AT1454 Datasheet, PDF (15/18 Pages) Aimtron Technology – Photoflash Capacitor Charger for DSC

AT1454/AT1454A/AT1454B
Preliminary Product Information
Photoflash Capacitor Charger for DSC
Adjustable Input Current
The AT1454/1454A/B can adjust N-MOS switch on-time by a resistor connecting to
Rsense pin. This resistor determines the primary peak current and on-time of primary
N-MOS as the following equation:
I _{PK −PRI}
= ^{VBAT × 2 ×10−6}
V_Rsense × L_PRI
,V_Rsense
= V_BAT (or,V_CC ) ×
25KΩ
R₄ + 25KΩ
T_ON
=
I _{PK −PRI} × L_PRI
V_BAT
where
L_PRI: primary inductance (µH)
I_PK-PRI: peak primary current (A)
R4: It is recommended several KΩ grade
If setting constant on-time by a resistor R10 is connected to VCC, then R4 resistor
need to remove from application circuitry. In this case, on-time is a constant. At
another topology, if R4 connect to VBAT to set constant on-time, then R10 need to
remove from application circuitry. However, on-time can change dependent on VBAT
because battery voltage level is different from full energy to low power. External
capacitor Css is connected to VCC and Rsense to perform soft-start function to reduce
inrush current on VBAT input current and avoid the internal switching noise.
VBAT
L1 33uH
/Option
T1
ST-982610A
1:25
10uH/6.1mH
VCC
R10
C1
R4 22u/6V3
Css
0.1uF
VCC
Rsense
LX
AT1454/AT1454A/AT1454B
Isec
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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