MAX9717(2004) 查看數據表（PDF） - Maxim Integrated
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MAX9717 Datasheet PDF : 19 Pages
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Low-Cost, Mono, 1.4W BTL Audio Power
Amplifiers
CIN
AUDIO
RIN
INPUT
BIAS
OUT-
IN+ MAX9716
OUT+
IN-
RF
Figure 2. Setting the MAX9716/MAX9717A Gain
Adjustable Gain
Gain-Setting Resistors
External feedback resistors set the gain of the
MAX9716 and MAX9717A. Resistors RF and RIN (see
Figure 2) set the gain of the amplifier as follows:
AV
=
⎛
2⎝⎜
RF
RIN
⎞
⎠⎟
Where AV is the desired voltage gain. Hence, an RIN of
20kΩ and an RF of 20kΩ yields a gain of 2V/V, or 6dB.
RF can be either fixed or variable, allowing the use of a
digitally controlled potentiometer to alter the gain under
software control.
The gain of the MAX9717 in a single-ended output
configuration is half the gain when configured as BTL
output. Choose RF between 10kΩ and 50kΩ for the
MAX9716 and MAX9717A. Gains for the MAX9717B/C/D
are set internally.
Input Filter
CIN and RIN form a highpass filter that removes the DC
bias from an incoming signal. The AC-coupling capaci-
tor allows the amplifier to bias the signal to an optimal
DC level. Assuming zero-source impedance, the -3dB
point of the highpass filter is:
f−3dB
=
1
2 πRINCIN
Setting f-3dB too high affects the low-frequency
response of the amplifier. Use capacitors with
dielectrics that have low-voltage coefficients, such as
tantalum or aluminum electrolytic. Capacitors with high-
voltage coefficients, such as ceramics, can increase
distortion at low frequencies.
Output-Coupling Capacitor
The MAX9717 require output-coupling capacitors to
operate in single-ended (headphone) mode. The out-
put-coupling capacitor blocks the DC component of the
amplifier output, preventing DC current from flowing to
the load. The output capacitor and the load impedance
form a highpass filter with a -3dB point determined by:
f−3dB
=
1
2πRLCOUT
As with the input capacitor, choose COUT such that
f-3dB is well below the lowest frequency of interest.
Setting f-3dB too high affects the amplifier’s low-fre-
quency response. Load impedance is a concern when
choosing COUT. Load impedance can vary, changing
the -3dB point of the output filter. A lower impedance
increases the corner frequency, degrading low-fre-
quency response. Select COUT such that the worst-
case load/COUT combination yields an adequate
response. Select capacitors with low ESR to minimize
resistive losses and optimize power transfer to the load.
Differential Input
The MAX9716 can be configured for a differential input.
The advantage of differential inputs is that any com-
mon-mode noise is attenuated and not passed through
the amplifier. This input improves noise rejection and
provides common-mode rejection (Figure 3). External
components should be closely matched for high
CMRR. Figure 4 shows the MAX9716 configured for a
differential input.
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
0
-10
VRIPPLE = 200mVP-P
RL = 8Ω
-20
CBIAS = 1µF
-30
-40
-50
-60
-70
-80
-90
-100
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 3. CMRR with Differential Input
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