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

determined by the value of the sense resistors.

applications (i.e. 4

Ω bridged), this board’s overcurrent may trip prematurely. This is indicated by the

amplifier going into mute; to clear, toggle the mute or cycle the power. To reduce overcurrent sensitivity,

set too low of a value, this may result in an overcurrent threshold that is so high the amplifier will try to

drive a short circuit, possibly damaging the output FETs.

Finally, the Break-Before-Make (or “BBM”) lines are used to control the “dead time” of the output FETs.

The “dead time” is the period of time between the turn-off of one device and the turn-on of the opposite

device on the same channel. If the two devices are both on at the same time, current “shoots through”

from one supply to the other, bypassing the load altogether. Obviously, this will have a great impact on

the overall efficiency of the amplifier. However, if the dead time is too long, linearity suffers. The

optimum BBM setting will change with different output FETs, different operating voltages, different layouts

and different performance requirements. For this reason, Tripath has provided a means to adjust the

BBM0 setting, via jumper J2, on the 3-pin header (see Figure 6). Please note that BBM1 is hardwired to

“0” on the RB-TA3020 since operating the reference board with BBM delays of 40nS or less will result in

significant shoot through current and possible MOSFET destruction.

These settings should be verified over the full temperature and load range of the application to ensure

that any thermal rise of the output FETs and TA3020 does not impact the performance of the amplifier.

This amplifier board is set to 80nS, and the table below shows the BBM values for various settings of the

jumpers (Figure 7).

B M1

B M0

Delay

1)

0

0

120nS

2)

0

1

80nS

3)

1

0

40nS

4)

1

1

0nS

1

1

Note: The default delay jumper setting is 80nS.

BB

BBM

J2

J3

0

0

M0

1

Figure 7

7

RB-TA3020, Rev. 3.0/03.02