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參數(shù)資料
| 型號： | LM3478MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Efficiency Low-Side N-Channel Controller for Switching Regulator |
| 中文描述： | 1 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | MSOP-8 |
| 文件頁數(shù)： | 16/21頁 |
| 文件大?。?/td> | 624K |
| 代理商： | LM3478MM |
Typical Applications
(Continued)
CURRENT LIMIT WITH ADDITIONAL SLOPE
COMPENSATION
If an external slope compensation resistor is used (see
Figure 4
) the internal control signal will be modified and this
will have an effect on the current limit. The control signal is
given by:
V
CS
= V
SENSE
(D
*
V
SL
)
Where V
and V
are defined parameters in the elec-
trical characteristics section. If R
is used, then this will add
to the existing slope compensation. The command voltage
will then be given by:
V
CS
= V
SENSE
(D
*
( V
SL
+
V
SL
) )
Where
V
SL
is the additional slope compensation generated
and can be calculated by use of
Figure 5
or is equal to 40 x
10
6
*
R
SL
. This changes the equation for R
SEN
to:
Therefore R
can be used to provide an additional method
for setting the current limit.
POWER DIODE SELECTION
Observation of the boost converter circuit shows that the
average current through the diode is the average load cur-
rent, and the peak current through the diode is the peak
current through the inductor. The diode should be rated to
handle more than its peak current. The peak diode current
can be calculated using the formula:
I
D(Peak)
= I
OUT
/ (1D) +
I
L
In the above equation, I
OUT
is the output current and
I
L
has
been defined in
Figure 9
The peak reverse voltage for boost converter is equal to the
regulator output voltage. The diode must be capable of
handling this voltage. To improve efficiency, a low forward
drop schottky diode is recommended.
POWER MOSFET SELECTION
The drive pin of LM3478 must be connected to the gate of an
external MOSFET. In a boost topology, the drain of the
external N-Channel MOSFET is connected to the inductor
and the source is connected to the ground. The drive pin
(DR) voltage depends on the input voltage (see typical per-
formance characteristics). In most applications, a logic level
MOSFET can be used. For very low input voltages, a sub-
logic level MOSFET should be used.
The selected MOSFET directly controls the efficiency. The
critical parameters for selection of a MOSFET are:
1.
Minimum threshold voltage, V
TH
(MIN)
2.
On-resistance, R
DS
(ON)
3.
Total gate charge, Q
g
4.
Reverse transfer capacitance, C
RSS
5.
Maximum drain to source voltage, V
DS(MAX)
The off-state voltage of the MOSFET is approximately equal
to the output voltage. V
of the MOSFET must be
greater than the output voltage. The power losses in the
MOSFET can be categorized into conduction losses and ac
switching or transition losses. R
is needed to estimate
the conduction losses. The conduction loss, P
, is the
I
2
R loss across the MOSFET. The maximum conduction loss
is given by:
10135520
FIGURE 10. Adjusting the Output Voltage
L
www.national.com
16
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|---|---|
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| LM3478MM/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 |
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| LM3478MMX/HALF | 制造商:Texas Instruments 功能描述: |
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