MAX1775 查看數據表（PDF） - Maxim Integrated

零件编号

产品描述 (功能)

比赛名单

MAX1775

Dual-Output Step-Down DC-DC Converter for PDA/Palmtop Computers

Maxim Integrated 

Dual-Output Step-Down

DC-DC Converter for PDA/Palmtop Computers

IN

2.7V TO 5.5V

C1

6

8 1µF

IN CVH 15

ON OFF 1 SHDNM

INC M1

ON OFF 2 SHDNC

PDRV 7

C6

10µF

LM

R1

5µH

33mΩ

C2

1µF

C3

0.22µF

5 CVL

NDRV 4

M2

9 REF

MAX1775 CS+ 11

CS- 12

FBM 10

3 PGND

14 GND

LXC 16

LC

5.4µH

R4

FBC 13

CORE

C5 1.8V

22µF 1.5A

R5

MAIN

3.3V

2A

C4

R2

47µF

R3

Figure 1. Typical Application Circuit (Low Input Voltage)

Detailed Description

The MAX1775 dual step-down DC-DC converter is

designed to power PDA, palmtop, and subnotebook

computers. Normally, these devices need two separate

power supplies—one for the processor and another

higher voltage supply for the peripheral circuitry. The

MAX1775 provides an adjustable +1.25V to +5.5V main

output designed to power the peripheral circuitry of

PDAs and similar devices. The main output delivers

over 2A output current. The lower voltage core convert-

er has an adjustable +1.0V to +5.0V output, providing

up to 1.5A output current. Both regulators utilize a pro-

prietary regulation scheme, allowing PWM operation at

medium to heavy loads, and automatically switch to

pulse skipping at light loads for improved efficiency.

Figure 1 is the typical application circuit.

Operating Modes for the

Step-Down Converters

When delivering low output currents, the MAX1775

operates in discontinuous conduction mode. Current

through the inductor starts at zero, rises above the min-

imum current limit, then ramps down to zero during

each cycle (see Typical Operating Characteristics).

The switch waveform may exhibit ringing, which occurs

at the resonant frequency of the inductor and stray

capacitance, due to the residual energy trapped in the

core when the rectifier MOSFET turns off. This does not

degrade the circuit performance.

When delivering medium-to-high output currents, the

MAX1775 operates in PWM continuous-conduction

mode. In this mode, current always flows through the

inductor and never ramps to zero. The control circuit

adjusts the switch duty cycle to maintain regulation

without exceeding the peak switching current set by

the current-sense resistor.

100% Duty Cycle and Dropout

The MAX1775 operates with a duty cycle up to 100%.

This feature extends the input voltage range by turning

the MOSFET on continuously when the supply voltage

approaches the output voltage. This services the load

when conventional switching regulators with less than

100% duty cycle would fail. Dropout voltage is defined

as the difference between the input and output volt-

ages when the input is low enough for the output to

drop out of regulation. Dropout depends on the MOS-

FET drain-to-source on-resistance, current-sense resis-

tor, and inductor series resistance, and is proportional

to the load current:

Dropout voltage =

IOUT ✕ [RDS(ON) + RSENSE + RINDUCTOR]

10 ______________________________________________________________________________________

Share Link: