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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)： | 19/59頁 |
| 文件大?。?/td> | 1072K |
| 代理商： | LP3972 |
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Buck Converter Operation
(Continued)
During PFM operation, the converter positions the output
voltage slightly higher than the nominal output voltage during
PWM operation, allowing additional headroom for voltage
drop during a load transient from light to heavy load. The
PFM comparators sense the output voltage via the feedback
pin and control the switching of the output FETs such that the
output voltage ramps between
<
0.6% and
<
1.7% above the
nominal PWM output voltage. If the output voltage is below
the “high” PFM comparator threshold, the PMOS power
switch is turned on. It remains on until the output voltage
reaches the ‘high’ PFM threshold or the peak current ex-
ceeds the IPFM level set for PFM mode. The typical peak
current in PFM mode is: IPFM = 112 mA+ V
/27
. Once the
PMOS power switch is turned off, the NMOS power switch is
turned on until the inductor current ramps to zero. When the
NMOS zero-current condition is detected, the NMOS power
switch is turned off. If the output voltage is below the ‘high’
PFM comparator threshold (see
Figure 3
), the PMOS switch
is again turned on and the cycle is repeated until the output
reaches the desired level. Once the output reaches the ‘high’
PFM threshold, the NMOS switch is turned on briefly to ramp
the inductor current to zero and then both output switches
are turned off and the part enters an extremely low power
mode. Quiescent supply current during this ‘sleep’ mode is
21 μA(typ), which allows the part to achieve high efficiencies
under extremely light load conditions. When the output drops
below the ‘low’ PFM threshold, the cycle repeats to restore
the output voltage (average voltage in PFM mode) to
<
1.15% above the nominal PWM output voltage. If the load
current should increase during PFM mode (see
Figure 3
)
causing the output voltage to fall below the ‘low2’ PFM
threshold, the part will automatically transition into fixed-
frequency PWM mode. Typically when V
= 3.6V the part
transitions from PWM to PFM mode at 100 mA output
current .
SHUTDOWN MODE
During shutdown the PFET switch, reference, control and
bias circuitry of the converters are turned off. The NFET
switch will be open in shutdown to discharge the output.
When the converter is enabled, EN, soft start is activated. It
is recommended to disable the converter during the system
power up and undervoltage conditions when the supply is
less than 2.7V.
20207612
FIGURE 2. Typical PFM Operation
20207613
FIGURE 3. Operation in PFM Mode and Transfer to PWM Mode
L
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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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