Balanced Technology Extended (BTX) Interface
PWR_OK
PWR_OK is a power good signal asserted by the system power supply to indicate that the +5VDC, +3.3VDC, and +12VDC outputs are above the under voltage thresholds of the power supply. When this signal is asserted high, the system power supply has sufficient energy stored by the converter to guarantee continuous power operation for a minimum hold-up time per the system power supply’s specification. Conversely, when one or more of the output voltages fall below their undervoltage threshold, or when mains power has been removed for a time sufficiently long so that power supply operation is no longer guaranteed beyond the holdup time, PWR_OK will be de-asserted to a low state by the power supply.
Table 4-3. PWR_OK Signal Characteristics
Parameter | Value |
Signal type | +5V TTL compatible |
Logic level low | <0.4V while sinking 4 mA |
Logic level high | Between 2.4V and 5V output while sourcing 200 µA |
High-state output impedance | 1 kΩ from output to common |
PWR_OK delay | 100 ms < T3 < 500 ms |
PWR_OK rise time | T4 ≤ 10 ms |
AC loss to PWR_OK hold-up time | T5 ≥ 16 ms |
Power-down warning | T6 ≥ 1 ms |