Cirrus Logic CRD44800-ST-FB - Manual (Page 3)

CRD44800-ST-FB
3
1. SCHEMATIC DESCRIPTIONS
1.1 CRD44800-ST-FB PWM Amplifier
The CS44800 shown in Figure 2 employs a built-in Sample Rate Converter (SRC) to support
all popular sampling frequencies between 32 kHz and 192 kHz. The CS44800 produces a
PWM frequency of either 384 kHz or 768 kHz (refer to CS44800 data sheet). In this design,
analog or digital audio signals are always output at a 384 kHz PWM rate.
The CS4461 ADC is used to monitor the signal and line frequency related ripple that is inev-
itable on the power supply rail when the amplifiers operate. The ripple voltage is digitized
and fed back to the CS44800. The CS44800 uses this information to substantially reduce
ripple related distortion and noise in the audio output signal.
Four ST Micro STA500s provide the power back end to drive the speaker loads. Each
STA500 consists of a pair of fully current and temperature protected full-bridge PWM output
stages. The STA500 is optimized for use in open loop Class-D amplifier systems.
1.2 CRD44800-ST-FB Driver Board
The CRD44800-ST-FB Driver board provides a convenient source of PCM I²S signals to drive
the CRD44800-ST-FB PWM Amplifier board. Eight analog inputs allow multi-channel analog
audio signals to be used for evaluation of the amplifier. In addition, either optical or coaxial
stereo S/PDIF signals can be used to evaluate the amplifier. In this case, the left and right
digital input signals are distributed to each STA500.
The CRD44800-ST-FB Driver board provides two modes of operation: stand-alone and re-
mote. In the stand-alone mode, basic evaluation of the CS44800 is possible. The user can
select between analog and digital S/PDIF input signals (jumpers J17 and J18), control the
system volume, mute and unmute the system (switch S2), and enable or disable switching
on the PWM output (switch S3).
In the Remote mode, the DB-9 connector (J14, labelled RS-232) is connected to a host PC.
All aspects of the CS44800 may then be evaluated using the supplied software.
1.3 Switched Mode Power Supply
The SMPS used for the CRD44800-ST-FB is a 155 W OEM supply. The supply provides
+30 V for the STA500 PWM back ends, and +5 V to power all the signal level circuitry. The
SMPS is fully over-current and over-temperature protected.