Rainbow-electronics MAX711 Manual do Utilizador descarregar pdf (Página 8)

MAX710/MAX711

3.3V/5V or Adjustable,

Step-Up/Down DC-DC Converters

8 _______________________________________________________________________________________

MAX710

SHDN LX

STBY

N/E

LBO

LBI+

LBI-

REF

PGND

0.1µF

GND ILIM

OUT

4.7µF

100µF

= +1.8V TO +11V

100µF

3/5

MAX710

SHDN LX

STBY

N/E

LBO

R5 = R6

- V

REF

)

REF

R5 = R6 (4.08)

WHEN V

REF

= 1.28V

AND V

= 6.5V

LBI+

LBI-

REF

PGND

0.1µF

GND ILIM

OUT

4.7µF

100µF

= +1.8V TO +11V

100µF

3/5

Figure 2a. High-Efficiency Operating Configuration for

BATT

< V

OUT

Figure 2b. High-Efficiency Operating Configuration for

BATT

< 6.5V

In high-efficiency mode (N/E = low), the maximum

input voltage is limited to 7V. This voltage limitation is

easily overcome, however, by configuring the LBO out-

put to change modes based on input voltage, allowing

an 11V maximum input with high-efficiency configura-

tions. Four operating configurations are described in

Table 1 and in the following subsections.

Configuration 1: High Efficiency, 7V Max V

With N/E connected to GND, when the IC boosts, the

linear regulator operates only as a switch, with mini-

mum forward drop, until V

> V

OUT

(where linear regu-

lation begins). This configuration is limited to no more

than 7V input, but provides best efficiency for battery-

only operation or low-voltage AC adapter usage.

Configuration 2: High Efficiency, V

BATT

< V

OUT

In this configuration, N/E is driven high by LBO when

> V

OUT

(Figure 2a). When V

< V

OUT

, the IC

boosts, and the linear regulator operates as a switch,

with minimum forward drop. When V

> V

OUT

, the lin-

ear regulator operates with V

forward drop, while V

increases by V

so that OUT maintains regulation. V

is set inside the IC to approximately 0.5V (at 5V V

OUT

When V

is only slightly higher than V

OUT

, conversion

efficiency is poorer than in configuration 1, so configu-

ration 2 is most suitable when the battery voltage is less

than V

OUT

, but the AC adapter output is greater than

OUT

Up to 11V2

Up to 11V4

Up to 11V3

High efficiency,

BATT

< V

OUT

(Figure 2a)

Low noise

High efficiency,

11V, V

BATT

< 6.5V

(Figure 2b)

DESCRIPTION

High efficiency,

7V max V

INPUT

VOLTAGE

Up to 7V1

NO.

LBO = N/E

LBI- = V

OUT

LBI+ = V

N/E = PS

LBO = N/E

LBI- = REF

LBI+ = R5, R6

CONNECTIONS

N/E = GND

Table 1. Operating Configurations

1 2 3 4 5 6 7 8 9 10 11 12

MAX710/MAX711 1
3.3V/5V or Adjustable 1

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