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| 型号： | IRU3007CWTR |
| 厂商： | International Rectifier |
| 文件页数： | 12/17页 |
| 文件大小： | 0K |
| 描述： | IC CTRL/REG SYNC BUCK 28-SOIC |
| 标准包装： | 1,000 |
| 应用： | 控制器，Intel Pentium? II |
| 输入电压： | 5V，12V |
| 输出数： | 4 |
| 输出电压： | 1.3 V ~ 3.5 V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 28-SOIC W |
| 包装： | 带卷 (TR) |
IRU3007
of the 1500 m F, 6MV1500GX type Sanyo capacitors. With
Rs=5m V , the maximum ESR becomes 9.5m V which is
equivalent to ≈ 4 caps. Another important consideration
is that if a trace is being used to implement the resistor,
the power dissipated by the trace increases the case
temperature of the output capacitors which could seri-
ously affect the life span of the output capacitors.
Output Inductor Selection
The output inductance must be selected such that un-
der low line and the maximum output voltage condition,
the inductor current slope times the output capacitor
ESR is ramping up faster than the capacitor voltage is
drooping during a load current step. However, if the in-
ductor is made too small, the output ripple current and
ripple voltage will become too large. One solution to bring
the ripple current down is to increase the switching fre-
quency, however that will be at the cost of reduced effi-
ciency and higher system cost. The following set of for-
mulas are derived to achieve optimum performance with-
out many design iterations.
The maximum output inductance is calculated using the
following equation:
T = 1 / Fsw
Vsw = Vsync = Io 3 R DS
D ≈ (Vo + Vsync) / (V IN - Vsw + Vsync)
T ON = D 3 T
T OFF = T - T ON
D Ir = (Vo + Vsync) 3 T OFF / L
D Vo = D Ir 3 ESR
In our example for Vo = 2.8V and 14.2 A load, assuming
IRL3103 MOSFET for both switches with maximum on
resistance of 19m V , we have:
T = 1 / 200000 = 5 m s
Vsw = Vsync = 14.2 3 0.019 = 0.27V
D ≈ (2.8 + 0.27) / (5 - 0.27 + 0.27) = 0.61
T ON = 0.61 3 5 = 3.1 m s
T OFF = 5 - 3.1 = 1.9 m s
D Ir = (2.8 + 0.27) 3 1.9 / 3 = 1.94A
D Vo = 1.94 3 0.006 = 0.011V = 11mV
Power Component Selection
Vcore
L = ESR 3 C 3
Where:
(V IN(MIN) - Vo (MAX) )
(2 3 D I)
Assuming IRL3103 MOSFETs as power components,
we will calculate the maximum power dissipation as fol-
lows:
V IN(MIN) = Minimum input voltage
For Vo = 2.8V and D I = 14.2A, we get:
For high side switch the maximum power dissipation
L = 0.006 3 9000 3
(4.75 - 2.8)
(2 3 14.2)
= 3.7 m H
happens at maximum Vo and maximum duty cycle.
D MAX ≈ (2.8 + 0.27) / (4.75 - 0.27 + 0.27) = 0.65
Assuming that the programmed switching frequency is
set at 200KHz, an inductor is designed using the
Micrometals’ powder iron core material. The summary
of the design is outlined below:
The selected core material is Powder Iron, the selected
core is T50-52D from Micro Metal wound with 8 turns of
#16 AWG wire, resulting in 3 m H inductance with ≈ 3 m V
of DC resistance.
P DH = D MAX 3 Io 2 3 R DS(MAX)
P DH = 0.65 3 14.2 2 3 0.029 = 3.8W
R DS(MAX) =Maximum R DS(ON) of the MOSFET at 125 8 C
For synch MOSFET, maximum power dissipation hap-
pens at minimum Vo and minimum duty cycle.
D MIN ≈ (2 + 0.27) / (5.25 - 0.27 + 0.27) = 0.43
P DS = (1 - D MIN ) 3 Io 2 3 R DS(MAX)
P DS = (1 - 0.43) 3 14.2 2 3 0.029 = 3.33W
Assuming L=3 m H and Fsw=200KHz (switching fre-
quency), the inductor ripple current and the output ripple
voltage is calculated using the following set of equations:
T ≡ Switching Period
D ≡ Duty Cycle
Vsw ≡ High-side MOSFET ON Voltage
R DS ≡ MOSFET On-Resistance
Vsync ≡ Synchronous MOSFET ON Voltage
D Ir ≡ Inductor Ripple Current
D Vo ≡ Output Ripple Voltage
3.3V Supply
Again, for high side switch the maximum power dissipa-
tion happens at maximum Vo and maximum duty cycle.
The duty cycle equation for non synchronous replaces
the forward voltage of the diode with the Synch MOSFET
on voltage. In equations below:
Vf = 0.5V
D MAX ≈ (3.3 + 0.5) / (4.75 - 0.27 + 0.5) = 0.76
12
www.irf.com
Rev. 2.1
08/20/02
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| IRU3008CWTR | 功能描述:IC REG 24-SOIC(W) RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:20 系列:SIMPLE SWITCHER® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:12V 输入电压:4 V ~ 60 V PWM 型:电压模式 频率 - 开关:52kHz 电流 - 输出:1A 同步整流器:无 工作温度:-40°C ~ 125°C 安装类型:通孔 封装/外壳:16-DIP（0.300"，7.62mm） 包装:管件 供应商设备封装:16-DIP 其它名称:*LM2575HVN-12LM2575HVN-12 |
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