Datasheet

ADM1075 Data Sheet
Rev. B | Page 26 of 52
FET HEALTH
The ADM1075 features 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 GPO1/
ALERT1
/CONV if
the FET health status indicates a bad FET is present. FET health
is considered bad if all of the following conditions are true:
• The ADM1075 is holding the FET off, for example, during
the initial power-on cycle time.
• V
SENSE
> 2 mV for the ADM1075-1 and 4 mV for the
ADM1075-2.
• V
GATE
< ~1 V.
POWER MONITOR
The ADM1075 features an integrated ADC that accurately
measures the current sense voltage and the ADC_V voltage.
It can also optionally monitor the ADC_AUX voltage. The
measured input voltage (ADC_V) and the current being
delivered to the load are multiplied to give a power value that
can be read back. Each power value is also added to an accumula-
tor that can be read back to allow an external device to calculate
the energy consumption of the load.
The PEAK_IOUT, PEAK_VIN, and PEAK_VAUX commands
can be used to read the highest peak current or voltage since the
value was last cleared.
An averaging function is provided for voltage and current that
allows a number of samples to be averaged by the ADM1075.
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. It has two input
ranges and can be selected using the PMBus interface. The
input ranges are ±25 mV and ±50 m V.
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 ADM1075 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 ADC runs in continuous mode by default at
power-up.
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 to 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 I
2
C 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.
Each time a current sense and input voltage measurement is
taken, a power calculation is performed, multiplying the two
measurements together. This can be read from the device using
the READ_PIN command, returning the input power.
At the same time, the calculated power value is added to a
power accumulator register that may increment a rollover
counter if the value exceeds the maximum accumulator value,
and that also increments a power sample counter.
The power accumulator and power sample counter are read
back using the same READ_EIN command to ensure that the
accumulated value and sample count are from the same point in
time. The bus host reading the data assigns a timestamp to show
when the data is read. By calculating the time difference
between consecutive uses of READ_EIN and determining the
delta in power consumed, it is possible for the host to determine
the total energy consumed over that period.
ISOLATION
Isolation is usually required in −48 V systems because there can
be a large voltage difference between different ground planes in
the system. The ADM1075 is referenced to −48 V, whereas the
MCU is usually referenced to 0 V. In almost all cases, the I
2
C
signals must be isolated. Any other ADM1075 digital input and
output signals that go to or come from the MCU must also be
isolated.
Analog Devices, Inc., provide a range of digital isolators using
iCoupler® technology. iCoupler technology is based on chip
scale transformers rather than the LEDs and photodiodes used
in optocouplers. The ADuM1250 is a dual I
2
C isolator and can
be used in conjunction with the ADM1075 for I
2
C isolation.
VDD1
SCL2
SCL1
GND1
VDD2
SDA2
SCL2
GND2
–48V
–48V
GND_ISO
GND_ISO
5V_ISO
5V
100nF
100nF
SDA
SDA_ISO
SCL
SCL_ISO
ISOLATED SIDE
(SECONDARY)
–48V SIDE
(PRIMARY)
VDD1
10kΩ
10kΩ
ADuM1250
09312-147
Figure 53. ADuM1250 I
2
C Isolation
In cases where more digital signals need to be isolated, the
ADuM3200 is a dual-channel digital isolator whereas the
ADuM5404 is a quad-channel isolator with isoPower®, an
integrated, isolated dc-to-dc converter.
The ADuM1250 and ADuM3200 must be powered from both
the primary and secondary sides. The ADuM5404 only needs to