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TTP-248M Bar Code Printer
Service Manual
3.3 Reset Circuit
/RST
1
GND
2
VCC3
3
VCC5
4
VCCA
5
U10
LTC1728
VCC
VDD
VCCL
R2
3.4K
R3
3.0K
GND
R130
10K
C77
0.1uF
C78
0.1uF
GND GND
VCC
RESET
GND
Fig. 3.3 Reset Circuit
This is the reset circuit. The LTC1728IC detects three kinds of DC Voltage (5V, 3V
and 1.9V).
VCC3 (VCC, DC3V) input threshold is 3.086
VCC5 (VDD, DC5V) threshold is 4.675.
R2
VCCA ( R1+R3 ×VCCL, DC1V ) is 1.000
RST is reasserted whenever any one of the Vcc inputs drops below its predetermined
threshold and remains asserted until 200ms after all of the Vcc inputs are above their
thresholds.