AT1450
Preliminary Product Information
Photoflash Capacitor Charger for DSC
(2) Error amplifier
The error amplifier detects the output voltage of the switching regulator and sets the PWM
control signal. The voltage gain is fixed. The system is made stable by connecting a phase
compensation capacitor to the FB pin (pin 8).
(3) PWM comparator
The voltage comparator includes one inverting and three non-inverting inputs. The comparator is
a voltage to pulse width converter that controls the ON time of the output pulse depending on the
level of input voltage. The output level remains high when the sawtooth wave is lower than the
error amplifier output voltage, the soft start setting voltage, and the idle period setting voltage.
(4) Output circuit
The output circuit can drive an external NPN transistor directly and has a totem pole
configuration. The value of the ON/OFF current can be set by a resistor connected to the
BR/CTL pin (pin 4). Stand-by mode (supply current 1µA or less) can be set by connecting the
BR/CTL pin (pin4) to VCC or by making the pin open.
(5) Under-Voltage Lockout (UVLO)
Transients during powering on or instantaneous glitches in the supply voltage can cause the
control IC to malfunction and damage the system. To prevent malfunction at low input voltage,
the circuit compares the supply voltage to the internal reference voltage to detect a low input
voltage. Once detected, the circuit sets the output pin low.
To cancel the status, set V
CC
below the reset voltage V
R
(0.9V) and then set V
CC
up to the
recommended operation range and the latch will be restored to operate normally.
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
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AIMTRON [ AIMTRON TECHNOLOGY ]
