AT1454 Datasheet, PDF (13/18 Pages) Aimtron Technology – Photoflash Capacitor Charger for DSC

AT1454/AT1454A/AT1454B
Preliminary Product Information
Photoflash Capacitor Charger for DSC
Vout: Target Output Voltage
V_DS(MAX):Maximum drain to source voltage of NMOS.
Adjustable Output Voltage
The AT1454/1454A/B senses output voltage by a voltage divider connecting to output
terminal. R7 to (R8+R9) ratio determines the output voltage as shown in the
application circuit Figure 1. The feedback reference voltage is 1.1V. Calculate the
remaining resistors with following equations:
V_OUT
= V_FB
× (1 +
R₈ + R_{9 )}
R₇
R8and R9 must be greater than 0805 size resistor for enduring secondary HV.
Rectifying Diode
The rectifying diode should be low capacitance type with sufficient reverse
recovery-voltage and forward current ratings. The peak reverse recovery-voltage that
diode is approximately:
V_PK-R≅ V_OUT + (N x V_CC)
The peak current of the diode is simply:
I_PK-SEC= I_PK-PRI / N
Primary Inductance
A fly-back transformer needs to store substantial amounts of energy in the core during
each switching cycle. The transformer will generally require an air gap. The use of an
air gap in the core makes the energy storage. While the power switch is off, energy
transferred to the output capacitor is proportional to the primary inductance for a
constant primary current. The primary inductance needs to be equal or larger than a
certain minimum value to ensure that AT1454 series has adequate time to respond to
the fly-back waveform. The switch off time should be 500ns or larger for the AT1454
series. The minimum inductance can be calculated with the following formula:
L_PRI
≥
500 ×10^−9 ×V_OUT
N × I _{PK −PRI}
Vout: Target Output Voltage
N: Transformer Turns Ratio
I_PK-PRI: Primary Peak Current
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone] Fax: [phone]
WWW: http://www.aimtron.com.tw
3/24/2006 REV:1.2
Email: [e-mail]
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