AS1702, AS1703, AS1704, AS1705
Data Sheet
austriam
i c r o
systems
BTL Amplifier
7.1 BTL Amplifier
All devices are designed to drive loads differentially in a bridge-tied load (BTL) configuration.
Figure 4. Bridge Tied Load Configuration
+1
V
OUT(P-P)
2 x V
OUT(P-P)
-1
V
OUT(P-P)
The BTL configuration doubles the output voltage (illustrated in Figure 4) compared to a single-ended amplifier under
similar conditions. Thus, the differential gain of the device (A
VD
) is twice the closed-loop gain of the input amplifier. The
effective gain is given by:
A
VD
= 2 x
R
F
R
IN
(EQ 2)
Substituting 2 x V
OUT(P-P)
for V
OUT(P-P)
into (EQ 3) and (EQ 4) yields four times the output power due to doubling of
the output voltage:
V
RMS
=
V
OUT(P-P)
2 2
V
RMS2
R
L
(EQ 3)
P
OUT
=
(EQ 4)
Since the BTL outputs are biased at mid-supply, there is no net DC voltage across the load. This eliminates the need
for the large, expensive, performance degrading DC-blocking capacitors required by single-ended amplifiers.
7.2 Power Dissipation and Heat Sinking
Normally, the devices dissipate a significant amount of power. The maximum power dissipation is given in Table 1 as
Continuous Power Dissipation, or it can be calculated by:
P
DISSPKF(MAX)
=
T
J(MAX)
-T
A
Θ
JA
(EQ 5)
where T
J(MAX)
is +150°C, T
AMB
(see Table 1) is the ambient temperature, and
Θ
JA
is the reciprocal of the derating fac-
tor in °C/W as specified in Table 1. For example,
Θ
JA
of the TQFN package is +59.2°C/W.
The increased power delivered by a BTL configuration results in an increase in internal power dissipation versus a sin-
gle-ended configuration. The maximum internal power dissipation for a given V
CC
and load is given by:
P
DISSPKF(MAX)
=
2V
CC2
π
2
R
L
(EQ 6)
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