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TPS61020DRCR 参数 Datasheet PDF下载

TPS61020DRCR图片预览
型号: TPS61020DRCR
PDF下载: 下载PDF文件 查看货源
内容描述: 96%高效同步升压转换器 [96% EFFICIENT SYNCHRONOUS BOOST CONVERTER]
分类和应用: 转换器稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管输出元件升压转换器
文件页数/大小: 27 页 / 549 K
品牌: TI [ TEXAS INSTRUMENTS ]
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TPS61020, TPS61024, TPS61025  
TPS61026, TPS61027, TPS61028  
TPS61029  
www.ti.com  
SLVS451DSEPTEMBER 2003REVISED FEBRUARY 2006  
CAPACITOR SELECTION  
Input Capacitor  
At least a 10-µF input capacitor is recommended to improve transient behavior of the regulator and EMI  
behavior of the total power supply circuit. A ceramic capacitor or a tantalum capacitor with a 100-nF ceramic  
capacitor in parallel, placed close to the IC, is recommended.  
Output Capacitor  
The major parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of  
the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is  
possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by  
using Equation 6:  
  ǒVOUT BATǓ  
I
* V  
OUT  
C
+
min  
ƒ   DV   V  
OUT  
(6)  
Parameter f is the switching frequency and V is the maximum allowed ripple.  
With a chosen ripple voltage of 10 mV, a minimum capacitance of 24 µF is needed. The total ripple is larger due  
to the ESR of the output capacitor. This additional component of the ripple can be calculated using Equation 7:  
DV  
+ I  
  R  
ESR  
OUT  
ESR  
(7)  
An additional ripple of 16 mV is the result of using a tantalum capacitor with a low ESR of 80 m. The total  
ripple is the sum of the ripple caused by the capacitance and the ripple caused by the ESR of the capacitor. In  
this example, the total ripple is 26 mV. Additional ripple is caused by load transients. This means that the output  
capacitor has to completely supply the load during the charging phase of the inductor. A reasonable value of the  
output capacitance depends on the speed of the load transients and the load current during the load change.  
With the calculated minimum value of 24 µF and load transient considerations the recommended output  
capacitance value is in a 47 to 100 µF range. For economical reasons, this is usually a tantalum capacitor.  
Therefore, the control loop has been optimized for using output capacitors with an ESR of above 30 m. The  
minimum value for the output capacitor is 10 µF.  
SMALL SIGNAL STABILITY  
When using output capacitors with lower ESR, like ceramics, the adjustable voltage version is recommended.  
The missing ESR can be compensated in the feedback divider. Typically a capacitor in the range of 4.7 pF in  
parallel to R3 helps to obtain small signal stability with lowest ESR output capacitors. For more detailed analysis,  
the small signal transfer function of the error amplifier and the regulator, which is given in Equation 8, can be  
used:  
4   (R3 ) R4)  
R4   (1 ) i   w   0.9 ms)  
d
A
+
+
REG  
V
FB  
(8)  
LAYOUT CONSIDERATIONS  
As for all switching power supplies, the layout is an important step in the design, especially at high peak currents  
and high switching frequencies. If the layout is not carefully done, the regulator could show stability problems as  
well as EMI problems. Therefore, use wide and short traces for the main current path and for the power ground  
tracks. The input capacitor, output capacitor, and the inductor should be placed as close as possible to the IC.  
Use a common ground node for power ground and a different one for control ground to minimize the effects of  
ground noise. Connect these ground nodes at any place close to one of the ground pins of the IC.  
The feedback divider should be placed as close as possible to the control ground pin of the IC. To lay out the  
control ground, it is recommended to use short traces as well, separated from the power ground traces. This  
avoids ground shift problems, which can occur due to superimposition of power ground current and control  
ground current.  
17  
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