Texas Instruments Filterless High Efficiency Stereo 1.2W Switching Audio Amplifier LM4666SDBD/NOPB LM4666SDBD/NOPB 데이터 시트
제품 코드
LM4666SDBD/NOPB
SNAS189A – MAY 2004 – REVISED MAY 2013
REFERENCE DESIGN BOARD SCHEMATIC
Figure 28.
In addition to the minimal parts required for the application circuit, a measurement filter is provided on the
evaluation circuit board so that conventional audio measurements can be conveniently made without additional
equipment. This is a balanced input, grounded differential output low pass filter with a 3dB frequency of
approximately 35kHz and an on board termination resistor of 300
evaluation circuit board so that conventional audio measurements can be conveniently made without additional
equipment. This is a balanced input, grounded differential output low pass filter with a 3dB frequency of
approximately 35kHz and an on board termination resistor of 300
Ω
(see
). Note that the capacitive load
elements are returned to ground. This is not optimal for common mode rejection purposes, but due to the
independent pulse format at each output there is a significant amount of high frequency common mode
component on the outputs. The grounded capacitive filter elements attenuate this component at the board to
reduce the high frequency CMRR requirement placed on the analysis instruments.
independent pulse format at each output there is a significant amount of high frequency common mode
component on the outputs. The grounded capacitive filter elements attenuate this component at the board to
reduce the high frequency CMRR requirement placed on the analysis instruments.
Even with the grounded filter the audio signal is still differential necessitating a differential input on any analysis
instrument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential
responding because the ring of the BNC is usually grounded.
instrument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential
responding because the ring of the BNC is usually grounded.
The commonly used Audio Precision analyzer is differential but its ability to accurately reject fast pulses of 160ns
width is questionable necessitating the on board measurement filter. When the signal needs to be single-ended,
use an audio signal transformer to convert the differential output to a single ended output. Depending on the
audio transformer's characteristics, there may be some attenuation of the audio signal which needs to be taken
into account for correct measurement of performance.
width is questionable necessitating the on board measurement filter. When the signal needs to be single-ended,
use an audio signal transformer to convert the differential output to a single ended output. Depending on the
audio transformer's characteristics, there may be some attenuation of the audio signal which needs to be taken
into account for correct measurement of performance.
Measurements made at the output of the measurement filter suffer attenuation relative to the primary, unfiltered
outputs even at audio frequencies. This is due to the resistance of the inductors interacting with the termination
resistor (300
outputs even at audio frequencies. This is due to the resistance of the inductors interacting with the termination
resistor (300
Ω
) and is typically about -0.35dB (4%). In other words, the voltage levels and corresponding power
levels indicated through the measurement filter are slightly lower than those that actually occur at the load placed
on the unfiltered outputs. This small loss in the filter for measurement gives a lower output power reading than
what is really occurring on the unfiltered outputs and its load.
on the unfiltered outputs. This small loss in the filter for measurement gives a lower output power reading than
what is really occurring on the unfiltered outputs and its load.
Copyright © 2004–2013, Texas Instruments Incorporated
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