AS1702_1 Datasheet, PDF (13/20 Pages) ams AG – 1.8W Single-Channel Audio Power Amplifiers

AS1702 - AS1705
Data Sheet - Application Information
BTL Amplifier
All devices are designed to drive loads differentially in a bridge-tied load (BTL) configuration.
Figure 32. Bridge Tied Load Configuration
+1
VOUT(P-P)
2 x VOUT(P-P)
-1
VOUT(P-P)
The BTL configuration doubles the output voltage (illustrated in Figure 32) compared to a single-ended amplifier under
similar conditions. Thus, the differential gain of the device (AVD) is twice the closed-loop gain of the input amplifier. The
effective gain is given by:
AVD = 2 x ^RF
RIN
(EQ 2)
Substituting 2 x VOUT(P-P) for VOUT(P-P) into (EQ 3) and (EQ 4) yields four times the output power due to doubling of
the output voltage:
VOUT(P-P)
VRMS =
22
(EQ 3)
POUT =
VRMS²
RL
(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.
Power Dissipation and Heat Sinking
Normally, the devices dissipate a significant amount of power. The maximum power dissipation is given in Table 3 as
Continuous Power Dissipation, or it can be calculated by:
TJ(MAX) -TA
PDISSPKF(MAX) =
ΘJA
(EQ 5)
where TJ(MAX) is +150ºC, TAMB (see Table 3) is the ambient temperature, and ΘJA is the reciprocal of the derating fac-
tor in ºC/W as specified in Table 3. For example, ΘJA of the TQFN package is +59.2ºC/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 VCC and load is given by:
PDISSPKF(MAX) = ^2VCC2
π²RL
(EQ 6)
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Revision 1.47
13 - 20