Using the AT89RFD-08 Board
2-26
AT89RFD-08 Hardware User Guide
4382E–MP3–05/06
10. How can I improve the USB VBUS detection to avoid the power through I/O if
AT8xC51SND2C is not powered?
You can use the VBUS detection described in AT89RFD-08 schematics.
11. Can I connect AT8xC51SND2C reset pin to a Controller GPIO?
You can use the following schematic:
12. What the effect to change the INGND, CBP, AUDVREF, AUDVCM capacitor
values?
n INGND is the reference input of the LINE_IN input stages. Should be chosen equal to
two times the input LINE_IN capacitors. For a full audio bandwidth, Zin_min=9kOhms,
Cin=1uF, INGND capa =2.2uF recommended. For a vocal-range bandwidth,
Cin=100nF, INGND cap =220nF (for a 200Hz cut-off frequency).
n CBP capacitor value: This is the decoupling capacitor of the internal half-supply
reference of the power amplifier. 100nF are recommended. Should be reduced down
to 10nF for a vocal-range usage (300-3000 Hz bandwidth).
n AUDVREF capacitor: decoupling capacitor of the reference of the DAC. 10uF is
mandatory to insure a proper reference. It should not be reduced.
n AUDVCM capacitor: decoupling capacitor of the common mode reference of the
headset/line-out amplifiers, the common mode reference of the MONO PA driver, the
common-mode reference of the LINE_IN input stages, the common-mode reference
of the AUX input stage, and the common mode reference of the DACs. Can not be
reduced, in order to insure proper references.
13. Shall I add a high pass filter to avoid noise on PA output (<1KHz)?
It is possible to change the capacitors of PA input (PAINP, PAINN) to adjust the low cut-
ting frequency. The input impedance also depends on the selected gain:
F(-3 dB) = 1/ (2 PI Cin Zin)
where Cin is the capacitor value and Zin the PA input impedance.
Table 2-7.
PA Gain / Zin
PA Gain (dB)
PA Zin (ohm)
20
15 K
17 21
K
14 27
K
11
36 K
AT8xC51SND2C RST
R=150 Ohms
Controller GPIO