MAX710C/D Просмотр технического описания (PDF) - Maxim Integrated

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MAX710C/D

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

______________________________________________________________Pin Description

PIN

MAX710 MAX711

1

1

2

2

3

3

4

4

5

5

6

—

—

6

7

7

8

8

9

9

10

10

11

11

12

12

13

13

14

14

15

15

16

16

NAME

LX

PGND

ILIM

SHDN

STBY

3/5

FB

N/E

LBO

OUT

LBI-

LBI+

PS

REF

GND

PGND

LX

FUNCTION

Drain Connection for internal N-channel power MOSFET

Power Ground

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

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

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

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

Feedback Input

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

lowest noise. See Operating Configurations section.

Low-Battery Comparator Output

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

Negative Input to Low-Battery Comparator

Positive Input to Low-Battery Comparator

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

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

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

Power Ground

Drain Connection for internal N-channel power MOSFET

_______________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 0.7Ω (at

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

a conventional linear regulator when VIN > VOUT. This

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

headroom (VFV, typically 0.5V at 5V output) across the

linear regulator. Boost mode efficiency is then about

10% lower than with N/E high.

6

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