Data Sheet
ac
dc
August 12, 2014 ©2012 General Electric Company. All rights reserved. Page 9
Block read format:
Linear Data Format The definition is identical to Part II of the
PMBus Specification. All standard PMBus values, with the
exception of output voltage related functions, are
represented by the linear format described below. Output
voltage functions are represented by a 16 bit mantissa.
Output voltage has a E=-9 constant exponent.
The Linear Data Format is a two byte value with an 11-bit,
two’s complement mantissa and a 5-bit, two’s complement
exponent or scaling factor, its format is shown below.
The relationship between the Mantissa, Exponent, and Actual
Value (V) is given by the following equation:
Where: V is the value, M is the 11-bit, two’s
complement mantissa, E is the 5-bit, two’s
complement exponent
Notes: Settings and read backs above support the 12Vdc
main output. There are no adjustments or read backs of the
standby output. Failure of the standby output is reported by
the STATUS_MFR_SPECIFIC register. The code does not check
the validity of, or whether the data being changed is within the
expected boundary. The user is responsible to make sure that
data placed in the registers is within the monitored range.
Command Descriptions
Operation (01) : By default the Power supply is turned ON at
power up as long as Power ON/OFF signal pin is active HI. The
Operation command is used to turn the Power Supply ON or
OFF via the PMBus. The data byte below follows the
OPERATION command.
To RESET the power supply cycle the power supply OFF, wait
at least 2 seconds, and then turn back ON. All alarms and
shutdowns are cleared during a restart.
Clear_faults (03): This command clears all STATUS and
FAULT registers and resets the SMBAlert# line.
If a fault still persists after the issuance of the clear_faults
command the specific registers indicating the fault are reset
and the SMBAlert# line is activated again.
WRITE_PROTECT register (10): Used to control writing to the
PMBus device. The intent of this command is to provide
protection against accidental changes. All supported
command parameters may have their parameters read,
regardless of the write_protect settings. The contents of this
register can be stored to non-volatile memory using the
Store_default_code command. The default setting of this
register is disable_all_writes except write_protect 0x80h.
Disable all writes except write_protect
Disable all writes except write_protect and
OPERATION
Vout_Command (21) : This command is used to change the
output voltage of the power supply. Changing the output
voltage should be performed simultaneously to all power
supplies operating in parallel using the Global Address
(Broadcast) feature. If only a single power supply is instructed
to change its output, it may attempt to source all the required
power which can cause either a power limit or shutdown
condition.
Software programming of output voltage permanently
overrides the set point voltage configured by the Vprog
signal pin. The program no longer looks at the ‘Vprog pin’ and
will not respond to any hardware voltage settings. If power is
removed from the µController it will reset itself into its default
configuration looking at the Vprog signal for output voltage
control. In many applications, the Vprog pin is used for
setting initial conditions, if different that the factory setting.
Software programming then takes over once I2C
communications are established.
To properly hot-plug a power supply into a live backplane,
the system generated voltage should get re-configured into
either the factory adjusted firmware level or the voltage level
reconfigured by the margin pin. Otherwise, the voltage state
of the plugged in power supply could be significantly different
than the powered system.
Vout_OV_warn_limit (42): OV_warning is extremely useful
because it gives the system controller a heads up that the
output voltage is drifting out of regulation and the power
supply is close to shutting down. Preemptive action may be
taken before the power supply would shut down and
potentially disable the system.
OC and OT_fault_ response (47, 50): The default response
for both OC and OT is auto_restart (hiccup). Each register,
individually, can be reconfigured into a latched state.
Latched and hiccup are the only supported states.
Restart after a latch off: Either of four restart possibilities are
available. The hardware pin Remote ON/OFF may be turned
OFF and then ON. The unit may be commanded to restart via
i2c through the Operation command by first turning OFF then
turning ON . The third way to restart is to remove and reinsert
the unit. The fourth way is to turn OFF and then turn ON ac
power to the unit. Each of these commands must keep the
power supply in the OFF state for at least 2 seconds, with the
exception of changing to restart.
A power system that is comprised of a number of power
supplies could have difficulty restarting after a shutdown
event because of the non-synchronized behavior of the
individual power supplies. Implementing the latch-off
mechanism permits a synchronized restart that guarantees
the simultaneous restart of the entire system.
A synchronous restart can be implemented by;