LM3875 datasheet(17/20 Pages) NSC

17 / 20 page

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 specifica-

tions are not guaranteed 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 pro-

ducing 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 re-

sponse 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 compo-

nent is removed by a bandreject (notch) filter and all remain-

ing 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 suffi-

ciently 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 stan-

dard) assumes that with normal music program material the

amplifier power supplies will sag insignificantly.

Peak Power: Most commonly referred to as the power out-

put 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 volt-

age. 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 out-

put voltage and a large input overdrive. The limiting current

drops with time once SPiKe protection circuitry is activated.

Output Saturation Threshold (Clipping Point): The output

swing limit for a specified input drive beyond that required for

zero output. It is measured with respect to the supply to

which the output is swinging.

Output Resistance: The ratio of the change in output volt-

age to the change in output current with the output around

zero.

Power Dissipation Rating: The power that can be dissi-

pated for a specified time interval without activating the

protection circuitry. For time intervals in excess of 100 ms,

dissipation capability is determined by heat sinking of the IC

package rather than by the IC itself.

Thermal Resistance: The peak, junction-temperature rise,

per unit of internal power dissipation (units in ˚C/W), above

the case temperature as measured at the center of the

package bottom.

The DC thermal resistance applies when one output transis-

tor is operating continuously. The AC thermal resistance

applies with the output transistors conducting alternately at a

high enough frequency that the peak capability of neither

transistor is exceeded.

Power Bandwidth: The power bandwidth of an audio am-

plifier is the frequency range over which the amplifier voltage

gain does not fall below 0.707 of the flat band voltage gain

specified for a given load and output power.

Power bandwidth also can be measured by the frequencies

at which a specified level of distortion is obtained while the

amplifier delivers a power output 3 dB below the rated out-

put. For example, an amplifier rated at 60W with

≤0.25%

THD + N, would make its power bandwidth measured as the

difference between the upper and lower frequencies at which

0.25% distortion was obtained while the amplifier was deliv-

ering 30W.

Gain-Bandwidth Product: The Gain-Bandwidth Product is

a way of predicting the high-frequency usefulness of an op

amp. The Gain-Bandwidth Product is sometimes called the

unity-gain frequency or unity-gain cross frequency because

the open-loop gain characteristic passes through or crosses

unity gain at this frequency. Simply, we have the following

relationship:

CL1 xf1 =ACL2 xf2

Assuming that at unity-gain

CL1 =1or0dB) fu=f1 = GBWP,

then we have the following:

GBWP = A

CL2 xf2

This says that once fu (GBWP) is known for an amplifier,

then the open-loop gain can be found at any frequency. This

LM3875 Datasheet(PDF) 17 Page - National Semiconductor (TI)

LM3875 Datasheet(HTML) 17 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL