參數(shù)資料
型號： LM2599-5.0MWC
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： 7.5 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC
封裝： WAFER
文件頁數(shù)： 21/36頁
文件大?。?/td> 897K
代理商： LM2599-5.0MWC
Application Information (Continued)
shown).
Figure 29 uses a zener diode to establish the
threshold voltage when the switcher begins operating. When
the input voltage is less than the zener voltage, resistors R1
and R2 hold the Shutdown /Soft-start pin low, keeping the
regulator in the shutdown mode. As the input voltage ex-
ceeds the zener voltage, the zener conducts, pulling the
Shutdown /Soft-start pin high, allowing the regulator to begin
switching. The threshold voltage for the undervoltage lockout
feature is approximately 1.5V greater than the zener voltage.
Figure 30 and 30 apply the same feature to an inverting
circuit.
Figure 30 features a constant threshold voltage for
turn on and turn off (zener voltage plus approximately one
volt). If hysteresis is needed, the circuit in
Figure 31 has a
turn ON voltage which is different than the turn OFF voltage.
The amount of hysteresis is approximately equal to the value
of the output voltage. Since the SD /SS pin has an internal
7V zener clamp, R2 is needed to limit the current into this pin
to approximately 1 mA when Q1 is on.
NEGATIVE VOLTAGE CHARGE PUMP
Occasionally a low current negative voltage is needed for
biasing parts of a circuit. A simple method of generating a
negative voltage using a charge pump technique and the
switching waveform present at the OUT pin, is shown in
Figure 32. This unregulated negative voltage is approxi-
mately equal to the positive input voltage (minus a few volts),
and can supply up to a 600 mA of output current. There is a
requirement however, that there be a minimum load of 1.2A
on the regulated positive output for the charge pump to work
correctly. Also, resistor R1 is required to limit the charging
current of C1 to some value less than the LM2599 current
limit (typically 4.5A).
This method of generating a negative output voltage without
an additional inductor can be used with other members of
the Simple Switcher Family, using either the buck or boost
topology.
DS012582-45
FIGURE 29. Undervoltage Lockout for a Buck
Regulator
DS012582-47
FIGURE 30. Undervoltage Lockout Without
Hysteresis for an Inverting Regulator
DS012582-46
FIGURE 31. Undervoltage Lockout With
Hysteresis for an Inverting Regulator
DS012582-48
FIGURE 32. Charge Pump for Generating a
Low Current, Negative Output Voltage
LM2599
www.national.com
28
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2599S-12 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2599S-12/NOPB 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2599S-3.3 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2599S-3.3/NOPB 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2599S-5.0 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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