參數(shù)資料
型號: MAX4411B
廠商: Maxim Integrated Products, Inc.
英文描述: 80mW, Fixed-Gain, DirectDrive, Stereo Headphone Amplifier with Shutdown
中文描述: 80mW、固定增益、DirectDrive、立體聲耳機(jī)放大器,帶有關(guān)斷
文件頁數(shù): 12/18頁
文件大小: 623K
代理商: MAX4411B
M
80mW, Fixed-Gain, DirectDrive, Stereo
Headphone Amplifier with Shutdown
12
______________________________________________________________________________________
output, supply, and ground traces improve the maxi-
mum power dissipation in the package.
Thermal-overload protection limits total power dissipa-
tion in the MAX4411. When the junction temperature
exceeds +140
°
C, the thermal protection circuitry dis-
ables the amplifier output stage. The amplifiers are
enabled once the junction temperature cools by 15
°
C.
This results in a pulsing output under continuous thermal-
overload conditions.
Output Power
The device has been specified for the worst-case sce-
nario
when both inputs are in phase. Under this con-
dition, the drivers simultaneously draw current from the
charge pump, leading to a slight loss in headroom of
V
SS
. In typical stereo audio applications, the left and
right signals have differences in both magnitude and
phase, subsequently leading to an increase in the max-
imum attainable output power. Figure 5 shows the two
extreme cases for in and out of phase. In reality, the
available power lies between these extremes.
Powering Other Circuits from a
Negative Supply
An additional benefit of the MAX4411 is the internally
generated, negative supply voltage (PV
SS
). This volt-
age provides the ground-referenced output level. PV
SS
can, however, also be used to power other devices
within a design limit current drawn from PV
SS
to 5mA;
exceeding this affects the headphone driver operation.
A typical application is a negative supply to adjust the
contrast of LCD modules.
PV
SS
is roughly proportional to PV
DD
and is not a regu-
lated voltage. The charge-pump output impedance
must be taken into account when powering other
devices from PV
SS
. The charge-pump output imped-
ance plot appears in the
Typical Operating
Characteristics
. For best results, use 2.2μF charge-
pump capacitors.
Component Selection
Input Filtering
The input capacitor (C
IN
), in conjunction with the inter-
nal R
IN,
forms a highpass filter that removes the DC
bias from an incoming signal (see
Typical Application
Circuit
). The AC-coupling capacitor allows the amplifier
to bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
R
IN
is the amplifier
s internal input resistance value
given in the
Electrical Characteristics
. Choose the C
IN
such that f
-3dB
is well below the lowest frequency of
interest. Setting f
-3dB
too high affects the amplifier
s low-
frequency response. Use capacitors whose dielectrics
have low-voltage coefficients, such as tantalum or
aluminum electrolytic ones. Capacitors with high-voltage
coefficients, such as ceramics, may result in increased
distortion at low frequencies.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100m
for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For best
performance over the extended temperature range,
select capacitors with an X7R dielectric. Table 1 lists sug-
gested manufacturers.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the charge
pump
s load regulation and output resistance. A C1
value that is too small degrades the device
s ability to
provide sufficient current drive, which leads to a loss of
output voltage. Increasing the value of C1 improves
load regulation and reduces the charge-pump output
resistance to an extent. See the Output Power vs.
Charge-Pump Capacitance and Load Resistance
graph in the
Typical Operating Characteristics
. Above
2.2μF, the on-resistance of the switches and the ESR of
C1 and C2 dominate.
Hold Capacitor (C2)
The hold capacitor value and ESR directly affect the
ripple at PV
SS
. Increasing the value of C2 reduces
f
R C
dB
3
=
1
2
π
OUTPUT POWER vs. SUPPLY VOLTAGE
M
SUPPLY VOLTAGE (V)
O
3.3
3.0
2.7
2.4
2.1
50
100
150
200
250
300
0
1.8
3.6
f
IN
= 1kHz
R
L
= 16
THD+N = 10%
INPUTS
IN PHASE
INPUTS 180
°
OUT OF PHASE
Figure 5. Output Power vs. Supply Voltage with Inputs In/Out of
Phase
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