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| 型号： | A8739EEETR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 14/23页 |
| 文件大小： | 0K |
| 描述： | IC PHOTOFLASH CHARGER 8-DFN |
| 标准包装： | 1 |
| 应用： | 照相机闪光灯电容器充电器，Xenon |
| 电流 - 电源： | 2mA |
| 电源电压： | 2.3 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 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（2x2） |
| 包装： | 标准包装 |
| 其它名称： | 620-1365-6 |
A8739
Ultra-Small Mobile Adjustable Xenon Photoflash
Capacitor Charger with IGBT Driver
Functional Description
General Operation Overview
The charging operation is started by a low-to-high signal on the
CHARGE pin, provided that V IN is above the V UVLO level. It is
strongly recommended to keep the CHARGE pin at logic low
during power-up. After V IN exceeds the UVLO level, a low-
to-high transition on the CHARGE pin is required to start the
charging.
The ˉDˉˉ ˉOˉ ˉˉNˉ ˉEˉ open-drain indicator is pulled low when CHARGE
is high and target output voltage is reached. The primary peak
current is set to 1.5 A by default, but it can be programmed from
1.5 A down to approximately 0.44 A in 15 steps. See the ILIM
Programming section for details.
When a charging cycle is initiated, the transformer primary side
current, I PRIMARY , ramps-up linearly at a rate determined by the
combined effect of the battery voltage, V BAT , and the primary
side inductance, L PRIMARY . When I PRIMARY reaches the current
limit, I SWLIM , the internal MOSFET is turned off immediately,
allowing the energy to be pushed into the photoflash capacitor,
C OUT , from the secondary winding. The secondary side current
drops linearly as C OUT charges. The switching cycle starts again,
either after the transformer flux is reset, or after a predetermined
time period, t OFF (max) (18 μ s), whichever occurs first.
The A8739 senses output voltage indirectly on primary side. This
eliminates the need for high voltage feedback resistors required
for secondary sensing. Flyback converter stops switching when
output voltage reaches:
V OUT = K × N – V d ,
Where:
K = 31.5 V typically,
Timer Mode and Fast Charging Mode
The A8739 achieves fast charging times and high efficiency by
operating in discontinuous conduction mode (DCM) through
most of the charging process. The relationship of Timer mode and
Fast Charging mode is shown in figure 2.
The IC operates in Timer mode when beginning to charge a com-
pletely discharged photoflash capacitor, usually when the output
voltage, V OUT , is less than approximately 30 V (depending on
transformer used). Timer mode is a fixed period, 18 μ s, off-time
control. One advantage of having Timer mode is that it limits the
initial battery current surge and thus acts as a “soft-start.” A time-
expanded view of a Timer mode interval is shown in figure 3.
V OUT
I IN
Figure 2. Timer mode and Fast Charging mode: V OUT = 50 V/div,
I IN = 100 mA/div., V IN = V BAT = 3.6 V, C OUT = 100 μ F / 330 V, ILIM = 1.0 A,
and t = 1 s/div.
V d is the forward drop of the output diode (approximately 2 V),
and
N is transformer turns ratio.
Switch On-Time and Off-Time Control
The A8739 implements an adaptive on-time/off-time control. On-
time duration, t on , is approximately equal to
t on = I SWlim × L PRIMARY / V BAT .
Off-time duration, t off , depends on the operating conditions
during switch off-time. The A8739 applies two charging modes:
Fast Charging mode and Timer mode, according to the conditions
described in the next section.
C4
C2,C3
C1
Figure 3. Expanded view of Timer mode: V OUT ≤ 10 V, V BAT = 5.5 V,
Ch1: V OUT = 20 V / div., Ch2: V BAT = 5 V / div., Ch3: V SW = 5 V / div.,
Ch4: I SW = 500 mA / div., t = 5 μ s / div.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
I SW
V SW
V BAT
V OUT
13
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相关代理商/技术参数 |
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| A8740EEETR-T | 功能描述:IC PHOTOFLASH CAP CHARGER 8DFN RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:6,000 系列:- 恒定电流:- 恒定电压:- 拓扑:开路漏极，PWM 输出数:4 内部驱动器:是 类型 - 主要:LED 闪烁器 类型 - 次要:- 频率:400kHz 电源电压:2.3 V ~ 5.5 V 输出电压:- 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘 供应商设备封装:8-HVSON 包装:带卷 (TR) 工作温度:-40°C ~ 85°C 其它名称:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
| A874C | 功能描述:通用继电器 RELAY RoHS:否 制造商:Omron Electronics 触点形式:1 Form A (SPST-NO) 触点电流额定值:150 A 线圈电压:24 VDC 线圈电阻:144 Ohms 线圈电流:167 mA 切换电压:400 V 安装风格:Chassis 触点材料: |
| A874L | 功能描述:通用继电器 CONTACTOR 3 PST RoHS:否 制造商:Omron Electronics 触点形式:1 Form A (SPST-NO) 触点电流额定值:150 A 线圈电压:24 VDC 线圈电阻:144 Ohms 线圈电流:167 mA 切换电压:400 V 安装风格:Chassis 触点材料: |
| A-874L | 制造商:MA-COM 制造商全称:M/A-COM Technology Solutions, Inc. 功能描述:A-874L 3PST, 335 Amps, 200 VAC, 400 Hz |
| A874WA1 | 功能描述:通用继电器 RELAY RoHS:否 制造商:Omron Electronics 触点形式:1 Form A (SPST-NO) 触点电流额定值:150 A 线圈电压:24 VDC 线圈电阻:144 Ohms 线圈电流:167 mA 切换电压:400 V 安装风格:Chassis 触点材料: |
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