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G1201 View Datasheet(PDF) - Global Mixed-mode Technology Inc

Part NameDescriptionManufacturer
G1201 Rail-to-Rail I/O, 100mA Output Single-Supply Amplifiers GMT
Global Mixed-mode Technology Inc GMT
G1201 Datasheet PDF : 9 Pages
1 2 3 4 5 6 7 8 9
Global Mixed-mode Technology Inc.
G1201
Input Overvoltage Protection
As with any semiconductor device, whenever the con-
dition exists for the input to exceed either supply volt-
age, the device’s input overvoltage characteristic must
be considered. When an overvoltage occurs, the am-
plifier could be damaged depending on the magnitude
of the applied voltage and the magnitude of the fault
current. Although not shown here, when the input
voltage exceeds either supply by more than 0.6V,
pn-junctions internal to the G1201 energize allowing
current to flow from the input to the supplies. the
G1201 does not have any internal current limiting re-
sistors, so fault currents can quickly rise to damaging
levels.
This input current is not inherently damaging to the
device as long a it is limited to 5 mA or less. For the
G1201, once the input voltage exceeds the supply by
more than 0.6V the input current quickly exceeds 5
mA. If this condition continues to exist, an external
series resistor should be added. The size of the resis-
tor is calculated by dividing the maximum overvoltage
by 5 mA. For example, if the input voltage could reach
10V, the external resistor should be (10V/ 5mA) = 2kΩ.
This resistance should be placed in series with either
or both inputs if they are exposed to an overvoltage
condition.
The audio signal is then ac-coupled to each input
through a 10µF capacitor. A large value is needed to
ensure that the 20Hz audio information is not blocked.
If the input already has the proper dc bias, the ac cou-
pling and biasing resistors are not required. A 270µF
capacitor is used at the output to couple the amplifier
to the headphone. This value is much larger than that
used for the input because of the low impedance of
the head-phones, which can range from 32Ω to 600Ω.
An additional 16Ω resistor is used in series with the
output capacitor to protect the op amp’s output stage
by limiting capacitor discharge current. When driving a
32Ω load, the circuit exhibits less than 0.3% THD+N at
output drive levels of 4.2 VP-P.
+V + 5V
50kΩ
50kΩ
+
10µF
LEFT
+
INPUT 10µF
100kΩ
+V
+V + 5V 1µF 0.1 µF
_
1/2
G1201
+
16Ω
270µF
+
50kΩ
LEFT
HEADPHONE
A Single-Supply Headphone Amplifier
Because of its speed and large output drive, the
G1201 make an excellent headphone driver, as illus-
trated in Figure 2. Its low supply operation and
rail-to-rail inputs and outputs give a maximum signal
swing on a single +5V supply. To ensure maximum
signal swing available to drive the headphone, the
amplifier inputs are biased to V+/2, which in this case
is 2.5V. The 100kΩ resistor to the positive supply is
equally split into two 50 kΩ resistors, with their com-
mon point bypassed by 10µF to prevent power supply
noise from contaminating the audio signal.
50kΩ
50kΩ
+
10µF
RIGHT
+
INPUT 10µF
100kΩ
_
1/2
G1201
+
16Ω
270µF
+
50kΩ
RIGHT
HEADPHONE
Figure 2. A Single-Supply, Stereo Headphone
Driver
Ver 1.2
Jul 24, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
4
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