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參數(shù)資料
| 型號： | LM27402SQX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 1350 kHz SWITCHING FREQ-MAX, QCC16 |
| 封裝： | 4 X 4 MM, 0.80 MM HEIGHT, 0.65 MM PITCH, LLP-16 |
| 文件頁數(shù)： | 9/32頁 |
| 文件大小： | 653K |
| 代理商： | LM27402SQX |
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30092619
FIGURE 10. DCR Sensing Circuit
The most accurate sensing of voltage across the DCR is
achieved by matching the time constant of the R
SCS filter with
the inductor L/R
DCR time constant. If the time constants are
matched, the voltage across the capacitor follows the voltage
across the DCR. A typical range of capacitance used in the
R
SCS network is 100 nF to 1F. The equation matching the
time constants is:
The current limit threshold can be adjusted to any level with
a single resistor from the current limit comparator to the output
voltage pin. Use the circuit in Figure 11 to set the current limit.
30092620
FIGURE 11. Setting the Current Limit Level
Since the voltage across the inductor DCR follows the current
through the inductor, the device will trip at the peak of the
inductor current. Capacitor C
SBY shown in Figure 11 filters the
input to the current sense comparator. A working range for
this capacitance is 47 pF to 100 pF. The equation to set the
resistor value of R
SET is:
I
LIMIT (A) is the desired current limit level, RDCR () is the rated
DC resistance of the inductor and I
cs- (A) is the 10 A current
source flowing out of the CS- pin.
The internal current source I
CS- is powered from the input
voltage rail (VIN). The minimum voltage required to power the
current source is 1V from VIN to V
OUT. If a condition occurs
where VIN - V
OUT < 1V, the LM27402 may prematurely initiate
hiccup mode. There are multiple options to avoid this situa-
tion. The first option is to enable the LM27402 after the input
voltage has risen 1V above the nominal output voltage as
seen in Figure 6. The second option is to lower the comparator
common mode voltage shown in Figure 12 such that the I
CS-
current source has enough headroom voltage.
30092681
FIGURE 12. Common Mode Voltage Resistor Divider
Network
Please refer to Application Note AN-2060 for design guide-
lines to adjust the common mode voltage of the current sense
comparator.
CONTROL LOOP COMPENSATION
The LM27402 voltage mode control system incorporates in-
put voltage feed-forward to eliminate the input voltage de-
pendence of the PWM gain. Input voltage feed-forward allows
the LM27402 to be stable throughout the entire input voltage
range and makes it easier for the designer to select the com-
pensation and power components. The following text will
describe how to set the output voltage and obtain the open
loop transfer function.
During steady state operation, the DC output voltage is set by
a feedback resistor network between V
OUT, FB and GND. The
FB voltage is nominally 0.6V ±1%. The equation describing
the output voltage is:
A good starting value for R
FB1 is 20 k. If an output voltage
of 0.6V is required, R
FB2 should not be used.
There are three main blocks of a voltage mode buck switcher
that the power supply designer must consider when designing
the control system: the powertrain, PWM modulator, and the
compensator. A diagram representing the control loop is
shown in Figure 13.
17
www.national.com
LM27402
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM27402SQX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)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(fēng)格: 封裝 / 箱體:CPAK |
| LM27403 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Synchronous Buck Controller with Temperature-Compensated, Inductor-DCR-Based Overcurrent Protection and Programmable Thermal Shutdown |
| LM27403EVM | 制造商:Texas Instruments 功能描述:LM27403EVM - Boxed Product (Development Kits) |
| LM27403EVM-POL600 | 制造商:Texas Instruments 功能描述:BOARD EVAL LM27403 |
| LM27403SQ | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Synchronous Buck Controller with Temperature-Compensated, Inductor-DCR-Based Overcurrent Protection and Programmable Thermal Shutdown |
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