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EPS1U Power Supply Design Guide, V1.1
8.3 ACWarning
STATUS
Optional
This is an output signal from the power supply which provides a warning to the system that the power supply has
lost its AC input. This signal also provides a signal to synchronize the turn on of multiple power supplies. At turn
on, this signal is pulled LOW when the supply’s internal bulk voltage has reached a level that allows it to turn on.
At turn off ACWarning goes HIGH when the internal bulk voltage drops low enough. The characteristics of the
ACWarning signal is shown in Table 22: ACWarning Signal Characteristics. Refer to Figure 5 for timing diagram.
Table 22: ACWarning Signal Characteristics
Signal Type
Open collector/drain output from power supply. Pull-
up to VSB located in system.
ACWarning = Low
Input voltage within operating range and power
supply is ready to turn on.
ACWarning = High
Input voltage is less than the operating range and the
power supply is turning off.
MIN MAX
Logic level low voltage, Isink=4mA
0V 0.4V
Logic level high voltage, Isink=50µA
5.25V
Sink current, ACWarning = low
4mA
Sink current, ACWarning = high
50µA
ACWarning Delay: T
acwarning_delay
8msec
ACWarning rise and fall time
100µsec
Power supply turn on voltage
75VAC 85VAC