參數(shù)資料
型號(hào)： LM3488MM
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： 500kHz and 1MHz High Efficiency 1.5A Switching Regulators; Package: SO; No of Pins: 8; Temperature Range: -40?°C to 85?°C
中文描述： 1 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO8
封裝： MSOP-8
文件頁(yè)數(shù)： 17/24頁(yè)
文件大?。?/td> 626K
代理商： LM3488MM
Typical Applications
(Continued)
The important quantities in determining a proper inductance
value are I
L
(the average inductor current) and
i
L
(the
inductor current ripple). If
i
L
is larger than I
L
, the inductor
current will drop to zero for a portion of the cycle and the
converter will operate in discontinuous conduction mode. If
i
is smaller than I
, the inductor current will stay above
zero and the converter will operate in continuous conduction
mode. All the analysis in this datasheet assumes operation
in continuous conduction mode. To operate in continuous
conduction mode, the following conditions must be met:
I
L
>
i
L
Choose the minimum I
OUT
to determine the minimum L. A
common choice is to set
i
to 30% of I
. Choosing an
appropriate core size for the inductor involves calculating the
average and peak currents expected through the inductor. In
a boost converter,
and I
L_peak
= I
L
(max) +
i
L
(max),
where
A core size with ratings higher than these values should be
chosen. If the core is not properly rated, saturation will
dramatically reduce overall efficiency.
The LM3488 can be set to switch at very high frequencies.
When the switching frequency is high, the converter can be
operated with very small inductor values. With a small induc-
tor value, the peak inductor current can be extremely higher
than the output currents, especially under light load condi-
tions.
The LM3488 senses the peak current through the switch.
The peak current through the switch is the same as the peak
current calculated above.
PROGRAMMING THE OUTPUT VOLTAGE AND OUTPUT
CURRENT
The output voltage can be programmed using a resistor
divider between the output and the feedback pins, as shown
in
Figure 12
. The resistors are selected such that the voltage
at the feedback pin is 1.26V. R
F1
and R
F2
can be selected
using the equation,
A 100pF capacitor may be connected between the feedback
and ground pins to reduce noise.
The maximum amount of current that can be delivered at the
output can be controlled by the sense resistor, R
. Current
limit occurs when the voltage that is generated across the
sense resistor equals the current sense threshold voltage,
V
SENSE
. Limits for V
SENSE
have been specified in the elec-
trical characteristics. This can be expressed as:
I
sw(peak)
*
R
SEN
= V
SENSE
V
SENSE
represents the maximum value of the control signal
as shown in
Figure 2
. This control signal, however, is not a
constant value and changes over the course of a period as a
result of the internal compensation ramp (see
Figure 3
).
Therefore the current limit will also change as a result of the
internal compensation ramp. The actual command signal,
V
, can be better expressed as a function of the sense
voltage and the internal compensation ramp:
V
CS
= V
SENSE
(D
*
V
SL
)
V
is defined as the internal compensation ramp voltage,
limits are specified in the electrical characteristics.
The peak current through the switch is equal to the peak
inductor current.
I
sw(peak)
= I
L
+
i
L
Therefore for a boost converter
Combining the three equation yields an expression for R
SEN
L
www.national.com
17
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM3488MM 制造商:Texas Instruments 功能描述:POWER CONTROLLER SMD 3488 MSOP8
LM3488MM/HALF 制造商:Texas Instruments 功能描述:
LM3488MM/NOPB 功能描述:DC/DC 開關(guān)控制器 HI EFF LOW-SIDE N CH CONTROLLER RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
LM3488MM/NOPB 制造商:Texas Instruments 功能描述:Pulse Width Modulation (PWM) Controller
LM3488MMX 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
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