SSI
EPS1U Power Supply Design Guide, V1.1
7Protection Circuits
STATUS
Required
Protection circuits inside the power supply shall cause only the power supply’s main outputs to shutdown. If the power supply latches off due to a protection circuit tripping, an AC cycle OFF for 15 seconds and a PSON# cycle HIGH for 1 second shall be able to reset the power supply.
7.1Current Limit
STATUS
Required
The power supply shall have current limit to prevent the +3.3 V, +5 V, and +12 V outputs from exceeding the values shown in Table 17. If the current limits are exceeded, the power supply shall shutdown and latch off. The latch will be cleared by toggling the PSON# signal or by an AC power interruption. The power supply shall not be damaged from repeated power cycling in this condition.
Table 17: Over Current Protection
Voltage
+3.3 V
+5 V
+12 V
Over Current Limit (Iout limit)
110% minimum; 150% maximum
110% minimum; 150% maximum
110% minimum; 150% maximum
7.2240VA Protection
STATUS
Recommended
System designs may require user access to energized areas of the system. In these cases the power supply may be required to meet regulatory 240VA limits for any power rail. Since the +12V rail combined power exceeds 240VA it must be divided into separate channels to meet this requirement. Each separate rail needs to be limited to less than 20A for each +12V rail. The separate +12V rails do not necessarily need to be independently regulated outputs. They can share a common power conversion stage. The +12V rail is divided into two rails for the 250W and 350W power levels. +12V1 is dedicated for providing power to the input of the processor voltage regulator(s). The +12V2 rail is used to power the rest of the main board +12V power needs and peripherals devices.
Table 18: Over Current Protection
Voltage | Over Current Limit (Iout limit) |
+3.3 V | 110% minimum; 150% maximum |
+5 V | 110% minimum; 150% maximum |
+12V1 | 18A minimum; 20A maximum |
+12V2 | 18A minimum; 20A maximum |
