- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄361030 > LM5642 (National Semiconductor Corporation) High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization PDF資料下載
參數(shù)資料
| 型號： | LM5642 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization |
| 中文描述： | 高電壓，雙同步降壓轉(zhuǎn)換器振蕩器同步 |
| 文件頁數(shù)： | 18/24頁 |
| 文件大?。?/td> | 667K |
| 代理商： | LM5642 |
Component Selection
(Continued)
Output Capacitor Selection
In applications that exhibit large and fast load current
swings, the slew rate of such a load current transient may be
beyond the response speed of the regulator. Therefore, to
meet voltage transient requirements during worst-case load
transients, special consideration should be given to output
capacitor selection. The total combined ESR of the output
capacitors must be lower than a certain value, while the total
capacitance must be greater than a certain value. Also, in
applications where the specification of output voltage regu-
lation is tight and ripple voltage must be low, starting from the
required output voltage ripple will often result in fewer design
iterations.
ALLOWED TRANSIENT VOLTAGE EXCURSION
The allowed output voltage excursion during a load transient
(
Vc_s) is:
(10)
Where
±
δ
% is the output voltage regulation window and
±
e
% is the output voltage initial accuracy.
Example: Vnom = 5V,
δ
% = 7%,
e
% = 3.4%, Vrip = 40mV
peak to peak.
(11)
Since the ripple voltage is included in the calculation of
Vc_s, the inductor ripple current should not be included in
the worst-case load current excursion. That is, the worst-
case load current excursion should be simply maximum load
current change specification,
Ic_s.
MAXIMUM ESR CALCULATION
Unless the rise and fall times of a load transient are slower
than the response speed of the control loop, if the total
combined ESR (Re) is too high, the load transient require-
ment will not be met, no matter how large the capacitance.
The maximum allowed total combined ESR is:
(12)
Example:
Vc_s = 160mV,
Ic_s = 3A. Then Re_max =
53.3m
.
Maximum ESR criterion can be used when the associated
capacitance is high enough, otherwise more capacitors than
the number determined by this criterion should be used in
parallel.
MINIMUM CAPACITANCE CALCULATION
In a switch mode power supply, the minimum output capaci-
tance is typically dictated by the load transient requirement.
If there is not enough capacitance, the output voltage excur-
sion will exceed the maximum allowed value even if the
maximum ESR requirement is met. The worst-case load
transient is an unloading transient that happens when the
input voltage is the highest and when the present switching
cycle has just finished. The corresponding minimum capaci-
tance is calculated as follows:
(13)
Notice it is already assumed the total ESR, Re, is no greater
than Re_max, otherwise the term under the square root will
be a negative value. Also, it is assumed that L has already
been selected, therefore the minimum L value should be
calculated before Cmin and after Re (see Inductor Selection
below). Example: Re = 20m
, Vnom = 5V,
Vc_s = 160mV,
Ic_s = 3A, L = 8μH
(14)
Generally speaking, Cmin decreases with decreasing Re,
Ic_s, and L, but with increasing Vnom and
Vc_s.
Inductor Selection
The size of the output inductor can be determined from the
desired output ripple voltage, Vrip, and the impedance of the
output capacitors at the switching frequency. The equation to
determine the minimum inductance value is as follows:
(15)
In the above equation, Re is used in place of the impedance
of the output capacitors. This is because in most cases, the
impedance of the output capacitors at the switching fre-
quency is very close to Re. In the case of ceramic capaci-
tors, replace Re with the true impedance.
20060113
FIGURE 10. Output Voltage Range
L
www.national.com
18
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM5642MTC | High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization |
| LM565 | Phase Locked Loop |
| LM565C | |
| LM565CH | Analog Phase-Locked Loop |
| LM565CN | Phase Locked Loop |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM5642_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization |
| LM5642EVAL-KIT | 功能描述:BOARD EVALUATION LM5642 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:PowerWise® 產(chǎn)品培訓(xùn)模塊:Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):升壓 頻率 - 開關(guān):3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| LM5642EVAL-KIT/NOPB | 功能描述:電源管理IC開發(fā)工具 LM5642 EVAL KIT RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM5642MH | 制造商:Texas Instruments 功能描述: |
| LM5642MH/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 |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。