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

Figure 6: Short circuit load current with unsaturated toroidal inductor and

saturated bobbin Inductor (shielded)

Output Filter Design

Tripath amplifiers generally have a higher switching frequency than PWM implementations allowing

the use of higher cutoff frequency filters, reducing the load dependent peaking/drooping in the 20kHz

audio band. This is especially important for applications where the end customer may attach any

speaker to the amplifier (as opposed to a system where speakers are shipped with the amplifier),

since speakers are not purely resistive loads and the impedance they present changes over

frequency and from speaker model to speaker model. An RC network, or “zobel” (RZ, CZ) must be

placed at the filter output to control the impedance “seen” by the TA2022. The TA2022 works well

with a 2nd order, 107kHz LC filter with LO = 10uH and CO = 0.22uF and RZ = 6.2ohm/2W and CZ =

0.22uF. Some applications may require a more aggressive filter to reduce out of band noise. Below

are some proven filter combinations:

- 49.5kHz 2nd order filter

LO = 22uH

CO = .47uF

RZ = 8Ω

CZ = .47uF

- 33.6kHz 2nd order filter

LO = 33uH

CO = .68uF

RZ = 6.2Ω

CZ = .68uF

- 65kHz 4th order filter

LO1 = 15uH

CO1 = 1uF

LO2 = 10uH

CO2 = .22uF

RZ = 10Ω

CZ = .47uF

Output inductor selection is a critical design step. The core material and geometry of the output filter

inductor affects the TA2022 distortion levels, efficiency, over-current protection, power dissipation and

EMI output. The inductor should have low loss at 700kHz with 80Vpp. It should be reiterated that

regardless of the systems maximum operating current, a 10A rating is required to ensure that peak

current conditions will not cause the inductor to saturate. During a short circuit event the inductor

current increases very quickly in a saturated core (see figure 6), compromising the current protection

scheme. A 10A rating is sufficient to ensure that current increases through the inductor are linear, and

provides a safety margin for the TA2022. There are two types of inductors available in the 10A range

that offers some EMI containment: they are the toroidal type and the bobbin (shielded) type inductor.

In bobbin construction, a ferrite shield is placed around the core of a bobbin inductor to help contain

radiated emissions. This shield can reduce the amount of energy the inductor can store in the core by

reducing the air gap, which can lower the peak current capability of the inductor. Typically, a 7-10A

shielded bobbin inductor will not have the peak current capability necessary to ensure that the core

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TA2022 – KLI/1.2/07-04

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