SAMHOP Microelectronics Corp.
3W STEREO AUDIO POWER AMPLIFIER WITH ADVANCED DC VOLUME CONTROL
SE/BTL OPERATION
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
state, which configures the SM7512 as an SE driver from LOUT+ and ROUT+. I
DD
is reduced by approximately
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.
APPLICATION INFORMATION (continued)
RLINEIN
_
+
BYP
BYP
V
DD
_
+
BYP
EN
SE/BTL
ROUT-
100KΩ
_
+
ROUT+
Co
330μF
1KΩ
100KΩ
LOUT+
Figure 2. SM7512 Resistor Divider Network Circuit
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
capacitor (C
O
) into the headphone jack.
Page 8
V.1.4 Revised May 28,2007
SAMHOP [ SAMHOP MICROELECTRONICS CORP. ]
