MAX9759 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX9759

3.2W, High-Efficiency, Low-EMI, Filterless, Class D Audio Amplifier

Maxim Integrated 

3.2W, High-Efficiency, Low-EMI, Filterless,

Class D Audio Amplifier

1µF

22kΩ

CW

50kΩ

1µF 22kΩ

IN-

MAX9759

IN+

Figure 10. Single-Ended Drive of MAX9759 Plus Volume

Control

Output Filter

The MAX9759 does not require an output filter for the

short speaker cable. The device passes FCC emissions

standards with 7.6cm of unshielded speaker cables.

However, output filtering can be used if a design is fail-

ing radiated emissions due to board layout, cable

length, or the circuit’s close proximity to EMI-sensitive

devices. Use an LC filter when radiated emissions are a

concern, or when long leads are used to connect the

amplifier to the speaker.

Supply Bypassing, Layout, and Grounding

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.

Use wide, low-resistance output traces. As load imped-

ance decreases, the current drawn from the device out-

puts increase. At higher current, the resistance of the

output traces decrease the power delivered to the load.

Wide output, supply, and GND traces also improve the

power dissipation of the device.

The MAX9759 thin QFN package features an exposed

thermal pad on its underside. This pad lowers the

package’s thermal resistance by providing a direct

heat conduction path. Due to the high efficiency of the

MAX9759’s Class D Amplifier, additional heatsinking is

not required. If additional heatsinking is required, con-

nect the exposed paddle to GND.

Stereo Configuration

Two MAX9759s can be configured as a stereo amplifier

(Figure 7). Device U1 is the master amplifier; its oscilla-

tor output, SYNC_OUT, drives the SYNC input of the

slave device (U2), synchronizing the switching frequen-

cies of the two devices. Synchronizing two MAX9759s

ensures that no beat frequencies within the audio spec-

trum occur on the power-supply rails. This stereo con-

figuration works when the master device is in either

FFM or SSM mode. There is excellent THD+N perfor-

mance and minimal crosstalk between devices due to

the SYNC and SYNC_OUT connection (Figures 8, 9).

Multiple MAX9759s can be cascaded and frequency

locked in a similar fashion (Figure 7). Repeat the stereo

configuration outlined in Figure 7 for multiple cascading

amplifier applications.

Volume Control

If volume control is required, connect a potentiometer

between the differential inputs of the MAX9759, as seen

in Figure 10. In this configuration, each input “sees”

identical RC paths when the device is powered up. The

variable resistive element appears between the two

inputs, meaning the setting affects both inputs the same

way. This configuration significantly improves transient

performance on power-up or release from SHDN.

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