AIC1641 Datasheet, PDF (9/12 Pages) List of Unclassifed Manufacturers – LOW VOLTAGE STEP-UP DC/DC CONVERTER

V_EXT
I_IN
I_PK
AIC1641
LOW VOLTAGE STEP-UP DC/DC CONVERTER
SPEC NO: DS-1641-00 05/04/00
≅
1
TON


VOUT + VD − VIN
VOUT + VD − VSW


where Vsw = switch drop and proportion to output
current.
INDUCTOR SELECTION
I_SW
I_D
V_SW
I_OUT
t
Continuous Conduction Mode
t the boundry between continuous and discontinuous
mode, output current (IOB) is determined by
I_OB
=
 ^VIN
 ^{VOUT +}
 ¹
VD _ 2
( ^VIN TON 1 −
L
x)
where Vd is the diode drop,
x = (R_ON+Rs)T_ON/L.
Ron= Switch turn on resistance, Rs= Inductor DC re-
sistance
T_ON = Switch ON time
In the discontinuous mode, the switching frequency
(fsw) is
F_SW =
2(L)(VOUT +
VIN ²
VD − VIN)(IOUT)
× 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
To operate as an efficient energy transfer element,
the inductor must fulfill three requirement. First, the
inductance must be low enough for the inductor to
store adquate energy under the worst case condition
of minimum input voltage and switch ON time. Sec-
ond, the inductance must also be high enough so
maximum current rating of AIC1641 and inductor are
not exceed at the other worst case cindition of
maximum input voltage and ON time. Lastly, the in-
ductor must have sufficiently low DC resistance so
excessive power is not lost as heat in the windings.
But unfotrunately this is inversely related to physical
size.
Minimum and Maximum input voltage, output volt-
age and output current must be established before
and incuctor can be selected.
In discontinuous mode operation, at the end of the
switch ON time, peak current and energy in the in-
ductor build according to
IPK =  ^VIN 1 − exp(− ^{RON + Rs} TON)
 ^{RON + Rs} 
L

≅  ^VIN (TON)1− ^x 
 ^L   ²ï£¸
≅ ^VIN TON
L
(simple lossless equation),
where x=(R_ON+Rs)T_ON/L
1 _{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 de-
rived from
ANALOG INTEGRATIONS CORPORATION
www.analog.com.tw
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: [phone] FAX:[phone]
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