Star Micronics TUP400 Series, Technical Manual

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2-5. +5V Line Voltage Detector Circuit
The voltage-detection IC detects momentary drops or unstable levels in the +5V line voltage.
The following illustrates the equivalence circuit of the voltage detector IC (Fig. 2-9 IC4).
Fig. 2-11 Equivalence Circuit for Voltage Detecting IC
The following operation timing chart shows control is performed by the voltage detector IC output. If the +5V line voltage
falls below 4.25V, the IC produces a reset signal from its OUT terminal, resetting the CPU and the gate array.
Fig. 2-12 Operation Timing Chart
1.25V
R1
R2
SµA typ
V
CC
1
GND
3
Cd
4
–
OUT
5
–
+
V
CC
Voltage
4.25V
0.8V
Output
Voltage
td td
t
t
td = 0.34
×
Cd (pF) [µs]