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參數(shù)資料
| 型號(hào)： | LM2853 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 3A 550 kHz Synchronous SIMPLE SWITCHER Buck Regulator |
| 中文描述： | 第3A 550千赫同步的SIMPLE SWITCHER降壓穩(wěn)壓器 |
| 文件頁(yè)數(shù)： | 8/12頁(yè) |
| 文件大小： | 620K |
| 代理商： | LM2853 |
Applications Information
(Continued)
Since it is undesirable for the power supply to start up in
current limit, a soft-start capacitor must be chosen to force
the LM2853 to start up in a more controlled fashion based on
the charging of the soft-start capacitance. In this example,
suppose a 3 ms start time is desired. Three time constants
are required for charging the soft-start capacitor to 95% of
the final reference voltage. So in this case RC = 1 ms. The
DAC resistor, R, is 450 k
so C can be calculated to be 2.2
nF. A 2.2 nF ceramic capacitor can be chosen to yield
approximately a 3 ms start-up time.
SOFT-START CAPACITOR (C
SS
) AND FAULT
CONDITIONS
Various fault conditions such as short circuit and UVLO of
the LM2853 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 LM2853 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
1 nF to 50 nF.
COMPENSATION
The LM2853 provides a highly integrated solution to power
supply design. The compensation of the LM2853, which is
type-three, is included on-chip. The benefit of 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
O
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 LM2853 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. For best performance when
output voltage ripple is a concern, ESR values near the
minimum of the recommended range should be paired with
capacitance values near the maximum. If a minimum output
voltage ripple solution from a 5V input voltage is desired, a
6.8 μH inductor can be paired with a 220 μF (50 m
)
capacitor without degraded phase margin.
TABLE 1. Recommended L
O
and C
O
Values
V
OUT
(V)
0.8
0.8
VIN (V)
5
3.3
L
O
(μH)
C
O
(μF)
C
ESR
(m
)
Min
4.7
4.7
Max
6.8
4.7
Min
120
150
Max
220
220
Min
70
50
Max
100
100
1
1
5
4.7
4.7
6.8
4.7
120
150
220
220
70
50
100
100
3.3
1.2
1.2
5
4.7
4.7
6.8
4.7
120
120
220
220
70
60
100
100
3.3
1.5
1.5
5
4.7
4.7
6.8
4.7
120
120
220
220
70
60
100
100
3.3
1.8
1.8
5
4.7
4.7
6.8
4.7
120
100
220
220
70
70
120
120
3.3
2.5
2.5
5
4.7
4.7
6.8
4.7
120
100
220
220
70
80
150
150
3.3
3.0
3.0
5
4.7
4.7
6.8
4.7
120
100
220
220
70
80
150
150
3.3
3.3
5
4.7
6.8
120
220
70
150
L
www.national.com
8
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2853-1.2EVAL | 功能描述:電源管理IC開發(fā)工具 LM2853 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM2853-1.2EVAL | 制造商:Texas Instruments 功能描述:EVAL BOARD, LM2853 1.2V, 3A SYNC STEP-DO |
| LM2853-1.8EVAL | 功能描述:BOARD EVAL LM2853-1.8 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評(píng)估板 - DC/DC 與 AC/DC（離線）SMPS 系列:PowerWise®, SIMPLE SWITCHER® 標(biāo)準(zhǔn)包裝:1 系列:- 主要目的:DC/DC，步降 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:3.3V 電流 - 輸出:3A 輸入電壓:4.5 V ~ 28 V 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):降壓 頻率 - 開關(guān):250kHz 板類型:完全填充 已供物品:板 已用 IC / 零件:L7981 其它名稱:497-12113STEVAL-ISA094V1-ND |
| LM2853-1.8EVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM2853 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM2853-3.3EVAL | 功能描述:電源管理IC開發(fā)工具 LM2853 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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