Rainbow Electronics MAX1635 - Manual (Page 8)

_______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
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.
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
8 _______________________________________________________________________________________
MAX1631
MAX1634
V+ SHDN VL SECFB
INPUT
ON/OFF
C3
GND
REF SEQ
1 µ F
+2.5V ALWAYS ON
*1A SCHOTTKY DIODE REQUIRED
FOR THE MAX1631 (SEE
OUTPUT
OVERVOLTAGE PROTECTION SECTION).
+5V ALWAYS ON
Q1
5V ON/OFF
3.3V ON/OFF
Q4
0.1 µ F 0.1 µ F
L2 R2 +3.3V OUTPUT
C2 *
4.7 µ F
0.1 µ F
4.7 µ F
0.1 µ F
10 Ω
0.1 µ F
Q3
0.1 µ F
DL3
CSH3
CSL3
FB3
RESET
RESET OUTPUT
SKIP
STEER
Q2
L1 R1 +5V OUTPUT
C1 DL5
LX5
DH5
BST5
BST3
SYNC
DH3
LX3
PGND
CSL5
CSH5
RUN/ON3
TIME/ON5
FB5
*
Figure 1. Standard 3.3V/5V Application Circuit (MAX1631/MAX1634)