adm1075-2aruz-rl7 Analog Devices, Inc., adm1075-2aruz-rl7 Datasheet - Page 34

• Manufacturer Part Number: adm1075-2aruz-rl7
• Description: −48 V Hot Swap Controller And Digital Power Monitor With Pmbus Interface
• Manufacturer: Analog Devices, Inc.

ADM1075
VAUX_OV_WARN_LIMIT and VAUX_UV_WARN_LIMIT
Commands
The VAUX_OV_WARN_LIMIT and VAUX_UV_WARN_
LIMIT commands are used to set the OV and UV thresholds
on the output voltage, as measured at the ADC_VAUX pin on
the ADM1075.
PIN_OP_WARN_LIMIT Command
The PIN_OP_WARN_LIMIT command is used to set the
overpower (OP) threshold for the power measurement register.
IOUT_OC_WARN_LIMIT Command
The IOUT_OC_WARN_LIMIT command is used to set the
overcurrent (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
represent real-world quantities such as voltage, current, and
power 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.
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, current, and power
conversions, the only difference being the values of the m, b,
and R coefficients used.
Table 7 lists all the coefficients required for the ADM1075. The
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 resistor divider scaling factor
on VIN/VAUX also needs to be taken into account when
performing a voltage or power calculation (see Example 4).
ADM1075
Y = ( mX + b ) × 10
X = 1/ m × ( Y × 10
uses the PMBus direct format internally to
R
−R
− b )
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(1)
(2)
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 stand-
ard; therefore, the maximum positive value that can be represented
is 32,767. If the m value is greater than that, and is to be stored
in PMBus standard form, the m coefficients should be divided
by 10, and the R coefficient increased by a value of 1. For example,
if performing a power calculation on the
10 mΩ sense resistor, the m coefficient is 8549, and the R
coefficient is 0.
Example 1
IOUT_OC_WARN_LIMIT requires a current limit value
expressed in direct format.
If the required current limit is 10 A, and the sense resistor is
2 mΩ, the first step is to determine the voltage coefficient. For
an ADM1075-1, this is simply m = 806 × 2, giving 1612.
Using Equation 1, and expressing X, in units of amps,
Writing a value of 3660 with the IOUT_OC_WARN_LIMIT
command sets an overcurrent warning at 10 A.
Example 2
The READ_IOUT command returns a direct format value of 3341,
representing the current flowing through a sense resistor of 1 mΩ.
To convert this value to the current flowing, use Equation 2,
with m = 806 × 1 (for the ADM1075-1):
This means that when READ_IOUT returns a value of 3341,
16.05 A is flowing in the sense resistor.
Note the following:
•
•
Y = ((1612 × 10) + 20,475) × 10
Y = 3659.5 = 3660 (rounded up to integer form)
X = 1/806 × (3341 × 10
X = 16.05 A
The same calculations that are used to convert power
values also apply to the energy accumulator value returned
by the READ_EIN command because the energy
accumulator is a summation of multiple power values.
The READ_PIN_EXT and READ_EIN_EXT commands
return 24-bit extended precision versions of the 16-bit
values returned by READ_PIN and READ_EIN. The direct
format values must be divided by 256 prior to being con-
verted with the coefficients shown in Table 7.
1
– 20,475)
−1
ADM1075-1
Data Sheet
with a