Rainbow-electronics MAX1844 Manual de usuario descargar pdf (Pagina 10)

Detailed Description

The MAX1844 buck controller is targeted for low-voltage

power supplies for notebook computers. Maxim’s propri-

etary Quick-PWM pulse-width modulator in the MAX1844

is specifically designed for handling fast load steps while

maintaining a relatively constant operating frequency

and inductor operating point over a wide range of input

voltages. The Quick-PWM architecture circumvents the

poor load-transient timing problems of fixed-frequency

current-mode PWMs while also avoiding the problems

caused by widely varying switching frequencies in con-

ventional constant-on-time and constant-off-time PWM

schemes.

5V Bias Supply (V

and V

)

The MAX1844 requires an external 5V bias supply in

addition to the battery. Typically, this 5V bias supply is

the notebook’s 95% efficient 5V system supply. Keeping

the bias supply external to the IC improves efficiency

and eliminates the cost associated with the 5V linear reg-

ulator that would otherwise be needed to supply the

PWM circuit and gate drivers. If stand-alone capability is

needed, the 5V supply can be generated with an exter-

nal linear regulator such as the MAX1615.

The battery and 5V bias inputs can be connected

together if the input source is a fixed 4.5V to 5.5V supply.

If the 5V bias supply is powered up prior to the

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

10 ______________________________________________________________________________________

UVP

7V TO 20V

BIAS SUPPLY

330µF

SEE TABLE 1 FOR OTHER COMPONENT SELECTIONS.

POWER-GOOD

INDICATOR

4.7µH

OUT

2.5V

SHDN

V+

CMPSH-3

3.3µF

0.1µF

0.22µF

270kΩ

130kΩ

100kΩ

SENSE

15mΩ

4.7µF

20Ω

SKIP

ILIM

ON/OFF

CONTROL

LOW-NOISE

CONTROL

BST

OUT

LATCH

OVP

PGOOD

MAX1844

TON

REF

GND

10µF

Figure 1. Standard Application Circuit

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 22 23

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Rainbow-electronics MAX1844 Manual de usuario Pagina 10

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