EVAL-ADM1275EBZ Datasheet, PDF (26/48 Pages) Analog Devices – Hot-Swap Controller and Digital Power

ADM1275
VOUT MEASUREMENT
The VOUT pin on the ADM1275-1 and ADM1275-3 can be
used to provide an alternate voltage for the power monitor to
measure. The user can choose to measure the voltage at the
SENSE+ pin or the voltage at the VOUT pin, using either the
low or high input voltage range.
If the VOUT pin will be used to measure the output voltage after
the FET, a 1 kΩ resistor should be inserted in series between the
source of the FET and the VOUT pin. This resistor provides some
separation between the ADM1275 and the FET source during a
fault condition, so that ADM1275 operation is not affected.
FET HEALTH
The ADM1275 provides a method of detecting a shorted pass
FET. The FET health status can be used to generate an alert on
the GPO1/ALERT1/CONV and GPO2/ALERT2 pins. By default
at power-up, an alert is generated on the GPO2/ALERT2 pin of
the ADM1275-1 and ADM1275-3 if the FET health status
indicates that a bad FET is present. FET health is considered
bad if all of the following conditions are true:
• The ADM1275 is holding the FET off, for example, during
the initial power-on cycle time.
• VSENSE > 2 mV.
• VGATE < ~1 V, that is, less than the FET gate threshold.
POWER MONITOR
The ADM1275 features an integrated ADC that is used to
accurately measure the current sense voltage and either the
input or output voltage. Because the ADM1275-1 and
ADM1275-3 have a VOUT pin, the power monitor can be
configured using the PMBus to measure either the input or the
output voltage. The ADM1275-2 does not have a VOUT pin, so
only the input voltage at the SENSE+ pin can be measured.
The ADM1275 can report the measured current and either the
input or output voltage. The PEAK_IOUT, PEAK_VIN, and
PEAK_VOUT commands can be used to read the highest peak
current or voltage since the value was last cleared.
Data Sheet
An averaging function is provided for voltage and current that
allows a number of samples to be averaged by the ADM1275.
This function reduces the need for postprocessing of sampled
data by the host processor. The number of samples that can be
averaged is 2^N, where N is in the range of 0 to 7.
The power monitor current sense amplifier is bipolar and can
measure both positive and negative currents. The power
monitor amplifier has an input range of ±25 mV.
Two input voltage ranges are available and can be selected using
the PMBus interface: 0 V to 6 V (low input range) and 0 V to
20 V (high input range).
The two basic modes of operation for the power monitor are
single shot and continuous. In single-shot mode, the power
monitor samples the input voltage and current a number of
times, depending on the averaging value selected by the user.
The ADM1275 returns a single value corresponding to the
average voltage and current measured. When configured for
continuous mode, the power monitor continuously samples
voltage and current, making the most recent sample available
to be read.
The single-shot mode can be triggered in a number of ways.
The simplest is by selecting the single-shot mode using the
PMON_CONFIG command and writing the CONVERT bit
using the PMON_CONTROL command. The CONVERT bit
can also be written as part of a PMBus group command. Using a
group command allows multiple devices to be written to as part
of the same I²C bus transaction, with all devices executing the
command when the stop condition appears on the bus. In this
way, several devices can be triggered to sample at the same time.
When the GPO1/ALERT1/CONV pin is set to the convert
(CONV) mode, an external hardware signal can be used to
trigger the single-shot sampling of one or more parts at the
same time.
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