Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Holder SOIC 8

_______________General Description

The MAX887 high-efficiency, step-down DC-DC con-

verter provides an adjustable output from 1.25V to

10.5V. It accepts inputs from 3.5V to 11V and delivers

600mA. Operation to 100% duty cycle minimizes

dropout voltage (300mV typ at 500mA). Synchronous

rectification reduces output rectifier losses, resulting in

efficiency as high as 95%.

Fixed-frequency pulse-width modulation (PWM)

reduces noise in sensitive communications applica-

tions. Using a high-frequency internal oscillator allows

tiny surface-mount components to reduce PC board

area, and eliminates audio-frequency interference. A

SYNC input allows synchronization to an external clock

to avoid interference with sensitive RF and data-

acquisition circuits.

The MAX887 features current-mode operation for supe-

rior load/line-transient response. Cycle-by-cycle current

limiting protects the internal MOSFET and rectifier. A

low-current (2.5µA typ) shutdown mode conserves bat-

tery life.

________________________Applications

Portable Instruments

Cellular Phones and Radios

Personal Communicators

Distributed Power Systems

Computer Peripherals

____________________________Features

♦ 95% Efficiency

♦ 600mA Output Current

♦ Cycle-by-Cycle Current Limiting

♦ Low-Dropout, 100% Duty-Cycle Operation,

300mV at 500mA

♦ Internal 0.6Ω (typ) MOSFET

♦ Internal Synchronous Rectifier

♦ High-Frequency Current-Mode PWM

♦ External SYNC or Internal 300kHz Oscillator

♦ Guaranteed 260kHz to 340kHz Internal Oscillator

Frequency Limits

♦ 2.5µA Shutdown Mode

MAX887

100% Duty Cycle, Low-Noise,

Step-Down, PWM DC-DC Converter

________________________________________________________________

Maxim Integrated Products

V+

SYNC

GND

SHDN

REF

MAX887

TOP VIEW

__________________Pin Configuration

MAX887

REF

165kΩ

100kΩ

0.047µF

2.2µF

47µF

100pF

0.33µF

33µH

V+ LX

GND

SYNC

SHDN

OUT

= 3.3V

OUT

= 1.25V (R1/R2 + 1)

= 3.5V to 11V

OFF

__________Typical Operating Circuit

19-1142 Rev 0; 9/96

PART

MAX887HC/D

MAX887HESA -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*

8 SO

EVALUATION KIT MANUAL

AVAILABLE

______________Ordering Information

Contact factory for availability. Dice are tested at T

= +25°C.

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

Summary of content (12 pages)

