ADM1275-1ACPZ-R7 datasheet(26/48 Pages) AD

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ADM1275

Data Sheet

Rev. D | Page 26 of 48

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.

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 2N, 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.

ADM1275-1ACPZ-R7 数据表(PDF) 26 Page - Analog Devices

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