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參數(shù)資料
| 型號： | LM25575Q0MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PDSO16 |
| 封裝： | TSSOP-16 |
| 文件頁數(shù)： | 8/22頁 |
| 文件大?。?/td> | 401K |
| 代理商： | LM25575Q0MHX |
Components R4 and C5 configure the error amplifier as a type
II configuration which has a pole at DC and a zero at f
Z = 1 /
(2
πR4C5). The error amplifier zero cancels the modulator
pole leaving a single pole response at the crossover frequen-
cy of the loop gain. A single pole response at the crossover
frequency yields a very stable loop with 90 degrees of phase
margin.
For the design example, a target loop bandwidth (crossover
frequency) of 15kHz was selected. The compensation net-
work zero (f
Z) should be selected at least an order of magni-
tude less than the target crossover frequency. This constrains
the product of R4 and C5 for a desired compensation network
zero 1 / (2
π R4 C5) to be less than 2kHz. Increasing R4, while
proportionally decreasing C5, increases the error amp gain.
Conversely, decreasing R4 while proportionally increasing
C5, decreases the error amp gain. For the design example
C5 was selected for 0.01F and R4 was selected for
49.9k
. These values configure the compensation network
zero at 320Hz. The error amp gain at frequencies greater than
f
Z is: R4 / R5, which is approximately 10 (20dB).
30071116
FIGURE 10. Error Amplifier Gain and Phase
The overall loop can be predicted as the sum (in dB) of the
modulator gain and the error amp gain.
30071117
FIGURE 11. Overall Loop Gain and Phase
If a network analyzer is available, the modulator gain can be
measured and the error amplifier gain can be configured for
the desired loop transfer function. If a network analyzer is not
available, the error amplifier compensation components can
be designed with the guidelines given. Step load transient
tests can be performed to verify acceptable performance. The
step load goal is minimum overshoot with a damped re-
sponse. C6 can be added to the compensation network to
decrease noise susceptibility of the error amplifier. The value
of C6 must be sufficiently small since the addition of this ca-
pacitor adds a pole in the error amplifier transfer function. This
pole must be well beyond the loop crossover frequency. A
good approximation of the location of the pole added by C6
is: f
p2 = fz x C5 / C6.
BIAS POWER DISSIPATION REDUCTION
Buck regulators operating with high input voltage can dissi-
pate an appreciable amount of power for the bias of the IC.
The V
CC regulator must step-down the input voltage VIN to a
nominal V
CC level of 7V. The large voltage drop across the
V
CC regulator translates into a large power dissipation within
the Vcc regulator. There are several techniques that can sig-
nificantly reduce this bias regulator power dissipation. Figure
output voltage. In each case the internal Vcc regulator is used
to initially bias the VCC pin. After the output voltage is estab-
lished, the VCC pin potential is raised above the nominal 7V
regulation level, which effectively disables the internal V
CC
regulator. The voltage applied to the VCC pin should never
exceed 14V. The V
CC voltage should never be larger than the
V
IN voltage.
www.national.com
16
LM25575Q0
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參數(shù)描述 |
|---|---|
| LM25575Q0MHX/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(fēng)格:SMD/SMT |
| LM25575-Q1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
| LM25575QMH | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
| LM25575QMH/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(fēng)格:SMD/SMT |
| LM25575QMHX | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
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