参数资料
型号: LT3757IDD#PBF
厂商: Linear Technology
文件页数: 25/36页
文件大小: 0K
描述: IC REG CTRLR BST FLYBK INV 10DFN
产品培训模块: LT3757 and LT3758 - Boost, Flyback, SEPIC and Inverting Controllers
标准包装: 121
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
电源电压: 2.9 V ~ 40 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 10-WFDFN 裸露焊盘
包装: 管件
LT3757/LT3757A
APPLICATIONS INFORMATION
D MAX =
? V OUT(P – P) = ? I L2 ? ? ESR COUT +
I RMS(CDC) > I O(MAX) ?
InvertingConverter:SwitchDutyCycleandFrequency
For an inverting converter operating in CCM, the duty
cycle of the main switch can be calculated based on the
negative output voltage (V OUT ) and the input voltage (V IN ).
The maximum duty cycle (D MAX ) occurs when the converter
has the minimum input voltage:
V OUT ? V D
V OUT ? V D ? V IN(MIN)
Inverting Converter: Inductor, Sense Resistor, Power
MOSFET, Output Diode and Input Capacitor Selections
The selections of the inductor, sense resistor, power
MOSFET, output diode and input capacitor of an invert-
ing converter are similar to those of the SEPIC converter.
Please refer to the corresponding SEPIC converter sections.
Inverting Converter: Output Capacitor Selection
The inverting converter requires much smaller output
capacitors than those of the boost, flyback and SEPIC
converters for similar output ripples. This is due to the fact
that, in the inverting converter, the inductor L2 is in series
with the output, and the ripple current flowing through the
output capacitors are continuous. The output ripple voltage
is produced by the ripple current of L2 flowing through
the ESR and bulk capacitance of the output capacitor:
? 1 ?
?
? 8 ? f ? C OUT ?
After specifying the maximum output ripple, the user can
select the output capacitors according to the preceding
equation.
The ESR can be minimized by using high quality X5R or
X7R dielectric ceramic capacitors. In many applications,
ceramic capacitors are sufficient to limit the output volt-
age ripple.
The RMS ripple current rating of the output capacitor
needs to be greater than:
I RMS(COUT) > 0.3 ? ? I L2
Inverting Converter: Selecting the DC Coupling Capacitor
The DC voltage rating of the DC coupling capacitor (C DC ,
as shown in Figure 10) should be larger than the maximum
input voltage minus the output voltage (negative voltage):
V CDC > V IN(MAX) – V OUT
C DC has nearly a rectangular current waveform. During
the switch off-time, the current through C DC is I IN , while
approximately –I O flows during the on-time. The RMS
rating of the coupling capacitor is determined by the fol-
lowing equation:
D MAX
1 ? D MAX
A low ESR and ESL, X5R or X7R ceramic capacitor works
well for C DC .
3757afd
25
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