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参数资料
| 型号： | LMZ14203EXTTZX-ADJ |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PSSO7 |
| 封装： | 10.16 X 13.77 MM, 4.57 MM HEIGHT, ROHS COMPLIANT, TO-PMOD-7 |
| 文件页数： | 2/18页 |
| 文件大小： | 3935K |
| 代理商： | LMZ14203EXTTZX-ADJ |
Application Block Diagram
30117808
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 LMZ14203EXT
Application
The LMZ14203EXT 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 LMZ14203EXT 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 V
IN. 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 such as 24V AC/DC systems where a lower boundary
of operation should be established. In the case of sequencing
supplies, the divider is connected to a rail that becomes active
earlier in the power-up cycle than the LMZ14203EXT output
rail. The two resistors should be chosen based on the follow-
ing ratio:
R
ENT / RENB = (VIN UVLO/ 1.18V) – 1 (1)
The LMZ14203EXT demonstration and evaluation boards
use 11.8k
for R
ENB and 68.1k for RENT resulting in a rising
UVLO of 8V. This divider presents 6.25V to the EN input when
the divider input is raised to 42V.
OUTPUT VOLTAGE SELECTION
Output voltage is determined by a divider of two resistors
connected between V
O and ground. The midpoint of the di-
vider is connected to the FB input. The voltage at FB is
compared to a 0.8V internal reference. In normal operation
an on-time cycle is initiated when the voltage on the FB pin
falls below 0.8V. The main MOSFET on-time cycle causes the
output voltage to rise and the voltage at the FB to exceed
0.8V. As long as the voltage at FB is above 0.8V, on-time
cycles will not occur.
The regulated output voltage determined by the external di-
vider resistors RFBT and RFBB is:
V
O = 0.8V * (1 + RFBT / RFBB) (2)
Rearranging terms; the ratio of the feedback resistors for a
desired output voltage is:
R
FBT / RFBB = (VO / 0.8V) - 1 (3)
These resistors should be chosen from values in the range of
1.0 kohm to 10.0 kohm.
www.national.com
10
LMZ14203EXT
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LMZ14203H | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Evaluation Board modules for high output voltage are easy-to-use DC-DC |
| LMZ14203H_1106 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:3A SIMPLE SWITCHER? Power Module for High Output Voltage |
| LMZ14203HEVAL/NOPB | 功能描述:电源管理IC开发工具 LMZ14203H EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LMZ14203HTZ | 制造商:Texas Instruments 功能描述:POWER MODULE, 42V, 3A, 7TOPMOD 制造商:Texas Instruments 功能描述:POWER MODULE, 42V, 3A, 7TOPMOD; Primary Input Voltage:42V; No. of Outputs:1; Output Voltage:30V; Output Current:3A; Voltage Regulator Case Style:TO-PMOD; No. of Pins:7; Operating Temperature Min:-40C; Operating Temperature ;RoHS Compliant: Yes |
| LMZ14203HTZ/NOPB | 功能描述:直流/直流开关转换器 42V,3A PWR MODULE RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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