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參數(shù)資料
| 型號： | LM2852YMXAX-2.5 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | STACKED MULTI-CHIP PACKAGE FLASH MEMORY AND SRAM (64 MBIT FLASH, 8 MBIT SRAM) |
| 中文描述： | 3.65 A SWITCHING REGULATOR, 625 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封裝： | TSSOP-14 |
| 文件頁數(shù)： | 9/13頁 |
| 文件大小： | 618K |
| 代理商： | LM2852YMXAX-2.5 |
Applications Information
(Continued)
SOFT-START CAPACITOR (C
SS
) AND FAULT
CONDITIONS
Various fault conditions such as short circuit and UVLO of
the LM2852 activate internal circuitry designed to control the
voltage on the soft-start capacitor. For example, during a
short circuit current limit event, the output voltage typically
falls to a low voltage. During this time, the soft-start voltage
is forced to track the output so that once the short is re-
moved, the LM2852 can restart gracefully from whatever
voltage the output reached during the short circuit event. The
range of soft-start capacitors is therefore restricted to values
1nF to 50nF.
COMPENSATION
The LM2852 provides a highly integrated solution to power
supply design. The compensation of the LM2852, which is
type three, is included on-chip. The benefit to integrated
compensation is straight-forward, simple power supply de-
sign. Since the output filter capacitor and inductor values
impact the compensation of the control loop, the range of L,
C and C
ESR
values is restricted in order to ensure stability.
OUTPUT FILTER VALUES
Table 1
details the recommended inductor and capacitor
ranges for the LM2852 that are suggested for various typical
output voltages. Values slightly different than those recom-
mended may be used, however the phase margin of the
power supply may be degraded.
TABLE 1. Output Filter Values
Frequency Option
V
OUT
(V)
0.8
0.8
1
1
1.2
1.2
1.5
1.5
1.8
1.8
2.5
2.5
3.3
PVIN (V)
3.3
5
3.3
5
3.3
5
3.3
5
3.3
5
3.3
5
5
L (μH)
C (μF)
C
ESR
(m
)
Min
70
70
70
70
70
70
70
70
100
100
95
95
100
Min
10
10
10
10
10
15
10
22
10
22
6.8
15
15
Max
15
15
15
15
15
22
15
22
15
33
10
22
22
Min
100
100
100
100
100
100
100
100
100
100
68
68
68
Max
220
120
180
180
180
120
120
120
120
120
120
120
100
Max
200
200
200
200
200
200
200
200
200
200
275
275
275
LM2852Y
(500kHz)
CHOOSING AN INDUCTANCE VALUE
The current ripple present in the output filter inductor is
determined by the input voltage, output voltage, switching
frequency and inductance according to the following equa-
tion:
where
I
L
is the peak to peak current ripple, D is the duty
cycle V
OUT
/V
IN
, V
is the input voltage applied to the output
stage, V
is the output voltage of the switcher, f is the
switching frequency and L is the inductance of the output
filter inductor. Knowing the current ripple is important for
inductor selection since the peak current through the induc-
tor is the load current plus one half the ripple current. Care
must be taken to ensure the peak inductor current does not
reach a level high enough to trip the current limit circuitry of
the LM2852.
As an example, consider a 5V to 1.2V conversion and a
500kHz switching frequency. According to
Table 1
, a 15μH
inductor may be used. Calculating the expected peak-to-
peak ripple,
The maximum inductor current for a 2A load would therefore
be 2A plus 60.8 mA, 2.0608A. As shown in the ripple equa-
tion, the current ripple is inversely proportional to induc-
tance.
OUTPUT FILTER INDUCTORS
Once the inductance value is chosen, the key parameter for
selecting the output filter inductor is its saturation current
(I
) specification. Typically I
is given by the manufacturer
as the current at which the inductance of the coil falls to a
certain percentage of the nominal inductance. The I
of an
inductor used in an application should be greater than the
maximum expected inductor current to avoid saturation. Be-
low is a table of inductors that may be suitable in LM2852
applications.
L
www.national.com
9
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| LM2852YMXAX-3.0/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 |
| LM2852YMXAX-3.3 | 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 |
| LM2852YMXAX-3.3/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 |
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