max9791 Maxim Integrated Products, Inc., max9791 Datasheet - Page 18

• Manufacturer Part Number: max9791
• Description: Windows Vista-compliant Class D Speaker Amplifiers With Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

Windows Vista-Compliant Class D Speaker
Amplifiers with DirectDrive Headphone Amplifiers
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.
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).
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.
18
Analog Line-Out Jack
(R
0.707V
Analog Headphone-Out
Jack (R
0.300V
L
= 10kΩ, FS =
______________________________________________________________________________________
DEVICE TYPE
RMS
RMS
L
= 32Ω, FS =
)
)
Class D Speaker Amplifier
THD+N
Dynamic range with signal
present
Line output crosstalk
THD+N
Dynamic range with signal
present
Headphone output
crosstalk
REQUIREMENT
≤ -65dB FS [100Hz, 20kHz]
≤ -80dBV, A-weighted [20Hz,
20kHz]
≤ -50dB [20Hz, 15kHz]
≤ -45dB FS [100Hz, 20kHz]
≤ -60dBV, A-weighted [20Hz,
20kHz]
≤ -50dB [20Hz, 15kHz]
WINDOWS PREMIUM
SPECIFICATIONS
MOBILE VISTA
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.
Figure 1. MAX9791 Efficiency vs. Class AB Efficiency
90
80
70
60
50
40
30
20
10
0
0
Ultra-Low EMI Filterless Output Stage
0.25
CLASS AB EFFICIENCY
EFFICIENCY vs. IDEAL
-98.9dB A-weighted [20Hz, 20kHz]
-91.5dB A-weighted [20Hz, 20kHz]
MAX9791
0.50
OUTPUT POWER (W)
TYPICAL PERFORMANCE
87dBFS [100Hz, 20kHz]
82dBFS [100Hz, 20kHz]
MAX9791/MAX9792
64dB [20Hz, 15kHz]
64dB [20Hz, 15kHz]
0.75
IDEAL CLASS AB
1.00
1.25
1.50