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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)： | 13/16頁 |
| 文件大?。?/td> | 304K |
| 代理商： | LM3103MHX |
If the output current I
is known, by assuming that I
=
I
, the peak and valley of I
can be determined. Beware that
the peak of I
should not be larger than the saturation current
of the inductor and the current rating of the main and syn-
chronous MOSFETs. Also, the valley of I
LR
must be positive
if CCM operation is required.
30029732
FIGURE 5. Inductor selection for V
OUT
= 3.3V
30029733
FIGURE 6. Inductor selection for V
OUT
= 0.6V
Figures 5 and 6 show curves on inductor selection for various
V
and R
. According to (8), V
is limited for small R
ON
.
Some curves are therefore limited as shown in the figures.
C
:
The capacitor on the V
output provides not only noise
filtering and stability, but also prevents false triggering of the
V
UVLO at the main MOSFET on/off transitions. C
should be no smaller than 1 μF for stability, and should be a
good quality, low ESR, ceramic capacitor.
C
and C
:
C
should generally be no smaller than
10 μF. Experimentation is usually necessary to determine the
minimum value for C
, as the nature of the load may require
a larger value. A load which creates significant transients re-
quires a larger C
OUT
than a fixed load.
C
is a small value ceramic capacitor located close to the
LM3103 to further suppress high frequency noise at V
OUT
. A
47 nF capacitor is recommended.
C
IN
and C
IN3
:
The function of C
is to supply most of the main
MOSFET current during the on-time, and limit the voltage rip-
ple at the VIN pin, assuming that the voltage source connect-
ing to the VIN pin has finite output impedance. If the voltage
source’s dynamic impedance is high (effectively a current
source), C
supplies the difference between the instanta-
neous input current and the average input current.
At the maximum load current, when the main MOSFET turns
on, the current to the VIN pin suddenly increases from zero
to the valley of the inductor’s ripple current and ramps up to
the peak value. It then drops to zero at turn-off. The average
current during the on-time is the load current. For a worst case
calculation, C
must be capable of supplying this average
load current during the maximum on-time. C
IN
is calculated
from:
(10)
where I
OUT
is the load current, t
on
is the maximum on-time,
and
Δ
V
IN
IN
.
C
’s purpose is to help avoid transients and ringing due to
long lead inductance at the VIN pin. A low ESR 0.1 μF ceramic
chip capacitor located close to the LM3103 is recommended.
C
BST
:
A 33 nF high quality ceramic capacitor with low ESR is
recommended for C
since it supplies a surge current to
charge the main MOSFET gate driver at each turn-on. Low
ESR also helps ensure a complete recharge during each off-
time.
C
:
The capacitor at the SS pin determines the soft-start
time, i.e. the time for the reference voltage at the regulation
comparator and therefore, the output voltage to reach their
final value. The time is determined from the following equa-
tion:
(11)
C
:
If the output voltage is higher than 1.6V, C
is needed
in the Discontinuous Conduction Mode to reduce the output
ripple. The recommended value for C
FB
is 10 nF.
PC BOARD LAYOUT
The LM3103 regulation, over-voltage, and current limit com-
parators are very fast so they will respond to short duration
noise pulses. Layout is therefore critical for optimum perfor-
mance. It must be as neat and compact as possible, and all
external components must be as close to their associated
pins of the LM3103 as possible. Refer to the functional block
diagram. The loop formed by C
, the main and synchronous
MOSFET internal to the LM3103, and the PGND pin should
be as small as possible. The connection from the PGND pin
to C
IN
should be as short and direct as possible. Vias should
be added to connect the ground of C
to a ground plane,
located as close to the capacitor as possible. The bootstrap
capacitor C
should be connected as close to the SW and
BST pins as possible, and the connecting traces should be
thick. The feedback resistors and capacitor R
FB1
, R
FB2
, and
C
FB
should be close to the FB pin. A long trace running from
V
to R
is generally acceptable since this is a low
impedance node. Ground R
FB2
directly to the AGND pin (pin
7). The output capacitor C
should be connected close to
the load and tied directly to the ground plane. The inductor L
should be connected close to the SW pin with as short a trace
as possible to reduce the potential for EMI (electromagnetic
interference) generation. If it is expected that the internal dis-
13
www.national.com
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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