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| 型号： | NCP1550SN30T1 |
| 厂商： | ON Semiconductor |
| 文件页数： | 14/17页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 5TSOP |
| 产品变化通告： | LTB Notification 03/Jan/2008 |
| 标准包装： | 3,000 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 690kHz |
| 占空比： | 100% |
| 电源电压： | 2.45 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 6-TSOP（0.059"，1.50mm 宽）5 引线 |
| 包装： | 带卷 (TR) |
| 其它名称： | NCP1550SN30T1OS |
NCP1550
APPLICATIONS INFORMATION
Inductor Value Calculation
Selecting the proper inductance is a trade?off between
inductor’s physical size, transient respond and power
conversion requirements. Lower value inductor saves cost,
PC board space and providing faster transient response, but
result in higher ripple current and core losses. Considering an
application with loading current, I OUT = 0.5 A and the
inductor ripple current, I L?RIPPLE(P?P) is designed to be less
than 40% of the load current, i.e. 0.5 A x 40% = 0.2 A.
The relationship between the inductor value and inductor
P?Channel switch duty cycle. At high input voltages, the
diode conducts most of the time. In case of V IN approaches
V OUT , the diode conducts only a small fraction of the cycle.
While the output terminals are shorted, the diode will subject
to its highest stress. Under this condition, the diode must be
able to safely handle the peak current circulating in the loop.
So, it is important to select a flywheel diode that can meet the
diode peak current and average power dissipation
requirements. Under normal conditions, the average current
conducted by the flywheel diode is given by:
L + ON
ID + VIN * VOUT IOUT (eq. 2)
ripple current is given by,
T * (VIN * RDS(ON) IOUT * VOUT)
IL * RIPPLE(P * P)
(eq. 1)
VIN ) VF
Where I D is the average diode current and V F is the forward
Where R DS(ON) is the ON resistance of the external
P?channel MOSFET. Figure 39 is a plot for recommended
inductance against nominal input voltage for different output
options.
diode voltage drop.
A fast switching diode must also be used to optimize
efficiency. Schottky diodes are a good choice for low forward
drop and fast switching times.
12
10
8
6
R DS(ON) = 0.1 W
1.9 V
1.8 V
2.5 V
Input and Output Capacitor Selection (C IN and C OUT )
In continuous mode operation, the source current of the
P?Channel MOSFET is a square wave of duty cycle (V OUT +
V F )/V IN . To prevent large input voltage transients, a low ESR
input capacitor that can support the maximum RMS input
current must be selected. The maximum RMS input current,
I RMS(MAX) can be estimated by the equation in below:
4
3.3 V
IRMS(MAX) [ IOUT
1
VOUT(VIN * VOUT) 2
VIN
(eq. 3)
2
0
2.7 V
3.0 V
Above estimation has a maximum value at V IN = 2V OUT ,
where I RMS(MAX) = I OUT /2. As a general practice, this simple
worst?case condition is used for design.
2.2
2.7
3.2
3.7
4.2
4.7
5.2
Selection of the output capacitor, C OUT is primarily
1
V IN , INPUT VOLTAGE OF NCP1550 (V)
Figure 39. Inductor Selection Chart
P?Channel Power MOSFET Selection
An external P?Channel power MOSFET must be used with
the NCP1550. The key selection criteria for the power
MOSFET are the gate threshold, V GS , the “ON” resistance,
R DS(ON) and its total gate charge, Q T . For low input voltage
operation, we need to select a low gate threshold device that
can work down to the minimum input voltage level. R DS(ON)
determines the conduction losses for each switching cycle,
the lower the ON resistance, the higher the efficiency can be
achieved. A power MOSFET with lower gate charge can give
lower switching losses but the fast transient can cause
unwanted EMI to the system. Compromise in between is
required during the design stage. For 1.0 A and 2.0 A load
current, NTGS3441T1 and NTGS3443T1 are tested to be
appropriate for most applications.
governed by the required effective series resistance (ESR) of
the capacitor. Typically, once the ESR requirement is met, the
capacitance will be adequate for filtering. The output voltage
ripple, V RIPPLE is approximated by:
VRIPPLE [ IL * RIPPLE(P * P)
(eq. 4)
(ESR ) )
4 FOSCCOUT
Where F OSC is the switching frequency and ESR is the
effective series resistance of the output capacitor.
From equation (4), it can be noted that the output voltage
ripple contributed by two parts. For most of the case, the
major contributor is the capacitor ESR. Ordinary
aluminum?electrolytic capacitors have high ESR and should
be avoided. Higher quality Low ESR aluminum?electrolytic
capacitors are acceptable and relatively inexpensive. For even
better performance, Low ESR tantalum capacitors should be
used. Surface?mount tantalum capacitors are better and
provide neat and compact solution for space sensitive
applications.
Flywheel Diode Selection
The flywheel diode is turned on and carries load current
during the off time. The average diode current depends on the
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| NCP1550SN30T1G | 功能描述:直流/直流开关转换器 1.8V 2A Buck PWM/PFM w/Enable Soft Start 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 |
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| NCP1560HDR2 | 功能描述:IC REG CTRLR FLYBACK PWM 16-SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
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