
UNITRODE CORPORATION
7 CONTINENTAL BLVD.
MERRIMACK, NH 03054
TEL. (603) 424-2410
FAX (603) 424-3460
4. Input Capacitor Selection (C
IN
)
To reduce noise on the supply voltage caused by the
switching action of a step-up regulator (ripple current
noise), VIN should be bypassed to ground. A good qual-
ity 0.1
μ
F capacitor with low ESR should provide suffi-
cient decoupling. If the UC2577 is located far from the
supply source filter capacitors, an additional electrolytic
(47
μ
F, for example) is required.
Nichicon -
Types PF, PX, or PZ
927 East StateParkway, Schaumburg, IL 60173
(708)843-7500
United Chemi-CON -
Types LX, SXF, or SXJ
9801 West Higgens, Rosemont, IL 60018
(708)696-2000
Figure 6. Aluminum Electrolytic Capacitors Recommended
for Switching Regulators
5. Output Diode Selection (D)
In the step-up regulator, the switching diode must with-
stand a reverse voltage and be able to conduct the peak
output current of the UC2577. Therefore a suitable diode
must have a minimum reverse breakdown voltage
greater than the circuit output voltage, and should also
be rated for average and peak current greater than
I
LOADmax
and I
Dpk
. Because of their low forward voltage
drop (and thus higher regulator efficiencies), Schottky
barrier diodes are often used in switching regulators. Re-
fer to Figure 7 for recommended part numbers and volt-
age ratings of 1A and 3A diodes.
V
OUTmax
Schottky
1A
1N5817
MBR120P MBR320P
1N5818
MBR130P MBR330P
11DQ03
1N5819
MBR140P MBR340P
11DQ04
MBR150
11DQ05
Fast Recovery
1A
3A
3A
20V
1N5820
30V
1N5821
31DQ03
1N5822
40V
31DQ04
MBR350
31DQ05
50V
1N4933
MUR105
1N4934
MUR110
10DL1
100V
MR851
30DL1
MR831
MBRxxx and MURxxx are manufactured by Motorola.
1DDxxx, 11Cxx and 31Dxx are manufactured by
International Rectifier
Figure 7. Diode Selection Chart
UC2577-ADJ
ORDERING INFORMATION
Unitrode Type Number
UC2577T-ADJ 5 Pin TO-220 Plastic Package
UC2577TD-ADJ 5 Pin TO-263 Plastic Package
APPLICATIONS INFORMATION (cont.)
7
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