Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Boost, Flyback, SEPIC SOIC 8

_______________General Description

The MAX629 low-power DC-DC converter features an

internal N-channel MOSFET switch and programmable

current limiting. It is designed to supply positive or neg-

ative bias voltages up to ±28V from input voltages in

the 0.8V to V

OUT

range, and can be configured for

boost, flyback, and SEPIC topologies.

The MAX629’s current-limited pulse-frequency-modula-

tion (PFM) control scheme provides high efficiency over

a wide range of load conditions. An internal, 0.5A N-

channel MOSFET switch reduces the total part count,

and a high switching frequency (up to 300kHz) allows

for tiny surface-mount magnetics.

The MAX629’s combination of low supply current, logic-

controlled shutdown, small package, and tiny external

components makes it an extremely compact and effi-

cient high-voltage biasing solution that’s ideal for bat-

tery-powered applications. The MAX629 is available in

an 8-pin SO package.

________________________Applications

Positive or Negative LCD Bias Generators

High-Efficiency DC-DC Boost Converters

Varactor Tuning Diode Bias

Palmtop Computers

2-Cell and 3-Cell Battery-Powered Applications

____________________________Features

♦ Internal, 500mA, 28V N-Channel Switch

(No External FET Required)

♦ Generates Positive or Negative Output Voltages

♦ 80µA Supply Current

♦ 1µA Max Shutdown Current

♦ Up to 300kHz Switching Frequency

♦ Adjustable Current Limit Allows Use of Small,

Inexpensive Inductors

♦ 8-Pin SO Package

MAX629

28V, Low-Power, High-Voltage,

Boost or Inverting DC-DC Converter

________________________________________________________________

Maxim Integrated Products

MAX629

SHDN

+2.7V

TO +5.5V

GND

ISET

POL

REF

POSITIVE OUTPUT VOLTAGE

MAX629

SHDN

-V

OUT

-28V

OUT

28V

+2.7V

TO +5.5V

GND

REF

POL

NEGATIVE OUTPUT VOLTAGE

ISET

___________________________________________________Typical Operating Circuit

19-1219; Rev 1; 6/97

PART TEMP. RANGE PIN-PACKAGE

______________Ordering Information

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

Note: To order tape-and-reel shipping, add “-T” to the end of

the part number.

Dice are tested at T

= +25°C, DC parameters only.

Pin Configuration appears at end of data sheet.

MAX629C/D 0°C to +70°C Dice*

MAX629ESA -40°C to +85°C 8 SO

EVALUATION KIT MANUAL

AVAILABLE

Summary of content (12 pages)

PAGE 1
9-1219; Rev 1; 6/97 ANUAL N KIT M IO T A U EVAL BLE AVAILA 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter The MAX629’s combination of low supply current, logiccontrolled shutdown, small package, and tiny external components makes it an extremely compact and efficient high-voltage biasing solution that’s ideal for battery-powered applications. The MAX629 is available in an 8-pin SO package.
PAGE 2
MAX629 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC to GND) ..................................-0.3V to +6V SHDN to GND...........................................................-0.3V to +6V ISET, REF, FB, POL to GND .......................-0.3V to (VCC + 0.3V) LX to GND ..............................................................-0.3V to +30V Continuous Power Dissipation (TA = +70°C) SO (derate 5.88mW/°C above +70°C) .......................
PAGE 3
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter MAX629 ELECTRICAL CHARACTERISTICS (continued) (VCC = +5V, CREF = 0.1µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) TYP MAX UNITS REF Load Regulation PARAMETER IREF = 0µA to 100µA, CREF = 0.47µF (Note 3) CONDITIONS MIN 10 25 mV Line Regulation Circuit of Figure 2, VOUT = 24V, VCC = 3V to 5.5V, ILOAD = 5mA 0.
PAGE 4
____________________________Typical Operating Characteristics (continued) (SHDN = VCC , CREF = 0.1µF, TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. INPUT VOLTAGE REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT VIN = VCC 500 VIN = VCC = 5V C4 = 0.47µF REFERENCE VOLTAGE (V) 600 IIN 400 IIN 300 200 ICC 100 MAX629-08 1.255 MAX629-07 700 1.250 1.245 1.240 1.235 0 1.
PAGE 5
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter PIN NAME FUNCTION 1 SHDN Active-Low Shutdown Input. A logic low puts the MAX629 in shutdown mode and reduces supply current to 1µA. 2 POL Polarity Input. Changes polarity and threshold of FB to allow regulation of either positive or negative output voltages. Set POL = GND for positive output voltage, or set POL = VCC for negative output voltage. 3 REF 1.25V Reference Output. Bypass to GND with a 0.1µF capacitor for IREF ≤ 10µA.
PAGE 6
MAX629 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter POL REF MIN OFF-TIME GENERATOR TRIG POLARITY 1.25V REF START-UP MAX629 Q ERROR AMP LX F/F S FB Q R START-UP COMPARATOR ISET TRIG 1V MAX ON-TIME GENERATOR (10µs) Q SHDN CONTROL VCC GND Figure 1. Functional Diagram without a significant loss of accuracy. Begin by selecting R2 to be in the 10kΩ to 200kΩ range, and calculate R1 using the applicable equation from the following subsections.
PAGE 7
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter Inductor Selection The MAX629’s high switching frequency allows for the use of a small inductor. The 47µH inductor shown in the VIN +0.8V TO +15V VIN +0.8V TO +24V VCC +2.7V TO +5.5V VCC +2.7V TO +5.5V C1 10µF 35V * L1 47µH C3 0.1µF SHDN ISET MAX629 FB R2 31.6k 1% POL REF VOUT +24V LX R1 576k 1% C1 10µF 35V * L1 47µH C3 0.1µF D1 MBR0540L VCC C4 0.1µF Typical Operating Circuit is recommended for most applications.
PAGE 8
MAX629 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter Diode Selection The MAX629’s high switching frequency demands a high-speed rectifier. Schottky diodes, such as the 1N5819 or MBR0530L, are recommended. Make sure that the diode’s peak current rating exceeds the peak current set by ISET, and that its breakdown voltage exceeds the output voltage. Schottky diodes are preferred due to their low forward voltage. However, ultrahigh-speed silicon rectifiers are also acceptable.
PAGE 9
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter R1 RB FB MAX629 VBIAS R2 GND (REF) ( ) ARE FOR NEGATIVE OUTPUT VOLTAGE CONFIGURATIONS. Figure 4. Adjustable Output Voltage increasing usable battery life. Using separate supplies for VCC and VIN also reduces noise injection onto VCC by isolating it from the switching transients, allowing a smaller, less-expensive input filter capacitor to be used in many applications.
PAGE 10
MAX629 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter __________________Pin Configuration ___________________Chip Information TRANSISTOR COUNT: 653 SUBSTRATE CONNECTED TO GND TOP VIEW SHDN 1 8 VCC 7 LX REF 3 6 GND FB 4 5 ISET POL 2 MAX629 SO 10 ______________________________________________________________________________________
PAGE 11
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter SOICN.
PAGE 12
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter MAX629 NOTES 12 ______________________________________________________________________________________