ADM1275-2ARQZ-R7 datasheet(32/48 Pages) AD

32 / 48 page

ADM1275

Data Sheet

Rev. D | Page 32 of 48

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

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) × 10R

(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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