G1431_06 Datasheet, PDF (12/14 Pages) Global Mixed-mode Technology Inc – 2W Stereo Audio Amplifier

Global Mixed-mode Technology Inc.
G1431
ting impedance which is on the feedback path. C_B is
the most important capacitor. Besides it is used to re-
duce the popping, C_B can also determine the rate at
which the amplifier starts up during startup or recovery
from shutdown mode.
De-popping circuitry of G1431 is shown as below Fig-
ure 1. The PNP transistor limits the voltage drop
across the 120kΩ by slewing the internal node slowly
when power is applied. At start-up, the voltage at
BYPASS capacitor is 0. The PNP is ON to pull the
mid-point of the bias circuit down. So the capacitor
sees a lower effective voltage, and thus the charging
is slower. This appears as a linear ramp (while the
PNP transistor is conducting), followed by the ex-
pected exponential ramp of an R-C circuit.
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.
VDD
For better performance, C_B is recommended to be at
least 1.5 times of input coupling capacitor C_I. For ex-
ample, if using 1µF input coupling capacitor, 2.2µF
ceramic or tantalum low-ESR capacitors are recom-
mended to achieve the better THD performance.
VDD
RL
VDD
Vo(PP)
2xVo(PP)
-Vo(PP)
Bypass
120 kΩ
100 kΩ
Figure 2
100 kΩ
Figure 1
Bridged-Tied Load Mode Operation
G1431 has two linear amplifiers to drive both ends of
the speaker load in Bridged-Tied Load (BTL) mode
operation. Figure 2 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
Shutdown mode
When the normal operation, the SHUTDOWN pin
should be held high. Pulling SHUTDOWN low will
mute the outputs and deactivate the most of the cir-
cuits. At this moment, the current of this device will be
reduced to about 160µA to save the battery energy.
The SHUTDOWN pin should never be left uncon-
nected during the normal applications.
INPUT *
AMPLIFIER STATE
SHUTDOWN
OUTPUT
Low
Mute
High
BTL
* Inputs should never be left unconnected
X= do not care
Ver: 1.5
Oct 25, 2006
TEL: [phone]
http://www.gmt.com.tw
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