ADM1075 datasheet(33/52 Pages) AD

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Data Sheet

ADM1075

Rev. A | Page 33 of 52

The settings that can be configured are as follows:

•

Single-shot or continuous sampling

•

Enable VAUX sampling

•

Current input range

•

Current and voltage sample averaging

Modifying the power monitor settings while the power monitor

is sampling is not recommended because it may cause spurious

data or warnings to be generated.

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_VAUX, and READ_IOUT Commands

The ADM1075 power monitor measures the voltage developed

across the sense resistor to provide a current measurement. The

input voltage from the ADC_V pin is always measured, and the

user can choose whether or not to measure the output voltage

present on the ADC_AUX pin as well.

READ_PIN, READ_PIN_EXT, READ_EIN, and

READ_EIN_EXT Commands

The VIN input voltage (12-bit) and IOUT current (12-bit)

measurement values are multiplied by the ADM1075 to give the

input power value. This is done using fixed point arithmetic and

produces a 24-bit value. It is assumed that the numbers are of

the 12.0 format, meaning there is no fractional part. It should

be noted that only positive IOUT values are used to avoid

returning a negative power.

This 24-bit value can be read from the ADM1075 using the

READ_PIN_EXT command, where the most significant bit

(MSB) is always a zero because PIN_EXT is a twos complement

binary value that is always positive.

The 16 most significant bits of the 24-bit value are used as the

value for input power (PIN). The MSB of the 16-bit PIN word is

always zero because PIN is a twos complement binary value that

is always positive.

Each time a power calculation is performed, the 24-bit power

value is added to a 24-bit energy accumulator register. This is a

twos complement representation as well; therefore, the MSB is

always zero. Each time this energy accumulator register rolls

over from 0x7FFFFF to 0x000000, a 16-bit rollover counter is

incremented. The rollover counter is straight binary, with a

maximum value of 0xFFFF before it rolls over.

There is also a 24-bit straight binary power sample counter that

is incremented by one each time a power value is calculated and

added to the energy accumulator.

These registers can be read back using one of two commands,

depending on the level of accuracy required for the energy

accumulator and the desire to limit the frequency of reads from

the ADM1075.

A bus host can read these values, and, using some difference

calculations, determine the amount of energy consumed since

the last read and the number of samples in that time. The bus

host, using an external real-time clock, can then determine the

power used in the last time period.

To avoid the loss of data, the bus host must read at a rate that

ensures the rollover counter does not wrap around more than

once and, if it does wrap around, that the next rollover value is

less than the previous one.

The READ_EIN command returns the top 16 bits of the energy

accumulator, the lower eight bits of the rollover counter, and the

full 24 bits of the sample counter.

The READ_EIN_EXT command returns the full 24 bits of the

energy accumulator, the full 16 bits of the rollover counter, and

the full 24 bits of the sample counter. The use of the longer

rollover counter means that the time interval between reads of

the part to ensure that no data is lost can be increased from

seconds to minutes.

PEAK_IOUT, PEAK_VIN, PEAK_VAUX, and PEAK_PIN

Commands

In addition to the standard PMBus commands for reading

voltage and current, the ADM1075 provides commands that

can report the maximum peak voltage, current, or power value

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 commands.

WARNING LIMIT SETUP COMMANDS

The ADM1075 power monitor can monitor a number of

different 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, overcurrent or overpower

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 ADC_V pin.

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