A8837 Datasheet, PDF (1/11 Pages) Allegro MicroSystems – Photoflash Capacitor Charger with IGBT Driver

A8837
Photoflash Capacitor Charger with IGBT Driver
Features and Benefits
▪ Power with 1 Li+ or 2 Alkaline/NiMH/NiCAD batteries
▪ Eight-level, digitally-programmable current limits from
700 mA to 2 A
▪ Voltage sensing feedback before output diode for low
leakage
▪ Adjustable output voltage
▪ No primary-side Schottky diode needed
▪ Integrated IGBT driver with trigger
▪ Charge complete indication
▪ >75% efficiency
▪ Low-profile (0.75 mm high) 3 mm × 3 mm MLP/TDFN
10-contact package
Package: 10-contact TDFN/MLP (suffix EJ)
Approximate Scale
Description
The A8837 is a highly integrated IC that charges photoflash
capacitors for digital and film cameras.An integrated MOSFET
switch drives the transformer in a flyback topology. It also
features an integrated IGBT driver that facilitates the flash
discharge function and saves board space.
The CHARGE pin enables the A8837 and starts the charging
of the output capacitor. When the designated output voltage is
reached, the A8837 stops the charging until the CHARGE pin
is toggled again. The ¯D¯¯¯O¯¯¯N¯¯E¯ pin is an open-drain indicator of
when the designated output voltage is reached.
The peak current limit can be adjusted to eight different levels
between 700 mA and 2 A, by clocking the CHARGE pin.
This allows the user to operate the flash even at low battery
voltages.
TheA8837 can be used with twoAlkaline/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 A8837 is available in a very low profile (0.75 mm)
10-contact 3 mm × 3 mm MLP/TDFN package, making it
ideal for space-constrained applications. It is lead (Pb) free,
with 100% matte-tin leadframe plating.
Applications include the following:
▪ Digital camera flash
▪ Film camera flash
▪ Cell phone flash
▪ Emergency strobe light
V_BIAS 3.0 to 5.5 V
V_BATT 1.5 to 5.5 V
N =10.2
T1
R4
100 k7
C1
0.1 μF
VIN
SW
CHARGE
R5
10 k7
FB
A8837
DONE
TRIGGER
IGBTDRV
R6
10 k7
GND
To IGBT Gate
Typical Applications
D1
R1
150 k7
1%
R2
150 k7
1%
VOUT
COUT
100 μF
330 V
R3
1.20 k7
1%
C1, C2:
X5R or X7R, 10 V
V_BIAS 3.0 to 5.5 V
T1
R4
100 k7
C1
0.1 μF
C2
4.7 μF
VIN
SW
CHARGE
R5
10 k7
FB
A8837
DONE
TRIGGER
IGBTDRV
R6
10 k7
GND
To IGBT Gate
D1
VOUT
R1
150 k7
R2
150 k7
COUT
R3
1.20 k7
Figure 1. Typical circuit with separate power supply to transformer
A8837-DS
Figure 2. Typical circuit with single power supply