MAX796 Maxim, MAX796 Datasheet - Page 10

• Manufacturer Part Number: MAX796
• Description: Step-Down Controllers with Synchronous Rectifier for CPU Power
• Manufacturer: Maxim

Step-Down Controllers with
Synchronous Rectifier for CPU Power
It is easy to adapt the basic MAX797 single-output 3.3V
buck converter (Figure 1) to meet a wide range of
applications with inputs up to 28V (limited by choice of
external MOSFET). Simply substitute the appropriate
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. Each of these circuits is rated for a continuous
load current at T
10A applications can withstand a continuous output
short-circuit to ground. The 3A and 5A applications can
withstand a short circuit of many seconds duration, but
the synchronous-rectifier MOSFET overheats, exceed-
ing the manufacturer’s ratings for junction temperature
by 50°C or more.
Figure 1. Standard 3.3V Application Circuit
10
______Standard Application Circuit
NOTE: KEEP CURRENT-SENSE
(OPTIONAL)
C1
INPUT
LOW-NOISE
______________________________________________________________________________________
0.01 F
CONTROL
CONTROL
LINES SHORT AND CLOSE
TOGETHER. SEE FIG. 10
ON/OFF
C6
6
2
1
C7
0.1 F
A
SHDN
SKIP
SS
= +85°C, as shown. The 1A, 2A and
10
7
FB
V+
MAX797
5
SYNC
11
VL
J1
150kHz/300kHz
JUMPER
PGND
GND
CSH
BST
CSL
REF
DH
DL
LX
16
14
15
13
12
8
9
4
3
D2
CMPSH-3
C3
0.1 F
C5
0.33 F
If the 3A or 5A circuit must be guaranteed to withstand
a continuous output short circuit indefinitely, see the
section MOSFET Switches under Selecting Other
Components . Don’t change the frequency of these cir-
cuits without first recalculating component values (par-
ticularly inductance value at maximum battery voltage).
The MAX796 is a BiCMOS, switch-mode power-supply
controller designed primarily for buck-topology regula-
tors in battery-powered applications where high effi-
ciency and low quiescent supply current are critical.
The MAX796 also works well in other topologies such
as boost, inverting, and CLK due to the flexibility of its
floating high-speed gate driver. Light-load efficiency is
enhanced by automatic idle-mode operation—a vari-
able-frequency pulse-skipping mode that reduces
Q1
Q2
_______________Detailed Description
D1
C4
4.7 F
L1
R1
C2
REF OUTPUT
+2.505V AT 100 A
+5V AT
5mA
+3.3V
OUTPUT
GND
OUT