AS1701, AS1706
Data Sheet - Application Information
9 Application Information
BTL Amplifier
The AS1701/AS1706 are designed to drive loads differentially in a bridge-tied load (BTL) configuration.
Figure 30. Bridge-Tied Load Configuration
VOUT(P-P)
+1
-1
2 x VOUT(P-P)
VOUT(P-P)
Driving the load differentially doubles the output voltage (illustrated in Figure 30) compared to a single-ended amplifier
under similar conditions. Thus, the differential gain of the device is twice the closed-loop gain of the input amplifier. The
effective gain is calculated by:
RF
(EQ 2)
AVD = 2 x
RIN
Substituting 2 x VOUT(P-P) into (EQ 3) and (EQ 4) yields four times the output power due to doubling of the output volt-
age.
VOUT(P-P)
(EQ 3)
VRMS =
2 2
2
VRMS
RL
(EQ 4)
POUT =
Since the differential outputs are biased at mid-supply, there is no net DC voltage across the load, eliminating 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 2 as
Continuous Power Dissipation, or it can be calculated by:
TJ(MAX) -TA
(EQ 5)
PDISSPKF(MAX) =
ΘJA
where TJ(MAX) is +150°C, TAMB (see Table 2) is the ambient temperature, and ΘJA is the reciprocal of the derating fac-
tor in °C/W.
The increased power delivered by a BTL configuration normally results in increased internal power dissipation versus
a single-ended configuration. The maximum internal power dissipation for a given VDD and load is calculated by:
2
2VDD
(EQ 6)
PDISSPKF(MAX) =
π2RL
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