参数资料
型号: A4401KL-T
厂商: Allegro Microsystems Inc
文件页数: 8/17页
文件大小: 0K
描述: IC QUASI FLYBACK CONVERTER 8SOIC
标准包装: 98
显示器类型: 真空荧光 (VF)
电流 - 电源: 2.3mA
电源电压: 7 V ~ 40 V
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOICN
包装: 管件
A4401
Automotive Quasi-Resonant Flyback Control IC
Switching Turn-On Losses The turn-on losses are
determined by the amount of energy the resonant
at least 20% of the maximum V DIODE voltage, calcu-
lated as follows:
capacitor, C11, has to discharge into the MOSFET. At
low battery voltage, the resonant swing should force
V DIODE = V BAT (max) ×
N S1
N P
+ V OUT
.
(14)
the volts across the capacitor to only a few volts, mak-
ing this loss negligible.
Total Losses The total MOSFET power loss can be
estimated as follows:
The maximum average current through the diode is
simply the maximum load current. The diode should
be rated to handle this current with some margin.
In addition, the diode should be able to handle the
power dissipation. The majority of the power loss is
P TOTAL = P STATIC + P TURNOFF
.
(11)
simply the static loss:
The thermal resistance, R θ JA , can be determined by
P STATIC = V f × I LOAD
.
(15)
T J – T A
R θ JA =
(12)
V DS = ? V OUT × ? + V BAT (max)
N OUT ? ?
?
two methods. One is by estimating a maximum junc-
tion temperature, T J (max). The other is to test for the
operating junction temperature, using the given device
package mounted on a printed circuit board with cop-
per trace area connected to the device. R θ JA is then
calculated as follows:
.
P TOTAL
The drain-to-source rating, V DS , is the sum of
the maximum input voltage, V BAT (max), plus the
reflected output voltage. Adequate margin should also
be added, to allow for tolerancing effects and parasitic
voltage ring. It can be calculated as follows:
? N P ?
.
(13)
D2, D3, and D4 Output Diodes Selection
For the low voltage outputs such as the filament sup-
ply, it is recommended that a Schottky diode be used.
For the higher voltage rails, ultrafast rectifier diodes
are recommended.
For each output, estimate the maximum reverse volt-
age, V RRM , and the maximum average current that the
diode is subjected to. The V RRM rating should exceed
The forward voltage drop, V f , can be found from the
diode characteristics at maximum load.
C1 Input Capacitor Selection
In the interests of cost and performance, it is recom-
mended that ultralow impedance electrolytic capaci-
tors be used. The ratio of the source impedance to the
impedance of the input capacitor will determine how
much of the input current is drawn from the input
capacitor. For example, if the source impedance is
relatively high, then the input capacitor would have
to supply the triangular current that flows through the
primary winding, the MOSFET Q1, and the current
sense resistor. This rms current was worked out in the
Current Sense Resistor Selection section.
Electrolytic capacitors experience heating effects
caused by the rms current flowing through the ESR
of the device. The maximum rms current is normally
quoted at 100 kHz and 105°C. Frequency correc-
tion factors for the ripple current are provided when
the operating frequencies are less than 100 kHz. A
50 VDC rating should be adequate for most applica-
tions.
C4, C6, and C8 Output Capacitors Selection
The overall equivalent capacitance on the output
should not be less 22 μ F (see Control Loop section
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
8
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