PAC1721 datasheet(22/92 Pages) MICROCHIP

22 / 92 page

PAC1721

DS-20007088A-page 22

 2026 Microchip Technology Inc. and its subsidiaries

To read and/or reset the VACC and ACC_COUNT

registers before they overflow, calculate the worst-case

time when these registers roll over or set a fullness limit

using the ACC_FULL_LIMIT register.

PAC1721 compares the 6 MSBs of the VACC register,

while ignoring its LSBs, to the ACC_FULL[5:0] bits in

the ACC_FULL_LIMIT register. It triggers an alert if the

6 MSBs of the VACC register exceed the set limit. The

ACC_FULL_LIMIT register can also limit accumulator

count to 3/4 (75%), 7/8 (~ 87%), 15/16 (~ 93%) or 100%

full. For more details, see Register 6-28.

Calculate the worst-case accumulator overflow time

assuming that every accumulated measurement is a

full scale number. Since the values stored in the

VPOWER register are 24 bits and the accumulator

uses 56 bits, up to 232 full scale samples can be

summed before overflow. For most applications, the

samples are not all full scale numbers, especially if

VBUS is very small compared to the maximum VBUS for

PAC1721. If the maximum VBUS of the system is

always lower than the FSR for VBUS, the maximum

number of full scale samples that can be accumulated

is scaled by FSR/maximum VBUS. If both VBUS and

VSENSE values are always near full scale, this can limit

the accumulation period (tACC) before overflow to

1,092 minutes at 8,192 sps or 233 hours at 8 sps.

4.8.3

ALTERNATIVE USES FOR THE

ACCUMULATOR

The VACC register can be used to accumulate VSENSE

or VBUS values instead of VPOWER values. This is done

by setting the ACC_CONFIG[1:0] bits in the CONTROL

Configuring the VACC register to accumulate VSENSE

values provides a measure of accumulated current,

which is the same thing as charge. This allows the

VACC register to be used as a Coulomb Counter.

For either VSENSE or VBUS, many samples can be

accumulated on PAC1721. The host first reads the

VACC and ACC_COUNT registers. It then divides the

accumulator value by the accumulator count to provide

an average value with a very long integration time and

reduced noise. This feature is also useful for testing,

allowing many averages to accumulate for fast and

easy averaging/noise reduction. Test time can be

further reduced by combining this with higher sample

rates.

4.9

Conversion Cycles

A conversion cycle for PAC1721 consists of an analog-

to-digital conversion for VBUS or VSENSE. The device

performs data conversion and processing in sequence:

It samples VBUS and then VSENSE

Converts VBUS and VSENSE results from analog

to digital values

Calculates VPOWER = VBUS × VSENSE

And then accumulates VPOWER results in the

VACC register and increments the ACC_COUNT

This sequence of operations completes the conversion

cycle and the following registers update afterward:

• VBUS_MIN and VBUS_MAX

• VSENSE_MIN and VSENSE_MAX

• VBUS_AVG and VSENSE_AVG

• VPOWER_MIN and VPOWER_MAX

• ALERT_STATUS

A special configuration is available to only sample

VBUS or VSENSE (sample modes 1010b and 1011b,

respectively). This speeds up the conversion cycle by

50%. For more details, see Section 4.2.9.

Switching between sample modes during the middle of

a conversion results in the ADC continuing the previous

sample mode. It changes to the new sample mode only

after the current conversion cycle completes.

Note:

The VACC and ACC_COUNT registers

saturate when reaching their maximum

value. They do not roll over and do not

reset until cleared. This is called accu-

mulator overflow. The VACC_PRESET

VACC register so it starts at the preset

level any time a Refresh or Refresh_G

command is sent. For more details, see

Note:

The Accumulator Count does not limit

the number of samples that can be

accumulated and counted.

Note:

If a Refresh_V command changes the

accumulation type (VPOWER, VBUS or

VSENSE), the VACC register does not

reset and the data it collected up to that

moment persists. To avoid this issue,

use a Refresh command when changing

the accumulation type.

Note:

Only the internal registers update during

conversion cycles. Readable registers

update only when issuing a Refresh

(any) command or while Auto-refresh is

enabled.

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