ATSAMB11XR datasheet(19/87 Pages) MICROCHIP

19 / 87 page

Table 6-1. 32.768 kHz External Clock Specification

Parameter

Min.

Typ.

Max Unit

Comments

Oscillation frequency

32.768

kHz Must be able to drive 6 pF load at desired frequency

VinH

0.7

1.2

High level input voltage

VinL

0.2

Low level input voltage

Stability – Temperature -250

+250 ppm

Additional internal trimming capacitors (C_onchip) are available. They provide the possibility to tune the

frequency output of RTC XO without changing the external load capacitors. Contact technical support for

usage of the internal trimming capacitors.

Note:

Refer the BluSDK BLE API Software Development Guide for details on how to enable the 32.768 kHz

clock output and tune the internal trimming capacitors.

Table 6-2. 32.768 kHz XTAL C_onchip Programming

C_onchip [pF]

0000

0.0

0001

1.0

0010

2.0

0011

3.0

0100

4.0

0101

5.0

0110

6.0

0111

7.0

1000

8.0

1001

9.0

1010

10.0

1011

11.0

1100

12.0

1101

13.0

1110

14.0

1111

15.0

6.3.2

RTC XO Design and Interface Specification

The RTC consists of two main blocks: The Programmable Gm stage and tuning capacitors. The

programmable Gm stage is used to guarantee start-up and to sustain oscillation. Tuning capacitors are

used to adjust the XO center frequency and control the XO precision for different crystal models. The

output of the XO is driven to the digital domain via a digital buffer stage with a supply voltage of 1.2V.

ATSAMB11XR/ZR

Datasheet Preliminary

DS70005342A-page 19

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