Datasheet

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1 1
1.1
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R C
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LM567 , LM567C
www.ti.com SNOSBQ4E –MAY 1999–REVISED DECEMBER 2014
10.3 Feature Description
10.3.1 Center Frequency
The center frequency of the LM567 tone decoder is equal to the free running frequency of the voltage controlled
oscillator. In order to set this frequency, external components should be placed externally. The component
values are given by:
where
• R
1
= Timing Resistor
• C
1
= Timing Capacitor (1)
10.3.2 Output Filter
To eliminate undesired signals that could trigger the output stage, a post detection filter is featured in the
LM567C. This filter consists of an internal resistor (4.7K-Ω) and an external capacitor. Although typically external
capacitor value is not critical, it is recommended to be at least twice the value of the loop filter capacitor. If the
output filter capacitor value is too large, the turn-on and turn off-time of the output will present a delay until the
voltage across this capacitor reaches the threshold level.
10.3.3 Loop Filter
The phase locked loop (PLL) included in the LM567 has a pin for connecting the low pass loop filter capacitor.
The selection of the capacitor for the filter depends on the desired bandwidth. The device bandwidth selection is
different according to the input voltage level. Refer to the Operation With V
i
< 200m – V
RMS
section and the
Operation With V
i
> 200m – V
RMS
section for more information about the loop filter capacitor selection.
10.3.4 Logic Output
The LM567 is designed to provide a transistor switch to ground output when the input signal frequency matches
the center frequency pass band. The logic output is an open collector power transistor that requires an external
load resistor that is used to regulate the output current level.
10.3.5 Die Characteristics
Figure 11. Die Layout (C - Step)
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