AS1701 datasheet(11/17 Pages) AMSCO

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AS1701, AS1706

Data Sheet - Ap p lica tio n In fo r m a tio n

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

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:

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.

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:

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:

-1

VOUT(P-P)

2 x VOUT(P-P)

AVD = 2 x

RIN

(EQ 2)

VRMS =

2 2

(EQ 3)

VOUT(P-P)

POUT =

(EQ 4)

VRMS

PDISSPKF(MAX) =

ΘJA

(EQ 5)

TJ(MAX) -TA

PDISSPKF(MAX) =

π2RL

(EQ 6)

2VDD

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