Tripath Technology, Inc. - Preliminary Information
Application Information
TDA1400 Basic Amplifier Operation
The audio input signal is fed to the processor internal to the TDA1400, where a switching pattern is
generated. The average idle (no input) switching frequency is approximately 700kHz. With an input
signal, the pattern is spread spectrum and varies between approximately 200kHz and 1.5MHz depending
on input signal level and frequency. These switching patterns are inputted to a MOSFET driver and then
outputted to LO_POS (LO_NEG) and HO_POS (HO_NEG) which are ac-coupled to a complementary
pair of power MOSFETs. The output of the MOSFETs is a power-amplified version of the switching
pattern that switches between VPP and PGND, in the typical single supply application. This signal is then
low-pass filtered to obtain an amplified reproduction of the audio input signal.
The processor is operated from a 5-volt supply while the FET driver is operated from a 10-volt supply.
The FET driver inserts a “break-before-make” dead time between the turn-off of one transistor and the
turn-on of the other in order to minimize shoot-through currents in the external MOSFETs. The dead time
can be programmed by adjusting RBBMSET. Feedback information from the output of the complementary
FETs is supplied to the processor via FBK_POS and FBK_NEG.
Complementary MOSFETs are used to formulate a full-bridge configuration for the power stage of the
amplfier. The gate capacitors, CG, are used to ac-couple the FET driver to the complementary
MOSFETs. The gate resistors, RG, are used to control MOSFET slew rate and thereby minimize voltage
overshoots. Additional circuits are explained in the RB-TDA1400 document.
Circuit Board Layout
The TDA1400 is a power (high current) amplifier that operates at relatively high switching frequencies.
The output of the amplifier switches between VPP and PGND at high speeds while driving large currents.
This high-frequency digital signal is passed through an LC low-pass filter to recover the amplified audio
signal. Since the amplifier must drive the inductive LC output filter and speaker loads, the amplifier
outputs can be pulled above the supply voltage and below ground by the energy in the output inductance.
To avoid subjecting the TDA1400 and the complementary MOSFETs to potentially damaging voltage
stress, it is critical to have a good printed circuit board layout. It is recommended that Tripath’s layout and
application circuit be used for all applications and only be deviated from after careful analysis of the
effects of any changes. Please refer to the TDA1400 reference board document, RB-TDA1400, for
additional information.
The trace that connects the drain of the p-channel output MOSFET to the drain of the n-channel output
MOSFET is very important. This connection should be as wide and short as possible to minimize
inductance. Inductance on this trace can cause the switching output to over/undershoot potentially
causing damage to both the TDA1400 and the output MOSFETs.
The following components are important to place near the TDA1400 or output MOSFET pins. The
recommendations are ranked in order of layout importance, either for proper device operation or
performance considerations.
-
The capacitors, CHBR, provide high frequency bypassing of the amplifier power supplies and will
serve to reduce spikes across the supply rails. Please note that both MOSFET half-bridges
must be decoupled separately. In addition, the voltage rating for CHBR should be at least 100V
as this capacitor is exposed to the full supply range, VPP-PGND (single supply) or VPP-VNN
(split supply).
-
-
CFB removes very high frequency components from the amplifier feedback signals and lowers
the output switching frequency by delaying the feedback signals. The capacitors, CFB, should
be surface mount types, located on the “solder” side of the board as close to their respective
TDA1400 pins as possible.
D
DS should be placed as close to the drain and source of the output MOSFETs as possible with
direct routing either from the drain of the p-channel MOSFET to the source of the n-channel
14
TDA1400 – Rev. 0.65/KLi/02.06
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
