|
|
PDF A8438 Data sheet ( Hoja de datos )
| Número de pieza | A8438 | |
| Descripción | Photoflash Capacitor Charger | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de A8438 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
|
No Preview Available !
www.DataSheet4U.com
Package EJ:
MLP/TDFN, 3 × 3 mm
0.75 mm nominal height
A8438
Photoflash Capacitor
Charger with IGBT Driver
Approximate Scale 1:1
The A8438 is a highly integrated IC that charges
photoflash capacitors for digital and film cameras. It
also features an integrated IGBT driver that facilitates
the flash discharge function and saves board space.
To charge the photoflash capacitor, the A8438
integrates a 40 V, DMOS switch that drives the trans-
former in a flyback topology, allowing optimized
design with tight coupling and high efficiency. A pro-
prietary control scheme optimizes the capacitor charg-
ing time. Low quiescent current and low shutdown
current further improve system efficiency and extend
battery life.
Three levels of switch current limit are provided:
1.6, 1.8, and 2.0 A. The level is determined by config-
uring the ILIM pin as grounded, floating, or pulled up
to IC supply voltage, respectively.
The CHARGE pin enables the A8438 and starts the
charging of the output capacitor. When the designated
output voltage is reached, the A8438 stops the charg-
ing until the CHARGE pin is toggled again. Pulling
the CHARGE pin low stops charging. The D¯¯¯O¯¯N¯¯E¯ pin
is an open-drain indicator of when the designated out-
put voltage is reached.
The A8438 can be used with two Alkaline/NiMH/
NiCAD or one single-cell Li+ battery connected to the
transformer primary. Connect the VIN pin to a 3.0 to
5.5 V supply, which can be either the system rail or the
Li+ battery, if used.
The A8438 is available in a very low profile
(0.75 mm) 10-terminal 3×3 mm MLP/TDFN package,
making it ideal for space-constrained applications. It is
lead (Pb) free, with 100% matte-tin leadframe plating.
FEATURES
Power with 1 Li+ or 2 Alkaline/NiMH/NiCAD batteries
Adjustable output voltage
>75% efficiency
Three levels of switch current limit: 1.6, 1.8, 2.0 A
Fast charge time
Charge complete indication
Integrated IGBT driver with trigger
No primary-side Schottky diode needed
Low-profile package (0.75 mm nominal height)
APPLICATIONS
Digital camera flash
Film camera flash
Cell phone flash
Emergency strobe light
VBIAS 3.0 to 5.5 V
Two Alkaline/NiMH/NiCAD or one Li+ battery
or 1.5 to 5.5 V
VBATT
T1
D1 VOUT
R5
100 kΩ
R4
10 kΩ
C1
0.1 μF
C2
4.7 μF
2.0 A
1.8 A (N.C.)
1.6 A
VIN
ILIM
CHARGE
DONE
SW
FB
A8438
TRIGGER
IGBTDRV
GND
To IGBT Gate
R1
R2
R3
COUT
Figure 1. Typical circuit with separate power supply to transformer
One Li+ battery
VBATT or 3.0 to 5.5 V
T1 D1 VOUT
R5
100 kΩ
R4
10 kΩ
C1
0.1 μF
C2
4.7 μF
2.0 A
1.8 A (N.C.)
1.6 A
VIN
ILIM
CHARGE
DONE
SW
FB
A8438
TRIGGER
IGBTDRV
GND
To IGBT Gate
R1
R2
R3
COUT
Figure 2. Typical circuit with single power supply
A8438-DS, Rev. 1
1 page  
A8438 Photoflash Capacitor Charger with IGBT Driver
Performance Characteristics
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
Symbol
C1
C4
t
Conditions
Parameter
VOUT
IBATT(Avg)
time
Parameter
VBATT
VBIAS
COUT
Units/Division
50 V
200 mA
1s
Value
3.6 V
3.3 V
100 μF
C4
C1
Symbol
C1
C4
t
Conditions
Parameter
VOUT
IBATT(Avg)
time
Parameter
VBATT
VBIAS
COUT
Units/Division
50 V
200 mA
1s
Value
4.5 V
3.3 V
100 μF
C4
C1
t
t
VOUT
IBATT
VOUT
IBATT
Symbol
C1
C4
t
Conditions
Parameter
VOUT
IBATT(Avg)
time
Parameter
VBATT
VBIAS
COUT
Units/Division
50 V
200 mA
1s
Value
5.0 V
3.3 V
100 μF
C4
C1
A8438-DS, Rev. 1
VOUT
IBATT
t
Allegro MicroSystems, Inc.
