GE Industrial Solutions 40A Digital MegaDLynx - Manual (Page 19)

GE
Data Sheet
40A Digital MegaDLynx TM : Non-Isolated DC-DC Power Modules
4.5Vdc –14.4Vdc input; 0.45Vdc to 2.0Vdc output; 40A Output Current
April 24, 2013 ©2012 General Electric Company. All rights reserved. Page 19
Power Good
The module provides a Power Good (PGOOD) signal that is
implemented with an open-drain output to indicate that the
output voltage is within the regulation limits of the power
module. The PGOOD signal will be de-asserted to a low state
if any condition such as overtemperature, overcurrent or loss
of regulation occurs that would result in the output voltage
going outside the specified thresholds. The PGOOD thresholds
are user selectable via the PMBus (the default values are as
shown in the Feature Specifications Section). Each threshold
is set up symmetrically above and below the nominal value.
The POWER_GOOD_ON command sets the output voltage
level above which PGOOD is asserted (lower threshold). For
example, with a 1.2V nominal output voltage, the
POWER_GOOD_ON threshold can set the lower threshold to
1.14 or 1.1V. Doing this will automatically set the upper
thresholds to 1.26 or 1.3V.
The POWER_GOOD_OFF command sets the level below which
the PGOOD command is de-asserted. This command also
sets two thresholds symmetrically placed around the nominal
output voltage. Normally, the POWER_GOOD_ON threshold is
set higher than the POWER_GOOD_OFF threshold.
Both POWER_GOOD_ON and POWER_GOOD_OFF commands
use the “Linear” format with the exponent fixed at –10
(decimal). The two thresholds are given by
10
) _ (
10
) _ (
2 ) _ _ (
2 ) _ _ (


 
 
OFF GOOD POWER V
ON GOOD POWER V
OFF PGOOD OUT
ON PGOOD OUT
Both commands use two data bytes with bit [7] of the high
byte fixed at 0, while the remaining bits are r/w and used to
set the mantissa using two’s complement representation.
Both commands also use the VOUT_SCALE_LOOP parameter
so it must be set correctly. The default value of
POWER_GOOD_ON is set at 1.1035V and that of the
POWER_GOOD_OFF is set at 1.08V. The values associated
with these commands can be stored in non-volatile memory
using the STORE_DEFAULT_ALL command.
The PGOOD terminal can be connected through a pullup
resistor (suggested value 100K
 ) to a source of 5VDC or
lower.
Measurement of Output Current, Output Voltage and
Input Voltage
The module is capable of measuring key module parameters
such as output current and voltage and input voltage and
providing this information through the PMBus interface.
Roughly every 200μs, the module makes 16 measurements
each of output current, voltage and input voltage. Average
values of these 16 measurements are then calculated and
placed in the appropriate registers. The values in the registers
can then be read using the PMBus interface.
Measuring Output Current Using the PMBus
The module measures current by using the inductor winding
resistance as a current sense element. The inductor winding
resistance is then the current gain factor used to scale the
measured voltage into a current reading. This gain factor is
the argument of the IOUT_CAL_GAIN command, and consists
of two bytes in the linear data format. The exponent uses the
upper five bits [7:3] of the high data byte in two-s
complement format and is fixed at –15 (decimal). The
remaining 11 bits in two’s complement binary format
represent the mantissa. During manufacture, each module is
calibrated by measuring and storing the current gain factor
into non-volatile storage.
The current measurement accuracy is also improved by each
module being calibrated during manufacture with the offset
in the current reading. The IOUT_CAL_OFFSET command is
used to store and read the current offset. The argument for
this command consists of two bytes composed of a 5-bit
exponent (fixed at -4d) and a 11-bit mantissa. This command
has a resolution of 62.5mA and a range of -4000mA to
+3937.5mA.
The READ_IOUT command provides module average output
current information. This command only supports positive or
current sourced from the module. If the converter is sinking
current a reading of 0 is provided. The READ_IOUT command
returns two bytes of data in the linear data format. The
exponent uses the upper five bits [7:3] of the high data byte in
two-s complement format and is fixed at –4 (decimal). The
remaining 11 bits in two’s complement binary format
represent the mantissa with the 11
th bit fixed at 0 since only
positive numbers are considered valid.
Note that the current reading provided by the module is not
corrected for temperature. The temperature corrected
current reading for module temperature T
Module
can be
estimated using the following equation
[( ) ]
where I
OUT_CORR
is the temperature corrected value of the
current measurement, I
READ_OUT
is the module current
measurement value, T
IND
is the temperature of the inductor
winding on the module. Since it may be difficult to measure
T
IND
, it may be approximated by an estimate of the module
temperature.
Measuring Output Voltage Using the PMBus
The module can provide output voltage information using the
READ_VOUT command. The command returns two bytes of
data all representing the mantissa while the exponent is fixed
at -10 (decimal).
During manufacture of the module, offset and gain correction
values are written into the non-volatile memory of the
module. The command VOUT_CAL_OFFSET can be used to
read and/or write the offset (two bytes consisting of a 16-bit
mantissa in two’s complement format) while the exponent is
always fixed at -10 (decimal). The allowed range for this offset
correction is -125 to 124mV. The command VOUT_CAL_GAIN
can be used to read and/or write the gain correction - two
bytes consisting of a five-bit exponent (fixed at -8) and a 11-
bit mantissa. The range of this correction factor is -0.125V to
+0.121V, with a resolution of 0.004V. The corrected output
voltage reading is then given by: