MAX9717DETA datasheet(11/19 Pages) MAXIM

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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:

Where AV is the desired voltage gain. Hence, an RIN of

20k

Ω 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 10k

Ω 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:

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:

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.

L OUT

−

IN IN

−

⎛

⎝⎜

⎞

⎠⎟

Low-Cost, Mono, 1.4W BTL Audio Power

Amplifiers

______________________________________________________________________________________

OUT-

OUT+

MAX9716

IN-

IN+

BIAS

RIN

CIN

AUDIO

INPUT

Figure 2. Setting the MAX9716/MAX9717A Gain

FREQUENCY (Hz)

10k

100

-90

-80

-70

-60

-50

-40

-30

-20

-10

-100

100k

VRIPPLE = 200mVP-P

RL = 8

Ω

CBIAS = 1

µF

COMMON-MODE REJECTION RATIO

vs. FREQUENCY

Figure 3. CMRR with Differential Input

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