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SAMHOP Microelectronics Corp.

3W STEREO AUDIO POWER AMPLIFIER WITH ADVANCED DC VOLUME CONTROL

The ability of the SM7512 to easily switch between BTL and SE modes is one of its most important cost saving

features. This feature eliminates the requirement for an additional headphone amplifier in applications where

internal stereo speakers are driven in BTL mode but external headphone or speakers must be accommodated.

Internal to the SM7512, two separate amplifiers drive OUT+ and OUT-. The SE/BTL input controls the operation

of the follower amplifier that drives LOUT- and ROUT-. When SE/BTL is held low, the amplifier is on and the

SM7512 is in the BTL mode. When SE/BTL is held high, the OUT- amplifiers are in a high output impedance

one-third in SE mode. Control of the SE/BTL input can be from a logic-level CMOS source or, more typically,

from a resistor divider network as shown in Figure 2. The trip level for the SE/BTL input can be found in the

recommended operating condition

table.

SE/BTL OPERATION

APPLICATION INFORMATION (continued)

+

_

ROUT+

ROUT-

RLINEIN

+

_

+

_

SE/BTL

BYP

EN

BYP

100KΩ

100KΩ

Co

330μF

1KΩ

LOUT+

Figure 2. SM7512 Resistor Divider Network Circuit

BYP

Using a 1/8-in. (3,5mm) stereo headphone jack, the control switch is closed when no plug is inserted. When

closed the 100KΩ/1KΩ divider pulls the SE/BTL input low. When a plug is inserted, the 1KΩ resistor is

disconnected and SE/BTL input is pulled high. When the input goes high, the OUT- amplifier is shut down

causing the speaker to mute (open-circuits the speaker). The OUT+ amplifier then drives through the output

V.1.4 Revised May 28,2007