5
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5 Page 
A8438 Photoflash Capacitor Charger with IGBT Driver
Applications Information
Transformer Design
Turns Ratio. The minimum transformer turns ratio, N,
(Secondary:Primary) should be chosen based on the following
formula:
N ≥ VOUT + VD_Drop
40 −VBATT
(2)
where:
VOUT (V) is the required output voltage level,
VD_Drop (V) is the forward voltage drop of the output diode(s),
VBATT (V) is the transformer battery supply, and
40 (V) is the rated voltage for the internal MOSFET switch,
representing the maximum allowable reflected voltage from the
output to the SW pin.
For example, if VBATT is 3.5 V and VD_Drop is 1.7 V (which could
be the case when two high voltage diodes were in series), and the
desired VOUT is 320 V, then the turns ratio should be at least 8.9.
In a worst case, when VBATT is highest and VD_Drop and VOUT are
at their maximum tolerance limit, N will be higher. Taking VBATT
= 5.5 V, VD_Drop = 2 V, and VOUT = 320 V × 102 % = 326.4 V as
the worst case condition, N can be determined to be 9.5.
In practice, always choose a turns ratio that is higher than the
calculated value to give some safety margin. In the worst case
example, a minimum turns ratio of N = 10 is recommended.
Primary Inductance. The A8438 has a minimum switch off-time,
tOFF(min) , of 300 ns, to ensure correct SW node voltage sensing.
As a loose guideline when choosing the primary inductance,
LPrimary (μH), use the following formula:
LPrimary
≥
300 ×10−9 ×VOUT
N × ISWLIM
.
(3)
Ideally, the charging time is not affected by transformer primary
inductance. In practice, however, it is recommended that a
primary inductance be chosen between 10 μH and 20 μH. When
LPrimary is less than 10 μH, parasitic elements associated with
flyback from the transformer lead to lower efficiency and longer
charging time. When LPrimary is greater than 20 μH, the rating
of the transformer must be dramatically increased to handle the
required power density, and the series resistances are usually
higher. A design that is optimized to achieve a small footprint
solution would have an LPrimary of 12 to 14 μH, with minimized
leakage inductance and secondary capacitance, and minimized
primary and secondary series resistance. Please refer to the table
Recommended Components for more information.
Leakage Inductance and Secondary Capacitance. The trans-
former design should minimize the leakage inductance to ensure
the turn-off voltage spike at the SW node does not exceed the
40 V limit. An achievable minimum leakage inductance for this
application, however, is usually compromised by an increase in
parasitic capacitance. Furthermore, the transformer secondary
capacitance should be minimized. Any secondary capacitance is
multiplied by N2 when reflected to the primary, leading to high
initial current swings when the switch turns on, and to reduced
efficiency.
VBIAS 3.0 to 5.5 V
Two Alkaline/NiMH/NiCAD or one Li +
VBATT 1.5 to 5.5 V
T1
D1
VOUT
R5
100 kΩ
R4
10 kΩ
C1
0.1 μF
C2
4.7 μF
VIN
ILIM
CHARGE
DONE
SW
FB
A8436
TRIGGER
IGBTDRV
GND
To IGBT Gate
R1
150 kΩ
R2
150 kΩ
R3
1.2 kΩ
COUT
303 V
Figure 6. Typical circuit for photoflash application. Configured for ISWLIM of 2.0 A.
A8438-DS, Rev. 1
Symbol
C1
C2
D1
T1
R1, R2
R3
R4, R5
Rating
0.1 μF, X5R or X7R, 10 V
4.7 μF, X5R or X7R, 10 V
Fairchild Semiconductor BAV23S
(dual diode connected in series)
TDK LDT565630T-041,
LPrimary = 4.7 μH, N = 10.2
1206 Resistor, 1 %
0603 Resistor, 1 %
Pull-up resistors
Allegro MicroSystems, Inc.
11
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet A8438.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| A8430 | White LED Driver Constant Current Step-up Converter | Allegro MicroSystems |
| A8431 | White LED Driver Constant Current Step-up Converter | Allegro MicroSystems |
| A8434 | 6-Channel High Efficiency Charge Pump White LED Driver | Allegro MicroSystems |
| A8435 | High Efficiency Charge Pump White LED Driver | Allegro MicroSystems |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |