G1428F31U
| Model | G1428F31U |
| Description | 2W Stereo Audio Amplifier |
| PDF file | Total 16 pages (File size: 339K) |
| Chip Manufacturer | GMT |
Global Mixed-mode Technology Inc.
Bridged-Tied Load Mode Operation
G1428 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.
G1428
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 160uA to
save the battery energy. The SHUTDOWN pin should
never be left unconnected during the normal applica-
tions.
INPUT *
HP/ LINE SE/ BTL
SHUTDOWN
X
Low
Low
High
High
X
Low
High
Low
High
Low
High
High
High
High
AMPLIFIER STATE
INPUT OUTPUT
X
Line
Line
head-
phone
head-
phone
Mute
BTL
SE
BTL
SE
* Inputs should never be left unconnected
X= do not care
VDD
Vo(PP)
R
L
2xVo(PP)
-Vo(PP)
VDD
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 0.1us. 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 also be dc-coupled to save
the coupling capacitor. This pin is set at mid-rail nor-
mally 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.
Figure 5
Input MUX And SE/BTL Operation
The G1428 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 ampli-
fiers are activated to drive the stereo speakers. When
SE/BTL is held high, two amplifiers are activated to
drive the stereo headphones. The other two amplifiers
are disable and keeping the outputs high impedance.
Ver: 1.2
Mar 31, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
15
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