AIC1553 查看數據表（PDF） - Analog Intergrations
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AIC1553 Datasheet PDF : 9 Pages
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AIC1553
the AIC1553 automatically enters a pulse
frequency modulation (PFM) mode. The
switching frequency depends on the loading
condition and with a minimum quiescent current
and maintains high efficiency. The high side P-
MOSFET operates intermittently. When output
voltage drops, the error comparator enable the
PFM controller and the output voltage rises until
the error comparator trips. When the output
voltage falls below until the error comparator trips
again and the next cycle will be started. At no
load connection, the quiescent current is typically
only 22µA.
Shutdown
The whole circuit is shutdown when SD pin is low
level. In shutdown mode, the supply current is
reduced to less 1µA. For proper operation, the
SD pin must be connected and must not be left
floating.
Low Dropout Operation
The dropout voltage of buck converter depends
on the maximum duty cycle and the voltage
across the high site switch. AIC1553 offers a low
input to output voltage difference, while it
operates in the 100% duty cycle mode. The
minimum input voltage to maintain regulation,
depending on the loading current and output
voltage.
The minimum input voltage can be calculated as:
VIN(MIN)≥VOUT +IOUT(MAX)(RDS(ON)+RL)
Where:
IOUT(MAX) = maximum output current
RDS(ON) = maximum P-MOSFET turn on
resistance
RL =DC resistance of the inductor
Selecting the Output Voltage
The output voltage can be set by a resistive
divider. Use the following equation to calculate:
VOUT=0.75V(1+R2/R1)
The feedback reference voltage 0.75V allows
low output voltages from 0.75V to input voltage.
For stability of feedback compensation, it is
required a small bypass capacitor 22pF in parallel
to the upper feedback resistor.
Inductor Selecting
The inductor value directly determines the
inductor ripple current. The larger the inductor
value, the small inductor ripple current and small
output ripple voltage. But, the larger the inductor
value causes a slower load transient response
and larger conduction losses of the inductor. The
∆IL can be calculated as:
∆IL
=
VOUT
f ×L
1−
VOUT
VIN
To avoid saturation of the inductor, the rated
current of the inductor should be less than the
peak current of the inductor.
IL(PEAK) =IOUT(MAX)+∆L/2
Input and Output Capacitor Selecting
The input capacitor must be sufficient to filter the
pulsating input current. A low ESR capacitor
provides the small drop voltage to stabilize the
input voltage during the transient loading. The
input capacitor should be larger than 10µF and
the ceramic capacitors and low ESR value of
tantalum capacitors are recommend.
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