Datasheet

_______Standard Application Circuit
The basic MAX1631A/MAX1634A 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. Do not change the frequen-
cy of these circuits without first recalculating compo-
nent values (particularly inductance value at maximum
battery voltage). Adding a Schottky rectifier across
each synchronous rectifier improves the efficiency of
these circuits by approximately 1%, but this rectifier is
otherwise not needed because the MOSFETs required
for these circuits typically incorporate a high-speed sili-
con diode from drain to source. Use a Schottky rectifier
rated at a DC current equal to at least 1/3 of the load
current.
MAX1630A–MAX1635A
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
8 _______________________________________________________________________________________
MAX1631A
MAX1634A
V+ SHDN VLSECFB
INPUT
ON/OFF
C3
GND
REF
SEQ
1
μ
F
+2.5V ALWAYS ON
*1A SCHOTTKY DIODE REQUIRED
FOR THE MAX1631A (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 (MAX1631A/MAX1634A)