EM357-RTR datasheet(43/240 Pages) ETC2

43 / 240 page

EM351 / EM357

6-8

120-035X-000D

Preliminary

Parameter

Test conditions

Min

Typ

Max

Unit

Current consumption at max bias

Crystal with high ESR

100

Ω

Load capacitance

Crystal capacitance

Crystal power dissipation

200

µW

Crystal with low ESR

Ω

Load capacitance

Crystal capacitance

Crystal power dissipation

6.3.3

Low-Frequency Internal RC Oscillator (OSCRC)

A low-frequency RC oscillator (OSCRC) is provided as an internal timing reference. The nominal frequency

coming out of reset is 10 kHz, and Ember software calibrates this clock to 10 kHz. From the tuned 10 kHz

oscillator (OSCRC) Ember software calibrates a fractional-N divider to produce a 1 kHz reference clock, CLK1K.

Table 6-8 contains the specification for the low frequency RC oscillator.

Table 6-8. Low-Frequency RC Oscillator Specification

Parameter

Test conditions

Min

Typ

Max

Unit

Nominal Frequency

After trimming

kHz

Analog trim step size

0.5

kHz

Supply dependence

For a voltage drop from 3.6 V to 3.1 V or 2.6 V to 2.1 V

(without re-calibration)

Temperature

dependence

Frequency variation with temperature for a change

from -40 oC to +85oC

(without re-calibration)

6.3.4

Low-Frequency Crystal Oscillator (OSC32K)

A low-frequency 32.768 kHz crystal oscillator (OSC32K) is provided as an optional timing reference for on-chip

timers. This oscillator is designed for use with an external watch crystal. When using the 32.768 kHz crystal,

you must connect it to GPIO PC6 and PC7, and must configure these two GPIOs for analog input. Alternatively,

when PC7 is configured as a digital input, PC7 can accept an external digital clock input instead of a

32.786 kHz crystal. The digital clock input signal must be a 1 V peak-to-peak sine wave with a DC bias of

0.5 V. Refer to Chapter 7, GPIO for GPIO configuration details. Using the low-frequency oscillator, crystal or

digital clock, is enabled through Ember software.

Table 6-9 contains the specification for the low frequency crystal oscillator.

Table 6-9. Low-Frequency Crystal Oscillator Specification

Parameter

Test conditions

Min

Typ

Max

Unit

Frequency

32.768

kHz

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