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參數(shù)資料
| 型號： | LM3103MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SIMPLE SWITCHER㈢ Synchronous 1MHz 0.75A Step-Down Voltage Regulator |
| 中文描述： | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 304K |
| 代理商： | LM3103MHX |
N-Channel MOSFET and Driver
The LM3103 integrates an N-Channel main MOSFET and an
associated floating high voltage main MOSFET gate driver.
The gate drive circuit works in conjunction with an external
bootstrap capacitor C
and an internal high voltage diode.
C
connected between the BST and SW pins powers the
main MOSFET gate driver during the main MOSFET on-time.
During each off-time, the voltage of the SW pin falls to ap-
proximately -1V, and C
charges from V
through the
internal diode. The minimum off-time of 240 ns provides
enough time for charging C
BST
in each cycle.
Soft-Start
The soft-start feature allows the converter to gradually reach
a steady state operating point, thereby reducing startup
stresses and current surges. Upon turn-on, after V
reaches
the under-voltage threshold and a 180 μs fixed delay, a 70 μA
internal current source charges an external capacitor C
SS
connecting to the SS pin. The ramping voltage at the SS pin
(and the non-inverting input of the regulation comparator as
well) ramps up the output voltage V
in a controlled man-
ner. An internal switch grounds the SS pin if any of the
following three cases happen: (i) V
CC
is below the under-volt-
age lockout threshold; (ii) a thermal shutdown occurs; or (iii)
the EN pin is grounded. Alternatively, the output voltage can
be shut off by connecting the SS pin to the ground using an
external switch. Releasing the switch allows the voltage of the
SS pin to ramp up and the output voltage to return to normal.
The shutdown configuration is shown in Figure 3.
30029729
FIGURE 3. Alternate Shutdown Implementation
Thermal Protection
The junction temperature of the LM3103 should not exceed
the maximum limit. Thermal protection is implemented by an
internal Thermal Shutdown circuit, which activates (typically)
at 165°C to make the controller enter a low power reset state
by disabling the main MOSFET, disabling the on-timer, and
grounding the SS pin. Thermal protection helps prevent
catastrophic failures from accidental device overheating.
When the junction temperature falls back below 145°C (typi-
cal hysteresis = 20°C), the SS pin is released and normal
operation resumes.
Applications Information
EXTERNAL COMPONENTS
The following guidelines can be used to select external com-
ponents.
R
FB1
and R
FB2
: These resistors should be chosen from stan-
dard values in the range of 1.0 k
to 10 k
, satisfying the
following ratio:
R
FB1
/R
FB2
= (V
OUT
/0.6V) - 1
For V
= 0.6V, the FB pin can be connected to the output
directly with a pre-load resistor drawing more than 20 μA. This
is because the converter operation needs a minimum inductor
current ripple to maintain good regulation when no load is
connected.
R
:
Equation (2) can be used to select R
if a desired op-
erating frequency is selected. But the minimum value of
R
is determined by the minimum on-time. It can be calcu-
lated as follows:
(7)
(8)
If R
calculated from (2) is smaller than the minimum value
determined in (8), a lower frequency should be selected to re-
calculate R
by (2). Alternatively, V
can also be limited
in order to keep the frequency unchanged. The relationship
of V
IN(MAX)
and R
ON
is shown in Figure 4.
On the other hand, the minimum off-time of 240 ns can limit
the maximum duty ratio. This may be significant at low V
. A
larger R
should be selected in any application requiring a
large duty ratio.
30029738
FIGURE 4. Maximum V
IN
for selected R
ON
L:
The main parameter affected by the inductor is the ampli-
tude of the inductor current ripple (I
LR
), which is recommend-
ed to be greater than 0.3A. Once I
LR
is selected, L can be
determined by:
(9)
where V
IN
is the input voltage and f
SW
is determined from (2).
www.national.com
12
L
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3103MHX/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 |
| LM310H | 制造商:National Semiconductor 功能描述:310 NSC'83 SB51C 制造商:Texas Instruments 功能描述: 制造商:Rochester Electronics LLC 功能描述: |
| LM310H/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog Buffer/Voltage Follower |
| LM310J | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Voltage Follower |
| LM310J/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog Buffer/Voltage Follower |
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