参数资料
型号: MAX5019ESA+T
厂商: Maxim Integrated Products
文件页数: 11/14页
文件大小: 0K
描述: IC REG CTRLR FLYBK ISO PWM 8SOIC
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 302kHz
占空比: 85%
电源电压: 13 V ~ 110 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
包装: 带卷 (TR)
Current-Mode PWM Controllers with Integrated
Startup Circuit
V OUT ? V REF ? 1 + 1 ?
1)  36V ≤ V IN ≤ 72V, V OUT = 5V, I OUT = 10A, V RIPPLE ≤
50mV
2) To set the output voltage calculate the values of
resistors R1 and R2 according to the following
equation:
? R ?
? R 2 ?
R 1 // R 2 << 50 k ?
V REF = V SS_ SHDN ? 2 . 4 V
of a forward converter is not delivered to the load
and must be returned back to the input; this is
accomplished with the reset winding.
The transformer primary to secondary leakage
inductance should be less than 1μH. Note that all
leakage energy will be dissipated across the MOS-
FET. Snubber circuits may be used to direct some or
all of the leakage energy to be dissipated across a
resistor.
To calculate the minimum duty cycle (D MIN ) use the
following equation:
? V IN_MAX × N ? - V D1
where  V REF is  the  reference  voltage  of  the  shunt
regulator, and R 1 and R 2 are the resistors shown in
Figures 2 and 3.
D MIN =
? N S ?
? P ?
V OUT
3) The turns ratio of the transformer is calculated based
on the minimum input voltage and the lower limit of
the maximum duty cycle for the MAX5020 (44%). To
enable the use of MOSFETs with drain-source
breakdown voltages of less than 200V use the
MAX5020 with the 50% maximum duty cycle.
Calculate the turns ratio according to the following
where V IN_MAX is the maximum input voltage (72V).
4) The reset winding turns ratio (N R /N P ) needs to be
low enough to guarantee that the entire energy in
the transformer is returned to V+ within the off cycle
at the maximum duty cycle. Use the following equa-
tion to determine the reset winding turns ratio:
equation:
N S
N P
V OUT + ( V D1 × D MAX )
D MAX × V IN_MIN
where:
N R ≤ N P ×
1-D MAX
D MAX ′
where:
N S /N P = Turns ratio (N S is the number of secondary
turns and N P is the number of primary turns).
N R /N P = Reset winding turns ratio.
D MAX ’ = Maximum value of Maximum Duty Cycle.
V OUT = Output voltage (5V).
V D1 = Voltage drop across D1 (typically 0.5V for
power Schottky diodes).
N R ≤ 1 4 ×
1- 0.5
0.5
= 14
N S 5V + ( 0.5V × 0.44 )
0 . 44 × 36 V
V DSMAX ≥ V IN_MAX × ? 1 +
D MAX = Minimum value of maximum operating duty
cycle (44%).
V IN_MIN = Minimum Input voltage (36V).
In this example:
≥ = 0 . 330
N P
Choose N P based on core losses and DC resis-
tance. Use the turns ratio to calculate N S , rounding
up to the nearest integer. In this example N P = 14
and N S = 5.
For a forward converter choose a transformer with a
magnetizing inductance in the neighborhood of
200μH. Energy stored in the magnetizing inductance
Round N R to the nearest smallest integer.
The turns ratio of the reset winding (N R /N P ) will
determine the peak voltage across the N-channel
MOSFET.
Use the following equation to determine the maxi-
mum drain-source voltage across the N-channel
MOSFET:
? N P ?
?
? N R ?
V DSMAX = Maximum MOSFET drain-source voltage.
V IN_MAX = Maximum input voltage.
______________________________________________________________________________________
11
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