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CS51413EDR8 参数 Datasheet PDF下载

CS51413EDR8图片预览
型号: CS51413EDR8
PDF下载: 下载PDF文件 查看货源
内容描述: [Switching Regulator, Current/voltage-mode, 4A, 594kHz Switching Freq-Max, PDSO8, 0.150 INCH, SO-8]
分类和应用: 开关光电二极管
文件页数/大小: 16 页 / 137 K
品牌: CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
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Application Information  
As shown in Figure 5, the BOOST pin current includes a  
VC × CCOMP  
ISOURCE  
TSS  
=
constant 7mA pre-driver current and base current propor-  
tional to switch conducting current. A detailed discussion  
of this current is conducted in Thermal Consideration sec-  
tion. A 0.1µF capacitor is usually adequate for maintaining  
the Boost pin voltage during the on time.  
where VC = VC pin steady-state voltage, which is approxi-  
mately equal to error amplifiers reference  
voltage.  
CCOMP = Compensation capacitor connected to the  
VC pin  
30  
25  
ISOURCE = OUTPUT SOURCE CURRENT of the  
error amplifier.  
Using a 0.1µF Ccomp, the calculation shows a TSS over 5ms  
which is adequate to avoid any current stresses. Figure 6  
shows the gradual rise of the VC, VO and envelope of the  
20  
15  
10  
5
V
SW during power up. There is no voltage over-shoot after  
the output voltage reaches the regulation. If the supply  
voltage rises slower than the VC pin, output voltage may  
over-shoot.  
0
1
1.5  
0.5  
0
Switching Current (A)  
Figure 5: The boost pin current includes 7mA pre-driver current and  
base current when the switch is turned on. The beta decline of the  
power switch further increases the base current at high switching cur-  
rent.  
BIAS Pin (CS51412 and CS51414 Only)  
The BIAS pin allows a secondary power supply to bias the  
control circuitry of the IC. The BIAS pin voltage should be  
between 3.3V and 6.0V. If the BIAS pin voltage falls below  
that range, use a diode to prevent current drain from the  
BIAS pin. Powering the IC with a voltage lower than the  
regulators input voltage reduces the IC power dissipation  
and improves energy transfer efficiency.  
Figure 6: The power up transition of C5141X regulator.  
Short Circuit  
Shutdown  
When the VFB pin voltage drops below FOLDBACK  
THRESHOLD, the regulator reduces the peak current limit  
by 40% and switching frequency to 1/ 4 of the nominal fre-  
quency. These features are designed to protect the IC and  
external components during over load or short circuit con-  
ditions. In those conditions, peak switching current is  
clamped to the current limit threshold. The reduced  
switching frequency significantly increases the ripple cur-  
rent, and thus lowers the DC current. The short circuit can  
causes the minimum duty cycle to be limited by MINI-  
MUM OUTPUT PULSE WIDTH. The foldback frequency  
reduces the minimum duty cycle by extending the switch-  
ing cycle. This protects the IC from overheating, and also  
limits the power that can be transferred to the output. The  
current limit foldback effectively reduces the current stress  
on the inductor and diode. When the output is shorted, the  
DC current of the inductor and diode can approach the  
current limit threshold. Therefore, reducing the current  
limit by 40% can result in an equal percentage drop of the  
inductor and diode current. The short circuit waveforms  
are captured in Figure 7, and the benefit of the foldback  
frequency and current limit is self-evident.  
The internal power switch will not turn on until the VIN pin  
rises above the START UP VOLTAGE. This ensures no  
switching until adequate supply voltage is provided to the  
IC.  
The IC enters a sleep mode when the SHDNB pin is pulled  
below SHUTDOWN THRESHOLD VOLTAGE. In the sleep  
mode, the power switch keeps open and the supply current  
reduces to SHUTDOWN QUIESCENT CURRENT. This pin  
has internal pull-up current. So when this pin is not used,  
leave the SHDNB pin open.  
Start-Up  
During power up, the regulator tends to quickly charge up  
the output capacitors to reach voltage regulation. This  
gives rise to an excessive in-rush current which can be  
TM  
detrimental to the inductor, IC and catch diode. In V2  
control , the compensation capacitor provides soft-start  
with no need for extra pin or circuitry. During the power  
up, the OUTPUT SOURCE CURRENT of the error amplifi-  
er charges the compensation capacitor which forces VC pin  
and thus output voltage ramp up gradually. The soft-start  
duration can be calculated by  
7
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