参数资料
型号: TPS82678SIP
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: 0.6 A SWITCHING REGULATOR, 6000 kHz SWITCHING FREQ-MAX, BGA8
封装: 2.30 X 2.90 MM, 1 MM HEIGHT, LEAD FREE, USIP-8
文件页数: 9/28页
文件大小: 943K
代理商: TPS82678SIP
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m
c
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m
f
B
+
D
×
=
+
×
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0dBV
0dBVref
F1
FENV,PEAK
Dfc
Non-modulatedharmonic
Side-bandharmonics
windowaftermodulation
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δ
m =
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D
d
SLVSAI0A
– OCTOBER 2010 – REVISED APRIL 2011
For additional flexibility, it is possible to switch from power-save mode to PWM mode during operation. This type
of operation allows efficient power management by adjusting the operation of the converter to the specific system
requirements.
SPREAD SPECTRUM, PWM FREQUENCY DITHERING
The goal of spread spectrum architecture is to spread out the emitted RF energy over a larger frequency range
so that any resulting electromagnetic interference (EMI) is similar to white noise. The end result is a spectrum
that is continuous and lower in peak amplitude. Spread spectrum makes it easier to comply with EMI standards.
It also makes it easier to comply with the power supply ripple requirements in cellular and non-cellular wireless
applications. Radio receivers are typically susceptible to narrowband noise that is focused on specific
frequencies.
Switching regulators can be particularly troublesome in applications where electromagnetic interference (EMI) is
a concern. Switching regulators operate on a cycle-by-cycle basis to transfer power to an output. In most cases,
the frequency of operation is either fixed or regulated, based on the output load. This method of conversion
creates large components of noise at the frequency of operation (fundamental) and multiples of the operating
frequency (harmonics).
The spread spectrum architecture varies the switching frequency by approximately
±10% of the nominal
switching frequency, thereby significantly reduces the peak radiated and conducting noise on both the input and
output supplies. The frequency dithering scheme is modulated with a triangle profile and a modulation frequency
fm.
Figure 41. Spectrum of a Frequency Modulated
Figure 42. Spread Bands of Harmonics in
Sin. Wave with Sinusoidal Variation in Time
Modulated Square Signals (1)
Figure 41 and Figure 42 show that after modulation the sideband harmonic is attenuated when compared to the
non-modulated harmonic, and when the harmonic energy is spread into a certain frequency band. The higher the
modulation index (mf) the larger the attenuation.
(1)
With:
fc is the carrier frequency (i.e. nominal switching frequency)
fm is the modulating frequency (approx. 0.016*fc)
δ is the modulation ratio (approx 0.1)
(2)
(1)
Spectrum illustrations and formulae (Figure 41 and Figure 42) copyright IEEE TRANSACTIONS ON ELECTROMAGNETIC
COMPATIBILITY, VOL. 47, NO.3, AUGUST 2005. See REFERENCES Section for full citation.
Copyright
2010–2011, Texas Instruments Incorporated
17
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