SN260 datasheet(20/88 Pages) STMICROELECTRONICS

20 / 88 page

Functional description

SN260

20/88

Table 12 lists the specifications for the high-frequency crystal.

5.10.2

Internal RC oscillator

The SN260 has a low-power, low-frequency RC oscillator that runs all the time. Its nominal

frequency is 10kHz. It is divided down to 1kHz using a variable divider to allow software to

accurately calibrate it. This calibrated clock is used by the sleep timer.

Time-keeping accuracy depends on temperature fluctuations the chip is exposed to, power

supply impedance, and the calibration interval, but in general it will be better than 150ppm

(including crystal error of 40ppm).

Table 13 lists the specifications of the RC oscillator.

Table 12.

High-frequency crystal specifications

Parameter

Test conditions

Min.

Typ.

Max.

Unit

Frequency

MHz

Duty cycle

Phase noise from 1kHz to

100kHz

- 120

dBc/Hz

Accuracy

Initial, temperature, and aging

- 40

+ 40

ppm

Crystal ESR

Load capacitance of 10pF

100

Crystal ESR

Load capacitance of 18pF

Start-up time to stable

clock (max. bias)

1ms

Start-up time to stable

clock (optimum bias)

2ms

Current consumption

Good crystal: 20

Ω ESR, 10pF load

0.2

0.3

Current consumption

Worst-case crystals (60

Ω, 18pF or

100

Ω, 10pF)

0.5

Current consumption

At maximum bias

Table 13.

RC oscillator specifications

Parameter

Test conditions

Min.

Typ.

Max.

Unit

Frequency

kHz

Analog trim steps

kHz

Frequency variation with supply

For a voltage drop from 3.6V

to 3.1V or 2.6V to 2.1V

0.75

1.5

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