PCF8564A datasheet(15/86 Pages) NXP

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NXP Semiconductors

PCA2131

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

7.3.1.1 Temperature measurement

The PCA2131 has a temperature sensor circuit used to perform temperature

compensation of the clock input to the RTC. 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 register CLKOUT_ctl. During the first approximately 60 s after start-

up the compensation will be inactive, after this period the temperature compensation is

active.

TCR[1:0]

Temperature measurement period

[1] 32 min

16 min

8 min

4 min

Table 17. Temperature measurement period

[1]

Default value.

7.3.2 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.

When read OTPR bit, its state is:

"0" until the OTP read state machine completes copying of the eFuse data into the

shadow registers. This could be due to a POR event or to writing a 0 > 1 to the OTPR

"1" when the OTP read state machine completes copying to the shadow registers from

the eFuse instances. During normal operation OTPR must be kept at 1 to prevent higher

power usage.

The OTP logic is not reset nor affected by the Software Reset. The OTPR functionality is

only reset by the initial digital POR.

During OTP refresh, VDD has to be above 1.8 V, the rising speed to 1.8 V needs to be

faster than 2 V/100 ms. After OTP refresh has finished, PCA2131 can operate with VDD

as low as 1.2 V.

7.3.3 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 at 25 °C to determine aging offset. The CLKOUT

output is not temperature compensated to prevent jitter due to digital compensation

method.

CLKOUT is a push-pull output and is enabled at power-on. When disabled, the output is

high-impedance.

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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