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參數(shù)資料
| 型號： | LM34910 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 抗輻射高效，5安培開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 7/11頁 |
| 文件大小： | 583K |
| 代理商： | LM34910 |
Start-up Regulator, V
CC
The start-up regulator is integral to the LM34910. The input
pin (V
) can be connected directly to line voltage up to 36V,
with transient capability to 40V. The V
output regulates at
7.0V, and is current limited to 9 mA. Upon power up, the
regulator sources current into the external capacitor at V
CC
(C3). When the voltage on the V
CC
pin reaches the under-
voltage lockout threshold of 5.8V, the buck switch is enabled
and the Softstart pin is released to allow the Softstart capaci-
tor (C6) to charge up.
The minimum input voltage is determined by the regulator’s
dropout voltage, the V
CC
UVLO falling threshold (
)
5.7V),
and the frequency. When V
falls below the falling thresh-
old the V
UVLO activates to shut off the output. If V
is
externally loaded, the minimum input voltage increases
since the output impedance at V
CC
is
)
140
. See
Figure 2
.
To reduce power dissipation in the start-up regulator, an
auxiliary voltage can be diode connected to the V
pin.
Setting the auxiliary voltage to between 8V and 14V shuts off
the internal regulator, reducing internal power dissipation.
The sum of the auxiliary voltage and the input voltage (V
CC
+ V
IN
) cannot exceed 50V. Internally, a diode connects V
CC
to V
IN
. See
Figure 5
.
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the
Softstart pin (2.5V). In normal operation (the output voltage
is regulated), an on-time period is initiated when the voltage
at FB falls below 2.5V. The buck switch stays on for the
on-time, causing the FB voltage to rise above 2.5V. After the
on-time period, the buck switch stays off until the FB voltage
falls below 2.5V. Bias current at the FB pin is nominally 100
nA.
Over-Voltage Comparator
The voltage at FB is compared to an internal 2.875V refer-
ence. If the voltage at FB rises above 2.875V the on-time
pulse is immediately terminated. This condition can occur if
the input voltage or the output load changes suddenly, or if
the inductor (L1) saturates. The buck switch remains off until
the voltage at FB falls below 2.5V.
ON-Time Timer, and Shutdown
The on-time for the LM34910 is determined by the R
resistor and the input voltage (V
IN
), and is calculated from:
(4)
See
Figure 3
. The inverse relationship with V
IN
results in a
nearly constant frequency as V
is varied. R
should be
selected for a minimum on-time (at maximum V
) greater
than 200 ns. This requirement limits the maximum frequency
for each application, depending on V
IN
and V
OUT
, calculated
from the following:
(5)
The LM34910 can be remotely shut down by taking the
R
/SD pin below 0.65V. See
Figure 6
. In this mode the SS
pin is internally grounded, the on-timer is disabled, and bias
currents are reduced. Releasing the R
/SD pin allows nor-
mal operation to resume. The voltage at the R
/SD pin is
between 1.5V and 3.0V, depending on V
IN
and the R
ON
resistor.
20110911
FIGURE 5. Self Biased Configuration
L
www.national.com
7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM34910C | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Voltage (50V, 1.25A) Step Down Switching Regulator |
| LM34910CSD | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述:STEP DOWN REG 50V 1.2A LLP-10 |
| LM34910CSD/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 |
| LM34910CSDE | 制造商:Texas Instruments 功能描述:HIGH VOLTAGE (50V 1.25A) STEP DOWN SWITCHING REGULATOR |
| LM34910CSDE/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 |
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