AS1705 datasheet(13/20 Pages) AMSCO

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AS1702 - AS1705

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

BTL Amplifier

All devices are designed to drive loads differentially in a bridge-tied load (BTL) configuration.

Figure 32. Bridge Tied Load Configuration

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:

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:

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:

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:

-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)

2VCC

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