参数资料
型号: LT3759HMSE#TRPBF
厂商: Linear Technology
文件页数: 20/32页
文件大小: 0K
描述: IC REG CTRLR BST INV PWM 12-MSOP
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
电源电压: 1.6 V ~ 42 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 150°C
封装/外壳: 12-TSSOP (0.118",3.00mm 宽)裸露焊盘
包装: 带卷 (TR)
LT3759
APPLICATIONS INFORMATION
≥ I O(MAX) ?
I RMS(COUT),DISCONTINUOUS
V OUT + V D
V IN(MIN) + V OUT + V D
I RMS(CIN),DISCONTINUOUS ≥
P OUT(MAX) 4 ? (3 ? D MAX )
V IN(MIN) ? η
I L1(MAX) = I IN(MAX) = I O(MAX)
The RMS ripple current rating of the output capacitors
in discontinuous operation can be determined using the
following equation:
4 ? (3 ? D2)
3 ? D2
Flyback Converter: Input Capacitor Selection
The input capacitor in a flyback converter is subject to
a large RMS current due to the discontinuous primary
current. To prevent large voltage transients, use a low
ESR input capacitor sized for the maximum RMS current.
The RMS ripple current rating of the input capacitors in
discontinuous operation can be determined using the
following equation:
?
3 ? D MAX
SEPIC CONVERTER APPLICATIONS
The LT3759 can be configured as a SEPIC (single-ended
primary inductance converter), as shown in Figure 1. This
topology allows for the input to be higher, equal, or lower
than the desired output voltage. The conversion ratio as
a function of duty cycle is:
The maximum duty cycle (D MAX ) occurs when the converter
has the minimum input voltage:
D MAX =
SEPIC Converter: Inductor and Sense Resistor
Selection
As shown in Figure 1, the SEPIC converter contains two
inductors: L1 and L2. L1 and L2 can be independent, but can
also be wound on the same core, since identical voltages
are applied to L1 and L2 throughout the switching cycle.
For the SEPIC topology, the current through L1 is the
converter input current. Based on the fact that, ideally, the
output power is equal to the input power, the maximum
average inductor currents of L1 and L2 are:
D MAX
1 – D MAX
I L2(MAX) = I O(MAX)
In a SEPIC converter, the switch current is equal to I L1 +
I L2 when the power switch is on, therefore, the maximum
average switch current is defined as:
I SW(MAX) = I L1(MAX) + I L2(MAX)
V OUT + V D
V IN
=
D
1 ? D
= I O(MAX) ?
1
1 – D MAX
I SW(PEAK) = ? 1 + ? ? I O(MAX) ?
Incontinuousconductionmode(CCM).
In a SEPIC converter, no DC path exists between the input
and output. This is an advantage over the boost converter
for applications requiring the output to be disconnected
from the input source when the circuit is in shutdown.
and the peak switch current is:
? χ ?
? 2 ?
1
1 – D MAX
SEPIC Converter: Switch Duty Cycle and Frequency
For a SEPIC converter operating in CCM, the duty cycle
of the main switch can be calculated based on the output
voltage (V OUT ), the input voltage (V IN ) and diode forward
voltage (V D ).
The constant χ in the preceding equations represents the
percentage peak-to-peak ripple current in the switch, rela-
tive to I SW(MAX) , as shown in Figure 8. Then, the switch
ripple current ΔI SW can be calculated by:
D I SW = c ? I SW(MAX)
3759fc
20
For more information www.linear.com/3759
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