Rainbow Electronics MAX1638 - Manual (Page 7)

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
0.056 µ F
REF
C4, 1.0 µ F
CERAMIC
RC1
1k
TO
AGND
R6
100k
C5
0.1 µ F
C6
10 µ F
R5
10 Ω
TO V
DD
FREQ
LG
D0
D1
D2
D3
D4
C7
0.1 µ F
D2
CMPSH-3
C3
0.1
µ F
L1
R1
V
IN
= 5V
C1
C2
LOCAL
BYPASSING
MAX1638
P1
C8
1
µ F
R2
V OUT = 1.3V
TO 3.5V
N3
LOAD
CSL