MAX9730 Просмотр технического описания (PDF) - Maxim Integrated

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MAX9730

2.4W, Single-Supply, Class G Power Amplifier

Maxim Integrated 

2.4W, Single-Supply, Class G Power Amplifier

In differential input configurations, the common-mode

rejection ratio (CMRR) is primarily limited by the exter-

nal resistor and capacitor matching. Ideally, to achieve

the highest possible CMRR, the following external com-

ponents should be selected where:

RFB+ = RFB−

RIN+ RIN−

and

CIN+ = CIN−

Component Selection

Input-Coupling Capacitor

The AC-coupling capacitors (CIN_) and input resistors

(RIN_) form highpass filters that remove any DC bias from

an input signal (see the Typical Application

Circuit/Functional Diagram). CIN_ blocks DC voltages

from the amplifier. The -3dB point of the highpass filter,

assuming zero source impedance due to the input signal

source, is given by:

( ) f−3dB

=

2π

1

× RIN_

× CIN_

Hz

Choose CIN so that f-3dB is well below the lowest fre-

quency of interest. Setting f-3dB too high affects the

amplifier’s low frequency response. Use capacitors with

low-voltage coefficient dielectrics. Aluminum electrolytic,

tantalum, or film dielectric capacitors are good choices

for AC-coupling capacitors. Capacitors with high-voltage

coefficients, such as ceramics (non-C0G dielectrics),

can result in increased distortion at low frequencies.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 50mΩ 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.

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. Increasing the value

of C1 improves load regulation and reduces the charge-

pump output resistance to an extent. Above 1µF, the on-

resistance of the switches and the ESR of C1 and C2

dominate. A 4.7µF capacitor is recommended.

Hold Capacitor (C2)

The output capacitor value and ESR directly affect the

ripple at PVSS. Increasing C2 reduces output ripple.

Likewise, decreasing the ESR of C2 reduces both rip-

ple and output resistance. A 10µF capacitor is recom-

mended.

Charge-Pump Frequency Set Resistor (RFS)

The charge pump operates in two modes. When the

charge pump is loaded below 100mA, it operates in a

slow mode where the oscillation frequency is reduced

to 1/4 of its normal operating frequency. Once loaded,

the charge-pump oscillation frequency returns to nor-

mal operation. In applications where the design may be

sensitive to the operating charge-pump oscillation fre-

quency, the value of the external resistor RFS can be

changed to adjust the charge-pump oscillation fre-

quency (see Figure 4).

CHARGE-PUMP OSCILLATION

FREQUENCY vs. RFS

600

ILOAD > 100mA

550

500

450

400

350

300

250

200

50

75

100

125

150

RFS (kΩ)

Figure 4. Charge-Pump Oscillation Frequency vs. RFS

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