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参数资料
| 型号： | LM20323AMHE |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 6 A SWITCHING REGULATOR, 570 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | TSSOP-20 |
| 文件页数： | 3/20页 |
| 文件大小： | 492K |
| 代理商： | LM20323AMHE |
LM20323A tri-states the power FETs and resets soft-start.
After the junction cools to approximately 150°C, the part starts
up using the normal start up routine. This feature is provided
to prevent catastrophic failures from accidental device over-
heating.
Design Guide
This section walks the designer through the steps necessary
to select the external components to build a fully functional
power supply. As with any DC-DC converter numerous trade-
offs are possible to optimize the design for efficiency, size, or
performance. These will be taken into account and highlight-
ed throughout this discussion. To facilitate component selec-
tion discussions the circuit shown in Figure 1 below may be
used as a reference. Unless otherwise indicated, all formulas
assume units of amps (A) for current, farads (F) for capaci-
tance, henries (H) for inductance and volts (V) for voltages.
30077229
FIGURE 1. Typical Application Circuit
The first equation to calculate for any buck converter is duty-
cycle. Ignoring conduction losses associated with the FETs
and parasitic resistances it can be approximated by:
INDUCTOR SELECTION (L)
The inductor value is determined based on the operating fre-
quency, load current, ripple current and duty cycle.
The inductor selected should have a saturation current rating
greater than the peak current limit of the device. Keep in mind
the specified current limit does not account for delay of the
current limit comparator, therefore the current limit in the ap-
plication may be higher than the specified value. To optimize
the performance and prevent the device from entering current
limit at maximum load, the inductance is typically selected
such that the ripple current,
Δi
L, is not greater than 30% of the
rated output current. Figure 2 illustrates the switch and in-
ductor ripple current waveforms. Once the input voltage, out-
put voltage, operating frequency and desired ripple current
are known, the minimum value for the inductor can be calcu-
lated by the formula shown below:
30077267
FIGURE 2. Switch and Inductor Current Waveforms
If needed, slightly smaller value inductors can be used, how-
ever, the peak inductor current, I
OUT + ΔiL/2, should be kept
below the peak current limit of the device. In general, the in-
ductor ripple current,
Δi
L, should be more than 10% of the
rated output current to provide adequate current sense infor-
mation for the current mode control loop. If the ripple current
in the inductor is too low, the control loop will not have suffi-
cient current sense information and can be prone to instability.
OUTPUT CAPACITOR SELECTION (C
OUT)
The output capacitor, C
OUT, filters the inductor ripple current
and provides a source of charge for transient load conditions.
A wide range of output capacitors may be used with the
LM20323A that provide excellent performance. The best per-
formance is typically obtained using ceramic, SP or OSCON
type chemistries. Typical trade-offs are that the ceramic ca-
pacitor provides extremely low ESR to reduce the output
ripple voltage and noise spikes, while the SP and OSCON
capacitors provide a large bulk capacitance in a small volume
for transient loading conditions.
When selecting the value for the output capacitor, the two
performance characteristics to consider are the output volt-
age ripple and transient response. The output voltage ripple
can be approximated by using the following formula:
where,
ΔV
OUT (V) is the amount of peak to peak voltage ripple
at the power supply output, R
ESR () is the series resistance
of the output capacitor, f
SW(Hz) is the switching frequency,
and C
OUT (F) is the output capacitance used in the design.
The amount of output ripple that can be tolerated is applica-
tion specific; however a general recommendation is to keep
the output ripple less than 1% of the rated output voltage.
Keep in mind ceramic capacitors are sometimes preferred
because they have very low ESR; however, depending on
package and voltage rating of the capacitor the value of the
capacitance can drop significantly with applied voltage. The
output capacitor selection will also affect the output voltage
droop during a load transient. The peak droop on the output
voltage during a load transient is dependent on many factors;
however, an approximation of the transient droop ignoring
loop bandwidth can be obtained using the following equation:
11
www.national.com
LM20323A
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM20323AMHX | 制造商:NSC 制造商全称:National Semiconductor 功能描述:36V, 3A 500 kHz Synchronous Buck Regulator |
| LM20323EVAL | 功能描述:电源管理IC开发工具 LM20323 EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM20323MH | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP Rail 制造商:Texas Instruments 功能描述:BUCK REG, 3A, 4V/36V, POWERWISE, 20TSSOP 制造商:Texas Instruments 功能描述:IC, DC-DC CONV; Primary Input Voltage:36V; No. of Outputs:1; Output Voltage:32V; Output Current:3A; No. of Pins:20; Operating Temperature Min:-40C; Operating Temperature Max:125C; Operating Temperature Range:-40C to +125C ;RoHS Compliant: Yes |
| LM20323MH/NOPB | 功能描述:直流/直流开关转换器 36V,3A 500 KHZ SYNC BUCK REG RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM20323MHE | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP T/R |
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