AIC3843 Datasheet, PDF (9/11 Pages) Analog Intergrations Corporation – Current-Mode PWM Controller

AIC3843
n PIN DESCRIPTIONS
PIN 1: COMP
- This pin is the error amplifier
output and is made available
for loop compensation.
PIN 2: VFB
- This is the inverting input of
the error amplifier. It is
normally connected to the
switching power supply output
through a resistor divider.
PIN 3: ISENSE - A voltage proportional to
inductor current is connected
to this input. The PWM uses
this information to terminate
the output switch conduction.
PIN 4: RT/CT
- The oscillator frequency and
maximum output duty cycle
are programmed by connect-
ing resistor R_T to V_REF and
capacitor C_T to ground. It is
feasible to operate when f
500KHz.
n APPLICATION INFORMATIONS
Under voltage Lockout
There are two separate under voltage lockout
comparators incorporated to make sure that the
IC is fully functional before the output stage is
enabled. One is for power supply voltage (VCC)
and the other is for reference output voltage
(VREF). Each has a built in hysteresis to prevent
erratic output behavior when their respective
thresholds are crossed. For VCC comparator the
upper and lower thresholds are 8.4V and 7.6V,
respectively. The large hysteresis and low start up
current (0.3mA) of the AIC3843 make it ideally
suited in off-line converter applications where
PIN 5: GND
- This pin is the combined control
circuitry and power ground.
PIN 6:
OUTPUT- This output directly drives the
gate of a power MOSFET.
Peak currents up to 1A are
sourced and sunk by this pin.
PIN 7: VCC - This pin is the positive supply of
the control IC.
PIN 8: VREF - This is the reference output. It
provides charging current for
capacitor CT through resistor
RT.
efficient bootstrap startup techniques are required.
A 34V zener is connected as a shunt regulator
from VCC to ground. Its purpose is to protect the
IC from excessive voltage that can occur during
system start-up.
Reference Output
The 5.0V reference output is trimmed to ±2.0%
tolerance at T_A=25°C. It supplies charging current
to the oscillator timing capacitor and is capable of
providing current in excess of 20mA for powering
additional control system circuitry. In case of
overload, the reference is short-circuit protected at
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