TTP-248M Bar Code Printer
Service Manual
3.3 Reset Circuit
VCC
VCCL
| VCC |
| 3 |
R3 | VDD |
3. 0K | 4 |
| 5 |
R2 | C77 |
3. 4K | C78 |
0. 1uF 0. 1uF
U10
VCC3
/RST
VCC5
GND
VCCA
LTC1 72 8
R130
10 K
1 
RESET
2
GND
GND GND
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.
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