MAX797CSLASHD datasheet(10/32 Pages) MAXIM

10 / 32 page

Step-Down Controllers with

Synchronous Rectifier for CPU Power

______________________________________________________________________________________

______Standard Application Circuit

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 TA = +85°C, as shown. The 1A, 2A and

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.

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).

_______________Detailed Description

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

MAX797

CSL

CSH

SYNC

V+

CMPSH-3

150kHz/300kHz

JUMPER

NOTE: KEEP CURRENT-SENSE

LINES SHORT AND CLOSE

TOGETHER. SEE FIG. 10

REF

GND

+5V AT

5mA

+3.3V

OUTPUT

GND

OUT

BST

LOW-NOISE

CONTROL

PGND

SKIP

ON/OFF

CONTROL

SHDN

INPUT

REF OUTPUT

+2.505V AT 100

µA

0.33

µF

4.7

µF

0.1

µF

0.01

µF

(OPTIONAL)

0.1

µF

Figure 1. Standard 3.3V Application Circuit

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