Datasheet MAX9727 (Maxim) - 10

Quad Audio Line Driver with 3VRMS Output Inverting Amplifier Configuration
Rauch/Multiple Feedback filter with a passband gain of Figure 3 shows a single channel of the MAX9727 con- 6dB and a -3dB (below passband) cutoff frequency of figured as an inverting amplifier. External resistors RF approximately 27kHz (see Figure 4 for Gain vs. and RIN set the voltage gain of the amplifier as follows: Frequency plot).
Input Filter
R A F V = − The input capacitor CIN, in conjunction with RIN, forms RIN a highpass filter that removes the DC bias from an
MAX9727
incoming signal. The AC-coupling capacitor allows the where AV is the desired voltage gain in V/V. amplifier to bias the signal to an optimum DC level. RF can be either fixed or variable, allowing the use of a Assuming zero-source impedance, the -3dB point of digitally controlled potentiometer to alter the gain under the highpass filter is given by: software control. 1
Active Filter Configuration
f− dB 3 = When the MAX9727 is used as a line driver to provide 2 R π C IN IN outputs that feed audio equipment (notebooks, desk- tops, receivers, and set-top boxes) with a digital-to- Setting f-3dB too high affects the low-frequency analog converter (DAC) used as an audio input source, response of the amplifier. Use capacitors with it is often desirable to eliminate any high-frequency dielectrics that have low-voltage coefficients, such as quantization noise produced by the DAC output before tantalum or aluminum electrolytic. Capacitors with high- it reaches the load. This high-frequency noise can voltage coefficients, such as ceramics, can increase cause the input stages of the line-in equipment to distortion at low frequencies. exceed slew-rate limitations or create excessive EMI
Charge-Pump Capacitor Selection
emissions on the cables between devices. Use capacitors with an ESR of less than 100mΩ for In order to suppress this noise, and to provide a 2VRMS optimum performance. Low-ESR ceramic capacitors standard audio output level from a single 5V supply, minimize the output resistance of the charge pump. For the MAX9727 can be configured as an active lowpass best performance over the extended temperature filter. The Functional Diagram/Typical Application range, select capacitors with an X7R dielectric. Circuit shows the MAX9727 connected as 2-pole R
ACTIVE FILTER GAIN vs. FREQUENCY
F 9 6 MAX9727 fig04 3 MAX9727 0 RIN IN_- -3 GAIN (dB) OUT_ -6 IN_+ -9 -12 -15 1 10 100 FREQUENCY (kHz) Figure 3. Inverting Amplifier Configuration Figure 4. MAX9727 Active Filter Gain vs. Frequency
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