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Stereo 3.7W Class D Amplifier

Detailed Description

The MAX98306 features low quiescent current, a low-

power shutdown mode, comprehensive click-and-pop

suppression, and excellent RF immunity.

The IC offers Class AB audio performance with Class D

efficiency in a minimal board-space solution.

The Class D amplifier features spread-spectrum modula-

tion, active emissions limiting, edge-rate, and overshoot

control circuitry that offers significant improvements to

switch-mode amplifier radiated emissions.

The amplifier also features click-and-pop suppression

that reduces audible transients on startup and shut-

down, as well as thermal-overload and short-circuit

protection.

Class D Speaker Amplifier

The filterless Class D amplifier output stage offers much

higher efficiency than Class AB amplifiers. The high effi-

ciency of a Class D amplifier is due to the pulse-width

modulated (PWM) rail-to-rail switching operation of the

output stage transistors. This ensures that any power

loss associated with the Class D output stage is mostly

quiescent current overhead.

EMI Filterless Output Stage

Traditional Class D amplifiers require the use of external

LC filters, or shielding, to meet EN55022B electromag-

netic-interference (EMI) regulation standards. Maxim’s

active-emissions-limiting edge-rate control circuitry and

spread-spectrum modulation reduce EMI emissions,

while maintaining up to 92% efficiency.

Spread-spectrum modulation and active emissions limit-

ing limit wideband spectral components, while propri-

etary techniques ensure that the cycle-to-cycle varia-

tion of the switching period does not degrade audio

reproduction or efficiency. The IC’s spread-spectrum

modulator randomly varies the switching frequency by

Q

20kHz around the center frequency (320kHz). Above

10MHz, the wideband spectrum looks like noise for EMI

purposes (Figure 1).

Speaker Current Limit

If the output current of the speaker amplifier exceeds

the current limit (3A typ), the IC disables the outputs for

approximately 100Fs. At the end of 100Fs, the outputs

are reenabled. If the fault condition still exists, the IC

continues to disable and reenable the outputs until the

fault condition is removed.

Selectable Gain

The IC offers five programmable gains selected using

the GAIN input.

Shutdown

The IC features a low-power shutdown mode, drawing

P

1FA (typ) of supply current. Drive SHDN low to place

the MAX98306 into shutdown. Drive SHDN above 1.4V

for normal operation.

Click-and-Pop Suppression

The IC speaker amplifier features Maxim’s comprehen-

sive click-and-pop suppression. During startup, the

click-and-pop suppression circuitry reduces any audible

transient sources internal to the device. When entering

shutdown, the differential speaker outputs ramp down to

PGND quickly and simultaneously.

Table 1. Gain Control Configuration

Figure 1. EMI with 12in of Speaker Cable and No Output Filter

GAIN PIN

MAXIMUM GAIN (dB)

Connect to PGND

18

Connect to PGND through

100kI

±5% resistor

15

Connect to PVDD

12

Connect to PVDD through

100kI

±5% resistor

9

Unconnected

6

FREQUENCY (MHz)

900

800

600 700

200 300 400 500

100

0

10

20

30

40

50

60

70

80

90

-10

0

1000