AIC2302 Datasheet, PDF (9/11 Pages) Analog Intergrations Corporation – 700mA Synchronous PWM Step-Down

AIC2302
 APPLICATION INFORMATION
Operation
The AIC2302 is a low-noise step-down DC/DC
converter with current-mode PWM control architecture.
It features an internal synchronous rectifier, which
eliminates the external Schottky diode and increases
efficiency. During normal operation, the AIC2302 can
regulate its output voltage through a feedback control
circuit, which is composed of an error amplifier; a
current comparator and several control signal
generators. By comparing the feedback voltage to the
reference voltage of 0.6V, the error amplifier varies its
output voltage. The output voltage of the error amplifier
is compared with the summing signal of current
sensing signal and slope compensation signal to
determine the duty cycle of internal main power switch
(P-channel MOSFET). While the main power switch is
turned on, the synchronous power switch (N-channel
MOSFET) will be turned off through anti-short-through
block. Similarly, when the main power switch is turned
off, the synchronous power switch will be turned on
until the inductor current starts to reverse or the
beginning of the next switching cycle. In order to
achieve better efficiency and prevent overcharging the
output capacitor.
Current Limitation
The AIC2302 provides current limit function by using
an internal sensing resistor. When the main power
switch turns on, current follows through the internal
sensing resistor. And current amplifier senses the
voltage, which crosses the resistor, and amplifies it.
While the sensed voltage gets higher than reference
voltage, the current limitation function is activated.
While the current limitation function is activated, the
duty cycle will be reduced to limit the output power to
protect the internal power switches.
Short Circuit Protection
While the output is shorted to ground, the switching
frequency of AIC2302 will be reduced to one third of
the normal switching frequency. This lower switching
frequency ensures the inductor current has more time
to discharge, thereby preventing inductor current
runaway. The switching frequency will automatically
return to its designed value while short circuit condition
is released.
Shutdown
By connecting the EN pin to GND, the AIC2302 can be
shut down to reduce the supply current to 0.1A
(typical). At this operation mode, the output voltage of
step-down converter is equal to 0V.
100% Duty Cycle Operation
When the input voltage approaches the output voltage,
the AIC2302 smoothly transits to 100% duty cycle
operation. This allows AIC2302 to regulate the output
voltage until AIC2302 completely enters 100% duty
cycle operation. In 100% duty cycle mode, the output
voltage is equal to the input voltage minus the voltage,
which is the drop across the main power switch.
The AIC2302 achieves 100% duty cycle operation by
extending the turn-on time of the main power switch. If
the summing signal of current sensing signal and slope
compensation signal does not reach the output voltage
level of the error amplifier at the end of 90% switching
period, the main power switch is continuously turned
on and the oscillator remains off until the summing
signal of current sensing signal and slope
compensation signal reaches the output voltage level
of the error amplifier. After the summing signal of
current sensing signal and slope compensation signal
reaches the output voltage level of the error amplifier,
the main power switch is turned off and the
synchronous power switch is turned on for a constant
off time. At the end of the constant off time, the next
switching cycle is begun. While the input voltage
approaches the output voltage, the switching
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