Datasheet

UNITRODE CORPORATION
7 CONTINENTAL BLVD.
•
MERRIMACK, NH 03054
TEL. [phone]
•
FAX [phone]
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
[phone]
United Chemi-CON -
Types LX, SXF, or SXJ
9801 West Higgens, Rosemont, IL 60018
[phone]
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 Fast Recovery
1A 3A 1A 3A
20V
1N5817 1N5820
MBR120P MBR320P
30V
1N5818 1N5821
MBR130P MBR330P
11DQ03 31DQ03
40V
1N5819 1N5822
MBR140P MBR340P
11DQ04 31DQ04
50V
MBR150 MBR350 1N4933
11DQ05 31DQ05 MUR105
100V
1N4934 MR851
MUR110 30DL1
10DL1 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
UC2577TKC-ADJ 5 Pin TO-220 Plastic Pkg -50 pc Tube
UC2577TDKTTT-ADJ 5 Pin TO-263 Plastic Pkg -50 pc Reel
APPLICATIONS INFORMATION (cont.)
7
UC2577TDTR-ADJ 5 Pin TO-263 Plastic Pkg -500 pc Reel