A8438-DS, Rev. 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.
Photoflash Capacitor
Charger with IGBT Driver
A8438
Package EJ:
MLP/TDFN, 3 × 3 mm
0.75 mm nominal height
FEATURES
APPLICATIONS
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)
Digital camera flash
Film camera flash
Cell phone flash
Emergency strobe light
Approximate Scale 1:1
Figure 1. Typical circuit with separate power supply to transformer
Figure 2. Typical circuit with single power supply
To IGBT Gate
kΩ
COUT
VOUT
D1T1
R1
R2
R3
R4
100 kΩ
R5
10
One Li+ battery
or 3.0 to 5.5 V
VBATT
C2
4.7 μF
C1
0.1 μF
2.0 A
1.8 A (N.C.)
1.6 A
A8438
CHARGE
GND
FB
SW
TRIGGER IGBTDRV
DONE
ILIM
VIN
2.0 A
1.8 A (N.C.)
1.6 A
+
To IGBT Gate
kΩ
COUT
V
OUT
D1
T1
R1
R2
R3
R4
100 kΩ
R5
10
V
BATT
Two Alkaline/NiMH/NiCAD or one Li+ battery
or 1.5 to 5.5 V
VBIAS 3.0to5.5V
C2
4.7 μF
C1
0.1 μF
A8438
CHARGE
GND
FB
SW
TRIGGER IGBTDRV
DONE
ILIM
VIN
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
2
Functional Block Diagram
VIN
VIN
S
W
CHARGE
GND
CMP2
ILIM
DONE
FB
Q
ILIM Decoder Adjustable
Reference
IGBTDRV
TRIGGER
1.2 V 40 V
DMOS
Q
Q
SET
CLR
S
R
Q
QSET
CLR
S
R
CMP3
CMP1
1.2 V
ILIM
Comparator
DCM
Comparator
H → L
Triggered Timer
Control Logic
Enable
18 μs
One-Shot
Terminal List Table
Ab so lute Max i mum Rat ings
10
9
8
7
6
ILIM
FB
DONE
TRIGGER
SW
1
2
3
4
5
NC
IGBTDRV
VIN
GND
CHARGE
Device Pin-out Diagram
RθJA = 45 °C/W, on a 4-layer board. Additional information is
available on the Allegro Web site.
Package Thermal Characteristics
Number Name Function
1 NC No connection
2 IGBTDRV IGBT driver gate drive output
3 VIN Power supply input
4 GND Device ground
5 CHARGE Charging enable; set to low to
power-off the A8438
6SW
Switch, internally connected to the
DMOS power FET drain
7 TRIGGER Strobe signal input
8¯D¯ ¯O¯ ¯N¯ ¯E¯
Open drain, when pulled low by
internal MOSFET, indicates that
charging target level has been
reached
9 FB Output voltage feedback
10 ILIM Switch current limit setting; sets
three discreet levels
Input or Output Voltage
SW pin, VSW............................................................ –0.3 to 40 V
IGBTDRV pin, VIGBTDRV.............................. –0.3 to VIN + 0.3 V
FB pin, VFB ............................................................... –0.3 to VIN
All other pins, Vx...................................................... –0.3 to 7 V
Operating Ambient Temperature, TA ................................ –40°C to 85°C
Maximum Junction Temperature, TJ(max) ........................................ 150°C
Storage Temperature, TS
.............................................. –55°C to 150°C
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
3
ELECTRICAL CHARACTERISTICS Typical values at TA = 25°C and VIN = 3.3 V (unless otherwise noted)
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Supply Voltage* VIN 3 – 5.5 V
Supply Current IIN
Charging – 5 – mA
Charging done – 1 10 μA
Shutdown (VCHARGE
= 0 V, VTRIGGER
= 0 V) – 0.01 1 μA
Primary Side Current Limit ISWLIM
VILIM = 0 V – 1.6 – A
ILIM pin floating 1.6 1.8 2.0 A
VILIM = VIN – 2.0 – A
SW On Resistance RDS(On)SW VIN = 3.3 V, ID = 800 mA, TA = 25°C – 0.27 – Ω
SW Leakage Current* ISWLKG VSW = 35 V – 0.2 1 μA
SW Maximum Off-Time tOFF(Max) –18–μs
CHARGE Input Current ICHARGE VCHARGE = VIN ––1μA
CHARGE Input Voltage* VCHARGE(H) 2––V
VCHARGE(L) – – 0.8 V
¯D¯ ¯O¯ ¯N¯ ¯E¯ Output Leakage Current* IDONELKG ––1μA
¯D¯ ¯O¯ ¯N¯ ¯E¯ Output Low Voltage* VDONE(L) 32 μA into ¯D¯ ¯O¯ ¯N¯ ¯E¯ pin – – 100 mV
FB Voltage Threshold* VFB 1.187 1.205 1.223 V
FB Input Current IFB VFB = 1.205 V – –120 – nA
UVLO Enable Threshold VUVLO VIN rising 2.55 2.65 2.75 V
UVLO Hysteresis VUVLOHYS – 150 – mV
IGBT Driver
IGBTDRV On Resistance to VIN RDS(On)I-V VIN = 3.3 V, VIGBTDRV = 1.5 V – 5 – Ω
IGBTDRV On Resistance to GND RDS(On)I-G VIN = 3.3 V, VIGBTDRV = 1.5 V – 6 – Ω
TRIGGER Input Current ITRIGGER VTRIGGER = VIN ––1μA
TRIGGER Input Voltage* VTRIGGER(H) 2––V
VTRIGGER(L) – – 0.8 V
Propagation Delay, Rising tDr Rgate=12 Ω, CLOAD = 6500 pF, VIN = 3.3 V – 30 – ns
Propagation Delay, Falling tDf Rgate=12 Ω, CLOAD = 6500 pF, VIN = 3.3 V – 30 – ns
Output Rise Time trRgate=12 Ω, CLOAD = 6500 pF, VIN = 3.3 V – 70 – ns
Output Fall Time tfRgate=12 Ω, CLOAD = 6500 pF, VIN = 3.3 V – 70 – ns
*Guaranteed by design and characterization over operating temperature range, –40°C to 85°C.
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
4
Performance Characteristics
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
Charging Waveforms: 100 μF photoflash capacitor
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 2.0 V
VBIAS 3.3 V
COUT 100 μF
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 2.5 V
VBIAS 3.3 V
COUT 100 μF
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 3.0 V
VBIAS 3.3 V
COUT 100 μF
t
IBATT
VOUT
C4
C1
t
IBATT
VOUT
C4
C1
t
IBATT
VOUT
C4
C1
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
5
Performance Characteristics
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 3.6 V
VBIAS 3.3 V
COUT 100 μF
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 4.5 V
VBIAS 3.3 V
COUT 100 μF
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 5.0 V
VBIAS 3.3 V
COUT 100 μF
t
IBATT
VOUT
C4
C1
t
IBATT
VOUT
C4
C1
t
IBATT
VOUT
C4
C1
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
6
Performance Characteristics
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
Charging Waveforms: 140 μF photoflash capacitor
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 2.0 V
VBIAS 3.3 V
IAVG 770 mA
ILIM 1.8 A
COUT 140 μF
t
IBATT
VOUT
C4
C1
t
IBATT
VOUT
C4
C1
Symbol Parameter Units/Division
C1 VOUT 50 V
C4 IBATT(Avg) 200 mA
t time 1 s
Conditions Parameter Value
VBATT 2.0 V
VBIAS 3.3 V
IAVG 820 mA
ILIM 2.0 A
COUT 140 μF
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
7
VOUT (V)
Efficiency (%)
VBATT (V)
Charge Time (s)
100 150 200 250 300
40
50
60
80
70
90
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
VBATT = VIN = 3.3 V
VBATT = 3.0 V, VIN = 5.0 V
1.5
2.5
3.5
5.5
4.5
6.5
VBATT = VIN = 5.0 V
Charge Time
VBIAS = 3.3 V, COUT = 100 μF, ILIM = 2 A, VOUT = 300 V
Connect VBATT to a separate power supply
Efficiency
TA = 25°C
Performance Characteristics, continued
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
IGBTDRV
TRIGGER
t
Dr
t
r
t
Df
t
f
50%
10%
90%
50%
10%
90%
IGBT Drive Timing Definition
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
8
Performance Characteristics, continued
Tests performed using application circuit shown in figure 6 (unless otherwise noted)
IGBT Drive Performance
Symbol Parameter Units/Division
C2 VIGBTDRV 1 V
C3 VTRIGGER 1 V
t time 50 ns
Conditions Parameter Value
tDr 22.881 ns
tr63.125 ns
CLOAD 6800 pF
Rgate 12 ΩC3
C2
t
VIGBTDRV
