Applications Information

Filterless Class D Operation

Traditional Class D amplifiers require an output filter.

The filter adds cost, size, and decreases efficiency and

THD+N performance. The MAX9830’s filterless modula-

tion scheme does not require an output filter.

Because the switching frequency of the MAX9830 is

well beyond the bandwidth of most speakers, voice coil

movement at the switching frequency is very small. Use

a speaker with a series inductance > 10µH. Typical 8

Ω

speakers exhibit series inductances in the 20µH to

100µH range.

Component Selection

Optional Ferrite Bead Filter

Although not normally needed, in applications where

constructed from an inexpensive ferrite bead and a

small-value capacitor to ground (Figure 2) to provide

additional EMI suppression. Use a ferrite bead with low

DC resistance, high frequency (

≥ 1MHz) impedance of

100

Ω to 600Ω, and rated for at least 1A. The capacitor

value varies based on the ferrite bead chosen and the

actual speaker lead length. Select the capacitor value

based on EMI performance.

Speaker Amplifier Power Supply Input (PVDD)

PVDD powers the speaker amplifier. PVDD ranges from

2.6V to 5.5V. Bypass PVDD with a 0.1µF capacitor to

PGND. Apply additional bulk capacitance at the device

if long input traces between PVDD and the power

source are used. Ensure a rate of voltage rise at PVDD

is limited to 1V/µs.

Input Filtering

highpass filter that removes the DC bias from the

incoming signal. These capacitors allow the amplifier to

bias the signal to an optimum DC level. Select 0.47µF

capacitors for optimum click-and-pop performance and

source-impedance, is:

Use capacitors with adequately low voltage-coefficient

for best low-frequency THD performance.

Layout and Grounding

Proper layout and grounding are essential for optimum

performance. Good grounding improves audio perfor-

mance and prevents switching noise from coupling into

the audio signal.

Use wide, low-resistance output traces. As load imped-

ance decreases, the current drawn from the device out-

puts increase. At higher current, the resistance of the

output traces decrease the power delivered to the load.

For example, if 2W is delivered from the speaker output

to a 4

Ω load through a 100mΩ trace, 49mW is con-

sumed in the trace. If power is delivered through a

10m

Ω trace, only 5mW is consumed in the trace. Wide

output, supply and ground traces also improve the

power dissipation of the device.

The MAX9830 is inherently designed for excellent RF

immunity. For best performance, add ground fills

around all signal traces on top and bottom PCB planes.

The MAX9830 TDFN package features an exposed

thermal pad on its underside. This pad lowers the pack-

age’s thermal resistance by providing a heat conduc-

tion path from the die to the PCB. Connect the exposed

thermal pad to the ground plane by using a large pad

and multiple vias.

Chip Information

PROCESS: CMOS

C

f

µF

IN

dB

=

8

3

[]

-

Mono 2W Class D Amplifier

8

_______________________________________________________________________________________

MAX9830

OUT+

OUT-

Figure 2. Optional Ferrite Bead Filter