MAX97200BEWC+ datasheet(9/13 Pages) MAXIM

Part #	MAX97200BEWC+

Description	Low-Power, Low-Offset, Dual Mode, Class H DirectDrive Headphone Amplifier

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Manufacturer	MAXIM [Maxim Integrated Products]

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Low-Power, Low-Offset, Dual Mode, Class H

DirectDrive Headphone Amplifier

9

Dual Mode Charge Pump

The MAX97200’s Dual Mode, charge pump outputs

either QPVIN/2 in high-efficiency mode or QPVIN in high-

power mode, resulting in a power-supply differential of

1.8V or 3.6V. The charge-pump mode changes based

on the level of the output signal needed. When the

output voltage is small, the voltage rails are reduced to

minimize power consumption. When the output voltage

is large, the voltage rails are increased to accommodate

the larger output need.

High-power mode is similar to Maxim’s traditional

DirectDrive architecture and is best suited for loads

that require high voltage swing. High-efficiency mode

improves power consumption by reducing the power-

supply voltage across the amplifier’s output stage by

half. The reduced power-supply voltage is good for idle

conditions or low-signal level conditions into a head-

phone.

Class H Operation

The MAX97200’s internal Class H amplifier uses a class

AB output stage with multiple, discrete power supplies.

This result’s in two power-supply differentials of 1.8V and

3.6V generated from a single 1.8V external supply. The

PVIN/2 power-supply differential is used when the output

voltage requirements are low, and the output is below

VTH2 as seen in Figure 2. The higher supply differential

is used when the output voltage exceeds the high

threshold VTH2, maximizing output power and voltage

swing. The transition time from high-efficiency mode to

high-power mode occurs when the threshold is crossed.

The switch from high-power mode to high-efficiency

mode occurs 32ms (typ) after the threshold is crossed.

Built-in hysteresis keeps the charge pump from erratic

mode switching when the output voltage is near the high

and low thresholds.

Click-and-Pop Suppression

In conventional single-supply audio amplifiers, the out-

put-coupling capacitor contributes significantly to audi-

ble clicks and pops. Upon startup, the amplifier charges

the coupling capacitor to its bias voltage, typically half

the supply. Likewise, on shutdown, the capacitor is dis-

charged. This results in a DC shift across the capacitor,

which appears as an audible transient at the speaker.

Since the MAX97200 does not require output coupling

capacitors, this problem does not arise. Additionally,

the MAX97200 features extensive click-and-pop sup-

pression that eliminates any audible transient sources

internal to the device.

Typically, the output of the device driving the MAX97200

has a DC bias of half the supply voltage. At startup, the

input-coupling capacitor, CIN, is charged to the pream-

plifier’s DC bias voltage through the MAX97200 input

resistor, RIN. This DC shift across the capacitor results

in an audible click-and-pop. The MAX97200 precharges

the input capacitors when power is applied to ensure

that no audible clicks or pops are heard when SHDN is

pulled high.

Shutdown

The MAX97200 features a 1FA, low-power shutdown

mode that reduces quiescent current consumption and

extends battery life. Shutdown is controlled by the SHDN

input. Driving the SHDN input low disables the drive

amplifiers and charge pump and sets the headphone

amplifier output resistance to 100I.

Applications Information

Component Selection

Input-Coupling Capacitor

The input capacitor (CIN), in conjunction with the ampli-

fier input resistance (RIN_), forms a highpass filter that

removes the DC bias from the incoming signal. The

AC-coupling capacitor allows the amplifier to bias the sig-

nal to an optimum DC level. Assuming zero source imped-

ance, the -3dB point of the highpass filter is given by:

3dB

IN IN

1

f-

2R C

=

π

Figure 2. Inverting and Split Mode Transitions

10ms/div

VPVDD

VPVSS

IN_

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