A2432
AUDIO AMPLIFIER
AiT Semiconductor Inc.
www.ait-ic.com
2X3W CLASS-D WITH DC VOLUME CONTROL AND EARPHONE OUTPUT
spikes, or digital hash on the line a good low equivalent series resistance (ESR) ceramic capacitor, typically
1μF, placed as close as possible to the device PVDD lead works best. Placing this decoupling capacitor close
to the A2432 is important for the efficiency of the Class-D amplifier, because any resistance or inductance in
the trace between the device and the capacitor can cause a loss in efficiency. For filtering lower-frequency
noise signals, a 4.7μF or greater capacitor placed near the audio power amplifier would also help, but it is not
required in most applications because of the high PSRR of this device.
Input Capacitors (CI)
The A2432 does not require input coupling capacitors if the design uses a differential source that is biased
from 0.5V to VDD-0.8V. If the input signal is not biased within the recommended common-mode input range, if
high pass filtering is needed, or if using a single-ended source, input coupling capacitors are required.
The input capacitors and input resistors from a high-pass filter with the corner frequency, fC, determined in
below equation
1
R
fC=
2π
I
CI
The value of input capacitor is important to consider as it directly affects the bass (low frequency)
performance of the circuit. Speaker in wireless phones cannot usually respond well to low frequencies, so the
corner frequency can be set to block low frequencies in this application. Not using input capacitors can
increase out offset. Below equation is used to solve for the input coupling capacitance.
1
R
CI=
2π
IfC
If the corner frequency is within the audio band, the capacitors should have tolerance of ±10% or better,
because any mismatch in capacitance causes an impedance mismatch at the corner frequency and below.
Analog Reference Bypass Capacitor (CREF
)
The Analog Reference Bypass Capacitor (CREF) is the most critical capacitor and serves several important
functions. During start-up or recovery from shutdown mode, C determines the rate at which the amplifier starts
up. The second function is to reduce noise caused by the power supply coupling into the output drive signal.
This noise is from the internal analog reference to the amplifier, which appears as degraded PSRR and
THD+N. A ceramic bypass capacitor (CBYP) with values of 0.47μF to 1.0μF is recommended for the best THD
and noise performance. Increasing the bypass capacitor reduces clicking and popping noise from power
on/off and entering and leaving shutdown.
REV1.1
- MAY 2012 RELEASED, MAR 2017 UPDATED -
- 11 -
AITSEMI [ AiT Semiconductor ]
