AIC1642 데이터 시트보기 (PDF) - Analog Intergrations
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AIC1642 Datasheet PDF : 14 Pages
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AIC1642
■ APPLICATION INFORMATION
GENERAL DESCRIPTION
AIC1642 PFM (pulse frequency modulation) control-
ler ICs combine a switch mode regulator, N-channel
power MOSFET, precision voltage reference, and
voltage detector in a single monolithic device. They
offer extreme low quiescient current, high efficiency,
and very low gate threshold voltage to ensure start-
up with low battery voltage (0.8V typ.). Designed to
maximize battery life in portable products, and
minimize switching losses by only switching as
needed service the load.
PFM controllers transfer a discrete amount of en-
ergy per cycle and regulate the output voltage by
modulating switching frequency with the constant
turn-on time. Switching frequency depends on load,
input voltage, and inductor value, and it can range
up to 100KHz. The SW on-resistance is typically 1.9
to 2.2Ω to minimize switch losses.
When the output voltage drops, the error compara-
tor enables 100kHz oscillator that turns on the
MOSFET around 7.5us and 2.5us off time. Turning
on the MOSFET allows inductor current to ramp up,
storing energy in a magnetic field. When MOSFET
turns off that force inductor current through diode to
the output capacitor and load. As the stored energy
is depleted, the current ramp down until the diode
turns off. At this point, inductor may ring due to re-
sidual energy and stray capacitance. The output ca-
pacitor stores charge when current flowing through
the diode is high, and release it when current is low,
thereby maintaining a steady voltage across the
load.
As the load increases, the output capacitor dis-
charges faster and the error comparator initiates cy-
cles sooner, increasing the switching frequency.
The maximum duty cycle ensure adequate time for
energy transfer to output during the second half
each cycle. Depending on circuit, PFM controller
can operate in either discontinuous mode or con-
tinuous conduction mode. Continuous conduction
mode means that the inductor current does not
ramp to zero during each cycle.
VIN
IIN
SW
EXT
Isw
ID
IOUT
+
VOUT
Ico
VEXT
IIN
IPK
ISW
Charge Co.
ID
IOUT
TDIS Discharge Co.
VSW
t
Discontinuous Conduction Mode
10
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