NXP Semiconductors OM13260, Руководство по установке, Страница: 48 / 71

NXP Semiconductors
UMxxxxx
Install Guide
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Preliminary 1
— September 6, 2013
© NXP B.V. 2013. All rights reserved.
48 of 70
6.2 Circuit Description
The schematic diagram has multiple sheets. For clarification only fragments of the schematic are
shown here. The full schematic should be downloaded if required. The following pages are divided in to
several sections covering the Window Comparator, Push Switches, Bias Circuit, and Connectors.
6.2.1 Window Comparator
Channel 0 is shown; channels 1 through 7 are identical. The input signal is applied to two comparators,
(IC01A and IC01B).
If the input (IO0) is higher than the threshold set by VH and resistor divider (R03 and R04), the output
of the comparator (IC01A) switches to near ground. This turns on the green LED (D01). Resistor (R04)
applies positive feedback hysteresis (about 150mV) to the comparator, shifting the trip point to a
slightly lower voltage, to stop the circuit from oscillation around the switch point.
The input (IO0) is attenuated slightly by a resistor divider (R07 and R08), if the resulting voltage is lower
than the threshold set by VL the output of the comparator (IC1B) switches to near ground. This turns
on the red LED (D01). Resistor (R08) applies positive feedback hysteresis (about 125mV) to the
comparator, shifting the trip point to a slightly higher voltage, to stop the circuit from oscillation
around the switch point.
LED current is limited by resistors R05 and R09, which are selected to give approximately equal
brightness to the Green and Red LED elements. See figure 6.3
The operation of the window circuit is shown by applying a ramp waveform, see figure 6.4 and figure
6.5.