Data Sheet

SSM2305

Rev. B | Page 11 of 16

APPLICATIONS INFORMATION

OVERVIEW

The SSM2305 mono Class-D audio amplifier features a filterless

modulation scheme that greatly reduces the external components

count that, in turn, conserves board space, thereby reducing

systems cost. The SSM2305 does not require an output filter,

relying instead on the inherent inductance of the speaker coil

and the natural filtering of the speaker and human ear to fully

recover the audio component of the square wave output. Most

Class-D amplifiers use some variation of pulse-width modulation

(PWM), but the SSM2305 uses Σ-Δ modulation to determine the

switching pattern of the output devices, resulting in a number of

important benefits. Σ-Δ modulators do not produce a sharp peak

with many harmonics in the AM frequency band, as pulse-width

modulators often do. Σ-Δ modulation provides the benefits of

reducing the amplitude of spectral components at high frequencies,

that is, reducing EMI emission that might otherwise be radiated

by speakers and long cable traces. Due to the inherent spread-

spectrum nature of Σ-Δ modulation, the need for oscillator

synchronization is eliminated for designs incorporating multiple

SSM2305 amplifiers.

The SSM2305 also offers protection circuits for overcurrent and

temperature protection.

SHUTDOWN

0.1µF

VDD

POP/CLICK

SUPPRESSION

OUT+

OUT–

IN+

VBATT

2.5V TO 5.5V

IN–

MODULATOR

(Σ-Δ)

GND

10µF

47nF*

47nF*

*INPUT CAPACITORS ARE OPTIONAL IF INPUT DC COMMON-MODE

SD

AUDIO IN–

AUDIO IN+

SSM2305

37kΩ

296kΩ

296kΩ

37kΩ

FET

DRIVER

BIAS

INTERNAL

OSCILLATOR

Figure 32. Differential Input Configuration, User-Adjustable Gain

SHUTDOWN

0.1µF

VDD

POP/CLICK

SUPPRESSION

OUT+

OUT–

MODULATOR

(Σ-Δ)

GND

10µF

SD

SSM2305

37kΩ

296kΩ

296kΩ

37kΩ

FET

DRIVER

BIAS

INTERNAL

OSCILLATOR

IN+

IN–

AUDIO IN+

VBATT

2.5V TO 5.5V

47nF

47nF

Figure 33. Single-Ended Input Configuration, User-Adjustable Gain