_______________Detailed Description

The MAX710/MAX711 integrate a step-up DC-DC con-

verter with a linear regulator to provide step-up/down

voltage conversion. The step-up switch-mode regulator

contains an N-channel power MOSFET switch. It also

shares a precision voltage reference with a linear regu-

lator that contains a P-channel MOSFET pass element

(Figure 1).

Step-Up Operation

A pulse-frequency-modulation (PFM) control scheme

with a constant 1µs off-time and variable on-time con-

trols the N-channel MOSFET switch. The N-channel

switch turns off when the part reaches the peak current

limit or the 4µs maximum on-time. The ripple frequency

is a function of load current and input voltage.

Step-Down Operation

The low-dropout linear regulator consists of a refer-

ence, an error amplifier, and a P-channel MOSFET. The

reference is connected to the error amplifier’s inverting

input. The error amplifier compares this reference with

the selected feedback voltage and amplifies the differ-

ence. The difference is conditioned and applied to the

P-channel pass transistor’s gate.

Operating Configurations

The MAX710/MAX711 have several operating configu-

rations to minimize noise and optimize efficiency for dif-

ferent input voltage ranges. These configurations are

accomplished via the N/E input, which controls opera-

tion of the on-chip linear regulator.

With N/E low, the linear regulator behaves as a 0.7

Ω (at

5V output) PFET switch when the IC is boosting, and as

provides optimum boost efficiency, but the PFET does

little to reject boost-converter output ripple. With N/E

high, boost ripple rejection is optimized by maintaining

linear regulator. Boost mode efficiency is then about

10% lower than with N/E high.

3.3V/5V or Adjustable,

Step-Up/Down DC-DC Converters

6

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______________________________________________________________Pin Description

Drain Connection for internal N-channel power MOSFET

LX

1

Power Ground

PGND

2

Shutdown Input. When low, the entire circuit is off and OUT is actively pulled to GND.

SHDN

4

Inductor Current-Limit-Select Input. Connect to GND for 1.5A limit and to PS for 0.8A limit.

ILIM

3

Standby Input. Connect to GND to disable boost circuit. Connect to PS for normal operation.

STBY

5

Selects low-noise or high-efficiency mode. Connect to GND for high efficiency and to PS for

lowest noise. See

Operating Configurations section.

N/E

7

Selects the output voltage. Connect to GND for 5V output and to OUT for 3.3V output.

3/5

6

2

4

3

5

7

—

1

Low-Battery Comparator Output

LBO

8

8

Negative Input to Low-Battery Comparator

LBI-

10

Source of internal PFET regulator. The IC is powered from PS.

PS

12

Positive Input to Low-Battery Comparator

LBI+

11

1.28V Reference Voltage Output. Bypass with a 0.1µF capacitor to GND.

REF

13

Power Ground

PGND

15

Analog Ground. Must be low impedance. Solder directly to ground plane.

GND

14

10

12

11

13

15

14

9

Drain Connection for internal N-channel power MOSFET

LX

16

16

Linear-Regulator Output. Bypass with a 4.7µF capacitor to GND.

OUT

9

MAX711

MAX710

FUNCTION

NAME

PIN

Feedback Input

FB

—

6