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G1420F31U 参数 Datasheet PDF下载

G1420F31U图片预览
型号: G1420F31U
PDF下载: 下载PDF文件 查看货源
内容描述: 2W立体声音频放大器 [2W Stereo Audio Amplifier]
分类和应用: 音频放大器
文件页数/大小: 20 页 / 377 K
品牌: GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
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G1420  
Global Mixed-mode Technology Inc.  
MUTE and SHUTDOWN Mode Operations  
G1420 implements the mute and shutdown mode  
operations to reduce supply current, IDD, to the ab-  
solute minimum level during nonuse periods for  
battery-power conservation. When the shutdown  
pin (pin 8) is pulled high, all linear amplifiers will be  
deactivated to mute the amplifier outputs. And  
G1420 enters an extra low current consumption  
state, IDD is smaller than 5µA. If pulling mute-in pin  
(pin 11) high, it will force the activated linear ampli-  
fier to supply the VDD/2 dc voltage on the output to  
mute the AC performance. In mute mode operation,  
the current consumption will be a little different be-  
tween BTL, SE. (SE < BTL) Typically, the supply  
current is about 2.5mA in BTL mute operation.  
Shutdown and Mute-In pins should never be left  
unconnected, this floating condition will cause the  
amplifier operations unpredictable.  
VDD  
100 kΩ  
50 kΩ  
Bypass  
100 kΩ  
Figure D  
Junction Temperature Measurement  
Characterizing a PCB layout with respect to thermal  
impedance is very difficult, as it is usually impossi-  
ble to know the junction temperature of the IC.  
G1420 TJ (pin 2) sources a current inversely pro-  
portional to the junction temperature. Typically TJ  
sources–120µA for a 5V supply at 25°C. And the  
slope is approximately 0.22µA/°C. As the resistors  
have a tolerance of ±20%, these values should be  
calibrated on each device. When the temperature  
sensing function is not used, TJ pin can be left  
floating or tied to VDD to reduce the current con-  
sumption.  
Optimizing DEPOP Operation  
Circuitry has been implemented in G1420 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/(CBx100kΩ) 1/(CI*(RI+RF)).  
Where 100kΩ is the output impedance of the  
mid-rail generator, CB is the mid-rail bypass ca-  
pacitor, CI is the input coupling capacitor, RI is the  
input impedance, RF is the gain setting impedance  
which is on the feedback path. CB is the most im-  
portant capacitor. Besides it is used to reduce the  
popping, CB can also determine the rate at which  
the amplifier starts up during startup or recovery  
from shutdown mode.  
Temperature sensing circuit is shown on Figure E.  
VDD  
R
De-popping circuitry of G1420 is shown on Figure D.  
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.  
R
5R  
TJ  
Figure E  
TEL: 886-3-5788833  
http://www.gmt.com.tw  
Ver: 1.5  
Aug 04, 2005  
19  
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