Pwr_Ok; Ps_On; Table 13. Pwr_Ok Signal Characteristics - Intel ATX12V Design Manual

3.3.1. PWR_OK

PWR_OK is a "power good" signal. It should be asserted high by the power supply to
indicate that the +12 VDC, +5VDC, and +3.3VDC outputs are above the under-voltage
thresholds listed in Section 3.2.1 and that sufficient mains energy is stored by the converter
to guarantee continuous power operation within specification for at least the duration
specified in Section 3.2.11, "Voltage Hold-up Time." Conversely, PWR_OK should be de-
asserted to a low state when any of the +12 VDC, +5 VDC, or +3.3 VDC output voltages
falls below its under-voltage threshold, or when mains power has been removed for a time
sufficiently long such that power supply operation cannot be guaranteed beyond the power-
down warning time. The electrical and timing characteristics of the PWR_OK signal are
given in Table 13 and in Figure 6.

Table 13. PWR_OK Signal Characteristics

Signal Type
Logic level low
Logic level high
High-state output impedance
PWR_OK delay
PWR_OK risetime
AC loss to PWR_OK hold-up time
Power-down warning

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
14 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 10ms to 100ms during the decay of the power rails.
ATX12V Power Supply Design Guide
+5 V TTL compatible
< 0.4 V while sinking 4 mA
Between 2.4 V and 5 V output while sourcing 200 µA
Ω
1 k from output to common
100 ms < T < 500 ms
3
≤
T 10 ms
4
≥ 16 ms
T
5
≥ 1 ms
T
6
Version 2.0
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