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SY8089 参数 Datasheet PDF下载

SY8089图片预览
型号: SY8089
PDF下载: 下载PDF文件 查看货源
内容描述: []
分类和应用:
文件页数/大小: 11 页 / 3058 K
品牌: SILICONIMAGE [ Silicon image ]
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SY8089/8089A  
VOUT  
R1  
Operation Principle  
SY8089 is a synchronous buck regulator IC that  
integrates the PWM control, top and bottom switches  
on the same die to minimize the switching transition  
loss and conduction loss. With ultra low RDS(ON) power  
switches and proprietary PWM control, this regulator  
IC can achieve the highest efficiency and the highest  
switch frequency simultaneously to minimize the  
external inductor and capacitor size, and thus achieving  
the minimum solution footprint.  
FB  
R2  
GND  
Input capacitor CIN:  
This ripple current through input capacitor is clculated  
as:  
ICIN_RMS =IOUT × D(1-D)  
Short Circuit Protection  
This formula has a maximum at VIN=2VOUT condition,  
where ICIN_RMS=IOUT/2. simple worst-case  
condition is commonly used for DC/DC design.  
SY8089After the soft start is over, if the output  
voltage falls below 40% of the regulation level, IC will  
turn off both power switches, entering short circuit  
protection. It will remain in this state until the IN or EN  
voltage is recycled.  
With the maximum load current at 2.0A. A typical  
X5R or better grade ceramic capacitor with 6.3V rating  
and more than 1 pcs 22µF capacitor can handle this  
ripple current well. To minimize the potential noise  
problem, ceramic capacitor should really be placed  
cto the IN and GND pins. Care should be taken to  
minmize the loop area formed by CIN, and IN/GND  
pins  
(SY8089A) The frequency is folded back to about 30%  
of the nominal frequency and the current limit is folded  
back to 3.0A to prevent the inductor current from  
runaway and to reduce the power dissipation of the IC  
under short circuit conditions.  
Over-voltage Protection  
If the output voltage exceeds 120% of the regulation  
level for more than 20µs, IC will turn off both power  
switches and turn on the discharge switch, entering  
over-voltage protection. It will remain in this state until  
IN or EN voltage is recycled.  
Output capacitor COUT:  
The output capacitor is selected to handle the output  
ripple noise requirements. Both steady state ripple and  
transient requirements must be taken into consideration  
when selecting this capacitor. For the best performance,  
it is recommended to use X5R or better grade ceramic  
capacitor with 6.3V rating and greater than 22µF  
capacitance.  
Applications Information  
Because of the high integration in the SY8089 IC, the  
application circuit based on this regulator IC is rather  
simple. Only input capacitor CIN, output capacitor COUT  
output inductor L and feedback resistors (R1 and R2)  
need to be selected for the targeted applications  
specifications.  
,
Output inductor L:  
There are several considerations in choosing this  
inductor.  
1) Choose the inductance to provide the desired  
ripple current. It is suggested to choose the ripple  
current to be about 40% of the maximum output  
current. The inductance is calculated as:  
Feedback resistor dividers R1 and R2:  
Choose nd R2 to program the proper output  
voltage. To minimize the power consumption under  
light loads, it is desirable to choose large resistance  
values for both R1 and R2. A value of between 10k and  
1M is highly recommended for both resistors. If Vout  
is 1.8V, R1=100k is chosen, then R2 can be calculated  
to be 50k.:  
VOUT (1VOUT/VIN,MAX  
)
L =  
FSW × IOUT,MAX × 40%  
where Fsw is the switching frequency and IOUT MAX  
,
is  
the maximum load current.  
The SY8089 regulator IC is quite tolerant of different  
ripple current amplitude. Consequently, the final choice  
0.6V  
R2 =  
R1().  
VOUT -0.6V  
AN_SY8089/A Rev. 0.9  
Silergy Corp. Confidential- Prepared for Customer Use Only 8  
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