Datasheet

MAX9791/MAX9792
Windows Vista-Compliant Class D Speaker
Amplifiers with DirectDrive Headphone Amplifiers
______________________________________________________________________________________ 19
conserve board space and system cost, as well as
improve low-frequency response and distortion.
The MAX9791/MAX9792 amplifiers feature an under-
voltage lockout that prevents operation from an insuffi-
cient power supply and click-and-pop suppression that
eliminates audible transients on startup and shutdown.
The amplifiers include thermal overload and short-cir-
cuit protection.
Class D Speaker Amplifier
The MAX9791/MAX9792 integrate a filterless class D
amplifier that offers much higher efficiency than class AB
amplifiers. The high efficiency of a Class D amplifier is
due to the switching operation of the output stage tran-
sistors. In a Class D amplifier, the output transistors act
as current steering switches and consume negligible
additional power. Any power loss associated with the
Class D output stage is mostly due to the I2R loss of the
MOSFET on-resistance and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output power. Under normal operating levels (typical
music reproduction levels), efficiency falls below 45%,
whereas the MAX9791/MAX9792 exhibit 67% efficiency
under the same conditions (Figure 1).
Ultra-Low EMI Filterless Output Stage
In traditional Class D amplifiers, the high dv/dt of the
rising and falling edge transitions resulted in increased
electromagnetic-interference (EMI) emissions, which
required the use of external LC filters or shielding to
meet EN55022B EMI regulation standards. Limiting the
dv/dt normally results in decreased efficiency. Maxim’s
active emissions limiting circuitry actively limits the
dv/dt of the rising and falling edge transitions, providing
reduced EMI emissions while maintaining up to 83%
efficiency.
0
20
10
50
40
30
80
70
60
90
0 0.500.25 0.75 1.00 1.25 1.50
EFFICIENCY vs. IDEAL
CLASS AB EFFICIENCY
OUTPUT POWER (W)
EFFICIENCY (%)
IDEAL CLASS AB
MAX9791
Figure 1. MAX9791 Efficiency vs. Class AB Efficiency
DEVICE TYPE REQUIREMENT
WINDOWS PREMIUM
MOBILE VISTA
SPECIFICATIONS
MAX9791/MAX9792
TYPICAL PERFORMANCE
THD+N ≤ -65dB FS [100Hz, 20kHz] 87dBFS [100Hz, 20kHz]
Dynamic range with signal
present
≤ -80dBV, A-weighted [20Hz,
20kHz]
-98.9dB A-weighted [20Hz, 20kHz]
Analog Line-Out Jack
(R
L
= 10kΩ, FS =
0.707V
RMS
)
Line output crosstalk ≤ -50dB [20Hz, 15kHz] 64dB [20Hz, 15kHz]
THD+N ≤ -45dB FS [100Hz, 20kHz] 82dBFS [100Hz, 20kHz]
Dynamic range with signal
present
≤ -60dBV, A-weighted [20Hz,
20kHz]
-91.5dB A-weighted [20Hz, 20kHz]
Analog Headphone-Out
Jack (R
L
= 32Ω, FS =
0.300V
RMS
)
Headphone output
crosstalk
≤ -50dB [20Hz, 15kHz] 64dB [20Hz, 15kHz]
Table 1. Windows Premium Mobile Vista Specifications vs. MAX9791/MAX9792
Specifications
Note: THD+N, dynamic range with signal present, and crosstalk should be measured in accordance with AES17 audio measure-
ments standards.