VTRIGGER
Symbol Parameter Units/Division
C2 VIGBTDRV 1 V
C3 VTRIGGER 1 V
t time 50 ns
Conditions Parameter Value
tDf 27.427 ns
tf65.529 ns
CLOAD 6800 pF
Rgate 12 Ω
tr
VIGBTDRV
VTRIGGER
t
C3
C2
tf
Rising Signal
Falling Signal
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
9
Functional Description
Overview
The A8438 is a photoflash capacitor charger control IC with
adjustable input current limiting. It also integrates an IGBT
driver for strobe operation of the flash tube, dramatically saving
board space in comparison to discrete solutions for strobe flash
operation. The control logic is shown in the functional block
diagram.
The charging operation of the A8438 is started by a low-to-high
signal on the CHARGE pin. When a charging cycle is initiated,
the transformer primary side current, IPrimary, ramps up linearly at
a rate determined by the combined effect of the battery voltage,
VBATT
, and the primary side inductance, LPrimary. When IPrimary
reaches the current limit, ISWLIM , set by configuring the ILIM
pin, the internal MOSFET is turned off immediately, allowing the
energy to be pushed into the photoflash capacitor, COUT, from the
secondary winding. The secondary side current drops linearly as
COUT charges.
While the internal MOSFET switch is turned off, the output
voltage, VOUT, is sensed by a resistor string, R1 through R3, con-
nected between the anode of the output diode, D1, 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
voltage level based on a typical value of 1.205 V at the FB pin.
As soon as VOUT reaches the desired value, the charging process
is terminated. The user may toggle the CHARGE pin to refresh
the photoflash capacitor.
Switch On-Time and Off-Time Control
The A8438 implements an adaptive on-time/off-time control.
(For circuit details, please refer to the the Control Logic block
in the simplified Functional Block Diagram on page 2.) On-time
duration, tON , is determined by input voltage, VIN, transformer
primary inductance, LPrimary, and the set current limit, ISWLIM .
Off-time duration, tOFF , depends on the operating conditions
during switch off-time. The A8438 applies its two charging
modes, Fast Charging mode and Timer mode, according to those
conditions.
Fast Charging and Timer Modes
The IC operates in the Fast Charging mode when the photoflash
capacitor, COUT, is only partially discharged. In Fast Charging
mode, the converter operates near the discontinuous boundary,
and a sensing circuit tracks the fly-back voltage at the SW node.
As soon as this voltage swings below 1.2 V, the internal MOS-
FET switch is turned on again, starting the next charging cycle.
The IC operates in the Timer mode when beginning to charge a
completely discharged photoflash capacitor, usually when the
output voltage, VOUT, is less than approximately 10 to 20 V.
Timer mode is a fixed 18 μs off-time control. One advantage of
the A8438 watchdog timer control scheme is that it limits the
initial current surge and thus acts as a “soft-start.” As shown in
figure 3, the timer mode only lasts a small fraction of a second
(usually < 100 ms). It can be recognized by its lower initial input
charging current as a result of a lower duty cycle. As output
voltage rises to more than 10 to 20 V, the adaptive Fast Charging
mode takes over the control, raising the average input current
level.
