Datasheet

Accumulator_23 [n] - A ccumulator_23 [n-1]
Sample_count [n] - Sample_count [n-1]
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READ_EIN (86h)
The READ_EIN command is a standard PMBus command that returns information the host can use to calculate
average input power consumption. Accesses to this command should use the PMBus Block Read protocol.
Information provided by this command is independent of any device specific averaging period. Six bytes of data
are returned by this command. The first two bytes are the two's complement, signed output of an accumulator
that continuously sums samples of the instantaneous input power. These two data bytes are formatted in the
DIRECT format. The third data byte is a count of the rollover events for the accumulator. This byte is an
unsigned integer indicating the number of times that the accumulator has rolled over from it's maximum positive
value (7FFFh) to zero. The last three data bytes are a 24 bit unsigned integer that counts the number of samples
of the instantaneous input power that have been applied to the accumulator.
The combination of the accumulator and the rollover count may overflow within a few seconds. It is left to the
host software to detect this overflow and handle it appropriately. Similarly, the sample count value will overflow,
but this event only occurs once every few hours.
To convert the data obtained with the READ_EIN command to average power, first convert the accumulator and
rollover count to an unsigned integer:
Accumulator_23 = (rollover_count << 15) + accumulator
overflow detection and handling should be done on the 23 bits of accumulator data and the sample count now.
Data from the previous calculation should be saved and will be used in this calculation to get the unscaled
average power:
(36)
Where:
accumulator_23 [n] = overflow corrected, 23 bit accumulator data from this read
Sample_count [n] = Sample count data from this read
accumulator_23[n-1]= overflow corrected, 23 bit accumulator data from previous read
Sample_count [n-1] = Sample Count data from previous read
unscaled Average Power is now in the same units as the data from the READ_PIN command. Coefficients from
Table 43 are used to convert the Unscaled Average Power to Watts.
Table 16. READ_EIN
Bit Meaning Default
0 Sample Count High byte 0
1 Sample Count Mid byte 0
2 Sample Count Low byte 0
3 Power Accumulator Rollover Count 0
4 Power Accumulator High Byte 0
5 Power Accumulator Low Byte 0
6 Number of Bytes 6
READ_VIN (88h)
The READ_VIN command is a standard PMBus
™
command that returns the 12-bit measured value of the input
voltage. Reading this register should use the coefficients shown in Table 44. Accesses to this command should
use the PMBus
™
read word protocol. This value is also used internally for the VIN Over and Under Voltage
Warning detection.
Table 17. READ_VIN Register
Value Meaning Default
0h – 0FFFh Measured value for VIN 0000h
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