G1427 Datasheet, PDF (15/16 Pages) Global Mixed-mode Technology Inc – 2W Stereo Audio Amplifier

Global Mixed-mode Technology Inc.
G1427
Bridged-Tied Load Mode Operation
G1427 has two linear amplifiers to drive both ends of
the speaker load in Bridged-Tied Load (BTL) mode
operation. Figure 5 shows the BTL configuration. The
differential driving to the speaker load means that
when one side is slewing up, the other side is slewing
down, and vice versa. This configuration in effect will
double the voltage swing on the load as compared to a
ground reference load. In BTL mode, the peak-to-peak
voltage V_O(PP) on the load will be two times than a
ground reference configuration. The voltage on the
load is doubled, this will also yield 4 times output
power on the load at the same power supply rail and
loading. Another benefit of using differential driving
configuration is that BTL operation cancels the dc off-
sets, which eliminates the dc coupling capacitor that is
needed to cancelled dc offsets in the ground reference
configuration. Low-frequency performance is then lim-
ited only by the input network and speaker responses.
Cost and PCB space can be minimized by eliminating
the dc coupling capacitors.
Shutdown mode
When the normal operation, the SHUTDOWN pin
should be held high. Pulling SHUTDOWN low will
mute the outputs and deactivate almost circuits except
PC-BEEP monitoring block. At this moment, the cur-
rent of this device will be reduced to about 160µA to
save the battery energy. The SHUTDOWN pin should
never be left unconnected during the normal applica-
tions.
INPUT *
AMPLIFIER STATE
HP/ LINE SE/ BTL SHUTDOWN INPUT OUTPUT
X
X
Low
X
Mute
Low
Low
High
Low
High
Low
High
High
High
Line
BTL
Line
SE
head-
phone
BTL
High
High
High
head-
phone
SE
* Inputs should never be left unconnected
X= do not care
Input MUX And SE/ BTL Operation
VDD
RL
VDD
Vo(PP)
2xVo(PP)
-Vo(PP)
Figure 5
The G1427 allows two different input sources applied
to the audio amplifiers, which can be independent to
the SE/ BTL setting. When HP/ LINE is held high, the
headphone inputs are active. When the HP/ LINE is
held low, the line inputs are selected.
When SE/ BTL is held low, all four internal audio am-
plifiers are activated to drive the stereo speakers.
When SE/ BTL is held high, two amplifiers are acti-
vated to drive the stereo headphones. The other two
amplifiers are disable and keeping the outputs high
impedance.
PC-BEEP Operation
The PC-BEEP input allows a system beep to be sent
directly from a computer through the amplifier to the
speakers with a few external components. It is acti-
vated automatically by detecting the PC-BEEP input.
The preferred input signal is a square wave or pulse
train with an amplitude of 1-V_PP or greater. To be ac-
curately detected, the signal must be with at least
1-V_PP amplitude, 8 continuous rising edges, rise and
fall times less than 0.1µs. When the signal is no longer
detected, the amplifier will return its previous operating
mode and volume setting.
When the PC-BEEP mode is activated, both the
LINEIN and HPIN are deselected and the outputs will
be driven in BTL mode with the signal from PC-BEEP.
The gain setting will be also fixed at 0.3V/V, inde-
pendent of the volume setting. If the device is in the
SHUTDOWN mode, activating PC-BEEP will take the
device out of shutdown mode and output the
PC-BEEP input signal until the PC-BEEP signal no
longer detected. And then the device will return the
shutdown mode when no PC-BEEP signal is detected.
The PC-BEEP input can be dc-coupled to save the
coupling capacitor. This pin is set at mid-rail normally
when no signal is present.
If AC-coupling is desired, the value of the coupling
capacitor should be chosen to satisfy the equation:
C_PCB≧ 1/( 2πf_PCB*150KΩ)
C_PCB is the PC-BEEP AC-coupling capacitor. f_PCB is the
frequency of applied PC-BEEP input signal.
Ver: 1.3
Sep 23, 2005
TEL: [phone]
http://www.gmt.com.tw
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