Features and Benefits

  • 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
  • TDM or multichip I2S slave output interface
    • Up to 4 chips supported on a single bus
    • 8 kHz to 48 kHz operation
  • I2S/left justified slave output interface
    • 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)
  • 89% efficiency at 5.0 V, 1.4 W into 8 Ω + 0.2 Ω RSENSE speaker
  • >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

Product Details

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.

The outputs of these ADCs are available on the TDM or I2S output serial port. The SLOT pin is used to determine which of four possible output slots is used on the TDM interface. A stereo I2S interface can be selected by reversing the pin connections for 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).


  • Mobile phones
  • MP3 players
  • Portable electronics

Product Lifecycle icon-not-recommended Not Recommended for New Designs

This designates products ADI does not recommend broadly for new designs.

Evaluation Kits (1)

Evaluation Boards

Pricing displayed is based on 1-piece.

Up to two boards can be purchased through Analog.com. To order more than two, please purchase through one of our listed distributors.

Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.