Cirrus Logic AN285 - Manual (Page 8)

8 AN285REV1
AN285
7.2.2 CS5343/4 Full-Scale Voltage
The CS5333 full-scale input voltage is 0.78xVA Vpp whereas the CS5343/4 full-scale input voltage is
0.56xVA Vpp, a difference of nearly 3 dB. This means that without attenuation, a full-scale signal to the
CS5333 will over-range the CS5343/4. In migrating from the CS5333 to the CS5343/4, the input signal
should either be reduced by 3 dB at the source or resistor values should be chosen such that the
CS5343/4 input network provides 3 dB of attenuation. The following equation yields the attenuation (in
dB) of the input network where R1 represents the series resistor and R2 is the resistor to ground:
8. REFERENCE VOLTAGES
The reference voltage pins have the same configuration and usage on the CS5343/4 as the CS5333. FILT+ on both
devices outputs the full-scale voltage reference (VA), while the VQ pin outputs the common-mode voltage (VAx0.5
for the CS5333; VAx0.44 for the CS5343/4). Neither FILT+ nor VQ on either device can source current without de-
grading the analog performance of the device.
8.1 Filter Capacitors
The filter capacitors on these pins provide rejection of power-supply noise and consequently affect THD+N
performance. Both devices require 1
µF filter capacitors from the voltage reference pins to GND. Larger ca-
pacitors will improve low-frequency THD+N to within the limitations of the device. A small capacitor, such
as a 0.1
µF, placed close to the device will filter high-frequency noise.
8.2 Settling Time
Following initial power-up, the analog reference voltage requires time to settle before conversion can be
considered valid. Settling time of the reference voltage depends on the output impedance (R
out
) and the
value of the external capacitance (C
ext
) according to the following equation (time given in seconds):
For the same value capacitors on the CS5333 and CS5343/4 voltage reference pins, the CS5343/4 will re-
quire shorter settling time than the CS5333 due to the higher output impedance of the CS5333 FILT+. Typ-
ical output impedance of the CS5333 FILT+ is 250 k
Ω whereas CS5343/4 typical FILT+ output impedance
is 220 k
Ω. This means the CS5343/4 reference voltage will settle 12% faster than the CS5333 reference
voltage.
9. DIGITAL INTERFACE FORMAT
Please see Application Note AN282 for a complete overview of the serial audio interface (SAI).
9.1 CS5333 Interface Format
The CS5333 features a DIF pin to select between I²S and LJ digital audio formats. I²S digital audio format
is selected when DIF is tied low at start-up whereas the CS5333 will output LJ audio data when DIF is tied
to VL at start-up.
9.2 CS5343/4 Interface Format
The CS5343/4 family of converters supports both I²S and LJ digital audio format. Specifically, the CS5343
will support only I²S digital audio format while the CS5344 will output only LJ audio data.
20
R2
R1 R2 +
--------------------
⎝ ⎠
⎛ ⎞
log
×
SettlingTime s
( ) 5 Rout Cext Ч Ч
=