54
DS726PP2
CS4525
6.2
Hardware Mode
A limited feature set is available when the CS4525 powers up in hardware mode. The available features are
described in the following sections. All device configuration is achieved via hardware control input pins.
6.2.1
System Clocking
In hardware mode, the CS4525 must be clocked by a stable external clock source input on the SYS_CLK
pin. This input clock is used to synchronize the input serial audio signals with the internal clock domain
and to clock the internal digital processing, sample-rate converter, and PWM modulators. It is also used
to determine the sample rate of the serial audio input signals in order to automatically configure the vari-
ous internal filter coefficients.
To ensure proper operation, the CS4525 must be informed of the nominal frequency of the supplied
SYS_CLK signal via the ClkFreq[1:0] hardware control pins. These pins must be set to the appropriate
level before the RST signal is released to initiate a power-up sequence. The nominal clock frequencies
indicated by the states of the ClkFreq[1:0] pins are shown in
below. See the
table on
for complete input frequency range specifications.
WARNING: The SYS_CLK signal must never be removed or stopped while the RST pin is high and any
of the power output stages are connected to a load. Doing so may result in permanent damage to the
CS4525 and connected transducers.
below demonstrates a typical clocking configuration using the SYS_CLK input.
6.2.2
Power-Up and Power-Down
The CS4525 will remain in a completely powered-down state until the RST pin is brought high.
6.2.2.1
Recommended Power-Up Sequence
1.
Hold RST low until the power supplies and the input SYS_CLK signal are stable.
2.
Bring RST high.
Hardware mode will be entered after approximately 10 ms.
ClkFreq1
ClkFreq0
Nominal SYS_CLK Frequency
Low
Low
18.432 MHz
Low
High
24.576 MHz
High
Low
27.000 MHz
High
High
Reserved
Table 13. SYS_CLOCK Frequency Selection
SYS_CLK
RST
DSP
Reset_Out
Clock_In
Clock
XTI
XTO
Figure 22. Typical SYS_CLK Input Clocking Configuration
CS4525