100

200

4

2

10

8

6

250

150

50

0

400

800

BOOTSTRAP VOLTAGE (V)

3.5

2.5

1200

6.5

5.5

4.5

1000

600

200

0

7.5

8.5

1.21

1.23

TEMPERATURE (°C)

-40

-60

1.25

20

0

-20

1.24

1.22

1.20

1.19

40

60

80 100

1.26

4

8

SUPPLY VOLTAGE (V)

3.0

2.5

12

4.5

4.0

3.5

10

6

2

0

5.0

5.5

LM4962

www.ti.com

SNAS300C – DECEMBER 2005 – REVISED MARCH 2006

Typical Performance Characteristics (continued)

Supply Current

Feedback Voltage

vs

vs

Supply Voltage

Temperature

vs

vs

Application Information

BRIDGE CONFIGURATION EXPLANATION

The Audio Amplifier portion of the LM4962 has two internal amplifiers allowing different amplifier configurations.

The first amplifier’s gain is externally configurable, whereas the second amplifier is internally fixed in a unity-gain,

inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the

second amplifier’s gain is fixed by the two internal 20k

Ω resistors. Figure 1 shows that the output of amplifier one

serves as the input to amplifier two. This results in both amplifiers producing signals identical in magnitude, but

out of phase by 180°. Consequently, the differential gain for the Audio Amplifier is

(1)

By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as

“bridged mode” is established. Bridged mode operation is different from the classic single-ended amplifier

configuration where one side of the load is connected to ground.

A bridge amplifier design has a few distinct advantages over the single-ended configuration. It provides

differential drive to the load, thus doubling the output swing for a specified supply voltage.

BOOST CONVERTER POWER DISSIPATION

At higher duty cycles, the increased ON-time of the switch FET means the maximum output current will be

determined by power dissipation within the LM4962 FET switch. The switch power dissipation from ON-time

conduction is calculated by Equation 1.

(2)

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