DA9021 datasheet(41/142 Pages) DIALOG

41 / 142 page

DA9021/22

System PMIC with high efficiency USB power manager

Datasheet

Revision 2.5

17-Feb-2017

CFR0011-120-00 Rev 5

41 of 142

Real time clock and 32 kHz oscillator

The real time clock (RTC) block keeps track of the RTC clock counter and alarm function. The RTC

block will operate from the LDO_CORE power supply.

9.1

32 kHz oscillator

The clock oscillator cell is used to drive the RTC counter. It works with an external piezoelectric

oscillator crystal at 32.768 kHz.

In order to achieve the desired crystal frequency connect an external capacitor (10 pF to 20 pF,

depending on the parasitic capacitance of the board) to ground from each of the crystal pins. The

start-up time of the oscillator is typically 0.5 s over the voltage range. When the crystal is not

mounted, ground the unpopulated crystal pins. The 32 kHz clock signal is made available at the

OUT_32K pin and the buffer can be disabled from the sequencer during POWERDOWN mode.

The timekeeping error from the frequency variance of crystal oscillators (typ. +/- 20 ppm) can be

trimmed individually by +/- 242 ppm with a resolution of 1.9 ppm (1/(32768 * 16)). More advanced

solutions will be able to dynamically correct the temperature related oscillator frequency drift

(> 100 ppm) by using a periodic temperature measurement located close to the crystal. The

timekeeping correction will be applied only towards the on-chip RTC block. To avoid potential clock

jitter issues, the 32 kHz clock signal at the OUT_32K pin provides the original frequency of the

crystal.

9.2

RTC counter and alarm

The RTC counter can count the number of 32 kHz clock periods, providing a seconds, minutes,

hours, day, month and year output, up to 63 years. Year 0 corresponds to 2000. The value of the

RTC calendar shall be read-/write-able via the power manager communication. The calendar is reset

to zero when VDDCORE is lost.

There is an alarm register containing minutes, hours, day, month and year. When the RTC counter

wakeup (if DA9021/22 is in POWERDOWN mode) will be triggered. The trigger will also set a bit in

an event register to notify that an alarm has occurred. The alarm can alternatively be asserted from a

periodic tick signal that, depending on control TICK_TYPE, is either asserted every second or

minute. In the case the host has enabled both alarms it can determine from the status of

ALARM_TYPE whether the IRQ/wakeup was caused by the timer or the tick.

NOTE

The oscillator inputs can withstand a leakage current, corresponding to at least a 10

MΩ connected between the

pin and any signal level between VDDOUT and GND.

The power manager registers ALARM_ON and TICK_ON enable/disable the alarm/tick. The power manager

‘0’ each time the RTC is powered up. The software sets this bit to ‘1’ when setting

the time and date, which allows the software to detect a subsequent loss of the clock.

NOTE

Values written into the RTC calendar and alarm registers must be within the allowed range (see register

description, for example maximum 60 for seconds or minutes).

The RTC seconds registers define a 32-bit seconds counter (approximately 136 years), that can only

be reset via the nPOR and starts counting seconds after nPOR is released. Using the RTC input

clock the output port GPO10 can be toggled with a configurable periodic pulse. In this mode GPO10

offers blinking LED drivers that are able to run in POWERDOWN mode.

DA9021 Datasheet(PDF) 41 Page - Dialog Semiconductor

DA9021 Datasheet(HTML) 41 Page - Dialog Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL