G1430 Datasheet, PDF (25/26 Pages) Global Mixed-mode Technology Inc – 2W Stereo Audio Amplifier

Global Mixed-mode Technology Inc.
G1430
SHUTDOWN Mode Operations
G1430 implements the shutdown mode operations
to reduce supply current, I_DD, to the absolute mini-
mum level during nonuse periods for battery-power
conservation. When the shutdown pin (pin 2) is
pulled high, all linear amplifiers will be deactivated
to mute the amplifier outputs. And G1430 enters an
extra low current consumption state, I_DD is smaller
than 5µA. Shutdown pin should never be left un-
connected, this floating condition will cause the am-
plifier operations unpredictable.
De-popping circuitry of G1430 is shown on Figure 4.
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.
Optimizing DEPOP Operation
Circuitry has been implemented in G1430 to mini-
mize the amount of popping heard at power-up and
when coming out of shutdown mode. Popping oc-
curs 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 capaci-
tor, 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 important
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
50 kΩ
VDD
100 kΩ
100 kΩ
Figure 4
Ver: 1.0
Jan 15, 2004
TEL: [phone]
http://www.gmt.com.tw
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