Flying Capacitor (C1)

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

regulation and the 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 the load regulation and reduces the

charge-pump output resistance to an extent. See the

Charge-Pump Output Voltage vs. Output Current

graphs in the

Typical Operating Characteristics. Above

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

C1 and C2 dominate.

Hold Capacitor (C2)

The hold 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 voltage levels. See the Charge-Pump

Output Voltage vs. Output Current graphs in the

Typical

Operating Characteristics. C2 should be greater than

or equal to the value of C1.

ance of the power supply and reduces the impact of

the MAX9727’s charge-pump switching transients.

the value of C1.

Supply Bypassing

Proper power-supply bypassing ensures low-noise,

low-distortion performance. Connect a 1µF ceramic

Layout and Grounding

Good PC board layout is essential for optimizing perfor-

mance. Use large traces for the power-supply inputs

and amplifier outputs to minimize losses due to trace

resistance. Good grounding improves audio perfor-

mance, minimizes crosstalk between channels, and

prevents any digital switching noise from coupling into

the audio signal. Route PGND and all traces that carry

switching transients away from traces and components

in the audio signal path.

Place the charge-pump capacitors (C1 and C2) as

together at capacitor C2.

Thermal-Overload Protection

Thermal-overload protection limits the total power dissi-

pation in the MAX9727. When the junction temperature

exceeds +160°C, the thermal protection circuitry dis-

ables the amplifier output stages. The junction temper-

ature must cool by 15°C before normal operation can

continue.

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11

Chip Information

PROCESS: BiCMOS