Datasheet

MAX1638
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
_______________________________________________________________________________________ 7
Figure 1. Standard Application Circuit
_____Standard Application Circuits
The predesigned MAX1638 circuit shown in Figure 1
meets a wide range of applications with output currents
up to 19A and higher. Use Table 1 to select compo-
nents appropriate for the desired output current range,
and adapt the evaluation kit PC board layout as neces-
sary. This circuit represent a good set of trade-offs
between cost, size, and efficiency while staying within
the worst-case specification limits for stress-related
parameters, such as capacitor ripple current.
The MAX1638 circuit was designed for the specified
frequency. Do not change the switching frequency
without first recalculating component values—particu-
larly the inductance, output filter capacitance, and RC1
resistance values. Table 2 lists the voltage adjustment
DAC codes.
_______________Detailed Description
The MAX1638 is a BiCMOS power-supply controller
designed for use in switch-mode, step-down (buck)
topology DC-DC converters. Synchronous rectification
provides high efficiency. It is intended to provide the
high precision, low noise, excellent transient response,
and high efficiency required in today’s most demand-
ing applications.
N1
N2
D1
(OPTIONAL)
R3
(OPTIONAL)
R4
(OPTIONAL)
V
CC
V
DD
PWROK
BST
DH
LX
DL
PGND
CSH
FB
PDRV
NDRV
AGND
CC1
CC2
CC1
1000pF
CC2
0.056μF
REF
C4, 1.0μF
CERAMIC
RC1
1k
TO
AGND
R6
100k
C5
0.1μF
C6
10μF
R5
10Ω

TO V
DD
FREQ
LG
D0
D1
D2
D3
D4
C7
0.1μF
D2
CMPSH-3
C3
0.1μF
L1
R1
V
IN
= 5V
C1
C2
LOCAL
BYPASSING
MAX1638
P1
C8
1μF
R2
V
OUT
= 1.3V
TO 3.5V
N3
LOAD
CSL