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Power

Valid

Output

High

Low

All enabled channel bus voltages are

above the power-valid upper limit.

All enabled channel bus voltages are

not above the power-valid upper limit.

At least one bus voltage channel has

dropped below the power-valid lower limit.

All enabled channel bus voltages are

above the power-valid upper limit.

INA3221

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SBOS576B – MAY 2012 – REVISED MARCH 2016

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Feature Description (continued)

8.3.2.3 Power-Valid Alert

The power-valid alert verifies if all power rails are above the required levels. This feature manages power

sequencing, and validates the reported measurements based on system configuration. Power-valid mode starts

at power-up, and detects when each channel exceeds a 10-V threshold. This 10-V level is the default value

programmed into the Power-Valid Upper-Limit register. This value can be reprogrammed when the INA3221 is

powered up to a valid supply-voltage level of at least 2.7 V. When all three bus-voltage measurements reach the

programmed value loaded to the Power-Valid Upper-Limit register, the power-valid (PV) alert pin pulls high. PV

powers up in a low state, and does not pull high until the power-valid conditions are met, indicating all bus-

voltage rails are above the power-valid upper-limit value. This sequence is shown in Figure 19.

Figure 19. Power-Valid State Diagram

When the power-valid conditions are met, and the PV pin pulls high, the INA3221 monitors if any bus-voltage

measurements drop below 9 V. This 9-V level is the default value programmed into the Power-Valid Lower-Limit

V. If any bus-voltage measurement on the three channels drops below the Power-Valid Lower-Limit register

value, the PV pin goes low, indicating that the power-valid condition is no longer met. At this point, the INA3221

resumes monitoring the power rails for a power-valid condition set in the Power-Valid Upper-Limit register.

The power-valid alert function is based on the power-valid conditions requirement that all three channels reach

the intended Power-Valid Upper-Limit register value. If all three channels are not used, connect the unused-

channel IN– pin externally to one of the used channels in order to use the power-valid alert function. If the

unused channel is not connected to a valid rail, the power-valid alert function cannot detect if all three channels

reach the power-valid level. Float the unused channel IN+ pin.

The power-valid function also requires that bus-voltage measurements are monitored. To detect changes in the

power-valid state, enable bus-voltage measurements through one of the corresponding MODE-bit settings in the

Configuration register. The single-shot bus-voltage mode periodically cycles between the bus-voltage

measurements to make sure that the power-valid conditions are met.

When all three bus-voltage measurements are completed, the device compares the results to the power-valid

threshold values to determine the power-valid state. The bus-voltage measurement values remain in the

corresponding channel output registers until the bus-voltage measurements are taken again, thus updating the

output registers. When the output registers are updated, the values are again compared to the power-valid

thresholds. Without taking periodic bus-voltage measurements, the INA3221 is unable to determine if the power-

valid conditions are maintained.

INA3221 Datasheet(PDF) 13 Page - Texas Instruments

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