Tri path Technol og y, I nc. - Techni cal I nformati on
after the decoupling capacitors and use short returns to PGND1. These low side diodes, D1 and
D2, will prevent the outputs from going below ground. To be optimally effective they must have a
short and direct return path to its proper ground pin (PGND1) of the TA2021B. This can be
achieved with a ground plane or a trace. Additionally, each channel must use Schottky or Ultra
Fast Recovery diodes with short returns to VDD if the supply voltage exceeds 13.5V. These high
side diodes, D3 and D4, will prevent the outputs from going above VDD. To be optimally effective
they must have a short and direct return path to its proper VDD pin (VDD1) of the TA2021B. This
can be achieved with a ground plane or a trace.
The output inductors, L2 and L3, should be placed close to the TA2021B without compromising
the locations of the closely placed supply decoupling capacitors and output diodes. The purpose
of placing the output inductors close to the TA2021B output pins is to reduce the trace length of
the switching outputs. This will aid in reducing radiated emissions.
Please see the External Component Description section on page 6 for more details on the above-
mentioned components. The Application/ Test Circuit refers to the low side diodes as D
O
, The
high side diodes as D
H
, and both supply decoupling capacitors as C
SW
.
TA2021B Amplifier Gain
The gain of the TA2021B is set by the ratio of two external resistors, R
I
and R
F
, and is given by
the following formula:
V
O
R
= −
12
F
V
I
R
I
where V
I
is the input signal level and V
O
is the differential output signal level across the speaker.
Please note that OUTP1 and OUTP2 are 180° out of phase with their corresponding input
signals.
20 watts of RMS output power results from an 8.944 Vrms signal across a four-ohm speaker load.
If R
F
= R
I
, then 20 Watts will be achieved with 0.745 Vrms of input signal.
8.944 V
RMS
=
(R
L
∗
P
O
)
=
( 4
Ω ∗
20 W )
Protection Circuits
The TA2021B is guarded against over-temperature and over-current conditions. When the
device goes into an over-temperature or over-current state, the FAULT pin goes to a logic HIGH
state indicating a fault condition. When this occurs, the amplifier is muted, all outputs are TRI-
STATED, and will float to 1/2 of VDD.
Over-temperature Protection
An over-temperature fault occurs if the junction temperature of the part exceeds approximately
155°C. The thermal hysteresis of the part is approximately 45°C, therefore the fault will
automatically clear when the junction temperature drops below 110°C.
Over-current Protection
An over-current fault occurs if more than approximately 7 amps of current flows from any of the
amplifier output pins. This can occur if the speaker wires are shorted together or if one side of
the speaker is shorted to ground. An over-current fault sets an internal latch that can only be
cleared if the MUTE pin is toggled or if the part is powered down. Alternately, if the MUTE pin is
9
TA2021B – 3.0/04.03
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
