Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
MAX1630–MAX1635
INPUT
C3
10Ω
0.1µF
V+ SHDN SECFB VL
4.7µF
Q1
0.1µF
+5V OUTPUT
R1
L1
Q2
0.1µF
LX5
DL5
MAX1631
PGND
CSH5
CSL5
CSH3
CSL3
FB3
FB5
RESET
5V ON/OFF
3.3V ON/OFF
TIME/ON5
SKIP
RUN/ON3
STEER
GND
REF
SEQ
RESET OUTPUT
LX3
SYNC
BST5
DH5
BST3
DH3
0.1µF
Q3
0.1µF
L2
R2
+3.3V OUTPUT
0.1µF
ON/OFF
+5V ALWAYS ON
4.7µF
C1
*
MAX1634
DL3
*
Q4
C2
+2.5V ALWAYS ON
1µF
*1A SCHOTTKY DIODE REQUIRED
FOR THE MAX1631 (SEE
OUTPUT
OVERVOLTAGE PROTECTION
SECTION).
Figure 1. Standard 3.3V/5V Application Circuit (MAX1631/MAX1634)
_______Standard Application Circuit
The basic MAX1631/MAX1634 dual-output 3.3V/5V
buck converter (Figure 1) is easily adapted to meet a
wide range of applications with inputs up to 28V by
substituting components from Table 1. These circuits
represent a good set of tradeoffs between cost, size,
and efficiency, while staying within the worst-case
specification limits for stress-related parameters, such
as capacitor ripple current. Don’t change the frequency
8
of these circuits without first recalculating component
values (particularly inductance value at maximum bat-
tery voltage). Adding a Schottky rectifier across each
synchronous rectifier improves the efficiency of these
circuits by approximately 1%, but this rectifier is other-
wise not needed because the MOSFETs required for
these circuits typically incorporate a high-speed silicon
diode from drain to source. Use a Schottky rectifier
rated at a DC current equal to at least one-third of the
load current.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
