AA18380
Agamem Microelectronics Inc.
PRELIMINARY
Switching Regulator Controller
(4) PWM comparator
The voltage comparator has one inverting and three non-inverting inputs. The comparator is a voltage/pulse
width converter that controls the on-period of the output pulse according to its input voltage. The output
transistors are turned on during periods when the OSC pin (pin 7) triangular waveform is lower than the error
amplifier output voltage, soft start setting voltage, and idle period setting voltage.
(5) Output driver
The output circuit has a totem pole structure. A constant-current source output with line regulation can be set up
at an arbitrary voltage by connecting a current setting resistor to the BR/CTL pin (pin 4).
2. Power Supply On/Off Function
Stand-by mode (supply current 1 µA or less) can be set by connecting the BR/CTL pin (pin 4) to VCC or by
making the pin open circuit.
SW
Mode
AA18380
OFF
Stand-by mode
4
RB
SW
ON
Operating mode
3. Other Functions
(1) Soft start and short circuit detection
Soft start operation can be set by connecting capacitor CPE to the SCP pin (pin 2). Soft start prevents current
spike and overshoot.
When the soft start operation completes, the AA18380 enters the normal mode and enable short circuit detection
function. When the output voltage drops, the error amplifier output is fixed at VOM+ and capacitor CPE starts
charging. When it charges to above 0.8V, the output pin (pin 5) is set low and the SCP pin (pin 2) stays low.
Once the protection circuit operates, the output latch circuit will not reset until power is restarted. (See “■ HOW
TO SET THE TIME CONSTANT FOR SOFT START AND SHORT CIRCUIT DETECTION”.)
(2) Circuit to prevent malfunction at low input voltage
This circuit protects the system against degradation or destruction due to incorrect control operation when the
power supply voltage falls during power on or power off.
The low input voltage malfunction prevention circuit detects the internal reference voltage that changes with the
supply voltage level. While the supply voltage is rising, On detection, the circuit fixes the output pin to low. The
system recovers when the supply voltage rises back above the threshold voltage of the malfunction prevention
circuit.
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©Copyright Agamem Microelectronics Inc.
www.agamem.com.tw
2007/1/15
AGAMEM [ AGAMEM MICROELECTRONIC INC. ]
