SSM3302

Data Sheet

Rev. A | Page 16 of 20

APPLICATIONS INFORMATION

OVERVIEW

The SSM3302 stereo Class-D audio amplifier features a filterless

modulation scheme that greatly reduces the external component

count, conserving board space and reducing system cost. The

SSM3302 does not require an output filter; it relies on the inherent

inductance of the speaker coil and the natural filtering of the

speaker and human ear to recover the audio component of the

square wave output.

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

modulation (PWM), but the SSM3302 uses Σ-Δ modulation to

determine the switching pattern of the output devices, resulting in

several important benefits. Unlike pulse-width modulators, Σ-Δ

modulators do not produce a sharp peak with many harmonics in

the AM broadcast band. In addition, Σ-Δ modulation reduces the

amplitude of spectral components at high frequencies, 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 elim-

inated for designs incorporating multiple SSM3302 amplifiers.

The SSM3302 also integrates overcurrent and overtemperature

protection, as well as an overtemperature warning indicator pin.

ANALOG SUPPLY

The SSM3302 includes an integrated low dropout (LDO) linear

regulator to generate a 5 V supply for the input stage. This regulator

can be enabled using the REGEN pin. This analog supply voltage is

available at the VREG/AVDD pin. Connect a 2.2 μF decoupling

capacitor from this pin to the AGND pin.

Alternatively, an external 5 V analog supply can be connected to

the AVDD pin. In this case, tie REGEN low to disable the

internal regulator.

The internal 5 V regulator can supply up to 20 mA of current to

the VREG pin if other analog circuits use the same supply. The

regulator includes short-circuit protection, but no current

limiter or other protection is provided.

GAIN SELECTION

The preset gain of SSM3302 can be selected between 9 dB and

24 dB with one external resistor and no change to the input imped-

ance. Gain can be further adjusted to a user-defined setting by

inserting series external resistors at the inputs. A major benefit

of fixed input impedance is that there is no need to recalculate

input coupling components can be used for all gain settings.

Table 5. Gain Function Descriptions

Gain Setting (dB)

GAIN Pin Configuration

24

Tie to AVDD

18

Tie to AVDD through 47 kΩ

15

Open

12

Tie to AGND through 47 kΩ

9

Tie to AGND

AMPLIFIER PROTECTION

The SSM3302 includes protection circuitry to prevent damage

in case of overcurrent and overtemperature conditions. Shorts

across the output terminals, or between either terminal and

PVDD or PGND, are also detected; in this case, the output

transistors do not switch until the fault is removed.

If the temperature exceeds the threshold temperature (approxi-

mately 145°C), the chip is disabled until the temperature drops

below the recovery threshold (85°C). This hysteresis prevents

rapid cycling of the output at high temperatures.

Additionally, a temperature warning signal is available on the

THERM pin. If the die temperature rises above 120°C, a logic

high is output on this pin.

POP-AND-CLICK SUPPRESSION

Voltage transients at the outputs of the audio amplifiers may occur

when shutdown is activated or deactivated. Voltage transients as

small as 10 mV can be heard as an audible pop in the speaker.

Clicks and pops are defined as undesirable audible transients

generated by the amplifier system that do not come from the

system input signal.

Such transients may be generated when the amplifier system

changes its operating mode. For example, system power-up and

power-down can be sources of audible transients.

The SSM3302 has a pop-and-click suppression architecture that

reduces these output transients, resulting in noiseless activation

and deactivation.

EMI NOISE

The SSM3302 uses a proprietary modulation and spread spectrum

technology to minimize EMI emissions from the device. The

SSM3302 can pass FCC Class-B emissions testing with unshielded

20 inch cable using ferrite bead-based filtering. For applica-

tions that have difficulty passing FCC Class-B emission tests, the

SSM3302 includes a modulation select pin (ultralow EMI emission

mode) that significantly reduces the radiated emissions at the

Class-D outputs, particularly above 100 MHz. Note that reducing

the supply voltage greatly reduces radiated emissions.

MONO MODE

The SSM3302 can also be configured to stack its stereo outputs

into a monaural amplifier configuration by enabling the mono

output mode using the MONO pin. The user can drive a load as

small as 2 Ω up to 20 W continuous output power—a particularly

useful feature for driving the subwoofer in a 2.1 audio system.

To activate this operation, pull up the MONO pin to the level of

VREG/AVDD. In mono mode, OUTL+ and OUTR+ (Pin 2/Pin 3

and Pin 28/Pin 29) provide the noninverting output, and OUTL−

and OUTR− (Pin 4/Pin 5 and Pin 26/Pin 27) provide the inverting

output. While the device is in mono mode, audio input is taken

only from the left channel set of inputs: INL+ and INL− (Pin 11

and Pin 12).