Tr i p ath Technol ogy, I n c. - Techni cal I n for m ati on

The OEM may benefit from some experimentation in the filter design, but the values provided in the

ference design, 11.3uH and 0.22uF (nominal resonant frequency of 101kHz), provide excellent results

s, the material used in the core is important to the performance of

e filter. Core materials that saturates too easily will not provide acceptable distortion or efficiency

e an amplifier is powered up with no load

ttached. The Q of the LC output filter, with no load attached, rises quickly out to 80kHz. Resonant

g on the outputs of the FETs.

hese parts are placed as closely as possible to the leads of the FETs, and the leads of the capacitors

he amplifier is connected to the power supplies and load as shown in Figure 9. Note that an inverter

(i.e. Channel 2). The main reason for processing the

test bridged mode

peration. If the evaluation setup does not provide two out of phase signals, there is another way to

. The input signal is still

pplied to (J100) and is inverted on chip thus providing the input signal for Channel 2 via J200. If the gain

re

for most loads between 4

Ω and 8Ω.

As important as the values themselve

th

figures.

Tripath recommends a low-mu core, like type 2, iron powder cores.

Micrometals,

(www.micrometals.com), is a main supplier of iron powder cores. The core part number used on the RB-

TA3020 is T106-2 and is wound with 29 turns of 16AWG wire.

The Zobel circuits R117/C109 and R217/C209 are there in cas

a

currents in the filter and ringing on the output could reduce the reliability of the amplifier. The Zobel

eliminates these problems by reducing the Q of the network significantly above 50kHz. Modifying the LC

output filter should not require a recalculation of the Zobel value, though depending on application, the

power capability of R117 and R217 may need to be increased to 5W from 2W. The components used on

the reference board should be quite adequate for almost all applications.

The bypass capacitors C105/C205 are critical to the reduction of ringin

T

themselves are as short as practical. Their values will not change with different output FETs.

Connection Diagram for Bridge Mode Operation

T

has been added in front of one of the channel inputs

channels out of phase is to avoid potential problems with switching power supplies, but it also simplifies

the connections for bridged-mode operation. For bridged operation, simply connect the “-“ terminal to the

output of the inverted channel* (Channel 1 output, J101 pin 1) and the “+” terminal to the output of the

non-inverted channel with respect to the input signal (Channel 2 output, J201 pin 2).

The connection shown in Figure 9 is the easiest way to use the RB-TA3020 to

o

evaluate bridge mode operation. This requires the RB-TA3020 to be modified.

Change R201 to 20K

Ω from 49.9KΩ. Connect Pin 26 (OAOUT1) to IN2 on J200

a

of the system needs to be modified, R101 can be adjusted. R201 should be left at 20K

Ω. If stereo

operation is again desired, then the value of R101 and R201 must be made the same to ensure nominal

gain for both channels. Additionally, the connection between Pin 26 and IN2 on J200 should be removed.

9

RB-TA3020, Rev. 3.0/03.02