Datasheet

LM2524D, LM3524D
SNVS766E –JUNE 2009–REVISED MAY 2013 www.ti.com
Figure 13.
Error Amplifier
The error amplifier is a differential input, transconductance amplifier. Its gain, nominally 86 dB, is set by either
feedback or output loading. This output loading can be done with either purely resistive or a combination of
resistive and reactive components. A graph of the amplifier's gain vs output load resistance is shown in
Figure 14.
Figure 14.
The output of the amplifier, or input to the pulse width modulator, can be overridden easily as its output
impedance is very high (Z
O
≃ 5 MΩ). For this reason a DC voltage can be applied to pin 9 which will override the
error amplifier and force a particular duty cycle to the outputs. An example of this could be a non-regulating
motor speed control where a variable voltage was applied to pin 9 to control motor speed. A graph of the output
duty cycle vs the voltage on pin 9 is shown in Figure 15.
The duty cycle is calculated as the percentage ratio of each output's ON-time to the oscillator period. Paralleling
the outputs doubles the observed duty cycle.
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