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參數(shù)資料
| 型號： | LM2647MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Synchronous Buck Regulator Controller |
| 中文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數(shù)： | 10/25頁 |
| 文件大?。?/td> | 763K |
| 代理商： | LM2647MTC |
Operation Descriptions
GENERAL
The LM2647 provides two identical synchronously switched
buck regulator channels that operate 180 out of phase. A
voltage-mode control topology was selected to provide fixed-
frequency PWM regulation at very low duty cycles, in pref-
erence to current-mode control, because the latter has in-
herent limitations in being able to achieve low pulse widths
due to blanking time requirements. Because of a minimum
pulse width of about 30ns for the LM2647, very low duty
cycles (low output, high input) are possible. The main ad-
vantage of current-mode control is the fact that the slope of
its ramp (derived from the switch current), automatically
increases with increase in input voltage. This leads to im-
proved line rejection and fast response to line variations. In
typical voltage-mode control, the ramp is derived from the
clock, not from the switch current. But by using the input
voltage together with the clock signal to generate the ramp
as in the LM2647, this advantage of current-mode control
can in fact be completely replicated. The technique is called
line feedforward. In addition, the LM2647 features a user-
selectable Pulse-skip mode that significantly improves effi-
ciency at light loads by reducing switching losses, and driver
consumption, both of which are proportional to switching
frequency.
INPUT VOLTAGE FEEDFORWARD
The feedforward circuit of the LM2647 adjusts the slope of
the internal PWM ramp in proportion to the regulator input
voltage. See
Figure 1
for an illustration of how the duty cycle
changes as a result of the change in the slope of the ramp,
even though the error amplifier output has not had time to
react to the line disturbance. The almost instantaneous duty
cycle correction provided by the feedforward circuit signifi-
cantly improves line transient rejection.
FORCED-PWM MODE AND PULSE-SKIP MODE
Forced-PWM mode (FPWM) leads to Continuous Conduc-
tion Mode (CCM) even at very light loads. It is one of two
user-selectable
modes
of
LM2647. When FPWM is chosen (FPWM pin high), the
bottom FET will always be turned ON whenever the top FET
is OFF. See
Figure 2
for a typical FPWM plot.
operation
provided
by
the
20056309
FIGURE 1. Voltage Feedforward
20056310
CH1: HDRV, CH2: LDRV, CH3: SW, CH4: I
L
(0.2A/div)
Output 1V
@
0.04A, VIN = 10V, FPWM, L = 10μH, f = 300kHz
FIGURE 2. Normal FPWM Mode Operation at Light
Loads
L
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM2647MTC/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2647MTCX | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2647MTCX/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM2648 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Two-Phase, Synchronous Step-Down 3-Channel Switching Regulator Controller |
| LM26480 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators |
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