EFM32WG880 Datasheet, PDF (29/85 Pages) Silicon Laboratories – Operation from backup battery when main power drains out

3.9.4 HFRCO
Table 3.12. HFRCO
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Symbol
Parameter
Condition
Min
Typ
Max
Unit
28 MHz frequency band
27.5
28.0
28.5 MHz
21 MHz frequency band
20.6
21.0
21.4 MHz
f_HFRCO
Oscillation frequen-
cy, V_DD= 3.0 V,
T_AMB=25°C
14 MHz frequency band
11 MHz frequency band
7 MHz frequency band
13.7
14.0
14.3 MHz
10.8
11.0
11.2 MHz
6.48
6.60
6.72 MHz
1 MHz frequency band
1.15
1.20
1.25 MHz
t_{HFRCO_settling} Settling time after
start-up
f_HFRCO = 14 MHz
0.6
Cycles
f_HFRCO = 28 MHz
165
215 µA
f_HFRCO = 21 MHz
134
175 µA
I_HFRCO
Current consump-
tion
f_HFRCO = 14 MHz
f_HFRCO = 11 MHz
106
140 µA
94
125 µA
f_HFRCO = 6.6 MHz
77
105 µA
f_HFRCO = 1.2 MHz
25
40 µA
DC_HFRCO
Duty cycle
f_HFRCO = 14 MHz
48.5
50
51 %
TUNESTEP_H- Frequency step
FRCO
for LSB change in
TUNING value
0.3¹
%
1_{The TUNING field in the CMU_HFRCOCTRL register may be used to adjust the HFRCO frequency. There is enough adjustment}
range to ensure that the frequency bands above 7 MHz will always have some overlap across supply voltage and temperature. By
using a stable frequency reference such as the LFXO or HFXO, a firmware calibration routine can vary the TUNING bits and the
frequency band to maintain the HFRCO frequency at any arbitrary value between 7 MHz and 28 MHz across operating conditions.
Figure 3.18. Calibrated HFRCO 1 MHz Band Frequency vs Supply Voltage and Temperature
1.45
1.40
1.35
1.30
1.25
1.20
- 40°C
25°C
85°C
1.15
1.10
1.05
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8
Vdd [V]
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
–4 0
2.0 V
3.0 V
3.8 V
–1 5
5
25
45
65
85
Tem perature [°C]
2014-06-13 - EFM32WG880FXX - d0197_Rev1.40
29
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