HM2012W datasheet(5/7 Pages) HMSEMI

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Decoupling Capacitor (CS)

The

HM2012 is a high-performance Class-D audio

amplifier that requires adequate power supply

decoupling to ensure the efficiency is high and total

harmonic distortion (THD) is low. For higher

frequency transients, spikes, or digital hash on the

line a good low equivalent-series-resistance (ESR)

ceramic capacitor, typically 1µF, placed as close as

possible to the device PVDD lead works best. Placing

this decoupling capacitor close to the

HM2012 is

important for the efficiency of the Class-D amplifier,

because any resistance or inductance in the trace

between the device and the capacitor can cause a

loss in efficiency. For filtering lower-frequency noise

signals, a 4.7µF or greater capacitor placed near the

audio power amplifier would also help, but it is not

required in most applications because of the high

PSRR of this device.

Audio Amplifier Gain Setting

The

HM2012 features four internally configured gain

settings. The device gain is selected through the two

gain select pins, G0 and G1. The gain settings are

shown in the following table.

Gain (V/V)

Gain (dB)

RI (KΩ)

28.1

17.3

9.8

5.2

Gain Setting Table

Input Capacitors (CI)

The input capacitors and input resistors form a

high-pass filter with the corner frequency, fC,

determined in Equation 1.

)

(1)

The value of the input capacitor is important to

consider as it directly affects the bass (low

frequency) performance of the circuit. Speakers in

wireless phones cannot usually respond well to low

frequencies, so the corner frequency can be set to

block low frequencies in this application. Not using

input capacitors can increase output offset.

Equation 2 is used to solve for the input coupling

capacitance.

)

(

(2)

If the corner frequency is within the audio band, the

capacitors should have a tolerance of ±10% or

better, because any mismatch in capacitance

causes an impedance mismatch at the corner

frequency and below.

Operation with DACs and CODECs

In using Class-D amplifiers with CODECs and DACs,

sometimes there is an increase in the output noise

floor from the audio amplifier. This occurs when

mixing of the output frequencies of the CODEC/DAC

mix with the switching frequencies of the audio

amplifier input stage. The noise increase can be

solved by placing a low-pass filter between the

CODEC/DAC and audio amplifier. This filters off the

high frequencies that cause the problem and allow

proper performance.

Filter Free Operation and Ferrite Bead

Filters

A ferrite bead filter can often be used if the design is

failing radiated emissions without an LC filter and

the frequency sensitive circuit is greater than 1MHz.

This filter functions well for circuits that just have to

pass FCC and CE because FCC and CE only test

radiated emissions greater than 30MHz. When

choosing a ferrite bead, choose one with high

impedance at high frequencies, and very low

impedance at low frequencies. In addition, select a

ferrite bead with adequate current rating to prevent

distortion of the output signal.

Use an LC output filter if there are low frequency

(<1MHz) EMI sensitive circuits and/or there are long

leads from amplifier to speaker.

Figure 6 shows typical ferrite bead and LC output

filters.

Figure6. Typical ferrite chip bead filter

HM2012

HM2012W Datasheet(PDF) 5 Page - Shenzhen Huazhimei Semiconductor Co., Ltd

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