MAX1790 Maxim, MAX1790 Datasheet - Page 8

• Manufacturer Part Number: MAX1790
• Description: Low-Noise Step-Up DC-DC Converter
• Manufacturer: Maxim

Low-Noise Step-Up DC-DC Converter
Table 1. Component Selection
Table 2. Component Suppliers
External component value choice is primarily dictated
by the output voltage and the maximum load current,
as well as maximum and minimum input voltages.
Begin by selecting an inductor value. Once L is known,
choose the diode and capacitors.
Inductor selection depends on input voltage, output
voltage, maximum current, switching frequency, size,
and availability of inductor values. Other factors can
include efficiency and ripple voltage. Inductors are
8
Inductors
Coilcraft
Coiltronics
Sumida USA
Toko
Capacitors
AVX
Kemet
Sanyo
Taiyo Yuden
Diodes
Central
Semiconductor
International
Rectifier
Motorola
Nihon
Zetex
V
(V)
3.3
3.3
3.3
3.3
_______________________________________________________________________________________
IN
SUPPLIER
V
(V)
OUT
12
12
5
5
f
640k
1.2M
640k
1.2M
(Hz)
OSC
847-639-6400
561-241-7876
847-956-0666
847-297-0070
803-946-0690
408-986-0424
619-661-6835
408-573-4150
516-435-1110
310-322-3331
602-303-5454
847-843-7500
516-543-7100
PHONE
CDRH5D18-100NC)
CDRH5D18-5R4NC)
CDRH5D18-5R4NC)
CDRH4018-2R7)
5.4 (Sumida
5.4 (Sumida
2.7 (Sumida
10 (Sumida
Inductor Selection
(µH)
L
847-639-1469
561-241-9339
847-956-0702
847-699-1194
803-626-3123
408-986-1442
619-661-1055
408-573-4159
516-435-1824
310-322-3332
602-994-6430
847-843-2798
516-864-7630
FAX
TPSD336020R0200)
TPSD336020R0200)
33 tantalum (AVX
33 tantalum (AVX
47 tantalum
47 tantalum
(6TPA47M)
(6TPA47M)
C
(µF)
OUT
specified by their inductance (L), peak current (I
and resistance (L
tions are useful in choosing the inductor values based
on the application. They allow the trading of peak cur-
rent and inductor value while allowing for consideration
of component availability and cost.
The equation used here includes a constant LIR, which
is the ratio of the inductor peak-peak AC current to
maximum average DC inductor current. A good com-
promise between size of the inductor and loss and out-
put ripple is to choose an LIR of 0.3 to 0.5. The peak
inductor current is then given by:
The inductance value is then given by:
Considering the typical application circuit, the maxi-
mum DC load current (I
output. The inductance value is then chosen to be
5.4µH, based on the above equations and using 85%
efficiency and a 640kHz operating frequency. The
inductor saturation current rating should be greater
than I
should be less than 0.5Ω. To minimize radiated noise in
sensitive applications, use a shielded inductor.
The output diode should be rated to handle the output
voltage and the peak switch current. Make sure that the
diode’s peak current rating is at least I
PK
L
I
. The resistance of the inductor windings
R
PK
=
(kΩ)
COMP
120
180
62
91
(
V
=
V
OUT
IN(MIN)




(
I
OUT(MAX)
2
r
). The following boost-circuit equa-
⋅
η
C
)
1200
LIR
COMP
(pF)
⋅
650
820
390
2
V
⋅ ⋅
OUT(MAX)
IN(MIN)
η
⋅
⋅
I
(
OUT(MAX)
V
V
OUT
OUT
C
COMP2
(pF)
) is 500mA with a 5V
33
20
56
33
)
Diode Selection




−
⋅
V



IN(MIN)
1
⋅
PK
+
f
OSC
LIR
I
and that its
TYPICAL
OUT(MAX)
2
)
(mA)
250
250
800
800



PK
),