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參數(shù)資料
| 型號： | LM34919BQTLX |
| 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)： | 6/20頁 |
| 文件大小： | 488K |
| 代理商： | LM34919BQTLX |
30102714
FIGURE 4. Inductor Current - Current Limit Operation
N - Channel Buck Switch and Driver
The LM34919B integrates an N-Channel buck switch and as-
sociated floating high voltage gate driver. The peak current
allowed through the buck switch is 1.5A, and the maximum
allowed average current is 1A. The gate driver circuit works
in conjunction with an external bootstrap capacitor and an in-
ternal high voltage diode. A 0.022 F capacitor (C4) connect-
ed between BST and SW provides the voltage to the driver
during the on-time. During each off-time, the SW pin is at ap-
proximately -1V, and C4 charges from V
CC through the inter-
nal diode. The minimum off-time forced by the LM34919B
ensures a minimum time each cycle to recharge the bootstrap
capacitor.
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 10.5 A 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 un-
der-voltage lockout threshold, or if the RON/SD pin is ground-
ed.
Thermal Shutdown
The LM34919B should be operated so the junction tempera-
ture does not exceed 125°C. If the junction temperature in-
creases, an internal Thermal Shutdown circuit, which acti-
vates (typically) at 175°C, takes the controller to a low power
reset state by disabling the buck switch. This feature helps
prevent catastrophic failures from accidental device over-
heating. When the junction temperature reduces below 155°
C (typical hysteresis = 20°C) normal operation resumes.
Applications Information
EXTERNAL COMPONENTS
The procedure for calculating the external components is il-
lustrated with the following design example. Referring to the
Block Diagram, the circuit is to be configured for the following
specifications:
- V
OUT = 3.3V
- V
IN = 6V to 24V
- Minimum load current = 200 mA
- Maximum load current = 600 mA
- Switching Frequency = 1.5 MHz
- Soft-start time = 5 ms
R1 and R2:
These resistors set the output voltage. The ratio
of the feedback resistors is calculated from:
R1/R2 = (V
OUT/2.5V) - 1
For this example, R1/R2 = 0.32. R1 and R2 should be chosen
from standard value resistors in the range of 1.0 k
- 10 k
which satisfy the above ratio. For this example, 2.49k
is
chosen for R2 and 787
for R1.
R
ON: This resistor sets the on-time, and (by default) the
switching frequency. The switching frequncy must be less
than 1.53 MHz to ensure the minimum forced on-time does
not interfere with the circuit's proper operation at the maxi-
mum input voltage. The R
ON resistor is calculated from the
following equation, using the minimum input voltage.
Check that this value resistor does not set an on-time less
than 90 ns at maximum V
IN.
A standard value 28 k
resistor is used, resulting in a nominal
frequency of 1.49 MHz. The minimum on-time is
129 ns at
Vin = 24V, and the maximum on-time is
424 ns at Vin = 6V.
Alternately, R
ON can be determined using Equation 4 if a spe-
cific on-time is required.
www.national.com
14
LM34919B
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM34919BQTLX/NOPB | 功能描述:直流/直流開關調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關頻率: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: 安裝風格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM34919BTL | 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 |
| LM34919BTL/NOPB | 功能描述:直流/直流開關調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關頻率: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/直流開關調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關頻率: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: 安裝風格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
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