AIC2359 Datasheet, PDF (9/11 Pages) Analog Intergrations Corporation – 1A Dual Synchronous Step-down DC/DC Converter

AIC2359
 APPLICATION INFORMATION
Operation
frequency of AIC2359 will be reduced to one third of the
The AIC2359 is a low-noise step-down DC/DC converter
with current-mode PWM/PSM control architecture. It
features an internal synchronous rectifier, which
eliminates the external Schottky diode and increases
efficiency. During normal operation, the AIC2359 can
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.
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
Shutdown
By connecting the EN pin to GND, the AIC2359 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.
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, AIC2359 will enter pulse-skipping-
modulated mode (PSM) operation while working at light
load conditions.
Current Limitation
100% Duty Cycle Operation
When the input voltage approaches the output voltage,
the AIC2359 smoothly transits to 100% duty cycle
operation. This allows AIC2359 to regulate the output
voltage until AIC2359 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 AIC2359 achieves 100% duty cycle operation by ex-
tending the turn-on time of the main power switch. If the
summing signal of current sensing signal and slope com-
pensation 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 oscilla-
The AIC2359 provides current limit function by using an in- _{tor remains off until the summing signal of current sensing}
ternal sensing resistor. When the main power switch turns _{signal and slope compensation signal reaches the output}
on, current follows through the internal sensing resistor. And _{voltage level of the error amplifier. After the summing signal}
current amplifier senses the voltage, which crosses the re- _{of current sensing signal and slope compensation signal}
sistor, and amplifies it. While the sensed voltage gets higher _{reaches the output voltage level of the error amplifier,}
than reference voltage, the current limitation function is acti- _{the main power switch is turned off and the synchronous}
vated. While the current limitation function is activated, the _{power switch is turned on for a constant off time. At the end}
duty cycle will be reduced to limit the output power to protect _{of the constant off time, the next switching cycle is begun.}
the internal power switches.
While the input voltage approaches the output voltage, the
Short Circuit Protection
switching frequency decreases gradually to smoothly transit
While the output is shorted to ground, the switching ^{to 100% duty cycle operation.}
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