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
VOUT(P-P)
+1
-1
2 x VOUT(P-P)
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:
RF
(EQ 2)
AVD = 2 x
RIN
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)
(EQ 3)
VRMS =
2 2
2
VRMS
RL
(EQ 4)
POUT =
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
(EQ 5)
PDISSPKF(MAX) =
ΘJA
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:
2
2VCC
(EQ 6)
PDISSPKF(MAX) =
π2RL
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13 - 20
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