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參數(shù)資料
| 型號： | LT3751IUFD#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PQCC20 |
| 封裝： | 4 X 5 MM, LEAD FREE, PLASTIC, QFN-20 |
| 文件頁數(shù)： | 7/34頁 |
| 文件大?。?/td> | 403K |
| 代理商： | LT3751IUFD#TRPBF |
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LT3751
15
3751fb
APPLICATIONS INFORMATION
The LT3751 charger controller can be optimized for either
capacitor charging only or low noise regulation applica-
tions. Several equations are provided to aid in the design
process.
Safety Warning
Large capacitors charged to high voltage can deliver a lethal
amount of energy if handled improperly. It is particularly
important to observe appropriate safety measures when
designing the LT3751 into applications. First, create a dis-
charge circuit that allows the designer to safely discharge
the output capacitor. Second, adequately space high voltage
nodes from adjacent traces to satisfy printed circuit board
voltage breakdown requirements.
Selecting Operating Mode
Tie the FB pin to GND to operate the LT3751 as a capacitor
charger. In this mode, the LT3751 charges the output at
peak primary current in boundary mode operation. This
constitutes maximum power delivery and yields the fast-
est charge times. Power delivery is halted once the output
reaches the desired output voltage set by the RVOUT and
RBG pins.
Tie a resistor divider from the FB pin to VOUT and GND
to operate the LT3751 as a low noise voltage regulator
(refer to Low Noise regulation section for proper design
procedures). The LT3751 operates as a voltage regulator
using both peak current and duty cycle modulation to vary
output current during different loading conditions.
Selecting Component Parameters
Most designs start with the initial selection of VTRANS,
VOUT, COUT, and either charge time, tCHARGE, (capacitor
charger) or POUT,MAX (regulator). These design inputs
are then used to select the transformer ratio, N, the peak
primary current, IPK, and the primary inductance, LPRI.
Figure 7 can be used as a rough guide for maximum power
output for a given VTRANS and IPK.
Selecting Transformer Turns Ratio
The transformer ratio, N, should be selected based on the
input and output voltages. Smaller N values equate to faster
charge times and larger available output power. Note that
drastically reducing N below the VOUT/VTRANS ratio will
increase the yback voltage on the drain of the NMOS and
increase the current through the output diode. The ratio,
N, should not be drastically increased either, due to the
increased capacitance, N2 CSEC, reected to the primary.
A good choice is to select N equal to VOUT/VTRANS.
N
≤
V
OUT
V
TRANS
Choosing Capacitor Charger IPK
When operating the LT3751 as capacitor charger, choose
IPK based on the required capacitor charge time, tCHARGE,
and the initial design inputs.
I
PK =
2 N V
TRANS + VOUT
()C
OUT VOUT
Efficiency V
TRANS tCHARGE td
()
The converter efciency varies over the output voltage
range. The IPK equation is based on the average ef-
ciency over the entire charging period. Several factors can
cause the charge time to increase. Efciency is the most
dominant factor and is mainly affected by the transformer
winding resistance, core losses, leakage inductance, and
transistor RDS. Most applications have overall efciencies
above 70%.
Figure 7. Maximum Power Output
PEAK PRIMARY CURRENT (A)
V
TRANS
(V)
3751 F07
100
10
20
30
40
50
60
70
80
90
0
1
10
100
P = 20 WATTS
P = 50 WATTS
P = 100 WATTS
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| LT3751EUFD | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PQCC20 |
| LT3751IFE#TRPBF | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO20 |
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