PCF2129 datasheet(13/86 Pages) PHILIPS

13 / 86 page

PCF2129

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 7 — 19 December 2014

13 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

8.3.1 Temperature compensated crystal oscillator

The frequency of tuning fork quartz crystal oscillators is temperature-dependent. In the

PCF2129, the frequency deviation caused by temperature variation is corrected by

adjusting the load capacitance of the crystal oscillator.

The load capacitance is changed by switching between two load capacitance values using

a modulation signal with a programmable duty cycle. In order to compensate the spread of

the quartz parameters every chip is factory calibrated.

The frequency accuracy can be evaluated by measuring the frequency of the square

wave signal available at the output pin CLKOUT. However, the selection of

fCLKOUT = 32.768 kHz (default value) leads to inaccurate measurements. Accurate

frequency measurement occurs when fCLKOUT = 16.384 kHz or lower is selected (see

Table 15).

8.3.1.1

Temperature measurement

The PCF2129 has a temperature sensor circuit used to perform the temperature

compensation of the frequency. The temperature is measured immediately after power-on

and then periodically with a period set by the temperature conversion rate TCR[1:0] in the

[1]

Default value.

8.3.2 OTP refresh

Each IC is calibrated during production and testing of the device. The calibration

parameters are stored on EPROM cells called One Time Programmable (OTP) cells. It is

recommended to process an OTP refresh once after the power is up and the oscillator is

operating stable. The OTP refresh takes less than 100 ms to complete.

To perform an OTP refresh, bit OTPR has to be cleared (set to logic 0) and then set to

logic 1 again.

8.3.3 Clock output

A programmable square wave is available at pin CLKOUT. Operation is controlled by the

COF[2:0] control bits in register CLKOUT_ctl. Frequencies of 32.768 kHz (default) down

to 1 Hz can be generated for use as system clock, microcontroller clock, charge pump

input, or for calibrating the oscillator.

CLKOUT is an open-drain output and enabled at power-on. When disabled, the output is

high-impedance.

Table 14.

Temperature measurement period

TCR[1:0]

Temperature measurement period

[1] 4min

2 min

1 min

30 seconds

PCF2129 数据表(PDF) 13 Page - NXP Semiconductors

PCF2129 数据表(HTML) 13 Page - NXP Semiconductors

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

数据表下载