AIC1638 AIC [Analog Intergrations Corporation], AIC1638 Datasheet - Page 13

• Manufacturer Part Number: AIC1638
• Description: 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
• Manufacturer: AIC [Analog Intergrations Corporation]

ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
At
discontinuous
determined by
where V
x = (R
R
resistance
T
In the discontinuous mode, the switching frequency
(fsw) is
In the continuous mode, the switching frequency is
where Vsw = switch drop and proportion to output
current.
INDUCTOR SELECTION
To operate as an efficient energy transfer element,
the inductor must fulfill three requirements. First, the
inductance must be low enough for the inductor to
store adequate energy under the worst case
condition of minimum input voltage and switch ON
time. Second, the inductance must also be high
enough so maximum current rating of AIC1638 and
inductor are not exceed at the other worst case
condition 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 unfortunately this is inversely
related to physical size.
Minimum and Maximum input voltage, output voltage
and output current must be established before and
inductor can be selected.
In discontinuous mode operation, at the end of the
switch ON time, peak current and energy in the
inductor build according to
I
fsw
fsw
OB
ON
ON
= Switch turn on resistance, Rs= Inductor DC
= Switch ON time
the
ON
2(L)(V
T
V
ON
1
+Rs)Ton/L.
D
OUT
T
is the diode drop,
ON
1
V
boundary
(V
IN
OUT
V
OUT
V
OUT
V
V
IN
V
mode,
D
OUT
OUT
2
V
1
2
V
V
D
T
D
V
D
ON
L
V
IN
V
between
V
D
V
D
2
output
IN
V
T
SW
IN
ON
)(I
V
V
SW
)
OUT
IN
1
[1
x
)
current
x
2
(1
continuous
(
V

x
OUT
V
IN
(IOB)
V
V
D
SW
and
V
SW
is
)]
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
where x=(R
Power required from the inductor per cycle must be
equal or greater than
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
Valley current (Iv) is
I
P
I
Iv
PK
PK
L
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/f
SW
T
V
V
ON
L
Ron
V
V
V
IN
OUT
L
IN
EL
IN
OUT
(V
V
T
Vin
1
2L
V
IN
ON
OUT
T
IN
V
Rs
ON
x
2
V
ON
SW
1
2
V
V
D
+R
L
V
D
SW
SW
1
V
1
S
T
V
Ipk
)T
D
V
ON
SW
(Simple losses equation),
exp(
SW
x
2
ON
2
VI
1
/L
N
x
2
SPEC NO: DS-1638-00 03/01/00
)(I
2
x
x
2
Ron
I
OUT
OUT
I
OUT
L
)(
Rs
f
SW
1
V
Ton)
IN
)
AIC1638
2L
V
SW
13