To understand the Timer mode, it is noted that the secondary
winding charge current, ISecondary, decreases linearly at a rate of:
V
OUT
dI
Secondary
dt
=N2
LPrimary
(1)
where:
I
Secondary is the secondary side current,
LPrimary is the primary side inductance, and
N is the transformer turns ratio (NSecondary
/ NPrimary).
Fast Charging Mode
Timer
Mode
I
BATT(Avg)
V
OUT
Figure 3. Sequencing of Timer mode and Fast Charging mode (time
axis scale is 1 s per division)
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
10
When the A8438 charges a fully-discharged photoflash capacitor,
ISecondary decreases very slowly due to the low initial VOUT. The
A8438 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 .
Input Current Limiting
The peak input current, ISWLIM , can be set to three levels by
configuring the ILIM pin:
ISWLIM Setting
(A)
ILIM Pin
Connection
1.6 External ground
1.8 Float
2.0 Pull up to IC supply voltage
with a 1 to 10 kΩ resistor
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.
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
11
Transformer Design
Turns Ratio. The minimum transformer turns ratio, N,
(Secondary:Primary) should be chosen based on the following
formula:
V
BATT
V
D_Drop
V
OUT
N
−
+
≥
40
(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:
SWLIM
IN
VOUT
Primary
L
9
10300
×
××
≥
−
.
(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.
Applications Information
Symbol Rating
C1 0.1 μF, X5R or X7R, 10 V
C2 4.7 μF, X5R or X7R, 10 V
D1 Fairchild Semiconductor BAV23S
(dual diode connected in series)
T1 TDK LDT565630T-041,
LPrimary = 4.7 μH, N = 10.2
R1, R2 1206 Resistor, 1 %
R3 0603 Resistor, 1 %
R4, R5 Pull-up resistors
+
To IGBT Gate
kΩ
COUT
VOUT
D1
T1
R1
R2
R3
R4
100 kΩ
150 kΩ
150 kΩ
1.2 kΩ
R5
10
VBATT 1.5to5.5V
Two Alkaline/NiMH/NiCAD or one Li +
VBIAS 3.0to5.5V
C2
4.7 μF 303 V
C1
0.1 μF
A8436
CHARGE
GND
FB
SW
TRIGGER IGBTDRV
DONE
ILIM
VIN
Figure 6. Typical circuit for photoflash application. Configured for ISWLIM of 2.0 A.
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
12
Adjusting Output Voltage
The A8438 senses output voltage during switch off-time. This
allows the voltage divider network, R1 through R3 (see figure
6), to be connected at the anode of the high voltage output diode,
D1, eliminating power loss due to the feedback network when
charging is complete. The output voltage can be adjusted by
selecting proper values of the voltage divider resistors. Use the
following equation to calculate values for Rx (Ω):
3
21
−=
+
FB
V
V
OUT
R
RR 1 .
(4)
R1 and R2 together need to have a breakdown voltage of at
least 300 V. A typical 1206 surface mount resistor has a 150 V
breakdown voltage rating. It is recommended that R1 and R2
have similar values to ensure an even voltage stress between
them. Recommended values are:
R1 = R2 = 150 kΩ (1206)
R3 = 1.2 kΩ (0603)
which together yield a stop voltage of 303 V.
Using higher resistance ratings for R1, R2, and R3 does not
offer significant efficiency improvement, because the power loss
of the feedback network occurs mainly during switch off-time,
and because the off-time is only a small fraction of each charging
cycle.
Output Diode Selection
Choose the rectifying diode(s), D1, to have small parasitic
capacitance (short reverse recovery time) while satisfying the
reverse voltage and forward current requirements.
The peak reverse voltage of the diode, VD_Peak
, occurs when the
internal MOSFET switch is closed, and the primary-side current
starts to ramp-up. It can be calculated as:
BATT
.
VNV
OUT
D_Peak
V×+=
(5)
The peak current of the rectifying diode, ID_Peak, is calculated
as :
.
