Texas Instruments TPA3003D2 - Manual (Page 23)

TPA3003D2
SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003
23
www.ti.com
APPLICATION INFORMATION
The value of C
i
is important, as it directly affects the bass (low frequency) performance of the circuit. Consider
the example where Z
i
is 20 k Ω and the specification calls for a flat bass response down to 20 Hz. Equation 6
is reconfigured as equation 7.
C
i
+ 1
2
p
Z
i
f
c
In this example, C
i
is 0.4
µ
F, so one would likely choose a value in the range of 0.47
µ
F to 1
µ
F. If the gain is
known and will be constant, use Z
i
to calculate C
i
. Calculations for C
i
should be based off the impedance at the
lowest gain step intended for use in the system. A further consideration for this capacitor is the leakage path
from the input source through the input network (C
i
) and the feedback network to the load. This leakage current
creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especially in high gain
applications. For this reason a low-leakage tantalum or ceramic capacitor is the best choice. When polarized
capacitors are used, the positive side of the capacitor should face the amplifier input in most applications as
the dc level there is held at 2.5 V, which is likely higher than the source dc level. Note that it is important to confirm
the capacitor polarity in the application.
power supply decoupling, C
S
The TPA3003D2 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
µ F placed as close as possible to the device V
CC
lead works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10
µ
F or greater placed near
the audio power amplifier is recommended. The 10-
µ
F capacitor also serves as a local storage capacitor for
supplying current during large signal transients on the amplifier outputs.
BSN and BSP capacitors
The full H-bridge output stages use only NMOS transistors. They therefore require bootstrap capacitors for the
high side of each output to turn on correctly. A 10-nF ceramic capacitor, rated for at least 25 V, must be connected
from each output to its corresponding bootstrap input. Specifically, one 10-nF capacitor must be connected from
xOUTP to xBSP, and one 10-nF capacitor must be connected from xOUTN to xBSN. (See the application circuit
diagram in Figure 21.)
VCLAMP capacitors
To ensure that the maximum gate-to-source voltage for the NMOS output transistors is not exceeded, two
internal regulators clamp the gate voltage. Two 1-
µ
F capacitors must be connected from VCLAMPL (pin 25)
and VCLAMPR (pin 36) to ground and must be rated for at least 25 V. The voltages at the VCLAMP terminals
vary with V
CC
and may not be used for powering any other circuitry.
internal regulated 5-V supply (AV
DD
)
The AV
DD
terminal (pin 29) is the output of an internally-generated 5-V supply, used for the oscillator,
preamplifier, and volume control circuitry. It requires a 0.1-
µ
F to 1-
µ
F capacitor, placed very close to the pin,
to ground to keep the regulator stable. The regulator may not be used to power any external circuitry.
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