AS8228 datasheet(38/123 Pages) AMSCO

38 / 123 page

Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 38 of 123

System Timing and Real Time Clock (RTC)

A low power crystal oscillator using a 3.0 to 4.0MHz crystal provides the AS8218 / AS8228 system timing. The

low power oscillator is internally connected to a low power divider, which provides a 1Hz signal to the real time

clock, which may be precision trimmed.

Low Power

Oscillator

Low Power

Divider

RTC

Interface

1Hz

div[19:0]

MCU

Mclk

XIN

XOUT

VDD_BAT

clk_1hz

Figure 5:

System timing and RTC block diagram

Low Power Oscillator (LP_OSC)

The low power oscillator is connected to an external 3.0 to 4.0MHz crystal. The oscillator can be operated in

two modes, namely normal mode or low power mode. The low power mode is operational when the remainder

of the circuit is off (not operational).

Should a suitable external clock signal be preferred, this may be directly connected to the XIN pin, which is fed

through to output ‘Mclk’. In this case, XOUT is left unconnected.

Parameter

Symbol

Min

Typ

Max

Unit

Notes

Current consumption, normal mode

Iosc,norm

µA

Current consumption, low power mode

Iosc,bat

µA

VDD_BAT = 2VDC @

25°C

Frequency range

fosc

3.0

3.579545

4.0

MHz

Supply voltage range

VDD_BAT

2.0

3.3

3.6

Duty cycle

duty_cyc

Low Power Divider (LP_DIV, 9130h – 9132h)

The main oscillator output frequency (Mclk) is divided down to 1Hz for the real time clock (RTC). The option to

use alternative crystal frequencies and still derive a 1Hz clock signal for the real time clock (RTC), is provided

through this internally programmable divider.

For power-saving reasons, the fast oscillator clock is first divided down by a fixed ratio (divide by 5) and then

the programmable divider follows.

AS8228 Datasheet(PDF) 38 Page - ams AG

AS8228 Datasheet(HTML) 38 Page - ams AG

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