IPrimary_Peak
D_Peak
I
=
N
/
(6)
Input Capacitor Selection
Ceramic capacitors with X5R or X7R dielectrics are recom-
mended for the input capacitor, C2. It should be rated at least
4.7 μF / 6.3 V to decouple the battery input, VBATT , at the primary
of the transformer. When using a separate bias, VBIAS , for the
A8438 VIN supply, connect at least a 0.1 μF / 6.3 V bypass
capacitor to the VIN pin.
Layout Guidelines
Key to a good layout for the photoflash capacitor charger circuit
is to keep the parasitics minimized on the power switch loop
(transformer primary side) and the rectifier loop (secondary side).
Use short, thick traces for connections to the transformer primary
and SW pin.
Output voltage sensing circuit elements must be kept away from
switching nodes such as SW pin. It is important that the ¯D¯ ¯O¯ ¯N¯
¯E¯ signal trace be routed away from the transformer and other
switching traces, in order to minimize noise pickup. In addition,
high voltage isolation rules must be followed carefully to avoid
breakdown failure of the circuit board.
Recommended Components Table
Component Rating Part Number Source
C1 Input Capacitor 0.1 μF, ± 10%, 16 V X7R ceramic capacitor (0603) GRM188R71C104KA01D Murata
C2 Input Capacitor 4.7 μF, ± 10%, 10 V, X5R ceramic capacitor (0805) LMK212BJ475KG Taiyo Yuden
COUT Photoflash
Capacitor 20 to 180 μF, 330 V Chemi-Con
D1
Output Diode
2 x 250 V, 225 mA, 5 pF BAV23S Philips Semiconductor,
Fairchild Semiconductor
2 x 300 V, 225 mA, 5 pF GSD2004S Vishay
R1, R2,
FB Resistors 150 kΩ, 1/4 W ± 1% (1206) 9C12063A1503FKHFT Yageo
R3
FB Resistors 1.20 kΩ 1/10 W ± 1% (0603) 9T06031A1201FBHFT Yageo
T1
Transformer
1:10, LPrimary = 10.8 μH, for ILIM = 1.6 or 1.8 A ST-532517A Asatech
1:10.4, LPrimary = 4.7 μH, for ILIM = 2.0 A LDT565630T-041 TDK
1:10.2, LPrimary = 12 μH, for ILIM = 1.6 A T-16-024A Tokyo Coil Engineering
A8438-DS, Rev. 1 Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
Photoflash Capacitor Charger with IGBT Driver
A8438
13
Package EJ, 10-Contact MLP/TDFN
1.64
NOM
.065
2.38
NOM
.094
0.30
0.18
.012
.007
0.50
0.30
.020
.012
0.80
0.70
.031
.028
0.05
0.00
.002
.000
3.15
2.85
.124
.112
3.15
2.85
.124
.112
0.20
REF
.008
A
B
C
SEATING
PLANE
C0.08 [.003]
10X
0.50 .020
10X
0.10 [.004] M C A B
0.05 [.002] M C
10
10
2
1
2
1
A
ATerminal #1 mark area
BExposed thermal pad (reference dimensions only,
terminal #1 identifier appearance at supplier discretion)
Preliminary dimensions, for reference only
(reference JEDEC MO-229 WEED)
Dimensions in millimeters
U.S. Customary dimensions (in.) in brackets, for reference only
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
B
0.225 x 0.225
REF
.009 x .009
The products described here are manufactured under one or more U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detailed
spec i fi ca tions as may be required to permit improvements in the per for mance, reliability, or manufacturability
of its products. Before placing an order, the user is cautioned to verify that the information being relied upon
is current.
Allegro products are not authorized for use as critical components in life-support devices or sys tems without
express written approval.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc.
assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which
may result from its use.
Copyright©2005 Allegr oMicrosystems, Inc.
Part Number Packaging
A8438EEJTR-T 7-in. reel, 1500 pieces/reel
Use the following complete part number when ordering:
