SH3003 Datasheet, PDF (15/30 Pages) Semtech Corporation – MicroBuddy® Support IC for Microcontrollers

SH3003
POWER MANAGEMENT
Application Information (continued)
Programmable Spectrum Spreading (continued)
Setting
En CFG1 CFG0
0x
x
10
0
10
1
11
0
11
1
Spreading
Bandwidth kHz
Off
32
64
128
256
Peak EMI Reduction Peak EMI Reduction
(guaranteed db)
(measured db)
0
0
-3
-3
-6
-7
-9
-10
-12
-15
Table 2 - EMI reduction with Spectrum Spreading
Spectrum Spreading is created by varying the frequency of the HF oscillator with a pseudo-random sequence (with
a zero-average DC component). The Maximum-Length Sequence (MLS) 8-bit random number generator, clocked by
32.768kHz, is used. Only four, five, six, or seven bits of the generated 8-bit random number are used, according to the
configuration setting.
Maximum fluctuations of the frequency depend on the selected frequency range and the position within the range.
Selecting the HF oscillator frequency to be near the high end of the range limits the peak variations to 0.1%, ±0.2%,
±0.4%, or ±0.8% (corresponding to the configuration setting).
©2006 Semtech Corp.
15
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