Semtech 2005
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7-5
XE8801A – SX8801R
fRC=fRcmin(1+9RcFreqRange)(1+RcFreqCoarse)(1.014)
RcFreqFine
with fRcmin the RC oscillator frequency if the registers are all 0. At higher frequencies, the frequency may deviate
from the value predicted by the equation.
00000
0
010
000
10000
0
1100
00
111
01000
0
10000
0
110
00
0
111
11
1
0100
00
10000
0
1100
00
11111
1
0100
00
100
000
110
00
0
111
010
000
10
0000
11
00
111
00
0000
010
000
10000
0
1100
00
111111 01000
0
100000
110
000
11111
1
0100
00
10000
0
11000
0
11111
1
0100
00
100
000
1100
00
1111
11
0100
00
10
0000
1100
00
111
0000
0001
0011
0111
1111
1E+04
1E+05
1E+06
1E+07
1E+08
RcFreqCoarse(3:0)
Nomina
lRC
os
c
illa
to
rf
re
que
nc
y
[
H
z]
RcFreqRange='1'
RcFreqRange='0'
RcFreqFine(5:0)
Figure 7-2. RC oscillator nominal frequency tuning.
7.5.1.3
RC oscillator specifications
symbol
description
min
typ
max
unit
Comments
fRCmin
Lowest RC frequency
40
80
120
kHz
Note 1
RcFreqFine
fine tuning step
1.4
2.0
%
RC_su
startup time
30
50
us
BiasRc=0
3
5
us
BiasRc=1
PSRR @ DC
Supply voltage
TBD
%/V
Note 2
dependence
TBD
%/V
Note 3
f/T
Temperature
dependence
0.1
%/
°C
Table 7-7. RC oscillator specifications
Note 1: this is the frequency tolerance when all trimming codes are 0.
Note 2: frequency shift as a function of VBAT with normal regulator function.
Note 3: frequency shift as a function of VBAT while the regulator is short-circuited to VBAT.
Not
Recommended
for
New
Designs