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參數(shù)資料
| 型號： | LM2696MXAX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3A, Constant On Time Buck Regulator |
| 中文描述： | 6.4 A SWITCHING REGULATOR, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | TSSOP-16 |
| 文件頁數(shù)： | 7/19頁 |
| 文件大?。?/td> | 833K |
| 代理商： | LM2696MXAX |
Block Diagram
20153419
Application Information
CONSTANT ON-TIME CONTROL OVERVIEW
The LM2696 buck DC-DC regulator is based on the constant
on-time control scheme. This topology relies on a fixed
switch on-time to regulate the output. The on-time can be set
manually by adjusting the size of an external resistor (R
ON
).
The LM2696 automatically adjusts the on-time inversely with
the input voltage (AV
) to maintain a constant frequency. In
continuous conduction mode (CCM) the frequency depends
only on duty cycle and on-time. This is in contrast to hyster-
etic regulators where the switching frequency is determined
by the output inductor and capacitor. In discontinuous con-
duction mode (DCM), experienced at light loads, the fre-
quency will vary according to the load. This leads to high
efficiency and excellent transient response.
The on-time will remain constant for a given V
unless an
over-current or over-voltage event is encountered. If these
conditions are encountered the FET will turn off for a mini-
mum pre-determined time period. This minimum T
(250
ns) is internally set and cannot be adjusted. After the T
period has expired the FET will remain off until the compara-
tor trip-point has been reached. Upon passing this trip-point
the FET will turn back on, and the process will repeat.
Switchers that regulate using an internal comparator to
sense the output voltage for switching decisions, such as
hysteretic or constant on-time, require a minimum ESR. A
minimum ESR is required so that the control signal will be
dominated by ripple that is in phase with the switchpin. Using
a control signal dominated by voltage ripple that is in phase
with the switchpin eliminates the need for compensation,
thus reducing parts count and simplifying design. Alterna-
tively, an RC feed forward scheme may be used to eliminate
the need for a minimum ESR.
INTERNAL OPERATION
UNDER-VOLTAGE COMPARATOR
An internal comparator is used to monitor the feedback pin
for sensing under-voltage output events. If the output voltage
drops below the UVP threshold the power-good flag will fall.
ON-TIME GENERATOR SHUTDOWN
The on-time for the LM2696 is inversely proportional to the
input voltage. This scheme of on-time control maintains a
constant frequency over the input voltage range. The on-
time can be adjusted by using an external resistor connected
between the PVIN and RON pins.
CURRENT LIMIT
The LM2696 contains an intelligent current limit off-timer. If
the peak current in the internal FET exceeds 4.9A the
present on-time is terminated; this is a cycle-by-cycle current
L
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2696MXAX/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 安裝風格:SMD/SMT |
| LM2698EVAL | 功能描述:電源管理IC開發(fā)工具 EVAL BOARDFOR LM2698 RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM2698MM-ADJ | 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 安裝風格:SMD/SMT |
| LM2698MM-ADJ/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 1.35A BOOST REG 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 安裝風格:SMD/SMT |
| LM2698MM-ADJ/NOPB | 制造商:Texas Instruments 功能描述:DC/DC Converter (DC-DC) / Switching Regu |
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