MAX9746 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX9746

1.2W, Low-EMI, Filterless, Class D Audio Amplifier

Maxim Integrated 

1.2W, Low-EMI, Filterless,

Class D Audio Amplifier

Single-Ended Input

The MAX9746 can be configured as a single-ended

input amplifier by capacitively coupling either input to

GND and driving the other input (Figure 5).

DC-Coupled Input

The input amplifier can accept DC-coupled inputs that

are biased within the amplifier’s common-mode range

(see the Typical Operating Characteristics). DC cou-

pling eliminates the input-coupling capacitors, reduc-

ing component count to potentially one external

component (see the System Diagram). However, the

low-frequency rejection of the capacitors is lost, allow-

ing low-frequency signals to feedthrough to the load.

Component Selection

Input Filter

An input capacitor, CIN, in conjunction with the input

impedance of the MAX9746 forms a highpass filter that

removes the DC bias from an incoming signal. The AC-

coupling capacitor allows the amplifier to bias the sig-

nal to an optimum DC level. Assuming zero source

impedance, the -3dB point of the highpass filter is

given by:

f−3dB

=

1

2πRINCIN

Choose CIN so f-3dB is well below the lowest frequency

of interest. Setting f-3dB too high affects the low-fre-

quency response of the amplifier. Use capacitors

whose dielectrics have low-voltage coefficients, such

as tantalum or aluminum electrolytic. Capacitors with

high-voltage coefficients, such as ceramics, may result

in increased distortion at low frequencies.

Other considerations when designing the input filter

include the constraints of the overall system and the

actual frequency band of interest. Although high-fidelity

audio calls for a flat gain response between 20Hz and

20kHz, portable voice-reproduction devices such as

cellular phones and two-way radios need only concen-

1µF

SINGLE-ENDED

AUDIO INPUT

1µF

IN+

MAX9746

IN-

Figure 5. Single-Ended Input

trate on the frequency range of the spoken human

voice (typically 300Hz to 3.5kHz). In addition, speakers

used in portable devices typically have a poor response

below 150Hz. Taking these two factors into considera-

tion, the input filter may not need to be designed for a

20Hz to 20kHz response, saving both board space and

cost due to the use of smaller capacitors.

Output Filter

The MAX9746 does not require an output filter. The

device passes FCC emissions standards with 100mm

of unshielded speaker cables. However, output filtering

can be used if a design is failing radiated emissions

due to board layout or cable length, or the circuit is

near EMI-sensitive devices. Use an LC filter when radi-

ated emissions are a concern, or when long leads are

used to connect the amplifier to the speaker.

Supply Bypassing/Layout

Proper power-supply bypassing ensures low-distortion

operation. For optimum performance, bypass VDD to

GND and PVDD to PGND with separate 0.1µF capaci-

tors as close to each pin as possible. A low-imped-

ance, high-current power-supply connection to PVDD is

assumed. Additional bulk capacitance should be

added as required depending on the application and

power-supply characteristics. GND and PGND should

be star connected to system ground. Refer to the

MAX9746 evaluation kit for layout guidance.

12 ______________________________________________________________________________________

Share Link: