Using the AT89RFD-08 Board
2-22
AT89RFD-08 Hardware User Guide
4382E–MP3–05/06
Figure 2-22.
Headset Output when adding serial resistor Rs
Cutting Frequency is now:
F
c
=1/(2.PI.(R
LOAD
+Rs).C)
The effective power is now given by the following formula:
P
EFF MAX
= 0.72.R
LOAD
/ (Rs+R
LOAD
)
2
[W Rms]
Table 2-6.
Cutting Frequency Versus Effective Power when adding Rs
Note:
When adding the serial resistor Rs, attenuation is: 20.log[R
LOAD
/(Rs+R
LOAD
)] = -12 dB.
4. I don’t use HSL and HSR, can they stay unconnected?
HSR HSL can stay unconnected if not used and not activated.
5. Regarding the AT89RFD-08 schematics, I want to use 2.7 V for AT8xC51SND2C
instead of 3V, and AUDVBAT connected to battery 3.6V, is it possible?
Yes, it is possible but AT8xC51SND2C power supply shall be at least 3V for USB oper-
ation to comply USB specification. In this case, you can use the power supply schematic
described below.
Note:
The schematic refer to Sipex SP6231EN-33: 500mA, 3.3V Linear Regulator with Auxil-
iary Backup.The SP6231 is a 500mA, 3.3V LDO with an integrated auxiliary voltage input
switch. During normal operation, the SP6231 acts as a standard LDO with an output volt-
age of 3.3V delivering up to 500mA. When the USB VBUS 5V input drops below 4.4V,
the 3.3V, VAUX input is switched to the output through an internal PFET, maintaining a
constant “glitch free” output voltage.
HSL
AUDVSS
R
LOAD
C
HSR
Rs
Capacitor C (
m
F)
Load Resistance Rs + R
LOAD
(32+96 Ohms)
Cutting Frequency (Hz)
Effective Power (mW Rms)
100 128
12
1.4
22 128
57
1.4
10 128
124
1.4