Reset Circuit; Power Fail Detect Circuit - Sam4s ER-5200 Service Manual

7-2 RESET and Power Fail Circuit

7-2-1 Reset Circuit

Reset signal is a signal in order to start-up CPU under Power-on. Reset circuit uses a reset IC M51953B(U13). When
+5VDC is fallen under 4.3Vdc by Power-off, reset signal prohibits the system from miss-operation by lowering down
to 0V.
VCC
26ms
nRESET
P_FAIL
VDRV(24V)

7-2-2 Power Fail Detect Circuit

Power Fail Sensing Circuit detects sudden power-off to backup the needed data and current CPU status into RAM
before 35ms just before +5V drops. When power is turned on, the CPU does the operations which were working
before power-off. This system is designed to sense the time when the AC Line voltage is goes down to 89Vac(USA)
or 170Vac(Europe) . That is, when +24Vdc goes down to +14Vdc.
The waveform of power fail signal refer to Figure 7-2
SAM4S ER-5200 Series
Figure 7-2 Reset and Power Fail Waveform (Power On and Off)
Figure 7-3 Power Fail Detect Circuit
VCC
nRESET
14V
200ms
P_FAIL
VDRV(24V)
7 Special Circuit Descriptions
4.3V
7-3