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PDF A8436 Data sheet ( Hoja de datos )
| Número de pieza | A8436 | |
| Descripción | Photoflash Capacitor Charger | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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A8436
Photoflash Capacitor Charger with IGBT Driver
Features and Benefits
▪ Power with 1 Li+ or 2 Alkaline/NiMH/NiCAD batteries
▪ Adjustable output voltage
▪ >75% efficiency
▪ Three levels of switch current limit: 1.0, 1.2, 1.4 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)
Package: 10 pin TDFN/MLP (suffix EJ)
Approximate Scale 1:1
Description
The A8436 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 A8436 integrates a
40 V, DMOS switch that drives the transformer in a flyback
topology, allowing optimized design with tight coupling and
high efficiency. A proprietary control scheme optimizes the
capacitor charging time. Low quiescent current and low
shutdown current further improve system efficiency and
extend battery life.
Three levels of switch current limit are provided: 1.0, 1.2,
and 1.4 A. The level is determined by configuring the ILIM
pin as grounded, floating, or pulled up to IC supply voltage,
respectively.
The CHARGE pin enables the A8436 and starts the charging
of the output capacitor. When the designated output voltage
is reached, the A8436 stops the charging 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 output voltage is reached.
TheA8436 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 A8436 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.
Typical Applications
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
One Li+ battery
VBATT or 3.0 to 5.5 V
T1 D1 VOUT
R5
100 k7
R4
10 k7
C1
0.1 μF
C2
4.7 μF
1.4 A
1.2 A (N.C.)
1.0 A
VIN
ILIM
SW
FB
R6
10 k7
DONE
A8436
CHARGE
TRIGGER
IGBTDRV
R7
10 k7
GND
To IGBT Gate
R1
R2
R3
COUT
Figure 1. Typical circuit with separate power supply to transformer
R5
100 k7
R4
10 k7
C1
0.1 μF
C2
4.7 μF
1.4 A
1.2 A (N.C.)
1.0 A
VIN
ILIM
SW
FB
R6
10 k7
DONE
A8436
CHARGE
TRIGGER
IGBTDRV
R7
10 k7
GND
To IGBT Gate
Figure 2. Typical circuit with single power supply
R1
R2
R3
COUT
A8436-DS, Rev. 3
1 page  
A8436
Photoflash Capacitor Charger with IGBT Driver
Operation Timing Diagram
VUVLO
VIN
CHARGE
SW
Target VOUT
VOUT
DONE
TRIGGER
IGBTDRV
A
B
C
DE
F
Explanation of Events:
A. Start charging by pulling CHARGE to high, provided that VIN is above the VUVLO level.
B. Charging stops when VOUT reaches the target voltage. ¯D¯¯O¯¯N¯¯E¯ goes low, to signal the
completion of the charging process.
C. Start a new charging process with a low-to-high transition at the CHARGE pin.
D. Pull CHARGE to low, to put the controller in low-power standby mode.
E. Charging does not start, because VIN is below VUVLO level when CHARGE goes high.
F. After VIN goes above VUVLO, another low-to-high transition at the CHARGE pin is
required to start charging.
Allegro MicroSystems, Inc.
5
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5 Page 
A8436
Photoflash Capacitor Charger with IGBT Driver
To understand the Timer mode, it is noted that the secondary
winding charge current, ISecondary, decreases linearly at a rate of:
where:
dISecondary =
dt
VOUT
LPrimary N 2
(1)
ISecondary is the secondary side current,
LPrimary is the primary side inductance, and
N is the transformer turns ratio (NSecondary / NPrimary).
As shown in the three panels of figure 4, when the A8436 charges
a fully-discharged photoflash capacitor, ISecondary decreases very
slowly due to the low initial VOUT. The A8436 internal timer
(Timer mode) sets a maximum timeframe of 18 μs for the off-
time as long as the SW node voltage is greater than 1.2 V. When
the off-time passes 18 μs, the internal MOSFET switch is turned
on, initiating the next charging cycle .
Lower input current offers the advantage of a longer battery
lifetime. For faster charging time, however, use the highest
current limit.
ISWLIM may be adjusted during charging. Figure 5 shows a
waveform of ISWLIM being adjusted during charging. ISWLIM is
lowered from 1.4 to 1.2 A, and charging slows slightly at the
lower current level.
ISWLIM = 1.4 A
ISWLIM = 1.2 A
Input Current Limiting
The peak input current, ISWLIM , can be set to three levels by
configuring the ILIM pin:
IIN(Avg)
VOUT
ISWLIM Setting
(A)
1.0
1.2
1.4
ILIM Pin
Connection
External ground
Float
Pull up to IC supply voltage
with a 1 to 10 kΩ resistor
Figure 5. Reducing ISWLIM during charging
Allegro MicroSystems, Inc.
11
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet A8436.PDF ] | |
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