2.6W Stereo Audio Power Amplifier and

DirectDrive Headphone Amplifier

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SUPPLIER

PHONE

FAX

WEBSITE

Taiyo Yuden

800-348-2496

847-925-0899

www.t-yuden.com

TDK

807-803-6100

847-390-4405

www.component.tdk.com

Table 2. Suggested Capacitor Manufacturers

BIAS Capacitor

BIAS is the output of the internally generated DC bias

PSRR and THD+N by reducing power supply and other

noise sources at the common-mode bias node, and

also generates the clickless/popless, startup/shutdown

DC bias waveforms for the speaker amplifiers. Bypass

BIAS with a 1µF capacitor to GND.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100m

Ω for opti-

mum performance. Low-ESR ceramic capacitors mini-

mize the output resistance of the charge pump. For

best performance over the extended temperature

range, select capacitors with an X7R dielectric. Table 4

lists suggested manufacturers.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the load

regulation and output resistance of the charge pump. A

C1 value that is too small degrades the device’s ability

to provide sufficient current drive, which leads to a loss

of output voltage. Increasing the value of C1 improves

load regulation and reduces the charge-pump output

resistance to an extent. See the Output Power vs.

Charge-Pump Capacitance and Load Resistance

graph in the Typical Operating Characteristics. Above

2.2µF, the on-resistance of the switches and the ESR of

C1 and C2 dominate.

Output Capacitor (C2)

The output capacitor value and ESR directly affect the

output ripple. Likewise, decreasing the ESR of C2

reduces both ripple and output resistance. 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.

impedance of the power supply and reduces the

impact of the MAX9779’s charge-pump switching

to the MAX9779 Evaluation Kit for a suggested layout).

Powering Other Circuits from a

Negative Supply

An additional benefit of the MAX9779 is the internally gen-

by the MAX9779 to provide the negative supply for the

headphone amplifiers. It can also be used to power other

be limited to 5mA; exceeding this affects the operation of

the headphone amplifier. A typical application is a nega-

tive supply to adjust the contrast of LCD modules.

The charge-pump output impedance plot appears in

the Typical Operating Characteristics.

Layout and Grounding

Proper layout and grounding are essential for optimum

performance. Use large traces for the power-supply

inputs and amplifier outputs to minimize losses due to

parasitic trace resistance, as well as route head away

from the device. Good grounding improves audio per-

formance, minimizes crosstalk between channels, and

prevents any switching noise from coupling into the audio

signal. Connect CPGND, PGND, and GND together at a

single point on the PC board. Route CPGND and all traces

that carry switching transients away from GND, PGND,

and the traces and components in the audio signal path.

Connect all components associated with the charge

pump capacitors (C1, C2, and C3) as close to the

0.1µF capacitor to GND. Place the bypass capacitors

as close to the device as possible.

Use large, 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.