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參數(shù)資料
| 型號： | LMZ12002EXTTZX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PSSO7 |
| 封裝： | 10.16 X 13.77 MM, 4.57 MM HEIGHT, ROHS COMPLIANT, TO-PMOD, 7 PIN |
| 文件頁數(shù)： | 3/20頁 |
| 文件大小： | 3951K |
| 代理商： | LMZ12002EXTTZX |
Application Block Diagram
30117408
General Description
The LMZ12002EXT SIMPLE SWITCHER power module is
an easy-to-use step-down DC-DC solution capable of driving
up to 2A load with exceptional power conversion efficiency,
line and load regulation, and output accuracy. The
LMZ12002EXT is available in an innovative package that en-
hances thermal performance and allows for hand or machine
soldering.
The LMZ12002EXT can accept an input voltage rail between
4.5V and 20V and deliver an adjustable and highly accurate
output voltage as low as 0.8V. The LMZ12002EXT only re-
quires three external resistors and four external capacitors to
complete the power solution. The LMZ12002EXT is a reliable
and robust design with the following protection features: ther-
mal shutdown, input under-voltage lockout, output over-volt-
age protection, short-circuit protection, output current limit,
and allows startup into a pre-biased output. A single resistor
adjusts the switching frequency up to 1 MHz.
COT Control Circuit Overview
Constant On Time control is based on a comparator and an
on-time one shot, with the output voltage feedback compared
with an internal 0.8V reference. If the feedback voltage is be-
low the reference, the main MOSFET is turned on for a fixed
on-time determined by a programming resistor R
ON. RON is
connected to V
IN such that on-time is reduced with increasing
input supply voltage. Following this on-time, the main MOS-
FET remains off for a minimum of 260 ns. If the voltage on the
feedback pin falls below the reference level again the on-time
cycle is repeated. Regulation is achieved in this manner.
Design Steps for the LMZ12002EXT
Application
The LMZ12002EXT is fully supported by Webench and of-
fers the following: Component selection, electrical and ther-
mal simulations as well as the build-it board for a reduction in
design time. The following list of steps can be used to manu-
ally design the LMZ12002EXT application.
Select minimum operating V
IN with enable divider resistors
Program V
O with divider resistor selection
Program turn-on time with soft-start capacitor selection
Select C
O
Select C
IN
Set operating frequency with R
ON
Determine module dissipation
Layout PCB for required thermal performance
ENABLE DIVIDER, R
ENT AND RENB SELECTION
The enable input provides a precise 1.18V band-gap rising
threshold to allow direct logic drive or connection to a voltage
divider from a higher enable voltage such as Vin. The enable
input also incorporates 90 mV (typ) of hysteresis resulting in
a falling threshold of 1.09V. The maximum recommended
voltage into the EN pin is 6.5V. For applications where the
midpoint of the enable divider exceeds 6.5V, a small zener
can be added to limit this voltage.
The function of this resistive divider is to allow the designer to
choose an input voltage below which the circuit will be dis-
abled. This implements the feature of programmable under
voltage lockout. This is often used in battery powered systems
to prevent deep discharge of the system battery. It is also
useful in system designs for sequencing of output rails or to
prevent early turn-on of the supply as the main input voltage
rail rises at power-up. Applying the enable divider to the main
input rail is often done in the case of higher input voltage sys-
tems where a lower boundary of operation should be estab-
lished. In the case of sequencing supplies, the divider is
connected to a rail that becomes active earlier in the power-
up cycle than the LMZ12002EXT output rail. The two resistors
should be chosen based on the following ratio:
R
ENT / RENB = (VIN UVLO / 1.18V) – 1 (1)
The LMZ12002EXT demonstration and evaluation boards
use 11.8k
for R
ENB and 32.4k for RENT resulting in a rising
UVLO of 4.5V. This divider presents 5.34V to the EN input
when the divider input is raised to 20V.
OUTPUT VOLTAGE SELECTION
Output voltage is determined by a divider of two resistors
connected between V
O and ground. The midpoint of the di-
11
www.national.com
LMZ12002EXT
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMZ12002EXTTZX/NOPB | 功能描述:DC/DC轉(zhuǎn)換器 RoHS:否 制造商:Murata 產(chǎn)品: 輸出功率: 輸入電壓范圍:3.6 V to 5.5 V 輸入電壓（標(biāo)稱）: 輸出端數(shù)量:1 輸出電壓（通道 1）:3.3 V 輸出電流（通道 1）:600 mA 輸出電壓（通道 2）: 輸出電流（通道 2）: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體尺寸: |
| LMZ12002TZ-ADJ | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:2A SIMPLE SWITCHER? Power Module with 20V Maximum Input Voltage |
| LMZ12002TZ-ADJ/NOPB | 功能描述:DC/DC轉(zhuǎn)換器 12V,2A PWR MODULE RoHS:否 制造商:Murata 產(chǎn)品: 輸出功率: 輸入電壓范圍:3.6 V to 5.5 V 輸入電壓（標(biāo)稱）: 輸出端數(shù)量:1 輸出電壓（通道 1）:3.3 V 輸出電流（通道 1）:600 mA 輸出電壓（通道 2）: 輸出電流（通道 2）: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體尺寸: |
| LMZ12002TZADJNOPB | 制造商:Texas Instruments 功能描述:Module DC-DC 1-OUT 0.8V to 6V 2A 7-Pin TO-PMOD EP |
| LMZ12002TZE-ADJ | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:2A SIMPLE SWITCHER? Power Module with 20V Maximum Input Voltage |
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