AIC1639 데이터 시트보기 (PDF) - Analog Intergrations
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AIC1639 Datasheet PDF : 11 Pages
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VEXT
I IN
IPK
ISW
ID
VSW
IOUT
t
Continuous Conduction Mode
At the boundry between continuous and discontinu-
ous mode, output current (IOB) is determined by
IOB =
Vin
Vout +
Vd
1
2
Vin Ton(1− x )
L
where Vd is the diode drop,
x = (Ron+Rs)Ton/L.
Ron= Switch turn on resistance, Rs= Inductor DC re-
sistance
Ton = Switch ON time
In the discontinuous mode, the switching frequency
(fsw) is
fsw =
2(L)(Vout + Vd − Vin)(Iout)
Vin2 × Ton 2
(1
+
x)
In the continuous mode, the switching frequency is
fsw=
1 (Vout + Vd − Vin) [1+ x ( Vin − Vsw )]
Ton (Vout + Vd − Vsw) 2 Vout + Vd − Vsw
AIC1639
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1639-00 05/26/00
≅
1
Ton
Vout + Vd − Vin
Vout + Vd − Vsw
where Vsw = switch drop and proportion to output cur-
rent.
INDUCTOR SELECTION
To operate as an efficient energy transfer element, the
inductor must fulfill three requirement. First, the induc-
tance must be low enough for the inductor to store
adquate energy under the worst case condition of
minimum input voltage and switch ON time. Second,
the inductance must also be high enough so maxi-
mum current rating of AIC1639 and inductor are not
exceed at the other worst case cindition of maximum
input voltage and ON time. Lastly, the inductor must
have sufficiently low DC resistance so excessive
power is not lost as heat in the windings. But unfo-
trunately this is inversely related to physical size.
Minimum and Maximum input voltage, output voltage
and output current must be established before and in-
cuctor can be selected.
In discontinuous mode operation, at the end of the
switch ON time, peak current and energy in the induc-
tor build according to
IPK
=
Vin
Ron + Rs
1 −
exp( −
Ron + Rs
L
Ton)
≅
Vin
L
(Ton
)
1−
x
2
≅ Vin Ton
L
(simple lossless equation),
where x=(Ron+Rs)Ton/L
EL
=
1
2
L
×
Ipk
2
Power required from the inductor per cycle must be
equal or greater than
PL/fSW = (Vout + Vd − Vin)(Iout) ( 1 )
fsw
in order for the converter to regulate the output.
When loading is over IOB, PFM controller operates in
continuous mode. Inductor peak current can be derived
from
IPK
=
Vout + Vd − Vsw
Vin − Vsw
−
x
2
Iout
+
Vin
− Vsw
2L
Ton
1−
x
2
ANALOG INTEGRATIONS CORPORATION
www.analog.com.tw
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510
9
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