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| 型號(hào)： | LP3972SQX-5810 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, QCC40 |
| 封裝： | 5 X 5 MM, LLP-40 |
| 文件頁數(shù)： | 11/60頁 |
| 文件大?。?/td> | 1171K |
| 代理商： | LP3972SQX-5810 |
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FIGURE 2. Typical PFM Operation
During PFM operation, the converter positions the output volt-
age 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 exceeds
the IPFM level set for PFM mode. The typical peak current in
PFM mode is: IPFM = 112 mA + V
IN/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 com-
parator 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 out-
put 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. Typ-
ically when V
IN = 3.6V the part transitions from PWM to PFM
mode at 100 mA output current .
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FIGURE 3. Operation in PFM Mode and Transfer to PWM Mode
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 rec-
ommended to disable the converter during the system power
up and undervoltage conditions when the supply is less than
2.7V.
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
IN 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 ca-
pacitor and load current demanded at start-up. Typical start-
19
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LP3972
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP3972SQX-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 |
| LP3972SQXA413 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Power Management Unit for Advanced Application Processors |
| LP3972SQX-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 |
| LP3972SQX-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 |
| LP3972SQXA514 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Power Management Unit for Advanced Application Processors |
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