SI270X-A-EVB Silicon Laboratories Inc, SI270X-A-EVB Datasheet - Page 17

• Manufacturer Part Number: SI270X-A-EVB
• Description: BOARD EVAL FOR SI270X-A
• Manufacturer: Silicon Laboratories Inc

Specifications of SI270X-A-EVB

• Board Type: Fully Populated
• Amplifier Type: Class D
• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 5W x 2 @ 3 Ohm
• Voltage - Supply: 9V
• Utilized Ic / Part: SI270X-A
• Description/function: Audio Amplifiers
• Output Power: 5 W
• Product: Audio Modules
• For Use With/related Products: Si270x
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Operating Temperature: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1929

Si2704/05/06/07-A10
4.1. PWM Processing
The Si270x is designed to operate using a bridge-tied-load (BTL) output configuration where both sides of the
speaker are actively driven by the amplifier.
4.1.1. PWM Switching Rate Control
The output PWM switching frequency can be programmed via 2-wire control to be half rate (480 kHz) or full rate
(960 kHz). The different rates can be configured by setting property PWM_FREQ.
Full Rate PWM provides better audio performance and AM radio co-existence, while Half Rate PWM provides
lower switching losses and lower switching energy harmonics at high frequencies. For each configuration, the
switching frequency can be offset slightly for FM band frequency planning flexibility.
4.1.2. EMI Mitigation
By nature, the switching characteristic of Class D amplifiers that provides high power efficiency also creates
harmonic spurs at multiples of the PWM switching rate that can radiate as EMI. Common mode PWM switching
from ground to the supply translates into a radiated pattern with large energy components at the fundamental and
odd harmonics of the switching frequency. Fast pulse edge transitions and differential mode ripple currents flowing
through inductor windings further contribute to radiated interference. To simplify design for EMI compliance and
radio receiver co-existence, the Si270x features EMI mitigation modes for managing the PWM switching noise,
including pulse edge slew rate control, common mode switching noise spectral shifting, and common mode
switching noise spectral spreading/shaping.
4.1.2.1. Slew Rate Control
Output pulse edge slew rate can be programmed via 2-Wire control for 10 ns or 20 ns (property
PWM_OUTPUT_SLEW_RATE). While faster transition times are favorable for higher efficiency, slower transition
times are favorable for EMI attenuation.
4.1.2.2. Spectral Shifting
The frequency locations for the PWM common mode switching energy can be shifted to facilitate frequency
planning. This spectral shifting is useful for example in radios to avoid radiating interference at frequencies where
the radio is being tuned.
When spectral shifting is programmed for Integer Mode PWM, the common mode switching energy and harmonics
are located at F
x (2n–1) for all positive integers n, where Fc is the PWM switching frequency. Alternatively, when
C
programmed for Fractional Mode PWM, the common mode switching energy and harmonics are shifted down in
frequency by 50%, and are located at F
x (2n–1)/2.
C
The spectral shifting mode can be programmed dynamically by setting property PWM_CONFIG during normal
operation without adversely affecting the internal audio processing or the amplified audio signal integrity.
Rev. 0.6
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