NRF52820-QDAA-R datasheet(236/437 Pages) NORDIC

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Peripherals

Operation/Function

Jitter

START to COUNTER increment

+/- 15 μs

COMPARE to COMPARE 18

+/- 62.5 ns

Table 68: RTC jitter magnitudes on events

Note: 32.768 kHz clock jitter is additional to the numbers provided above.

CLEAR and STOP (and TRIGOVRFLW; not shown) will be delayed as long as it takes for the peripheral to

clock a falling edge and rising of the LFCLK. This is between 15.2585 μs and 45.7755 μs – rounded to 15 μs

and 46 μs for the remainder of the section.

0x000

SysClk

LFClk

PRESC

COUNTER

CLEARa

X+1

0x000000

0x000001

0 or more SysClk after

CLEAR

CLEARb

1 or more SysClk before

≤ ~46 µs

≥ ~15 µs

Figure 90: Timing diagram - DELAY_CLEAR

SysClk

LFClk

PRESC

COUNTER

STOPa

X+1

0 or more SysClk after

STOP

STOPb

1 or more SysClk before

≤ ~46 µs

≥ ~15 µs

0x000

Figure 91: Timing diagram - DELAY_STOP

The START task will start the RTC. Assuming that the LFCLK was previously running and stable, the first

increment of COUNTER (and instance of TICK event) will be typically after 30.5 μs +/-15 μs. In some

cases, in particular if the RTC is STARTed before the LFCLK is running, that timing can be up to ~250 μs.

The software should therefore wait for the first TICK if it has to make sure the RTC is running. Sending a

TRIGOVRFLW task sets the COUNTER to a value close to overflow. However, since the update of COUNTER

relies on a stable LFCLK, sending this task while LFCLK is not running will start LFCLK, but the update will

then be delayed by the same amount of time of up to ~250 μs. The figures show the shortest and longest

delays on the START task which appears as a +/-15 μs jitter on the first COUNTER increment.

18 Assumes RTC runs continuously between these events.

4463_156 v1.0

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