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| 型号： | A8740EEETR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 14/18页 |
| 文件大小： | 0K |
| 描述： | IC PHOTOFLASH CAP CHARGER 8DFN |
| 标准包装： | 24,000 |
| 拓扑： | 交直流离线开关，反激式，PFC |
| 输出数： | 1 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 闪灯/白光 |
| 电源电压： | 1.5 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-UFDFN 裸露焊盘 |
| 供应商设备封装： | 8-DFN-EP（2x2） |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 85°C |
A8740
Ultra Small Mobile Phone Xenon Photoflash
Capacitor Charger with IGBT Driver
Effects of Input Filters
Input Capacitor Selection
Ceramic capacitors with X5R or X7R dielectrics are recom-
mended for the input capacitor, C IN . During initial Timer mode
the device operates with 18 μ s off-time. The resonant period
V OUT
V BAT
caused by input filter inductor and capacitor should be at least
2 times greater or smaller than the 18 μ s Timer period, to reduce
input ripple current during this period. The typical input LC filter
is shown in figure 7.
The resonant period is given by:
C2
C3
C1
I BAT
T res = 2
( L × C IN ) 1/2 .
Figure 8. Input current waveforms with Li+ battery connected by
The effects of input filter components are shown in figures 8, 9,
and 10. It is recommended to use at least 10 μ F / 6.3 V to decou-
ple the battery input, VBAT , at the primary of the transformer.
Decouple the VIN pin using 0.1 μ F / 6.3 V bypass
capacitor.
Output Diode Selection
5-in. wire and decoupled by 4.7 μ F capacitor, C OUT = 100 μ F,
V IN = V BAT = 3.6 V, Ch1: V OUT = 50 V/div, Ch2: V BAT = 2 V/div,
Ch3: I BAT = 750 mA/div, t = 1 s/div
V OUT
V BAT
Choose rectifying diodes, D1, to have small parasitic capacitance
(short reverse recovery time) while satisfying the reverse voltage
and forward current requirements. The peak reverse voltage of
C2
C3
I BAT
the diodes, V DPeak , occurs when the internal MOSFET switch is
closed. It can be calculated as:
V DPeak = V OUT + N × V BAT .
The peak current of the rectifying diode, I DPeak , is calculated as:
I DPeak = I PRIMARY_Peak / N .
LIN
C1
Figure 9. Input current waveforms with Li+ battery connected through
4.7 μ H inductor and 4.7 μ F capacitor, C OUT = 100 μ F, V IN = V BAT = 3.6 V,
Ch1: V OUT = 50 V/div, Ch2: V BAT = 2 V/div, Ch3: I BAT = 300 mA/div,
t = 1 s/div
V OUT
V BAT
+
VBAT
CIN
A8740
C2
C3
I BAT
C1
Figure 7. Typical input section with input inductance (inductance, L IN , may
be an input filter inductor or inductance due to long wires in test setup)
Figure 10. Input current waveforms with Li+ battery connected through
4.7 μ H inductor and 10 μ F capacitor, C OUT = 100 μ F, V IN = V BAT = 3.6 V,
Ch1: V OUT = 50 V/div, Ch2: V BAT = 2 V/div, Ch3: I BAT = 300 mA/div,
t = 1 s/div
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
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