8002

8002

8002

8002

Page 13 of 17

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 1, the 8002 has two internal operational amplifiers. The first amplifier’s gain is externally

configurable, while 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

resistors. Figure 1 shows that the output of amplifier one

serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of

phase by 180°. Consequently, the differential gain for the IC is

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 classical 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, as it provides differential

drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as

compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that

the amplifier is not current limited or clipped. In order to choose an amplifier’s closed-loop gain without causing

excessive clipping, please refer to the Audio Power Amplifier Design section.

A bridge configuration, such as the one used in 8002,also creates a second advantage over single-ended amplifiers.

Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This

eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier

configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased

internal IC power dissipation and also possible loudspeaker damage.

POWER DISSIPATION

Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or

single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in

internal power dissipation. Since the 8002 has two operational amplifiers in one package, the maximum internal power

dissipation is 4 times that of a single-ended amplifier.

The maximum power dissipation for a given application can be derived from the power dissipation graphs or from

It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. TJMAX can be determined

from the power derating curves by using PDMAX and the PC board foil area. By adding copper foil, the thermal

resistance of the application can be reduced from the free air value of θJA, resulting in higher PDMAX values without

thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the leads

connected to the 8002. It is especially effective when connected to VDD, GND, and the output pins. Refer to the

application information on the 8002 reference design board for an example of good heat sinking. If TJMAX still

exceeds 150°C, then