LM3875 Datasheet, PDF (22/29 Pages) National Semiconductor (TI) – OverturTM Audio Power Amplifier Series High-Performance 56W Audio Power Amplifier

LM3875
SNAS083D – JUNE 1999 – REVISED APRIL 2013
www.ti.com
Definition of Terms
Input Offset Voltage: The absolute value of the voltage which must be applied between the input terminals
through two equal resistances to obtain zero output voltage and current.
Input Bias Current: The absolute value of the average of the two input currents with the output voltage and
current at zero.
Input Offset Current: The absolute value of the difference in the two input currents with the output voltage and
current at zero.
Input Common-Mode Voltage Range (or Input Voltage Range): The range of voltages on the input terminals
for which the amplifier is operational. Note that the specifications are not ensured over the full common-mode
voltage range unless specifically stated.
Common-Mode Rejection: The ratio of the input common-mode voltage range to the peak-to-peak change in
input offset voltage over this range.
Power Supply Rejection: The ratio of the change in input offset voltage to the change in power supply voltages
producing it.
Quiescent Supply Current: The current required from the power supply to operate the amplifier with no load
and the output voltage and current at zero.
Slew Rate: The internally limited rate of change in output voltage with a large amplitude step function applied to
the input.
Class B Amplifier: The most common type of audio power amplifier that consists of two output devices each of
which conducts for 180° of the input cycle. The LM3875 is a Quasi-AB type amplifier.
Crossover Distortion: Distortion caused in the output stage of a class B amplifier. It can result from inadequate
bias current providing a dead zone where the output does not respond to the input as the input cycle goes
through its zero crossing point. Also for ICs an inadequate frequency response of the output PNP device can
cause a turn-on delay giving crossover distortion on the negative going transistion through zero crossing at the
higher audio frequencies.
THD + N: Total Harmonic Distortion plus Noise refers to the measurement technique in which the fundamental
component is removed by a bandreject (notch) filter and all remaining energy is measured including harmonics
and noise.
Signal-to-Noise Ratio: The ratio of a system's output signal level to the system's output noise level obtained in
the absence of a signal. The output reference signal is either specified or measured at a specified distortion
level.
Continuous Average Output Power: The minimum sine wave continuous average power output in watts (or
dBW) that can be delivered into the rated load, over the rated bandwidth, at the rated maximum total harmonic
distortion.
Music Power: A measurement of the peak output power capability of an amplifier with either a signal duration
sufficiently short that the amplifier power supply does not sag during the measurement, or when high quality
external power supplies are used. This measurement (an IHF standard) assumes that with normal music
program material the amplifier power supplies will sag insignificantly.
Peak Power: Most commonly referred to as the power output capability of an amplifier that can be delivered to
the load; specified by the part's maximum voltage swing.
Headroom: The margin between an actual signal operating level (usually the power rating of the amplifier with
particular supply voltages, a rated load value, and a rated THD + N figure) and the level just before clipping
distortion occurs, expressed in decibels.
Large Signal Voltage Gain: The ratio of the output voltage swing to the differential input voltage required to
drive the output from zero to either swing limit. The output swing limit is the supply voltage less a specified quasi-
saturation voltage. A pulse of short enough duration to minimize thermal effects is used as a measurement
signal.
Output-Current Limit: The output current with a fixed output voltage and a large input overdrive. The limiting
current drops with time once SPiKe protection circuitry is activated.
22
Submit Documentation Feedback
Product Folder Links: LM3875
Copyright © 1999–2013, Texas Instruments Incorporated