Component Selection

Input Filtering

setting resistor form a highpass filter that removes any

DC bias from an input signal (see the

Functional

bias the signal to an optimum DC level. The -3dB point

of the highpass filter, assuming zero source imped-

ance, is given by:

high affects the amplifier’s low-frequency response. Use

capacitors with low-voltage coefficient dielectrics. Film or

C0G dielectric capacitors are good choices for AC-cou-

pling capacitors. Capacitors with high-voltage coeffi-

cients, such as ceramics, can result in increased

distortion at low frequencies.

Charge-Pump Capacitor Selection

Use capacitors with less than 100mΩ of ESR. Low-ESR

ceramic capacitors minimize the output impedance of the

charge pump. Capacitors with an X7R dielectric provide

the best performance over the extended temperature

range. Table 1 lists suggested capacitor manufacturers.

Flying Capacitor (C1)

The value of C1 affects the charge pump’s load regula-

tion and output impedance. Choosing C1 too small

degrades the MAX9725’s ability to provide sufficient

current drive and leads to a loss of output voltage.

Increasing the value of C1 improves load regulation

and reduces the charge-pump output impedance. See

the Output Power vs. Charge-Pump Capacitance and

Load Resistance graph in the

Typical Operating

Characteristics.

Hold Capacitor (C2)

The hold capacitor’s value and ESR directly affect the

ple. Choosing a capacitor with lower ESR reduces rip-

ple and output impedance. Lower capacitance values

can be used in systems with low maximum output

power levels. See the Output Power vs. Charge-Pump

Capacitance and Load Resistance graph in the

Typical

Operating Characteristics.

Power-Supply Bypass Capacitor (C3)

The power-supply bypass capacitor (C3) lowers the

output impedance of the power supply and reduces the

impact of the MAX9725’s charge-pump switching tran-

Layout and Grounding

Proper layout and grounding are essential for optimum

performance. Connect PGND and SGND together at a

with C3. Place capacitors C2 and C3 as close to the

MAX9725 as possible. Route PGND, and all traces that

carry switching transients, away from SGND and the

audio signal path.

The MAX9725 does not require additional heatsinking.

The thin QFN package features an exposed paddle that

improves thermal efficiency of the package. Ensure the

exposed paddle is electrically isolated from GND and

UCSP Applications Information

For the latest application details on UCSP construction,

dimensions, tape carrier information, printed circuit

board techniques, bump-pad layout , and recommend-

ed reflow temperature profile, as well as the latest infor-

mation on reliability testing results, go to Maxim’s

Application Note 1891:

Wafer-Level Packaging (WLP)

and Its Applications.

f

2C

-3dB

IN

=

××

1

π

Table 1. Suggested Capacitor Manufacturers

SUPPLIER

PHONE

FAX

WEBSITE

Murata

770-436-1300

—

www.murata.com

Taiyo Yuden

800-348-2496

847-925-0899

www.t-yuden.com

TDK

847-803-6100

847-390-4405

www.component.tdk.com

1V, Low-Power, DirectDrive, Stereo Headphone

Amplifier with Shutdown

______________________________________________________________________________________

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