参数资料
| 型号： | MC33470DW |
| 厂商： | ON Semiconductor |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC CONV DC/DC SYNC RECT 20-SOIC |
| 产品变化通告： | Product Obsolescence 11/Feb/2009 |
| 标准包装： | 38 |
| 应用： | 控制器，Intel Pentium? II |
| 输入电压： | 4.5 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | 1.8 V ~ 3.5 V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 20-SOIC |
| 包装： | 管件 |
MC33470
APPLICATIONS INFORMATION
Design Example
Given the following requirements, design a switching
dc?to?dc converter:
6. Feedback Loop Compensation
The corner frequency of the output filter with L = 1.5 m H and
C o = 1640 m F is 3.2 kHz. In addition, the ESR of each output
V CC =
V CCP =
VID4?0 bits =
Output current =
5.0 V
12 V
10111 ? Output Voltage = 2.8 V
0.3 A to 14 A
capacitor creates a zero at:
f z = 1/(2 π C ESR) = 1/(2 π x 820 m F x 0.012) = 16.2 kHz
The dc gain of the PWM is: Gain = V in /V pp = 5/1 = 5.0.
Where V pp is the peak?to?peak sawtooth voltage across the
Efficiency > 80% at full load
Output ripple voltage ≈ 1% of output voltage
1. Choose power MOSFETs.
In order to meet the efficiency requirement, MOSFETs
should be chosen which have a low value of R DS(on) . However,
the threshold voltage rating of the MOSFET must also be
greater than 1.5 V, to prevent turn on of the synchronous
rectifier MOSFETs due to dv/dt coupling through the Miller
capacitance of the MOSFET drain?to?source junction.
Figure 17 shows the gate voltage transient due to this effect.
In this design, choose two parallel MMSF3300 MOSFETs
for both the main switch and the synchronous rectifier to
maximize efficiency.
2. D ≈ V O /V in = 2.8/5.0 = 0.56
3. Inductor selection
In order to maintain continuous mode operation at 10% of
full load current, the minimum value of the inductor will be:
L min = (V in ? V O )(DTs)/(2I O min )
= (5 ? 2.8)(0.56 x 3.3 m s)/(2 x 1.4 A) = 1.45 m H
Coilcraft’s U6904, or an equivalent, provides a surface
mount 1.5 m H choke which is rated for for full load current.
4. Output capacitor selection
V ripple ≈ D I L x ESR, where ESR is the equivalent series
resistance of the output capacitance. Therefore:
ESR max = V ripple / D I L = 0.01 x 2.8 V/1.4 A = 0.02 W
maximum
The AVX TPS series of tantalum chip capacitors may be
chosen. Or OSCON capacitors may be used if leaded parts are
acceptable. In this case, the output capacitance consists of two
parallel 820 m F, 4.0 V capacitors. Each capacitor has a
maximum specified ESR of 0.012 W .
5. Input Filter
As with all buck converters, input current is drawn in pulses.
In this case, the current pulses may be 14 A peak. If a 1.5 m H
choke is used, two parallel OSCON 150 m F, 16 V capacitors
will provide a filter cutoff frequency of 7.5 kHz.
internal timing capacitor. In order to make the feedback loop
as responsive as possible to load changes, choose the unity
gain frequency to be 10% of the switching frequency, or
30 kHz. Plotting the PWM gain over frequency, at a frequency
of 30 kHz the gain is about ?16.5 dB = 0.15. Therefore, to have
a 30 kHz unity gain loop, the error amplifier gain at 30 kHz
should be 1/0.15 = 6.7. Choose a design phase margin for the
loop of 60 ° . Also, choose the error amp type to be an integrator
for best dc regulation performance. The phase boost needed by
the error amplifier is then 60 ° for the desired phase margin.
Then, the following calculations can be made:
k = tan [Boost/2 + 45 ° ] = tan [60/2 + 45] = 3.73
Error Amp zero freq = f c /K = 30 kHz/3.73 = 8.0 kHz
Error Amp pole freq = K fc = 3.73 x 30 kHz = 112 kHz
R2 = Error Amp Gain/G m = 6.7/800 m = 8.375 k ? use an
8.2 k standard value
C16 = 1/(2 π R2 f z ) = 1/(2 π x 8.2 k x 8.0 kHz)
= 2426 pF ? use 2200 pF
C17 = 1/(2 π R2 f p ) = 1/(2 π x 8.2 k x 112 kHz)
= 173 pF ? use 100 pF
The complete design is shown in Figure 14. The PC board
top and bottom views are shown in Figures 18 and 19.
Figure 17. Voltage Coupling Through Miller
Capacitance
http://onsemi.com
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相关代理商/技术参数 |
参数描述 |
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| MC33470DWG | 功能描述:直流/直流开关调节器 5-Bit Synchronous Rectification Buck RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MC33470DWR2 | 功能描述:直流/直流开关调节器 5-Bit Synchronous RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MC33470DWR2G | 功能描述:直流/直流开关调节器 5-Bit Synchronous Rectification Buck RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MC33486ADH | 功能描述:电源开关 IC - 配电 DUALHIGH-SIDE BRIDGE RoHS:否 制造商:Exar 输出端数量:1 开启电阻（最大值）:85 mOhms 开启时间（最大值）:400 us 关闭时间（最大值）:20 us 工作电源电压:3.2 V to 6.5 V 电源电流（最大值）: 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOT-23-5 |
| MC33486ADHR2 | 功能描述:电源开关 IC - 配电 DUALHIGH-SIDE BRIDGE RoHS:否 制造商:Exar 输出端数量:1 开启电阻（最大值）:85 mOhms 开启时间（最大值）:400 us 关闭时间（最大值）:20 us 工作电源电压:3.2 V to 6.5 V 电源电流（最大值）: 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOT-23-5 |
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