5 V/3 .3 V o r Ad ju s t a b le , 1 0 0 % Du t y-Cyc le ,
Hig h -Effic ie n c y, S t e p -Do w n DC-DC Co n t ro lle rs
/MAX1627
INPUT
INPUT
C2
C3
68µF LOW-ESR
TANTALUM
C2
C3
0.47µF
C5
0.47µF
68µF LOW-ESR
TANTALUM
68µF LOW-ESR
TANTALUM
V+
V+
R
0.15Ω
R
SENSE
0.15Ω
SENSE
MAX1627
MAX1626
3/5
N.C.
C4
OUT
SHDN
REF
CS
CS
U1
U1
LOGIC-LEVEL MOSFET
LOGIC-LEVEL MOSFET
P
SHDN
REF
P
EXT
EXT
L1
L1
ADJUSTABLE
22µH, 3A
68µH, 0.7A
OUTPUT
OUTPUT
GND
OUT
GND
FB
C1
220µF
LOW-ESR
TANTALUM
C4
0.1µF
C1
100µF
LOW-ESR
TANTALUM
D1
D1
0.1µF
R3
R2
L1: SUMIDA CDR1053-680
D1: MOTOROLA MBRS130T3
U1: MOTOROLA MMSF3P02HD
L1: SUMIDA CDRH125-220
D1: NIHON NSQ03A03
U1: MOTOROLA MMSF3P02HD
C
R2
Figure 8. MAX1627 Typical Operating Circuit
Figure 9. 0.5A Step-Down Converter
________________________Ap p lic a t io n s
3V TO 6V
INPUT
The MAX1626/MAX1627 typ ic a l op e ra ting c irc uits
(Figures 1 and 8) are designed to output 2A at a 5V
output voltage. The following circuits provide examples
and guidance for other applications.
C4
100µF
C5
100µF
C6
C7
C8
C9
1.0µF
0.1µF 0.1µF 1.0µF
Mic ro p o w e r S t e p -Do w n Co n ve rt e r
When designing a low-power, battery-based applica-
tion, choose an external MOSFET with low gate capaci-
tance (to minimize switching losses), and use a low
peak current limit to reduce I R losses. The circuit in
Figure 9 is optimized for 0.5A.
V+
CS
R
, R
CS1 CS2
0.025Ω
MAX1627
OUT
2
N.C.
Q1
SHDN
REF
LOGIC-LEVEL MOSFET
P
EXT
FB
L1
Hig h -Cu rre n t S t e p -Do w n Co n ve rt e r
The circuit in Figure 10 outputs 6A at 2.5V from a 5V or
3.3V input. High-current design is difficult, and board
layout is critical due to radiated noise, switching tran-
sients, and voltage gradients on the PC board traces.
Figure 11 is a recommended PC board design. Choose
OUTPUT
2.5V, 6A
2.7µH >8A
GND
C10
0.1µF
D1
R3
21.5k, 1%
R2
20k, 1%
C1
C2
C3
220µF
the external MOSFET to minimize R
. Keep the
DS(ON)
220µF 220µF
gate-charge factor below the MAX1626/MAX1627’s
d rive c a p a b ility (s e e Ext Ris e a nd Fa ll Time s vs .
Ca p a c ita nc e g ra p h in the Typ ic a l Op e ra ting
Characteristics). Otherwise, increased MOSFET rise
and fall times will contribute to efficiency losses. For
higher efficiencies, especially at low output voltages,
the MAX796 family of step-down controllers with syn-
chronous rectification is recommended.
C1–C3: SANYO OS-CON 220µF, 6.3V
C4, C5: SANYO OS-CON 100µF, 20V
RCS1, RCS2: 0.025Ω DALE WSL-2512
Q1: MOTOROLA MTB50PO3HDL
D1: NIEC C10T04Q
C
220pF
R2
L1: SUMIDA CDRH127-2R7NC
Figure 10. 6A Step-Down Converter
______________________________________________________________________________________ 13
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
