SI4700-EVB Datasheet, PDF (6/44 Pages) Silicon Laboratories – Si4700/01/02/03 EVALUATION BOARD USER’S GUIDE

Si4700/01/02/03-EVB
USB
J1
USB POWER
SW1
EXT POWER
R1 R2 R4
J7
J4
VRADIO
R25
NF
R14
0 ohm
U3
U6
VAUDIO
U2
VMCU/VIO
R30
NF
Figure 2. Power Configuration
3.1.4. Expansion I/O connector
The 20-pin Expansion I/O connector J3 provides access
to all the control signals of the Si4700/01/02/03
including the general purpose input/output pins. Pins for
the VA, VD, VIO, and RCLK pins of the Si4700/01/02/03
are also available. All test points on J3 are labeled
indicating the signal available at the pin.
Note: The unlabeled pins on J3 between (a) SCLK and
RST, and (b) RCLK and GPIO1, provide access to the
system ground.
3.2. Si4700/01/02/03 Daughter Card
3.2.1. Si4700/01/02/03 FM Tuner Chip
The Si4700/01/02/03 (U1) and its bypass capacitors*
are located on the daughter card. The Si4700/01/02/03
is configured to accept a single-ended FM input—the
FMIN pin is grounded and the FMIP pin is connected to
J1 through an ac-coupling capacitor. FMIP is also
connected to the ground wire of the headphone jack
(J3) for easy testing of a headphone wire as the
antenna. Refer to “AN231: Si4700/01 Headphone and
Antenna Interface” for more information.
*Note: We recommend a single bypass capacitor on VD. To
account for various supply designs and layouts, we
recommend that customers make provisions for
bypass capacitors at all supply pins.
3.2.2. Audio Amplifier
The daughter card includes a high-output drive dual op-
amp chip (U2—daughter card) to buffer the audio
outputs at the LOUT and ROUT pins of the
Si4700/01/02/03. The LOUT and ROUT pins are also
ac-coupled to the inputs of the op-amps on U4 -
daughter card. To drive the headphone jack, the op-
amps are connected in a unity-gain, noninverting
configuration and biased at the middle of the audio
power supply. The outputs of the U2 op-amps are in turn
ac-coupled to the BNC connectors J10 and J11 on the
baseboard.
The audio amplification network has been designed to
drive resistances of 10 k which is easily achievable on
most audio analyzers. The op-amps have enough drive
capability to drive resistances much lower than 10 k
(e.g. 32  headphones). In such cases, however, the
lower end of the audio spectrum (up to 2.5 kHz) will be
attenuated. This is because the 3-dB points of the high-
pass filters at the outputs of the op-amps move to higher
frequencies as the output resistance is decreased. Also
note that the op-amps are not protected against
extended short-circuit conditions. Hence, the audio
outputs at J10 and J11 should not be connected to a
mono input if the Si4700/01/02/03 is configured to
produce a stereo output.
6
Rev. 0.9