參數(shù)資料
型號: LM2707MFX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 顯示驅(qū)動器
英文描述: Inductive-Boost Series LED Driver with Programmable Oscillator Frequency
中文描述: LED DISPLAY DRIVER, PDSO8
封裝: SOT-23, 8 PIN
文件頁數(shù): 12/19頁
文件大?。?/td> 1039K
代理商: LM2707MFX
Product Description
(Continued)
Figure 5
graphs the relationship between inductor current
and current limit.
Figure 6
plots ideal inductor current wave-
forms to illustrate inductor current behavior.
Figure 7
gives
peak inductor current versus input voltage and shows the
two regions where the oscillator and current limit, respec-
tively, determine peak inductor current.
Note 12:
V
is a good approximation of the voltage across the inductor
during the charge phase. Actual voltage across the inductor will be slightly
lower due to the V
DS
voltage of the power transistor, but this factor is minimal
due to the low R
DS-ON
of the power transistor.
INCREASING CURRENT LIMIT AND PEAK INDUCTOR
CURRENT
It is possible to increase the current limit by placing an
external resistor between the V
IN
and L
X
pins, as shown in
Figure 8
. With the addition of the external resistor, only a
fraction of the total inductor current passes through internal
sense resistor. Thus, it takes more inductor current for the
voltage across the internal sense resistor to become large
enough to trip the current limit comparator.
The addition of an external current limit resistor modifies the
associated peak inductor equation to:
R
EXT
: External Current Limit Adjust Resistance
20099231
FIGURE 5. Peak Inductor Current and Current Limit vs.
Input Voltage
20099232
FIGURE 6. Ideal Inductor Current Waveforms
20099252
FIGURE 7. Peak Inductor Current vs. Input Voltage.
L = 22μH, C
X
= 68pF.
20099233
FIGURE 8. Increase Current Limit and Peak Inductor
Current by Adding R
EXT
L
www.national.com
12
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