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– 22 –
PRINCIPLES OF OPERATION
2-5. +5V Line Voltage Detector Circuit
The voltage-detection IC (IC3 in Fig. 2-13) detects momentary drops or unstable levels in the +5V line voltage. The
following shows an IC3-equivalent circuit.
Fig. 2-14 Equivalent Circuit, Voltage Detection IC
Figure 2-15 shows the IC’s operational timing. The IC asserts a reset signal at its output terminal when the -5V line voltage
falls below 4.25V, thereby resetting the CPU and the gate array.
Fig. 2-15 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
tdtd
t
t
td = 0.34 × Cd (pF) [µs]