ATX/ATX12V Power Supply Design Guide
Version 1.1
Page 18
Table 14. PWR_OK Signal Characteristics
Signal Type
+5 V TTL compatible
Logic level low
< 0.4 V while sinking 4 mA
Logic level high
Between 2.4 V and 5 V output while sourcing 200 µA
High-state output impedance
1 k
Ω
from output to common
PWR_OK delay
100 ms < T
3
< 500 ms
PWR_OK risetime
T
4
≤
10 ms
AC loss to PWR_OK hold-up time
T
5
≥
16 ms
Power-down warning
T
6
≥
1 ms
3.3.2. PS_ON#
PS_ON# is an active-low, TTL-compatible signal that allows a motherboard to remotely
control the power supply in conjunction with features such as soft on/off, Wake on LAN
†
,
or wake-on-modem. When PS_ON# is pulled to TTL low, the power supply should turn on
the five main DC output rails: +12VDC, +5VDC, +3.3VDC, -5VDC, and -12VDC. When
PS_ON# is pulled to TTL high or open-circuited, the DC output rails should not deliver
current and should be held at zero potential with respect to ground. PS_ON# has no effect
on the +5VSB output, which is always enabled whenever the AC power is present. Table
15 lists PS_ON# signal characteristics.
The power supply shall provide an internal pull-up to TTL high. The power supply shall
also provide debounce circuitry on PS_ON# to prevent it from oscillating on/off at startup
when activated by a mechanical switch. The DC output enable circuitry must be SELV-
compliant.
Table 15. PS_ON# Signal Characteristics
Min.
Max.
V
IL
, Input Low Voltage
0.0 V
0.8 V
I
IL
, Input Low Current (Vin = 0.4 V)
-1.6 mA
V
IH
, Input High Voltage (Iin = -200 µA)
2.0 V
V
IH
open circuit, Iin = 0
5.25 V
