Datasheet
Table Of Contents
- Features
- Applications
- Key Specifications
- Description
- Description (Continued)
- Absolute Maximum Ratings
- Operating Ratings
- Electrical Characteristics VDD = 5.0V
- Electrical Characteristics VDD = 3.3V
- Electrical Characteristics VDD = 3.0V
- Electrical Characteristics VDD = 2.4V
- Typical Performance Characteristics
- Typical Performance Characteristics LM4911/LM4911Q Specific Characteristics
- Application Information
- AMPLIFIER CONFIGURATION EXPLANATION
- OUTPUT CAPACITOR vs. CAPACITOR COUPLED
- MODE SELECT DETAIL
- POWER DISSIPATION
- EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS
- POWER SUPPLY BYPASSING
- MICRO POWER SHUTDOWN
- MUTE
- PROPER SELECTION OF EXTERNAL COMPONENTS
- SELECTION OF INPUT CAPACITOR SIZE
- AUDIO POWER AMPLIFIER DESIGN
- ESD PROTECTION

LM4911, LM4911Q
SNAS152M –MAY 2004–REVISED JUNE 2011
www.ti.com
From Equation 3, the minimum A
V
is 0.89; use A
V
= 1. Since the desired input impedance is 20kΩ, and with a A
V
gain of 1, a ratio of 1:1 results from for R
f
to R
i
. The values are chosen with R
i
= 20kΩ and R
f
= 20kΩ. The final
design step is to address the bandwidth requirements which must be stated as a pair of -3dB frequency points.
Five times away from a -3dB point is 0.17dB down from passband response which is better than the required ±
0.25dB specified.
f
L
= 100Hz/5 = 20Hz
f
H
= 20kHz * 5 = 100kHz
As stated in the External Components section, R
i
in conjunction with C
i
creates a
C
i
≥ 1 / (2π * 20kΩ * 20Hz) = 0.397µF; use 0.39µF.
The high frequency pole is determined by the product of the desired frequency pole, f
H
, and the differential gain,
A
V
. With an A
V
= 1 and f
H
= 100kHz, the resulting GBWP = 100kHz which is much smaller than the
LM4911/LM4911Q GBWP of 10MHz. This figure displays that is a designer has a need to design an amplifier
with higher differential gain, the LM4911/LM4911Q can still be used without running into bandwidth limitations.
Figure 62 shows an optional resistor connected between the amplifier output that drives the headphone jack
sleeve and ground. This resistor provides a ground path that suppressed power supply hum. This hum may
occur in applications such as notebook computers in a shutdown condition and connected to an external
powered speaker. The resistor's 100Ω value is a suggested starting point. Its final value must be determined
based on the tradeoff between the amount of noise suppression that may be needed and minimizing the
additional current drawn by the resistor (25mA for a 100Ω resistor and a 5V supply).
ESD PROTECTION
As stated in the Absolute Maximum Ratings, the LM4911/LM4911Q has a maximum ESD susceptibility rating of
2000V. For higher ESD voltages, the addition of a PCDN042 dual transil (from California Micro Devices), as
shown in Figure 64, will provide additional protection.
Figure 64. The PCDN042 provides additional ESD protection beyond the 2000V shown in the
Absolute Maximum Ratings for the V
O
C output
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