5A/2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
MAX724/MAX726
In DCM, ringing occurs at V
SW
in the latter part of the
switch off-cycle. This is due to the inductor resonating
with the parallel capacitance of the catch diode and the
V
SW
node. This ringing is harmless and does not
appear at the output. Furthermore, attempts to damp
this ringing by adding circuitry will reduce efficiency
and are not advised. No off-state ringing occurs in
CCM because the diode always conducts during the
switch-off time and consequently damps any reso-
nance at V
SW
.
_______________Component Selection
Table 1 lists component suppliers for inductors, capaci-
tors, and diodes appropriate for use with the
MAX724/MAX726. Be sure to observe specified ratings
for all components.
Table 1. Component Suppliers
Surface-Mount Components
(for designs typically below 2A)
Inductors:
Sumida Electric - CDR125 Series
USA: Phone (708) 956-0666
Japan: Phone 81-3607-5111
FAX 81-3607-5144
Coiltronics - CTX series
USA: Phone (305) 781-8900
FAX (305) 782-4163
Matsuo - 267 series
USA: Phone (714) 969-2491
FAX (714) 960-6492
Japan: Phone 81-6337-6450
Sprague - 595D series
USA: Phone (603) 224-1961
FAX (603) 224-1430
Motorola - MBRS series
USA: Phone (602) 244-5303
FAX (602) 244-4015
Nihon - NSQ series
USA: Phone (805) 867-2555
FAX (805) 867-2556
Japan: Phone 81-3-3494-7411
FAX 81-3-3494-7414
Sumida - RCH-110 series
(see above for phone number)
Cadell-Burns - 7070, 7300, 6860, and 7200 series
USA: Phone (516) 746-2310
FAX (516) 742-2416
Renco - various series
USA: Phone (516) 586-5566
FAX (516) 586-5562
Coiltronics - various series
(see above for phone number)
Nichicon - PL series low-ESR electrolytics
USA: Phone (708) 843-7500
FAX (708) 843-2798
Japan: Phone 81-7-5231-8461
FAX 81-7-5256-4158
United Chemi-Con - LXF series
USA: Phone (714) 255-9500
FAX (714) 255-9400
Sanyo - OS-CON low-ESR organic semiconductor
USA: Phone (619) 661-6835
FAX (619) 661-1055
Japan: Phone 81-7-2070-6306
FAX 81-7-2070-1174
General Purpose - 1N5820-1N5825
Motorola - MBR and MBRD series
(see above for phone number)
V
IN
Capacitors:
2.21V
REF
INTERNAL
BIAS
100kHz
OSCILLATOR
CURRENT-LIMIT
COMPARATOR
ERROR
AMPLIFIER
FB
V
C
PWM
LOGIC
CONTROL
Diodes:
SWITCH
MAX724
Through-Hole Components
GND
V
SW
Inductors:
Figure 1. MAX724 Block Diagram
INPUT
8V TO 40V
V
IN
220µF
V
SW
L
50µH (MAX724)
100µH (MAX726)
D
MBR745
FB
OUTPUT
5V at 5A (MAX724)
5V at 2A (MAX726)
R1
2.8k
C1
470µF
R2
2.2k
Capacitors:
V
C
R3
2.7k
C2
0.01µF
MAX724
MAX726
GND
Diodes:
Figure 2. Basic Step-Down Converter
6
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
