YB7002 Datasheet, PDF (7/8 Pages) YOBON TECHNOLOGIES,INC. – Photoflash Capacitor Charger with Automatic Refresh

YB7002
Photoflash Capacitor Charger with Automatic Refresh
Turn ratio N, primary inductance, primary
side series resistance, transformer leakage
inductance, secondary capacitance and
series resistance, transformer efficiency are
the main considerations when choosing a
transformer.
V_SWITCH
= V_BAT
+ ^{VOUT + VD}
N
Care must be exercised so that V_SWITCH will
not exceed the maximum voltage
breakdown voltage of 40V. Minimizing
primary side series resistance, transformer
leakage inductance, secondary capacitance
and series resistance will improve system
efficiency and performance.
Primary side inductance will affect the
charging time. Higher primary side
inductance will raise the average
discharging current into the output
capacitance, resulting a smaller charging
time. Yet, thermal effect will become
adversely affecting the system. So always
pay attention to the amount of dissipated
power.
Thermal Consideration:
When YB7002 is set to handle high switch
current will result in internal power
dissipation generating heat. For thermal
improvement can be made by use of vias to
connects the part and dissipate heat to an
internal ground plane.
Placing vias under the exposed thermal pad of
package can be lowered significant. Using larger
traces and more copper on the top site of board
can also further help. With careful PCB layout it
is possible to reduce the thermal effect.
Always beware the amount of power dissipated
during the charging process.
Too high the temperature built up inside the IC
will slow the charging cycle and lengthen the
charging time, further worsen the thermal
condition of the IC. To resolve the thermal built
up issue, reduce RLIMIT which lower the peak
switch current.
Layout consideration
The input bypass capacitor C2must be placed
close to the IC. This will reduce copper trace
resistance which effect input voltage ripple of
the IC.
The capacitor, C1, should also be placed close to
the transformer T1. The copper trace
connections for the C1, T1, and the YB7002
should be kept short as possible to eliminate
over-voltage condition on SW pin due to leakage
inductance of T1.
For improved thermal performance can increase
the top side copper to dissipate heat from the
package. Numerous vias from the ground
connection to the internal ground plane located
underneath the package will help.
YB7002 MRev1.0
www.yobon.com.tw
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