TA2022 Ver la hoja de datos (PDF) - Tripath Technology Inc.

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TA2022

STEREO 90W (4Ω) CLASS-T™ DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPP™) TECHNOLOGY

Tripath Technology Inc. 

Tripath Technology, Inc. - Technical Information

APPLICATION INFORMATION

TA2022 Basic Amplifier Operation

The TA2022 has three major operational blocks: the signal processor, the MOSFET driver, and the

power MOSFETs. The signal processor is a 5V CMOS block that amplifies the audio input signal and

converts the audio signal to a switching pattern. This switching pattern is spread spectrum with a

typical idle switching frequency of about 650kHz. The switching patterns for the two channels are not

synchronized and the idle switching frequencies should differ by at least 40kHz to avoid increasing

the audio band noise floor. The idle frequency difference can be accomplished by offsetting the value

of CFB for each channel. Typical values of CFB are 390pF for channel 1 and 560pF for channel 2.

The MOSFET driver level-shifts the signal processor’s 5V switching patterns to the power supply

voltages and drives the power MOSFETs. The MOSFET driver includes a switching power supply

integrated to generate the VN10 supply. The VN10 supply powers the low side gate drivers as well

provides the charging current need for the “bootstrapped” supplies (VBOOT1 and VBOOT2) that

power the high side MOSFET drivers. VN10 must be stable (regulated) at 10V to 12V above VNN.

The VN10 circuitry shown in the Application / Test Circuit typically produces 11V above VNN.

The power MOSFETs are N-channel devices configured in half-bridges and are used to supply power

to the output load. The outputs of the power MOSFETs (OUT1 and OUT2) must be low pass filtered

to remove the high frequency switching pattern. A residual voltage from the switching pattern will

remain on the speaker outputs when the recommended output LC filter is used, but this signal is

outside of the audio band and will not affect audio performance.

Circuit Board Layout

The TA2022 is a power (high current) amplifier that operates at relatively high switching frequencies.

The output of the amplifier switches between VPP and VNN 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 TA2022 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 TA2022 evaluation board document, EB-TA2022, available on the

Tripath website, at www.tripath.com.

The following components are important to place near their associated TA2022 pins and 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. CHBR should be kept within 1/8” (3mm)

of the VNN(8,9) and VPP(4,12) pins. Please note that both VNN1 and VPP1 as well as

VNN2 and VPP2 must be decoupled separately. In addition, the voltage rating for CHBR

should be 100V as this capacitor is exposed to the full supply range, VPP-VNN.

- DO, fast recovery PN junction diodes minimize undershoots of the outputs with respect to

power ground during switching transitions and abnormal load conditions such as output

shorts to ground. For maximum effectiveness, these diodes must be located close to the

output pins and returned to their respective VNN1(2). Please see Application/Test Circuit

for ground return pin.

- CFB removes very high frequency components from the amplifier feedback signals and

lowers the output switching frequency by delaying the feedback signals. In addition, the

value of CFB is different for channel 1 and channel 2 to keep the average switching

frequency difference greater than 40kHz. This minimizes in-band audio noise.

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TA2022 – KLI/1.2/07-04

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