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參數(shù)資料
| 型號： | LP3972 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Power Management Unit for Advanced Application Processors |
| 中文描述： | 電源管理單元的高級應(yīng)用處理器 |
| 文件頁數(shù)： | 20/59頁 |
| 文件大?。?/td> | 1072K |
| 代理商： | LP3972 |
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Buck Converter Operation
(Continued)
SOFT START
The buck converter has a soft-start circuit that limits in-rush
current during start-up. During start-up the switch current
limit is increased in steps. Soft start is activated only if EN
goes from logic low to logic high after V
reaches 2.7V. Soft
start is implemented by increasing switch current limit in
steps of 213 mA, 425 mA, 850 mA and 1700 mA (typ. Switch
current limit). The start-up time thereby depends on the
output capacitor and load current demanded at start-up.
Typical start-up times with 10 μF output capacitor and 1000
mA load current is 390 μs and with 1 mA load current
its 295 μs.
LDO - LOW DROP OUT OPERATION
The LP3672 can operate at 100% duty cycle (no switching;
PMOS switch completely on) for low drop out support of the
output voltage. In this way the output voltage will be con-
trolled down to the lowest possible input voltage. When the
device operates near 100% duty cycle, output voltage ripple
is approximately 25 mV. The minimum input voltage needed
to support the output voltage is
V
IN, MIN
= I
LOAD
* (R
DSON, PFET
+ R
INDUCTOR
) + V
OUT
I
LOAD
R
DSON, PFET
Load Current
Drain to source resistance of PFET
switch in the triode region
Inductor resistance
R
INDUCTOR
SPREAD SPECTRUM FEATURE
Periodic switching in the buck regulator is inherently a
noisier function block compared to an LDO. It can be chal-
lenging in some critical applications to comply with stringent
regulatory standards or simply to minimize interference to
sensitive circuits in space limited portable systems. The
regulator’s switching frequency and harmonics can cause
“noise” in the signal spectrum. The magnitude of this noise is
measured by its power spectral density. The power spectral
density of the switching frequency, F
, is one parameter that
system designers want to be as low as practical to reduce
interference to the environment and subsystems within their
products. The LP3972 has a user selectable function on
chip, wherein a noise reduction technique known as “spread
spectrum” can be employed to ease customer’s design and
production issues.
The principle behind spread spectrum is to modulate the
switching frequency slightly and slowly, and spread the sig-
nal frequency over a broader bandwidth. Thus, its power
spectral density becomes attenuated, and the associated
interference electro-magnetic energy is reduced. The clock
used to modulate the LP3972 buck regulator can be used as
a spread spectrum clock via 2 I
2
C control register (System
Control Register 1 (SCR1) 8h’80) bits bk_ssen, and slomod.
With this feature enabled, the intense energy of the clock
frequency can be spread across a small band of frequencies
in the neighborhood of the center frequency. The results in a
reduction of the peak energy!
The LP3972 spread spectrum clock uses a triangular modu-
lation profile with equal rise and fall slopes. The modulation
has the following characteristics:
The center frequency:
The modulating frequency,
Peak frequency deviation:
Modulation index
F
C
= 2 MHz, and
f
M
= 6.8 kHz or 12 kHz.
_f =
±
100 kHz (or
±
5%)
β
=
_f/f
M
= 14.7 or 8.3
Switching Energy RBW = 300 Hz
20207641
L
www.national.com
20
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP3972_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Power Management Unit for Advanced Application Processors |
| LP3972SQ-0514/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LP3972SQ-5810/NOPB | 功能描述:監(jiān)控電路 Pwr Mgmt Unit RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| LP3972SQ-A413 | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LP3972SQ-A413/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
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