Cirrus Logic CRD42L51 - Manual (Page 6)

6 DS679RD1
CRD42L51
3.8 Switch & Pushbutton
The POWER switch engages the AAA battery when switched to the ON position. Power is applied to the
board and the microcontroller initializes. The SELECT pushbutton switches allow the user to navigate back
and forth between the FUNCTION options. When both SELECT buttons are pushed simultaneously, the
state of the function that receives focus (indicated by a blinking LED) is toggled. The ADJUST buttons allow
the user to apply gain, attenuation and move the threshold levels of the ALC and Limiter (the level of each
is shown in the Level Meter LED’s). When both ADJUST buttons are pushed simultaneously, the state of
the CS42L51’s internal beep generator is toggled.
3.9 LEDs
The FUNCTION LEDs provide a visual indication of which functions are presently ON (constant illumination)
or OFF (no illumination) and which has received focus (periodic illumination). The Level Meter LEDs provide
a visual indication of the Line, MIC, S/PDIF, Bass and Treble volume levels as well as the Limiter and ALC
threshold levels (see
Section 2 for LED luminosity decode). When the selected function receives focus, the
Level Meter LEDs are illuminated for a brief moment, reflecting the volume/threshold level, and flash when
the adjustment reaches the default level.
3.10 Error Indicators
Low Battery: When the battery voltage level in the AAA battery drops below approximately 0.96 V, this LED
will illuminate. Operation will continue until the level drops to approximately 0.70 V; but after a power cycle,
the DC-DC converter will only start up when the level is at least 1.1 V.
Receiver Error: If the S/PDIF function is enabled and the CS8416 loses its PLL lock (triggered by unpluggin
the cable from the optical connector, OPT1, or turning off the S/PDIF audio source), this LED will illuminate.
If the Line or MIC function is presently enabled, the CRD will automatically switch from the CS8416’s master
clock to the on-board oscillator and configure the CS42L51 accordingly for uninterrupted operation of the
Line or MIC input.
3.11 Layout
The CS42L51 requires only a minimal set of components to achieve specified performance results. Its inte-
grated ground-centered amplifier eliminates the need for bulky DC-blocking capacitors and only requires
two tiny ceramic capacitors for the charge pump. Additional components include load-stabilization circuitry
and power supply decoupling. See the CS42L51 data sheet for further details.
Figure 1 on page 8 provides an overview of the connections to the CS42L51. Figure 6 on page 13 and Fig-
ure 7 on page 14 show the component placement. Figure 8 on page 15 shows the top layout; Figure 9 on
page 16 and Figure 10 on page 17 show the inner layers, and Figure 11 on page 18 shows the bottom lay-
out. The decoupling capacitors are located as close to the CS42L51 as possible. Extensive use of ground
plane fill in the reference design yields large reductions in radiated noise.