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ERP2U Power Supply Design Guide, V2.31
- 28 -
7
Protection 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 s and a PSON
#
cycle HIGH
for 1 s must be able to reset the power supply.
7.1 Current 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 27. 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. -12 V and 5 VSB shall be protected under over current or
shorted conditions so that no damage can occur to the power supply.
Table 26: Over Current Protection
Voltage Over Current Limit (Iout limit)
+3.3 V 110% minimum; 150% maximum
+5 V 110% minimum; 150% maximum
+12V (combined) Peak combine current minimum; 150% maximum
7.2 240VA 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 energy 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.
Table 27: Over Current Protection
Voltage Over Current Limit (Iout limit)
+3.3 V 110% minimum; 150% maximum
+5 V 110% minimum; 150% maximum
+12V1,2,3,4 Peak current minimum; 20A maximum
1. Peak currents shall be maintained for a minimum of 500msec. The maximum duration of the peak current exceeding the
240VA limit should be limited to meet safety regulations. A maximum duration of 1 second is recommended.