GE Industrial Solutions 20A Digital MicroDLynx - Manual (Page 22)

GE
Data Sheet
20A Digital MicroDLynx TM : Non-Isolated DC-DC Power Modules
3Vdc –14.4Vdc input; 0.45Vdc to 5.5Vdc output; 20A Output Current
April 24, 2013 ©2012 General Electric Company. All rights reserved. Page 22
PMBus Adjustable Input Undervoltage Lockout
The module allows adjustment of the input under voltage
lockout and hysteresis. The command VIN_ON allows setting
the input voltage turn on threshold, while the VIN_OFF
command sets the input voltage turn off threshold. For the
VIN_ON command, possible values are 2.75V, and 3V to 14V
in 0.5V steps. For the VIN_OFF command, possible values
are 2.5V to 14V in 0.5V steps. If other values are entered for
either command, they will be mapped to the closest of the
allowed values.
Both the VIN_ON and VIN_OFF commands use the “Linear”
format with two data bytes. The upper five bits represent the
exponent (fixed at -2) and the remaining 11 bits represent
the mantissa. For the mantissa, the four most significant bits
are fixed at 0.
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 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.
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 each of these measurements are
then calculated and placed in the appropriate registers.
These 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