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參數(shù)資料
| 型號(hào)： | LM34910SD |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 1.5 A SWITCHING REGULATOR, DSO10 |
| 封裝： | 4 X 4 MM, LLP-10 |
| 文件頁(yè)數(shù)： | 8/11頁(yè) |
| 文件大?。?/td> | 583K |
| 代理商： | LM34910SD |
ON-Time Timer, and Shutdown
(Continued)
Current Limit
Current limit detection occurs during the off-time by monitor-
ing the recirculating current through the free-wheeling diode
(D1). Referring to
Figure 1
, when the buck switch is turned
off the inductor current flows through the load, into S
,
through the sense resistor, out of I
and through D1. If that
current exceeds 1.25A the current limit comparator output
switches to delay the start of the next on-time period if the
voltage at FB is below 2.5V. The next on-time starts when
the current out of I
SEN
is below 1.25A and the voltage at FB
is below 2.5V. If the overload condition persists causing the
inductor current to exceed 1.25A during each on-time, that is
detected at the beginning of each off-time. The operating
frequency may be lower due to longer-than-normal off-times.
Figure 7
illustrates the inductor current waveform. During
normal operation the load current is Io, the average of the
ripple waveform. When the load resistance decreases the
current ratchets up until the lower peak reaches 1.25A.
During the Current Limited portion of
Figure 7
, the current
ramps down to 1.25A during each off-time, initiating the next
on-time (assuming the voltage at FB is
<
2.5V). During each
on-time the current ramps up an amount equal to:
I = (V
IN
- V
OUT
) x t
ON
/ L1
During this time the LM34910 is in a constant current mode,
with an average load current (I
OCL
) equal to 1.25A +
I/2.
The current limit threshold can be increased by connecting
an external resistor between S
and I
. The external
resistor will typically be less than 1
. The peak current out of
SW and I
must not exceed 3.5A. The average current out
of SW must be less than 3A, and the average current out of
I
must be less than 2A. Therefore I
in
Figure 7
must not
exceed 3.5A, and I
OCL
must not exceed 2A.
N - Channel Buck Switch and
Driver
The LM34910 integrates an N-Channel buck switch and
associated floating high voltage gate driver. The peak cur-
rent allowed through the buck switch is 3.5A, and the maxi-
mum allowed average current is 3A. The gate driver circuit
works in conjunction with an external bootstrap capacitor
and an internal high voltage diode.A0.022 μF capacitor (C4)
connected between BST and SW provides the voltage to the
driver during the on-time. During each off-time, the SW pin is
at approximately -1V, and C4 charges from V
through the
internal diode. The minimum off-time of 280 ns ensures a
minimum time each cycle to recharge the bootstrap capaci-
tor.
Softstart
The softstart feature allows the converter to gradually reach
a steady state operating point, thereby reducing start-up
stresses and current surges. Upon turn-on, after V
CC
reaches the under-voltage threshold, an internal 11.5 μA
current source charges up the external capacitor at the SS
pin to 2.5V. The ramping voltage at SS (and the non-
inverting input of the regulation comparator) ramps up the
output voltage in a controlled manner.
An internal switch grounds the SS pin if V
CC
is below the
under-voltage lockout threshold, if a thermal shutdown oc-
curs, or if the R
ON
/SD pin is grounded.
20110913
FIGURE 6. Shutdown Implementation
20110914
FIGURE 7. Inductor Current - Current Limit Operation
L
www.national.com
8
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM34910SD/NOPB | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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 |
| LM34910SDX | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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 |
| LM34910SDX/NOPB | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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 |
| LM34914 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit |
| LM34914EVAL | 功能描述:電源管理IC開(kāi)發(fā)工具 LM34914 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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