EVAL-ADM1275EBZ Datasheet, PDF (32/48 Pages) Analog Devices – Hot-Swap Controller and Digital Power

ADM1275
PMON_CONTROL Command
Power monitor sampling can be initiated via software or via
hardware, as follows:
• PMON_CONTROL command. This command can be
used with single-shot or continuous mode.
• GPO1/ALERT1/CONV pin. If this pin is configured for
convert mode, an external hardware signal can be used to
take this pin high, triggering the single-shot sampling of
one or more parts together.
READ_VIN, READ_VOUT, and READ_IOUT Commands
The ADM1275 power monitor measures the voltage developed
across the sense resistor to provide a current measurement. On
the ADM1275-1 and ADM1275-3, the user can choose to
measure either the input voltage from the SENSE+ pin or the
output voltage present on the VOUT pin. The ADM1275-2 can
measure only the input voltage from the SENSE+ pin.
PEAK_IOUT, PEAK_VIN, and PEAK_VOUT Commands
In addition to the standard PMBus commands for reading
voltage and current, the ADM1275 provides commands that
can report the maximum peak voltage or current sample since
the peak value was last cleared.
The peak values are updated only after the power monitor has
sampled and averaged the current and voltage measurements.
Individual peak values are cleared by writing a 0 value with the
corresponding command.
WARNING LIMIT SETUP COMMANDS
The ADM1275 power monitor can monitor a number of differ-
ent warning conditions simultaneously and report any current
or voltage values that exceed the user-defined thresholds using
the status commands.
All comparisons performed by the power monitor require the
measured voltage or current value to be strictly greater or less
than the threshold value.
At power-up, all threshold limits are set to either minimum
scale (for undervoltage or undercurrent conditions) or to
maximum scale (for overvoltage or overcurrent conditions).
This effectively disables the generation of any status warnings
by default; warning bits are not set in the status registers until
the user explicitly sets the threshold values.
VIN_OV_WARN_LIMIT and VIN_UV_WARN_LIMIT
Commands
The VIN_OV_WARN_LIMIT and VIN_UV_WARN_LIMIT
commands are used to set the OV and UV thresholds on the
input voltage, as measured at the SENSE+ pin.
VOUT_OV_WARN_LIMIT and VOUT_UV_WARN_LIMIT
Commands
The VOUT_OV_WARN_LIMIT and VOUT_UV_WARN_
LIMIT commands are used to set the OV and UV thresholds
Data Sheet
on the output voltage, as measured at the VOUT pin on the
ADM1275-1 and ADM1275-3.
IOUT_OC_WARN_LIMIT Command
The IOUT_OC_WARN_LIMIT command is used to set the OC
threshold for the current flowing through the sense resistor.
IOUT_WARN2_LIMIT Command
The IOUT_WARN2_LIMIT command provides a second current
warning threshold that can be programmed. The polarity of this
warning can be set to overcurrent or undercurrent using the
DEVICE_CONFIG command.
PMBus DIRECT FORMAT CONVERSION
The ADM1275 uses the PMBus direct format to represent real-
world quantities such as voltage and current values. A direct
format number takes the form of a 2-byte, twos complement,
binary integer value.
It is possible to convert between direct format value and real-
world quantities using the following equations. Equation 1
converts from real-world quantities to PMBus direct values,
and Equation 2 converts PMBus direct format values to real-
world values.
Y = (mX + b) × 10^R
(1)
X = 1/m × (Y × 10^−R − b)
(2)
where:
Y is the value in PMBus direct format.
X is the real-world value.
m is the slope coefficient, a 2-byte, twos complement integer.
b is the offset, a 2-byte, twos complement integer.
R is a scaling exponent, a 1-byte, twos complement integer.
The same equations are used for voltage and current conversions,
the only difference being the values of the m, b, and R coefficients
that are used.
Table 9 lists all the coefficients required for the ADM1275. The
current coefficients shown are dependent on the value of the
external sense resistor used in a given application. This means
that an additional calculation must be performed to take the
sense resistor value into account to obtain the coefficients for
a specific sense resistor value.
The sense resistor value used in the calculations to obtain the
coefficients is expressed in milliohms. The m coefficients are
defined as 2-byte twos complement numbers in the PMBus
standard, therefore the maximum positive value that can be
represented is 32767. If the m value is greater than that, and is
to be stored in PMBus standard form, then the m coefficients
should be divided by 10, and the R coefficient increased by a
value of 1. For example, if on the 20 V range, a 10 milliohm
sense resistor is used, the m coefficient is 6043, and the R
coefficient is −1.
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