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參數(shù)資料
| 型號： | NCP5423DR2G |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Out−of−Phase Synchronous Buck Controller with Current Limit |
| 中文描述： | 1.5 A DUAL SWITCHING CONTROLLER, 750 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | LEAD FREE, SOP-16 |
| 文件頁數(shù)： | 10/16頁 |
| 文件大?。?/td> | 171K |
| 代理商： | NCP5423DR2G |
NCP5422A, NCP5423
http://onsemi.com
10
Selecting the Switching Frequency
Selecting the switching frequency is a tradeoff between
component size and power losses. Operation at higher
switching frequencies allows the use of smaller inductor and
capacitor values. Nevertheless, it is common to select lower
frequency operation because a higher frequency results in
lower efficiency due to MOSFET gate charge losses.
Additionally, the use of smaller inductors at higher
frequencies results in higher ripple current, higher output
voltage ripple, and lower efficiency at light load currents.
The value of the oscillator resistor is designed to be
linearly related to the switching period. If the designer
prefers not to use Figure 8 to select the necessary resistor, the
following equation quite accurately predicts the proper
resistance for room temperature conditions.
21700
2.31
where:
R
OSC
= oscillator resistor in k ;
f
SW
= switching frequency in kHz.
ROSC
fSW
fSW
Figure 8. Switching Frequency
10
20
30
40
50
60
100
200
300
400
500
600
700
800
R
OSC (k )
F
Selection of the Output Inductor
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the
inductor value will decrease output voltage ripple, but
degrade transient response. There are many factors to
consider in selecting the inductor including cost, efficiency,
EMI and ease of manufacture. The inductor must be able to
handle the peak current at the switching frequency without
saturating, and the copper resistance in the winding should
be kept as low as possible to minimize resistive power loss.
There are a variety of materials and types of magnetic
cores that could be used for this application. Among them
are ferrites, molypermalloy cores (MPP), amorphous and
powdered iron cores. Powdered iron cores are very
commonly used. Powdered iron cores are very suitable due
to its high saturation flux density and have low loss at high
frequencies, a distributed gap and exhibit very low EMI.
The minimum value of inductance which prevents
inductor saturation or exceeding the rated FET current can
be calculated as follows:
(VIN(MIN)
fSW
VIN(MIN)
where:
L
MIN
= minimum inductance value;
V
IN(MIN)
= minimum design input voltage;
V
OUT
= output voltage;
f
SW
= switching frequency;
I
SW(MAX)
maximum design switch current.
The inductor ripple current can then be determined:
LMIN
VOUT)
VOUT
ISW(MAX)
IL
VOUT
(1
fSW
D)
L
where:
I
L
= inductor ripple current;
V
OUT
= output voltage;
L = inductor value;
D = duty cycle.
f
SW
= switching frequency
The designer can now verify if the number of output
capacitors will provide an acceptable output voltage ripple
(1.0% of output voltage is common). The formula below is
used:
IL
VOUT
ESRMAX
Rearranging we have:
ESRMAX
VOUT
IL
where:
ESR
MAX
= maximum allowable ESR;
V
OUT
= 1.0%
×
V
OUT
= maximum allowable output
voltage ripple ( budgeted by the designer );
I
L
= inductor ripple current;
V
OUT
= output voltage.
The number of output capacitors is determined by:
Number of capacitors
ESRCAP
ESRMAX
where:
ESR
CAP
= maximum ESR per capacitor (specified in
manufacturer’s data sheet).
The designer must also verify that the inductor value
yields reasonable inductor peak and valley currents (the
inductor current is a triangular waveform):
IL(PEAK)
IOUT
IL
2
where:
I
L(PEAK)
= inductor peak current;
I
OUT
= load current;
I
L
= inductor ripple current.
IL(VALLEY)
IOUT
IL
2
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| NCP5424AD | 功能描述:IC REG CTRLR BUCK PWM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
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