A8436EEJTR-T Allegro Microsystems Inc, A8436EEJTR-T Datasheet - Page 13

• Manufacturer Part Number: A8436EEJTR-T
• Description: IC PHOTOFLASH CHARGER 10-MLP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8436EEJTR-T

• Applications: Photoflash Capacitor Charger
• Current - Supply: 1.3mA
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-WFDFN Exposed Pad
• Input Voltage: 5.5V
• No. Of Outputs: 1
• Supply Voltage Range: 3V To 5.5V
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +85°C
• Termination Type: SMD
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 620-1098-2

A8436
Adjusting Output Voltage
The A8436 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):
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:
which together yield a stop voltage of 303 V.
Using higher resistance values 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, V
R1 = R2 = 150 kΩ (1206)
R3 = 1.2 kΩ (0603)
Recommended Components Table
C1 Input Capacitor
C2 Input Capacitor
COUT Photoflash Capacitor 330 V, 100 μF (or 19 to 180 μF)
D1 Output Diode
R1 and R2 FB Resistors
R3 FB Resistors
T1 Transformer
Component
R
1
R
3
R
2
V
V
OUT
FB
0.1 μF, ± 10%, 16 V X7R ceramic
capacitor (0603)
4.7 μF, ± 10%, 10 V, X5R ceramic
capacitor (0805)
2 x 250 V, 225 mA, 5 pF
2 x 300 V, 225 mA, 5 pF
150 kΩ,
1.20 kΩ
1:10.2, L
1:10.2, L
1:10, L
1:10.2, L
1 .
Primary
D_Peak
1
1
Primary
Primary
Primary
/
/
4
10
W ± 1% (1206)
W ± 1% (0603)
= 10.8 μH
, occurs when the
= 12 μH
= 9.8 μH
= 14.5 μH
Photoflash Capacitor Charger with IGBT Driver
Rating
(4)
internal MOSFET switch is closed, and the primary-side current
starts to ramp-up. It can be calculated as:
The peak current of the rectifying diode, ID_Peak, is calculated as :
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, V
of the transformer. When using a separate bias, V
A8436 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. Make sure that there is no GND
plane underneath R1 and R2, because parasitic capacitance to
ground will affect sensing accuracy. It is important that the
¯ N ¯ ¯ E ¯
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.
GRM188R71C104KA01D
LMK212BJ475KG
EPH-331ELL101B131S
BAV23S
GSD2004S
9C12063A1503FKHFT
9T06031A1201FBHFT
LDT565630T-002
T-16-024A
ST-532517A
SBL-5.6-1
signal trace be routed away from the transformer and other
Part Number
V
I
D _ Peak
D _ Peak
V
I
OUT
Primary_Peak
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
N
V
/
BATT
N
Murata
Taiyo Yuden
Chemi-Con
Philips Semiconductor,
Fairchild Semiconductor
Vishay
Yageo
Yageo
TDK
Tokyo Coil Engineering
Asatech
Kijima-Musen
.
.
BATT
Source
BIAS
, at the primary
, for the
(6)
(5)
¯ D ¯ ¯ O ¯
13