SSM3302 Datasheet, PDF (16/20 Pages) Analog Devices – 2 ×10 W Filterless Class-D

SSM3302
Data Sheet
APPLICATIONS INFORMATION
OVERVIEW
AMPLIFIER PROTECTION
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
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.
speaker and human ear to recover the audio component of the
square wave output.
If the temperature exceeds the threshold temperature (approxi-
mately 145°C), the chip is disabled until the temperature drops
Most Class-D amplifiers use some variation of pulse-width
modulation (PWM), but the SSM3302 uses Σ-Δ modulation to
below the recovery threshold (85°C). This hysteresis prevents
rapid cycling of the output at high temperatures.
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
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
EMI emission that might otherwise be radiated by speakers and
Voltage transients at the outputs of the audio amplifiers may occur
long cable traces. Due to the inherent spread spectrum nature of
when shutdown is activated or deactivated. Voltage transients as
Σ-Δ modulation, the need for oscillator synchronization is elim-
small as 10 mV can be heard as an audible pop in the speaker.
inated for designs incorporating multiple SSM3302 amplifiers.
Clicks and pops are defined as undesirable audible transients
The SSM3302 also integrates overcurrent and overtemperature
protection, as well as an overtemperature warning indicator pin.
generated by the amplifier system that do not come from the
system input signal.
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.
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
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
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 preset gain of SSM3302 can be selected between 9 dB and
the supply voltage greatly reduces radiated emissions.
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
the input corner frequency (fc) when gain is adjusted. The same
input coupling components can be used for all gain settings.
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.
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
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).
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