PAGE 1
9-1142 Rev 0; 9/96 ANUAL N KIT M IO T A U EVAL BLE AVAILA 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter ________________________Applications Portable Instruments ____________________________Features ♦ 95% Efficiency ♦ 600mA Output Current ♦ Cycle-by-Cycle Current Limiting ♦ Low-Dropout, 100% Duty-Cycle Operation, 300mV at 500mA ♦ Internal 0.
PAGE 2
MAX887 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter ABSOLUTE MAXIMUM RATINGS REF, FB, SYNC, VL to GND..................................... -0.3V to +6V V+ to GND ............................................................. -0.3V to +12V SHDN, LX to GND ....................................... -0.3V to (V+ + 0.3V) PGND to GND ...................................................... -0.3V to +0.3V Continuous Power Dissipation (TA = +70°C) SO (derate 9.09mW/°C above +70°C) ........................
PAGE 3
100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter MAX887 ELECTRICAL CHARACTERISTICS (V+ = +7V, PGND = GND = 0V, SHDN = V+, (TA = -40°C to +85°C), unless otherwise noted.) (Note 2) PARAMETER SYMBOL Supply Range CONDITIONS MIN V+ TYP 3.5 MAX UNITS 11.0 V Quiescent Supply Current (PWM Mode) IV+, PWM IOUT = 0mA, SYNC = 3.0V 2.7 4.0 mA Quiescent Supply Current (PFM Mode) IV+, PFM IOUT = 0mA, SYNC = GND 0.2 0.
PAGE 4
____________________________Typical Operating Characteristics (continued) (Circuit of Figure 2, TA = +25°C, unless otherwise noted.) VIN = 9V 30 IDLE MODE (SYNC = GND) VOUT = 3.3V 0.01 0.1 VIN = 7V IDLE MODE (SYNC = GND) VOUT = 5V 20 10 0.6 0.001 800 600 400 C2, C3 = 47µF L1 = 33µH VIN = 5V VOUT = 3.3V VOUT = -5% at IOUT(MAX) 200 A 2.0 A: VOUT = 3.3V, PWM MODE B: VOUT = 3.3V, PFM MODE 1.5 1.0 C 0.5 600 3.0 2 4 320 FREQUENCY (kHz) 330 310 300 290 280 VOUT = 3.
PAGE 5
100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter LIGHT-LOAD, PWM-MODE SWITCHING WAVEFORMS MAX887-12 MAX887-13 HEAVY-LOAD, PWM-MODE SWITCHING WAVEFORMS A A B B C C 0mA 1µs/div 1µs/div VIN = 5V, VOUT = 3.3V, LOAD = 0mA A: LX, 5V/div B: VOUT, 20mV/div, AC COUPLED C: INDUCTOR CURRENT, 500mA/div VIN = 5V, VOUT = 3.
PAGE 6
_____________________________Typical Operating Characteristics (continued) (Circuit of Figure 2, TA = +25°C, unless otherwise noted.) LINE-TRANSIENT RESPONSE MAX887-16 MAX887-17 LOAD-TRANSIENT RESPONSE A A B B C 200µs/div 40µs/div VIN = 5V TO 11V, VOUT = 3.3V, LOAD = 500mA, PWM MODE A: VIN, 5V/div B: VOUT, 20mV/div, AC COUPLED VIN = 5V, VOUT = 3.
PAGE 7
100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter PIN NAME FUNCTION 1 SHDN 2 FB 3 REF 4 VL 5 GND Ground 6 SYNC Oscillator Synchronization and PWM Control Input. SYNC is a logic-level input. Tie SYNC to VL for internal 300kHz PWM operation at all loads. The oscillator synchronizes to the negative edge of an external clock between 10kHz and 400kHz. The MAX887 operates in PWM mode when SYNC is clocked. Tying SYNC to GND allows a reduced supply-current mode at light loads.
PAGE 8
MAX887 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter _______________Detailed Description The MAX887 is a step-down, pulse-width modulation (PWM) DC-DC converter that provides an adjustable output from 1.25V to 10.5V. It accepts inputs from 3.5V to 11V and delivers up to 600mA. An internal MOSFET and synchronous rectifier reduce PC board area while maintaining high efficiency. Cycle-by-cycle current limiting protects the internal MOSFETs and reduces system stress during overload conditions.
PAGE 9
100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter Forced PWM and Idle Mode Operation Connect SYNC to VL for normal forced PWM operation. Forced PWM operation is desirable in sensitive RF and data-acquisition applications, to ensure that switchingnoise harmonics do not interfere with sensitive IF and data-sampling frequencies.
PAGE 10
MAX887 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter when to turn off this synchronous rectifier. A fourth comparator (ILIM) is used at the P-channel MOSFET switch for overcurrent detection. This protects the system, external components, and internal MOSFETs under overload conditions. ple and transient response. Lower oscillator frequencies require a larger-value output capacitor.
PAGE 11
100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter ___________________Chip Information TRANSISTOR COUNT: 2006 SUBSTRATE CONNECTED TO GND Output Diode Selection A 1A external diode (D1) is required as an output rectifier to pass inductor current during the second half of each cycle. This diode operates in PFM mode and during transition periods while the synchronous rectifier is off. Use a Schottky diode to prevent the slow internal diode of the N-channel MOSFET from turning on.
PAGE 12
MAX887 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter ________________________________________________________Package Information DIM D 0°-8° A 0.101mm 0.004in. e B A1 E 12 C H L Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.) A A1 B C E e H L INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016 DIM PINS D D D 8 14 16 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.