UG-373
Evaluation Board User Guide
Rev. 0 | Page 4 of 8
PASSIVE COMPONENT SELECTION
INPUT GAIN RESISTORS
If the desired gain of the amplifier is lower than the default 6 dB
or 0 dB gain settings, a series resistor can be placed in the input
signal path. This creates a voltage divider with the 18 kΩ input
resistance on each input pin, allowing an arbitrary reduction
of the input signal. Note that input signal attenuation directly
reduces SNR performance; therefore, large values compared
to the built-in input resistance should be avoided. These
components are populated with 0 Ω values on the evaluation
board (R1, R2, R3, R4).
INPUT COUPLING CAPACITORS
The input coupling capacitors, C1, C2, C3, and C4, should be
large enough to couple the low frequency signal components
in the incoming signal but small enough to reject unnecessary
extremely low frequency signals. For music signals, the cutoff
frequency is typically between 20 Hz and 30 Hz. The value of
the input capacitor is calculated by
C
= 1/(2
R
IN
f
c
)
where:
R
IN
= 18 kΩ + (R1
,
R2 or R3, R4).
f
c
is the desired cutoff frequency.
CHARGE PUMP FLYING CAPACITOR
The headphone amplifier uses Class-G architecture and generates
the required power supplies with a built-in charge pump, using a
flying capacitor connected across CF1 and CF2, C8. The value
of C8 is recommended to be 1.0 μF, X7R ceramic capacitor for
optimal charge pump operation.
DECOUPLING CAPACITORS FOR CPVDD AND
CPVSS
The charge pump within
SSM2932
generates CPVDD (positive)
and CPVSS (negative) voltage rails for headphone amplifier
headphone operation. C9 and C10 serve as a reservoir for the
amplifier. For best audio performance, it is recommended that
2.2 μF, X7R ceramic decoupling capacitors be used for CPVDD
and CPVSS.
