参数资料
型号: LM3102EVAL/NOPB
厂商: National Semiconductor
文件页数: 15/24页
文件大小: 0K
描述: EVAL BOARD FOR LM3102
标准包装: 1
系列: PowerWise®, SIMPLE SWITCHER®
主要目的: DC/DC,步降
输出及类型: 1,非隔离
输出电压: 3.3V
电流 - 输出: 2.5A
输入电压: 8 ~ 42 V
稳压器拓扑结构: 降压
频率 - 开关: 500kHz
板类型: 完全填充
已供物品: 板,文档
已用 IC / 零件: LM3102
SNVS515G – SEPTEMBER 2007 – REVISED JANUARY 2012
R ON : Equation 2 can be used to select R ON if a desired operating frequency is selected. But the minimum value
of R ON is determined by the minimum on-time. It can be calculated as follows:
R ON t
V IN(MAX) x 150 ns
1.3 x 10 -10
(8)
If R ON calculated from Equation 2 is smaller than the minimum value determined in Equation 8 , a lower frequency
should be selected to re-calculate R ON by Equation 2 . Alternatively, V IN(MAX) can also be limited in order to keep
the frequency unchanged. The relationship of V IN(MAX) and R ON is shown in Figure 27 .
On the other hand, the minimum off-time of 260 ns can limit the maximum duty ratio. Larger R ON should be
selected in any application requiring large duty ratio.
Figure 27. Maximum V IN for selected R ON
L: The main parameter affected by the inductor is the amplitude of inductor current ripple (I LR ). Once I LR is
selected, L can be determined by:
L=
V OUT x (V IN - V OUT )
I LR x f SW x V IN
where
?
V IN is the maximum input voltage
?
f SW is determined from Equation 2
(9)
where and .
If the output current I OUT is determined, by assuming that I OUT = I L , the higher and lower peak of I LR can be
determined. Beware that the higher peak of I LR should not be larger than the saturation current of the inductor
and current limits of the main and synchronous MOSFETs. Also, the lower peak of I LR must be positive if CCM
operation is required.
Figure 28. Inductor selection for V OUT = 3.3V
Copyright ? 2007–2012, Texas Instruments Incorporated
Product Folder Links: LM3102
15
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