lm25066apsqx National Semiconductor Corporation, lm25066apsqx Datasheet - Page 42

• Manufacturer Part Number: lm25066apsqx
• Description: Lm25066a System Power Management And Protection Ic With Pmbus
• Manufacturer: National Semiconductor Corporation

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Reading Input and Output Voltage
Coefficients for VIN and VOUT are fixed and are consistent
between read telemetry measurements (e.g., READ_VIN,
READ_AVG_VIN)
Reading Power
The power calculation of the LM25066A is a relative power
calculation meaning that full scale of the power register cor-
responds to simultaneous full scale values in the current
register and voltage register such that the power register has
the following relationship based on decimal equivalents of the
register contents:
1. Determine m' based on full scale analog input and full scale
digital range:
2. Determine exponent R necessary to set m' to integer value m
with desired accuracy:
3. Final values
Step
1. Determine full scale power from known full scale of input
current and input voltage
P
2. Determine m':
3. Optional: Determine exponent R necessary to set m' to integer
value m with desired accuracy:
4. Final values
IN_MAX
= V
IN_MAX
x I
IN_MAX
and
warning
Step
thresholds
(e.g.,
42
Select R to provide 5 digit accuracy for the integer value of m
(which would be 21703 in this example:
R = -2
m = 22026
R = -2
b =0
Example
Example: 125A application with 250 µΩ shunt.
P
Select R (in this case selected to provide 4 digit accuracy for the
integer value of m):
R = -3
m = 1823
R = -3
b = 0
IN_MAX
VIN_UV_WARN_LIMIT). Input and output voltage values are
read/written in Direct format with 12-bit resolution and a 4.54
mV LSB. An example of calculating the PMBus™ coefficients
for input voltage is shown below.
For this reason power coefficients will also vary depending on
the shunt value and must be calculated for each application.
The power LSB will vary depending on shunt value according
to 276 µW/Rsense for 46mV range or 138.2 µW/Rsense for
25mV range.
= (18.59V) x (120.8A) = 2246W
Example