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SLOS407D − FEBRUARY 2003 − REVISED AUGUST 2004
By driving the outputs into heavy clipping with a sine wave of less than 50 Hz, the bootstrap voltage can
decrease below the minimum V required to keep the high-side output MOSFET turned on. When this occurs,
gs
the output transistor becomes a source-follower and the output drops from V
on pins 25 and 36).
to approximately V
(voltage
CC
clamp
For the majority of applications, driving a square wave at low frequencies is not a design consideration and the
recommended bootstrap capacitor value of 10-nF is acceptable. However, if this is a concern, increasing the
bootstrap capacitors holds the gate voltage for a longer period of time and the drop in the output voltage does
not occur. A value of 220-nF is recommended with a 51 Ω resistor placed in series between the outputs and
bootstrap pins. The 51 Ω series resistor is necessary to limit the current charging and discharging the bootstrap
capacitors.
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-µF 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
and may not be used for powering any other circuitry.
CC
Internal Regulated 5-V Supply (AV
)
DD
The AV
terminal (pin 29) is the output of an internally-generated 5-V supply, used for the oscillator,
DD
preamplifier, and volume control circuitry. It requires a 0.1-µF to 1-µF capacitor, placed very close to the pin,
to ground to keep the regulator stable. The regulator may be used to power an external headphone amplifier
or other circuitry, up to a current limit specified in the specification table. When powering external circuitry, like
the TPA6110A2 headphone amplifier, an additional 10 µF or larger capacitor should be added to the AV
terminal.
DD
AV
− POWER-UP RESPONSE
DD
Power−Up
Ch1
(AV
AV
DD
(pin 29)
)
DD
AV
(pin 33)
CC
Ch2
(AV
)
CC
Ch1 2 V/div
Ch2 5 V/div
M 10.0 µs
Figure 46. Power-Up Response
Differential Input
The differential input stage of the amplifier cancels any noise that appears on both input lines of the channel.
To use the TPA3004D2 EVM with a differential source, connect the positive lead of the audio source to the INP
input and the negative lead from the audio source to the INN input. To use the TPA3004D2 with a single-ended
source, ac ground the INP input through a capacitor equal in value to the input capacitor on INN and apply the
audio source to the INN input. In a single-ended input application, the INP input should be ac-grounded at the
audio source instead of at the device input for best noise performance.
31
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