LM3875

SNAS083D – JUNE 1999 – REVISED APRIL 2013

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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.

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