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| 型号： | A8439EEJTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC CHARGER PHOTO FLASH 10-MLP |
| 标准包装： | 1 |
| 应用： | 照相机闪光灯电容器充电器 |
| 电流 - 电源： | 1.5mA |
| 电源电压： | 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： | 10-WFDFN 裸露焊盘 |
| 供应商设备封装： | 10-TDFN/MLP（3x3） |
| 包装： | 标准包装 |
| 产品目录页面： | 1142 (CN2011-ZH PDF) |
| 其它名称： | 620-1203-6 |
A8439
Photoflash Capacitor Charger with IGBT Driver and Refresh
Functional Description
Overview
The A8439 is a photoflash capacitor charger control IC with
adjustable input current limiting and automatic refresh. It also
integrates an IGBT driver for strobe operation of the flash tube,
dramatically saving board space in comparison to discrete solu-
tions for strobe flash operation. The control logic is shown in the
functional block diagram.
The charging operation of the A8439 is started by a low-to-high
signal on the CHARGE pin, provided that V IN is above V UVLO
level. If CHARGE is already high before V IN reaches V UVLO ,
another low-to-high transition on the CHARGE pin is required
to start the charging. The primary peak current is set by input
clock signals from the CHARGE pin. 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 BATT , 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
recharging 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 output voltage, V OUT , is sensed by a resistor string, R 1 , R 2 ,
and R 3 (see application circuit diagrams), connected between
the positive terminal of the output capacitor and ground. This
resistor string forms a voltage divider that feeds back to the FB
pin. The resistors must be sized to achieve a desired output volt-
age level based on a typical value of 1.205 V at the FB pin. As
soon as V OUT reaches the desired value, the charging process is
terminated. The A8439 automatically starts a new charging cycle
when the internal voltage sensing circuit detects a 10 % drop in
the output voltage. Toggling the CHARGE pin can also start a
refresh operation.
Auto-Refresh
The A8439 features auto-refresh when the feedback resistor
network is connected at the output. Auto-refresh initiates when
the output voltage drops to ≈ 90 % of the set stop voltage of the
resistor network. The operation is shown in figure 3.
Input Current Limiting
The peak current limit can be adjusted to eight different levels,
from 270 mA to 1.4 A, by clocking the CHARGE pin. An inter-
nal digital circuit decodes the input clock signals to a counter,
which sets the charging time. This flexible scheme allows the
user to operate the flash circuit according to different battery
input voltages. The battery life can be effectively extended by
setting a lower current limit at low battery voltages.
Figure 4 shows the ILIM clock timing scheme protocol. The
total ILIM setup time, t ILIM(SU) , denotes the time needed for the
Figure 3. Auto-refresh waveform of A8439.
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
9
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