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M440LX Server System Product Guide
167
System Current Monitor
The system current monitor on the power share backplane sends a power
usage report to the server via the I
2
C communications bus. The backplane
microcontroller contains analog-to-digital converters that monitor DC
voltage levels supplied by the current sense circuits. They represent the
current load on the +3.3 V output from the system board and the +5 V and
+12 V load at both the system board and the peripheral bays.
If either the +5 V or +12 V load from the system board or the peripherals
goes beyond the CSA Level 3 requirement of 240 VA, the power is shut off
immediately by disserting PON. It is impossible to draw 240 VA from the
3.3 Volt power supply output even when three supplies are installed in the
server. The following table shows the maximum current allowed by each
voltage output for a server with three 360 watt power supplies.
Voltage Maximum Current in Amperes 240 VA Limit
+3.3 V 33 A N/A
+5 V 96 A 48 A
+12 V 36 A (or 48 A for 12 ns maximum) 20 A
A voltage level within the range of 0 to 5 V is supplied by the current sense
circuits on the power share backplane. The current limit threshold is set to
44 A ±4 A for each +5 V channel and 16 A +4 A for each +12 V channel.
Power Supply FAULT
Each power supply provides a power good (PGOOD) signal that is asserted
high. If a power supply fails, its PGOOD signal goes low. The power
supply outputs are enabled through assertion of the PON signal. If the
PGOOD signal goes low, indicating a power bad condition while PON is
asserted, a FAULT is generated and applied to one of the FAULT inputs of
the backplane microcontroller.
Power Supply Presence DETECT
The DETECT signal senses the number of power supplies (operational or
not) in the server. Each power supply presents a grounding connection to
one of the backplane microcontroller input pins to show that a power
supply is present. If a power supply is not present, the backplane
microcontroller input pin will be pulled high through a pull-up resistor to
+5 V standby.