AT1450
Preliminary Product Information
Photoflash Capacitor Charger for DSC
Functional Description
Soft Start
At power-on, the AT1450 enters the soft-start mode to prevent current spike and overshoot. The
capacitor CS is charged from 0.2V at a constant current of 1µA.
The soft-start time for the duty cycle
t
S
(
s
)
=
0.8
×
CS
(
µ
F
)
Setting Oscillating Frequency
The oscillator circuit generates a triangular sawtooth wave with a peak of 0.8V and a trough of 0.1V
using the timing capacitor (CT) and the timing resistor (RT) that are connected to the OSC pin. This
oscillator can provide oscillating frequency in the range from 20KHz to 1MHz. The waveform of the
OSC pin is shown as Figure 2.
Figure 2 Oscillator Waveform
The cycle (T) can be determined as follows:
VX
)
VX
=
VHe
VH
T
= −
CT
×
RT
×
log
e
(0.1 / 0.8)
=
2.1
×
CT
×
RT
[
s
]
−
t
CT
×
RT
t
= −
CT
×
RT
×
log
e
(
Switching Regulator Function
(1) Reference voltage circuit
A temperature-compensated reference voltage (~1.25V) is generated by the reference voltage
circuit from the voltage supplied by the power supply pin (pin 3). The circuit also sets the idle
period besides providing the reference voltage for the switching regulator.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW:
http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email:
service@aimtron.com.tw
8
AIMTRON [ AIMTRON TECHNOLOGY ]
