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SWITCHING FREQUENCY
fs +
6.6
R
OSC COSC
(8)
POWER SUPPLY DECOUPLING, C
S
MIDRAIL BYPASS CAPACITOR, C
BYP
CBYP ≥ 10 × CI
(9)
DIFFERENTIAL INPUT
SHUTDOWN MODES
SLOS291F – MARCH 2000 – REVISED MARCH 2007
The switching frequency is determined using the values of the components connected to ROSC (pin 18) and COSC
(pin 7) and is calculated with the following equation:
The switching frequency was chosen to be centered on 250 kHz. This frequency is the optimum audio fidelity of
oversampling and of maximizing efficiency by minimizing the switching losses of the amplifier. The
recommended values are a resistance of 120 k
and a capacitance of 220 pF. Using these component values,
the amplifier operates properly by using 5% tolerance resistors and 10% tolerance capacitors. The tolerance of
the components can be changed, as long as the switching frequency remains between 200 kHz and 300 kHz.
Within this range, the internal circuitry of the device provides stable operation.
The TPA2000D2 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling
to ensure the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also
prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is
achieved by using two capacitors of different types that target different types of noise on the power supply leads.
For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance
(ESR) ceramic capacitor, typically 0.1 F placed as close as possible to the device VDD lead works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10 F or greater placed near
the audio power amplifier is recommended.
The midrail bypass capacitor, CBYP, is the most critical capacitor and serves several important functions. During
start-up or recovery from shutdown mode, CBYP determines the rate at which the amplifier starts up. The second
function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This
noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and
THD+N.
Bypass capacitor, CBYP, values of 0.47 F to 1 F ceramic or tantalum low-ESR capacitors are 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. To have minimal pop, CBYP should be 10 times larger than CI.
The differential input stage of the amplifier cancels any noise that appears on both input lines of a channel. To
use the TPA2000D2 EVM with a differential source, connect the positive lead of the audio source to the RINP
(LINP) input and the negative lead from the audio source to the RINN (LINN) input. To use the TPA2000D2 with
a single-ended source, ac ground the RINN and LINN inputs through a capacitor and apply the audio single to
the RINP and LINP inputs. In a single-ended input application, the RINN and LINN inputs should be
ac-grounded at the audio source instead of at the device inputs for best noise performance.
The TPA2000D2 employs a shutdown mode of operation designed to reduce supply current, IDD, to the absolute
minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN input terminal should
be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the outputs
to mute and the amplifier to enter a low-current state, IDD(SD) = 1 A. SHUTDOWN should never be left
unconnected, because amplifier operation would be unpredictable.
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