
EM358x
Rev. 0.4
43
Parameter
Test conditions
Min
Typ
Max
Unit
Crystal with high ESR
100
Ω
Load capacitance
10
pF
Crystal capacitance
7
pF
Crystal power dissipation
200
µW
Crystal with low ESR
60
Ω
Load capacitance
18
pF
Crystal capacitance
7
pF
Crystal power dissipation
1
mW
5.3.3
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 5-8 contains the specification for the low frequency RC oscillator.
Table 5-8. Low-Frequency RC Oscillator Specification
Parameter
Test conditions
Min Typ Max Unit
Nominal Frequency
After trimming
9
10
11
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)
1
%
Temperature dependence Frequency variation with temperature for a change
from -40
o
C to +85
o
C
(without re-calibration)
2
%
5.3.4
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 5-9 contains the specification for the low frequency crystal oscillator.
Table 5-9. Low-Frequency Crystal Oscillator Specification
Parameter
Test conditions
Min
Typ
Max
Unit
Frequency
32.768
kHz
Accuracy
At 25ºC
-20
+20
ppm
Load capacitance OSC32A
27
pF
Load capacitance OSC32B
18
pF
Summary of Contents for EMBER EM358 series
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