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參數(shù)資料
| 型號： | LM34919BTL |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PBGA10 |
| 封裝： | MICRO, SMD-10 |
| 文件頁數(shù)： | 4/20頁 |
| 文件大?。?/td> | 488K |
| 代理商： | LM34919BTL |
duction mode is one-half the inductor’s ripple current ampli-
tude. The operating frequency is approximately:
(1)
The buck switch duty cycle is approximately equal to:
(2)
In discontinuous conduction mode current through the induc-
tor ramps up from zero to a peak during the on-time, then
ramps back to zero before the end of the off-time. The next
on-time period starts when the voltage at FB falls below the
reference - until then the inductor current remains zero, and
the load current is supplied by the output capacitor. In this
mode the operating frequency is lower than in continuous
conduction mode, and varies with load current. Conversion
efficiency is maintained at light loads since the switching loss-
es decrease with the reduction in load and frequency. The
approximate discontinuous operating frequency can be cal-
culated as follows:
(3)
where R
L = the load resistance.
The output voltage is set by two external resistors (R1, R2).
The regulated output voltage is calculated as follows:
V
OUT = 2.5 x (R1 + R2) / R2
Output voltage regulation is based on ripple voltage at the
feedback input,normally obtained from the output voltage rip-
ple through the feedback resistors. The LM34919B requires
a minimum of 25 mV of ripple voltage at the FB pin. In cases
where the capacitor’s ESR is insufficient additional series re-
sistance may be required (R3).
Start-Up Regulator, V
CC
The start-up regulator is integral to the LM34919B. The input
pin (VIN) can be connected directly to line voltage up to 40V,
with transient capability to 44V. The V
CC output regulates at
7.0V, and is current limited at 15 mA. Upon power up, the
regulator sources current into the external capacitor at VCC
(C3). When the voltage on the VCC pin reaches the under-
voltage lockout threshold of 5.25V, the buck switch is enabled
and the Softstart pin is released to allow the Softstart capac-
itor (C6) to charge up.
The minimum input voltage is determined by the V
CC UVLO
falling threshold (
5.1V). When V
CC falls below the falling
threshold the V
CC UVLO activates to shut off the output. If
V
CC is externally loaded, the minimum input voltage increas-
es.
To reduce power dissipation in the start-up regulator, an aux-
iliary voltage can be diode connected to the V
CC pin. Setting
the auxiliary voltage to between 7V and 14V shuts off the in-
ternal regulator, reducing internal power dissipation. The sum
of the auxiliary voltage and the input voltage (V
CC + VIN) can-
not exceed 52V. Internally, a diode connects VCC to VIN. See
Figure 2.
30102711
FIGURE 2. Self Biased Configuration
www.national.com
12
LM34919B
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM34919BTL/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM34919BTLX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator |
| LM34919BTLX/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM34919C-Q1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM34919C-Q1 Ultra Small 50V, 600 mA Constant On-Time Buck Switching Regulator |
| LM34919CQSD/NOPB | 制造商:Texas Instruments 功能描述:IC REG BUCK ADJ 0.6A 12WSON |
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