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YB7002 Schematic ( PDF Datasheet ) - YOBON TECHNOLOGIES

Teilenummer YB7002
Beschreibung Photoflash Capacitor Charger
Hersteller YOBON TECHNOLOGIES
Logo YOBON TECHNOLOGIES Logo 



Gesamt 9 Seiten
YB7002 Datasheet, Funktion
YB7002
Photoflash Capacitor Charger with Automatic Refresh
Description
YB7002 charge high voltage photoflash
capacitors quickly and efficiently.
Designed for use in digital and film
cameras, these devices use flyback
topology to achieve efficiencies up to four
times better than the competing flash
modules. A unique peak inductor current
control
mechanism
maintains
current-limited mode transformer operation
throughout the entire charge cycle,
eliminating the high inrush current often
found in flash modules.
YB7002 output voltage sensing scheme
monitors the flyback voltage to directly
regulate the output voltage. This feature
allows the capacitor to be held at a fully
charged state without excessive power
consumption. Adjustable refresh time is
fully controllable by the user with a resistor.
The DONE pin signals that the capacitor is
full charged.
Features
„ Charge Any Size Photoflash Capacitor
„ Support Operation from Two AA Cells or
Any Supply from 1.8V to 16V
„ Use Standard Transformers
„ No High Voltage Zener Diode Required
„ Built in 40V Output Switch
„ Adjustable Output Voltage
„ Adjustable Peak Switch Current
„ Automatic Refresh with Adjustable Timer
„ Charge Complete Indicator
„ Small 10-Lead MSOP Packages
Applications
„ Digital Camera Flash unit
„ Film Camera Flash Unit
„ High Voltage Power Supplies
Typical Application Circuit
YB7002 Rev.1.1
Figure 1: Typical Application Circuit
www.yobon.com.tw
1






YB7002 Datasheet, Funktion
YB7002
Photoflash Capacitor Charger with Automatic Refresh
Application Information
Hysteresis voltage is setup by connecting a
resistor RHYST from VHYST to ground. A
resistor divider of 13.5K(internal resistor)
and RHYST from bandgap voltage will
determine hysteresis voltage. Once VFB
drops below VHYST voltage, charging cycle
is activated again. To calculate the refresh
time, consider the followings:
COUT
VOUT
t
+
VOUT
R1+ R2
+
I COUT
,LEAKAGE
=0
As the capacitor leakage current is a
function of output voltage, it can be
considered to be constant within the tiny
range of voltage from VOUT to
VHYST
R1+ R2
R2
,
where
R1
and
R2
are
the
resistor divider at the secondary side
output.
By solving the above equation, we can find
the time it takes for capacitor voltage to
drop from VOUT to
VHYST
R1+ R2
R2
For the convenience of the user, two tables
have been setup for reference. Table 3 is
for Limit Pin while Table 4 is for VHYST.
Please check the tables to pick the resistor
values for peak primary inductor current
and recharge voltage.
Table 3
RLIMIT
Peak
Current
10 K
0.8A
15 K
1A
20 K
1.2A
Table 4 (VOUT=300V)
RHYST
Hysteresis
ratio
436.5 K
3%
211.5 K
6%
136.5 K
9%
99 K
12%
Recharge
Voltage
291V
282V
273V
264V
Once capacitor reaches the designated
voltage, DONE pin will be pulled low to
indicate the completion of charging
process. When output voltage drops below
secondary capacitance, the 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
VHYST
R1+ R2
R2
,
DONE
is
released
to
signal
the re-start of charging process.
User always has the freedom to shut off the
operation of the chip by pulling the
ENABLE pin lower than 0.4V. Also to
activate the IC, ENABLE pin NEED needs
to be above 1.8V. In shutdown mode, the
chip is only drawing about 2μA current.
Component Selection
The rectifying diode must be of low
capacitance type while being able to
withstand peak reverse voltage and heavy
forward current.
YB7002 Rev.1.1
www.yobon.com.tw
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