PCF85263ATLSLASHA datasheet(43/100 Pages) NXP

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PCF85263A

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Product data sheet

Rev. 4.1 — 27 November 2015

43 of 100

NXP Semiconductors

PCF85263A

Tiny RTC with alarm, battery switch-over, and I2C-bus

Oscillator circuits suffer from jitter. In particular, ultra low-power oscillators like the one

used in the PCF85263A are optimized for power and not jitter. By setting the LOWJ bit,

the jitter performance can be improved at the cost of power consumption.

8.10.5 OSCD[1:0]: quartz oscillator drive control

[1]

Default value.

The oscillator is designed to be used with quartz with a series resistance up to 100 k

.

This covers the typical range of 32.768 kHz quartz crystals. Series resistance is also

referred to as: ESR, motional resistance, or RS.

A low drive mode is available for low series resistance quartz. This reduces the current

consumption.

For very high series resistance quartz, there is a high drive mode. Current consumption

increases substantially in this mode.

8.10.6 CL[1:0]: quartz oscillator load capacitance

[1]

Default value.

CL refers to the load capacitance of the oscillator circuit and allows for a certain amount of

package and PCB parasitic capacitance. When the oscillator circuit matches the CL

parameter of the quartz, then the frequency offset is zero.

The PCF85263A is designed to operate with quartz with CL values of 6.0 pF, 7.0 pF and

12.5 pF.

12.5 pF are generally the cheapest and most widely available, but also require the most

power to drive. The circuit also operates with 9.0 pF quartz, however the offset calibration

would be needed to compensate. If a 9.0 pF quartz is used, then it is recommended to set

CL to 7.0 pF.

Table 34.

OSCD[1:0] bits - oscillator control register (address 25h)

Bit

Symbol

Value

Description

3 to 2

OSCD[1:0]

oscillator drive bits

00[1]

normal drive; RS(max): 100 k

low drive; RS(max): 60 k; reduced IDD

10, 11

high drive; RS(max): 500 k; increased IDD

Table 35.

CL[1:0] bits - oscillator control register (address 25h)

Bit

Symbol

Value

Description

1 to 0

CL[1:0]

internal oscillator capacitor selection for

quartz crystals with the corresponding load

capacitance of CL:

00[1]

7.0 pF

6.0 pF

12.5 pF

PCF85263ATL/A Datasheet(PDF) 43 Page - NXP Semiconductors

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