PCF8564A datasheet(14/86 Pages) NXP

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NXP Semiconductors

PCA2131

Nano-power highly accurate RTC with integrated quartz crystal for automotive applications

Bits labeled as T are unused and return 0 when read.

Bit

Symbol

Value

Description

Reference

7 to 6

TCR[1:0]

see Table 17

temperature measurement period

no OTP refresh

OTPR

OTP refresh performed

Section 7.3.2

unused [1]

unused

2 to 0

COF[2:0]

see Table 18

CLKOUT frequency selection

Section 7.3.3

Table 16. CLKOUT_ctl - CLKOUT control register (address 13h) bit description

[1]

programming this bit to 1 may lead to a decrease of timing accuracy.

7.3.1 Temperature compensated Real Time Clock

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

PCA2131, the frequency deviation caused by temperature variation is corrected by

adjusting the RTC frequency divider with digital method.

The load capacitance is trimmed to the required value at 25 °C in order to compensate

the frequency deviation over process variation.

The frequency accuracy at 25 °C 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) can lead to inaccurate measurements. Accurate

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

Table 18).

The temperature compensated frequency input for the Real Time Clock cannot be

observed at the CLKOUT pin but can be evaluated by following these steps.

• Set Second Interrupt, bit SI in register Control_1 to 1

• Set bit TI_TP in register Watchdg_tim_ctl to 1 for a pulsed interrupt signal

• Set bit SIA in register INTA_MASK_1 to 0 to direct the Second Interrupt to pin INTA for

a 1 Hz pulse output.

The RTC temperature compensation works by adding or deleting pulses at the 32.768

kHz level. These correction pulses are spaced evenly over a sufficiently long period

of time to reach the required resolution and accuracy. Every second corrections

with a resolution of about 30.5 ppm (1/32768) can be generated by the temperature

compensation engine. If for instance a 10 ppm correction is called for, the correction

pulses will be generated approximately once every 3 seconds, for a 50 ppm correction

every 0.6 s and so on.

The 1 Hz interrupt output signal can be measured with a counter and by selecting an

appropriate gating time the measurement resolution can be set to the desired level. A

gating time of 100 s for instance will determine the averaged 1 second period with a

resolution of 0.3 ppm.

The feature of temperature compensation can be turned off for ultra low power

consumption by first performing a software reset (SR) followed by setting TC_DIS to ‘1’

within 5 seconds.

PCA2131

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

Product data sheet

Rev. 1.0 — 26 July 2021

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