A8438 Datasheet, PDF (1/13 Pages) Allegro MicroSystems – Photoflash Capacitor Charger with IGBT Driver

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
V_BIAS 3.0 to 5.5 V
Two Alkaline/NiMH/NiCAD or one Li+ battery
or 1.5 to 5.5 V
V_BATT
T1
D1
VOUT
C1
0.1 μF
C2
4.7 μF
R1
R5
R4
100 kΩ
10 kΩ
R2
2.0 A
VIN
SW
1.8 A (N.C.)
ILIM
1.6 A
FB
CHARGE
A8438
R3
DONE
TRIGGER
IGBTDRV
GND
To IGBT Gate
COUT
Figure 1. Typical circuit with separate power supply to transformer
One Li+ battery
V_{BATT or 3.0 to 5.5 V}
T1
D1
VOUT
C1
0.1 μF
C2
4.7 μF
R1
R5
R4
100 kΩ
10 kΩ
R2
2.0 A
VIN
SW
1.8 A (N.C.)
ILIM
1.6 A
FB
CHARGE
A8438
R3
DONE
TRIGGER
IGBTDRV
GND
To IGBT Gate
COUT
Figure 2. Typical circuit with single power supply
A8438-DS, Rev. 1