Intel ATX 3.0, Design Manual

Page: 38 / 89

Electrical
38 336521
Table 4-10: 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 kΩ from output to common
Max Ripple/Noise 400 mV p-p
4.3.2 Power-Up Cross Loading Condition – REQUIRED
In the time frame between PS_ON# assertion and PWR_OK assertion (T1+T3), the
power supply may be subjected to a cross load condition on the 12 V, 3.3 V and 5 V
rails. The power supply must be able to successfully power up and assert PWR_OK
when 12 V (or combination of 12V1 and 12V2) is loaded to ≤ 0.1 A and 3.3 V and/or 5
V are loaded to 0-5 A.
4.3.3 PS_ON# – REQUIRED
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 four main DC output rails: +12 VDC, +5 VDC, +3.3 VDC,
and -12 VDC. When PS_ON# is pulled to TTL high or open-circuited, the DC output
rails shall not deliver current and must 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. To support systems with ALPM this is required for
all power supplies. The power supply may be asked to turn back on before all voltage
rails have turned off. The power supply must be able to turn back on via a change in
the PS_ON# signal after 100 ms of the PS_ON# signal being de-asserted. Table 4-11
lists PS_ON# signal characteristics.
The power supply shall provide an internal pull-up to TTL high. The power supply shall
also provide de-bounce 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.
The power supply shall not latch into a shutdown state when PS_ON# is driven active
by pulses between 10 ms to 100 ms during the decay of the power rails. When
PS_ON# de-asserts (turn on the PSU) with a time that is greater than 100 ms, from
when it is first asserted (turns off), the PSU must respond to this request and turn
back on all voltages rails no matter where the voltage rails are in ramping down the
voltage to an Off state.
Table 4-11: PS_ON# Signal Characteristics
Parameter Minimum Maximum
V
IL
0 0.8 V
I
IL
(V
IN
= 0.4 V) - -1.6 mA 1
V
IH
(I
IN
= 200 uA) 2.0 V -