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参数资料
| 型号： | G1421F |
| 厂商： | Global Mixed-mode Technology Inc. |
| 英文描述： | 2W Stereo Audio Amplifier with No Headphone Coupling Capacitor Function |
| 中文描述： | 2W立体声音频放大器耦合电容器没有耳机功能 |
| 文件页数： | 16/24页 |
| 文件大小： | 442K |
| 代理商： | G1421F |
Ver: 1.6
Aug 04, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
23
G1421
Global Mixed-mode Technology Inc.
Optimizing DEPOP Operation
Circuitry has been implemented in G1421 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 100k
Ω 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.
De-popping circuitry of G1421 is shown on Figure E.
The PNP transistor limits the voltage drop across
the 50k
Ω 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.
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.
G1421 TJ (pin 2) sources a current inversely pro-
portional to the junction temperature. Typically TJ
sources–120A for a 5V supply at 25°C. And the
slope is approximately 0.22A/°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.
Temperature sensing circuit is shown on Figure F.
Bypass
VDD
100 k
Ω
100 k
Ω
50 k
Ω
Figure E
Bypass
VDD
100 k
Ω
100 k
Ω
50 k
Ω
Figure E
TJ
VDD
R
5R
Figure F
TJ
VDD
R
5R
Figure F
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