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The Speaker Company TTP 248M Benutzerhandbuch

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21 
TTP-248M Bar Code Printer 
Service Manua
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3.3 Reset Circuit 
/RST
1
GND
2
VCC3
3
VCC5
4
VCCA
5
U10
LTC1 72 8
VCC
VDD
VCCL
R2
3. 4K
R3
3. 0K
GND
R130
10 K
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.