
mode, CBYP determines the rate at which the amplifier
starts up.The second function is to reduce noise
reference to the amplifier,which appears as degraded
PSRR and THD+N.
A ceramic bypass capacitor(CBYP)with values of 0.47
μF to 1.0μF .is recommended for the best THD and
noise performance.Increasing the bypass capacitor
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