LM49120, LM49120TLEVAL

SNAS431C – JUNE 2008 – REVISED MAY 2013

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Table 6. Volume Control Table (continued)

Volume Step

_G4

_G3

_G2

_G1

_G0

Gain (dB)

19

1

0

0

1

0

–1.50

20

1

0

0

1

1

0.00

21

1

0

1

0

0

1.50

22

1

0

1

0

1

3.00

23

1

0

1

1

0

4.50

24

1

0

1

1

1

6.00

25

1

1

0

0

0

7.50

26

1

1

0

0

1

9.00

27

1

1

0

1

0

10.50

28

1

1

0

1

1

12.00

29

1

1

1

0

0

13.50

30

1

1

1

0

1

15.00

31

1

1

1

1

0

16.50

32

1

1

1

1

1

18.00

Table 7. Output Gain Control (Headphone)

HP_GAIN2

HP_GAIN1

HP_GAIN0

GAIN (dB)

0

0

0

0

0

0

1

–1.2

0

1

0

–2.5

0

1

1

–4.0

1

0

0

–6.0

1

0

1

–8.5

1

1

0

–12

1

1

1

–18

Table 8. Output Gain Control (Loudspeaker)

Gain (dB)

Gain (dB)

Bit

Value

Differential Input

Single-Ended Input

0

0

+6

LS_GAIN

1

+6

+12

BRIDGE CONFIGURATION EXPLAINED

The LM49120 loudspeaker amplifier is designed to drive a load differentially, a configuration commonly referred

to as a bridge-tied load (BTL). The BTL configuration differs from the single-ended configuration, where one side

of the load is connected to ground. A BTL amplifier offers advantages over a single-ended device. By driving the

load differentially, the output voltage is doubled, compared to a single-ended amplifier under similar conditions.

This doubling of the output voltage leads to a quadrupling of the output power, for example, the theoretical

maximum output power for a single-ended amplifier driving 8

Ω and operating from a 5V supply is 390mW, while

the theoretical maximum output power for a BTL amplifier operating under the same conditions is 1.56W. Since

the amplifier outputs are both biased about VDD/2, there is no net DC voltage across the load, eliminating the DC

blocking capacitors required by single-ended, single-supply amplifiers.

Headphone Amplifier

The LM49120 headphone amplifier features two different operating modes, output capacitor-less (OCL) and

single-ended (SE) capacitor coupled mode.

20

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