G1432 Datasheet, PDF (13/15 Pages) Global Mixed-mode Technology Inc – 2W Stereo Audio Amplifier

Global Mixed-mode Technology Inc.
Optimizing DEPOP Operation
Circuitry has been implemented in the G1432 to
minimize the amount of popping heard at power-up
and when coming out of shutdown mode. Popping
occurs whenever a voltage step is applied to the
speaker and making the differential voltage gener-
ated at the two ends of the speaker. To avoid the
popping heard, the bypass capacitor should be
chosen promptly, 1/(C_Bx100kΩ) ≦ 1/(C_I*(R_I+R_F)).
Where 100kΩ is the output impedance of the
mid-rail generator, C_B is the mid-rail bypass ca-
pacitor, C_I is the input coupling capacitor, R_I is the
input impedance, R_F is the gain setting impedance
which is on the feedback path. C_B is the most im-
portant capacitor. Besides it is used to reduce the
popping, C_B can also determine the rate at which
the amplifier starts up during startup or recovery
from shutdown mode.
Bypass
De-popping circuitry of the G1432 is shown on Fig-
ure B. The PNP transistor limits the voltage drop
across the 50kΩ 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 charg-
ing is slower. This appears as a linear ramp (while
the PNP transistor is conducting), followed by the
expected exponential ramp of an R-C circuit.
G1432
50 kΩ
VDD
100 kΩ
100 kΩ
Figure B
Ver: 1.1
Jun 21, 2006
TEL: [phone]
http://www.gmt.com.tw
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