MAX98307ETESLASHV+ datasheet(13/19 Pages) MAXIM

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Detailed Description

The MAX98307/MAX98308 fully differential mono Class

DG multilevel power amplifiers with integrated inverting

charge pumps offer highly efficient, high-power audio

solutions for portable applications.

The new Class DG multilevel modulation scheme extends

the dynamic range of the output signal by employing a

charge-pump-generated negative rail, which is used as

needed to extend the supply range. When the negative

rail is not needed, the output is drawn entirely from the

standard supply. This scheme results in high efficiency

over a wide output power range.

The power amplifier incorporates active emissions limiting

edge rate and overshoot control circuitry in combination

with the multilevel output modulation scheme to greatly

reduce EMI. These features eliminate the need for output

filtering as compared to traditional Class D amplifiers,

which reduces an application’s component count.

The MAX98307 has an adjustable gain set by external

resistors. The MAX98308 has preset fixed gains of 8.5dB,

11.5dB, 14.5dB, 17.5dB, and 20.5dB set by a gain select

input (GAIN).

Class DG Multilevel Operation

The ICs’ filterless Class DG multilevel amplifiers feature

a proprietary Maxim output stage that offers higher effi-

ciency over a greater output power range than previous

amplifiers. The amplifier combines Class D switching

output efficiency and Class G supply level shifting with a

multilevel output modulation scheme that with a 5V supply

has efficiency better than 80% efficiency over the 0.35W

to 2.2W output range.

The Class DG multilevel output stage uses pulse-width

modulation (PWM), a rail-to-rail digital output signal with

variable duty cycle, to approximate an analog input signal

as in a Class D amplifier. Rail-to-rail operation ensures

that any dissipation at the output is due solely to the

RDS(ON) of the power output MOSFETs. The Class DG

multilevel output stage also senses the magnitude of the

output signal and switches the supply rails as needed

to more efficiently supply the required signal power. For

a low output signal swing requirement (below the bat-

tery supply rail VPVDD), the output range is between

VPVDD and ground. When output swing above VPVDD

is required, VPVSS, an internal inverting charge-pump-

generated negative rail replaces ground as the lower sup-

ply. The high output swing range is then VPVDD to VPVSS,

approximately double the low swing range. This approach

efficiently manages power consumption by switching the

operating rails as needed according to the output swing

requirements. Additionally, multilevel output modulation is

employed in to draw the maximum possible power from

the lower impedance battery supply rail, VPVDD, rather

than the higher impedance charge-pump-generated rail

VPVSS. This is accomplished by generating PWM sig-

nals that swing from ground to VPVDD or from ground to

VPVSS at either end of the bridge tied load (BTL) rather

than continually swinging from VPVDD to VPVSS. The sig-

nals are modulated in such a way that VPVSS is used only

as necessary to generate low-end signal swing.

These combined operations ensure that power dissipation

due to RDS(ON) loss and charge-pump impedance is min-

imized, and that efficiency and output power is maximized

across the audio range. Class DG multilevel operation is

shown as Figure 1.

Figure 1. Class DG Multilevel Operation

MAX98307 fig01

400µs/div

OUT+

5V/div

OUT-

5V/div

OUT+ - OUT-

10V/div

MAX98307/MAX98308

3.3W Mono Class DG Multilevel Audio Amplifier

www.maximintegrated.com

Maxim Integrated │ 13

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