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MAX710

3.3V/5V or Adjustable, Step-Up/Down DC-DC Converters

Maxim Integrated 

MAX710/MAX711

3.3V/5V or Adjustable,

Step-Up/Down DC-DC Converters

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.

Table 1. Operating Configurations

NO.

DESCRIPTION

INPUT

VOLTAGE

CONNECTIONS

1

High efficiency,

7V max VIN

Up to 7V N/E = GND

High efficiency,

2

VBATT < VOUT

(Figure 2a)

Up to 11V

LBO = N/E

LBI- = VOUT

LBI+ = VIN

High efficiency,

LBO = N/E

3

11V, VBATT < 6.5V

Up to 11V LBI- = REF

(Figure 2b)

LBI+ = R5, R6

4

Low noise

Up to 11V N/E = PS

Configuration 1: High Efficiency, 7V Max VIN

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

linear regulator operates only as a switch, with mini-

mum forward drop, until VIN > VOUT (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, VBATT < VOUT

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

VIN > VOUT (Figure 2a). When VIN < VOUT, the IC

boosts, and the linear regulator operates as a switch,

with minimum forward drop. When VIN > VOUT, the lin-

ear regulator operates with VFV forward drop, while VPS

increases by VFV so that OUT maintains regulation. VFV

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

When VIN is only slightly higher than VOUT, conversion

efficiency is poorer than in configuration 1, so configu-

ration 2 is most suitable when the battery voltage is less

than VOUT, but the AC adapter output is greater than

VOUT.

VIN = +1.8V TO +11V

100µF

SHDN

LX

STBY

PS

N/E

OUT

LBO MAX710

LBI+

LBI-

REF

3/5

0.1µF

PGND GND ILIM

L1

100µF

4.7µF

VIN = +1.8V TO +11V

100µF

R5

R6

0.1µF

SHDN

LX

STBY

PS

N/E

OUT

LBO MAX710

LBI+

LBI-

REF

3/5

PGND GND ILIM

L1

100µF

4.7µF

(VIN - VREF)

R5 = R6 VREF

R5 = R6 (4.08)

WHEN VREF = 1.28V

AND VIN = 6.5V

Figure 2a. High-Efficiency Operating Configuration for

VBATT < VOUT

8

Figure 2b. High-Efficiency Operating Configuration for

VBATT < 6.5V

Maxim Integrated

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