Mono 2.9 W Class-D Audio Amplifier

with Digital Current and Voltage Output

Data Sheet

SSM4321

Rev. 0

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FEATURES

Filterless Class-D amplifier with spread-spectrum

Σ-Δ modulation

Digitized output of output voltage, output current,

and PVDD supply voltage

72 dB signal-to-noise ratio (SNR) on output current sensing

and 77 dB SNR on output voltage sensing

Up to 4 chips supported on a single bus

8 kHz to 48 kHz operation

1 or 2 chips supported on a single bus

8 kHz to 48 kHz operation

PDM output interface operates from 1 MHz to 6.144 MHz

2.2 W into 4 Ω load and 1.4 W into 8 Ω load at 5.0 V supply

with <1% total harmonic distortion plus noise (THD + N)

>100 dB signal-to-noise ratio (SNR)

High PSRR at 217 Hz: 86 dB

Amplifier supply operation from 2.5 V to 5.5 V

Input/output supply operation from 1.42 V to 3.6 V

Flexible gain adjustment pin: 0 dB to 12 dB in 3 dB steps

with fixed input impedance of 80 kΩ

<1 μA shutdown current

Smart power-down with loss of BCLK

Short-circuit and thermal protection with autorecovery

Available in a 16-ball, 0.4 mm pitch, 1.74 mm × 1.74 mm WLCSP

Pop-and-click suppression

APPLICATIONS

Mobile phones

MP3 players

Portable electronics

GENERAL DESCRIPTION

The SSM4321 is a fully integrated, high efficiency, Class-D

audio amplifier with digitized output of output voltage, output

current, and the PVDD supply voltage. It is designed to maximize

performance for mobile phone applications. The application circuit

requires a minimum of external components and operates from

a 2.5 V to 5.5 V supply for the amplifier and a 1.42 V to 3.6 V

supply for input/output. The SSM4321 is capable of delivering

2.2 W of continuous output power with <1% THD + N driving

a 4 Ω load from a 5.0 V supply with a 0.1 Ω V/I sense resistor.

The SSM4321 features a high efficiency, low noise modulation

scheme that requires no external LC output filters. The modulation

scheme provides high efficiency even at low output power. The

SSM4321 operates with 89% efficiency at 1.4 W into 8 Ω from

a 5.0 V supply with an SNR of >100 dB.

The SSM4321 includes circuitry to sense output current, output

voltage, and the PVDD supply voltage. Current sense is performed

using an external sense resistor that is connected between an

output pin and the load. The output current and voltage are sent

to ADCs with 16-bit resolution; the PVDD supply voltage is sent

to an ADC with 8-bit resolution.

output serial port. The SLOT pin is used to determine which of

four possible output slots is used on the TDM interface. A stereo

BCLK and FSYNC. Also, a direct PDM bit stream of voltage and

current data can be selected via the SLOT pin.

Spread-spectrum pulse density modulation (PDM) is used to

provide lower EMI-radiated emissions compared with other

Class-D architectures. The inherent randomized nature of

spread-spectrum PDM eliminates the clock intermodulation

(beating effect) of several amplifiers in close proximity.

The SSM4321 produces ultralow EMI emissions that significantly

reduce the radiated emissions at the Class-D outputs, particularly

above 100 MHz. The ultralow EMI emissions of the SSM4321 are

also helpful for antenna and RF sensitivity problems.

The device includes a highly flexible gain select pin that requires

only one series resistor to select a gain setting of 0 dB, 3 dB, 6 dB,

9 dB, or 12 dB. Input impedance is fixed at 80 kΩ, independent

of the selected gain.

The SSM4321 has a shutdown mode with a typical shutdown

current of <1 μA. Shutdown is enabled by removing the BCLK

input. A clock must be present on the BCLK pin for the part

to operate.

The device also includes pop-and-click suppression circuitry,

which minimizes voltage glitches at the output during turn-on

and turn-off, reducing audible noise on activation and deactivation.

The SSM4321 is specified over the industrial temperature range

of −40C to +85C. It has built-in thermal shutdown and output

short-circuit protection. It is available in a halide-free, 16-ball,

0.4 mm pitch, 1.74 mm × 1.74 mm wafer level chip scale package

(WLCSP).