PAC1721 datasheet(25/92 Pages) MICROCHIP

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DS-20007088A-page 25

PAC1721

To enable the following alerts, set the corresponding

bits in the ALERT_ENABLE register:

• Overvoltage and undervoltage alerts

• Overcurrent and undercurrent alerts

• Overpower alerts

• Rising and falling voltage and current alerts

• Accumulator and accumulator count alerts

For more details on enabling alerts, see Register 6-37.

Accumulator fullness limits are 2’s complement values,

regardless if unipolar or bipolar mode is used for VBUS

and VSENSE sampling. The ACC_FULL_LIMIT register

sets the accumulator and accumulator count fullness

and overflow limits. For details, see Register 6-28.

4.10.4

ALERT THRESHOLD LIMITS

Overvoltage, undervoltage, overcurrent, undercurrent,

overpower, rising and falling voltage and current events

trigger an alert only when the monitored parameter is

outside its set limits.

The registers for overcurrent (OC), undercurrent (UC),

overvoltage (OV), undervoltage (UV) and step limits

use 8 bits. PAC1721 compares the 8-bit limits (2’s

complement) to the first 8 MSBs of the corresponding

data 12-bit register.

The registers for overpower (OP) warning and critical

limits use 16 bits. PAC1721 compares the 16-bit limits

to the first 16 MSBs of the 24-bit VPOWER register.

Step limits are used to detect large changes in the most

recent conversion when compared to the appropriate

average register.

The alert thresholds are set in the following registers:

• OC_LIMIT – Register 6-29

• UC_LIMIT – Register 6-30

•OP_WARNING_LIMIT – Register 6-31

• OP_CRITICAL_LIMIT – Register 6-32

• OV_LIMIT – Register 6-33

• UV_LIMIT – Register 6-34

• STEP_LIMIT – Register 6-35

4.10.5

SAMPLES OVER LIMIT TO

TRIGGER ALERT

The N-SAMPLES_LIMIT register can be programmed

to specify how many consecutive samples must be

outside their configured limits before triggering an Alert

condition. For more details, see Register 6-36.

For overcurrent, overvoltage and overpower events,

exceeding the set threshold implies the measurement

is over the programmed limit. For undercurrent and

undervoltage, not exceeding the set threshold implies

the measurement is under the programmed limit. Both

events trigger an Alert condition.

When thresholds are negative, it implies that negative

numbers with large magnitudes trigger overcurrent,

overvoltage and overpower events, while negative

numbers with small magnitudes trigger undercurrent

and undervoltage events.

When sampling, PAC1721 detects if a measurement is

outside its programmed limits. By default, the number

of consecutive over limit detections that is required to

trigger the corresponding alert is 1, resulting in an alert

that occurs on the first sample that is not within the set

threshold. To change the number of consecutive over

limit detections required to trigger an alert, set the

appropriate bits in the N-SAMPLES_LIMIT register.

4.10.6

ACCUMULATOR-BASED ALERTS

The Alert function can be programmed to trigger when

the VACC and/or ACC_COUNT registers are filled to or

beyond a specified limit.

By default, the VACC register stores the accumulated

sum of VPOWER calculations. It can be programmed to

accumulate VBUS or VSENSE measurements instead.

PAC1721 compares the ACC_FULL[5:0] bits of the

ACC_FULL_LIMIT register with the 6 MSBs of the

VACC register. It determines if the accumulator has

exceeded its fullness limit and triggers the Accumulator

Full alert, if applicable.

The ACC_COUNT register stores the total number of

results accumulated in the VACC register. The Accu-

mulator Count Full limit determines the threshold

beyond which the ACC_COUNT register is considered

full and an alert condition triggers.

Note 1: Only the alert conditions set in the

ALERT_ENABLE register are capable

of triggering alerts. For more details,

see Register 6-37.

2: The ALERT_STATUS register displays

only enabled alerts. For more details,

see Register 6-18.

Note:

The maximum value that can be stored

in the ACC_FULL[5:0] bits is 111111b.

Do not use this value as the Accumulator

Full limit. Since this is the maximum

value, it cannot be exceeded and thus,

no alert is triggered. Use 111110b as

the maximum Accumulator Full limit.

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