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General Description

The MAX685 DC-DC converter provides low-noise dual

outputs for powering CCD imaging devices and LCDs.

This device uses a single inductor to provide indepen-

dently regulated positive and negative outputs.

Integrated power switches are included in a small 24-

Pin 4mm x 4mm Thin QFN package to save space and

reduce cost. A 16-pin QSOP package is also available.

Each output delivers up to 10mA from a +2.7V to +5.5V

input voltage range. Output voltages are set indepen-

dently up to 24V and down to -9V. With a few additional

low-cost components, the output voltages can be set at

up to 45V and down to -16V. Output ripple magnitude is

30mVp-p. The MAX685 uses a fixed-frequency, pulse-

width-modulated (PWM) control scheme at 220kHz or

400kHz to permit output noise filtering and to reduce

the size of external components. The frequency can

also be synchronized to an external clock signal

between 200kHz and 480kHz.

The MAX685 has a power-OK indicator output (POK)

that signals when both outputs are within regulation. A

logic-controlled shutdown completely turns off both out-

puts and reduces supply current to 0.1µA. The user

can also set which output turns on first.

The preassembled MAX685 evaluation kit is available to

reduce design time.

Applications

Camcorders LCDs

Digital Cameras CCD Imaging Devices

Notebooks

Features

♦ Dual Output Using a Single Inductor

♦ Low-Noise Output, 30mVp-p Ripple

♦ Output Voltages up to 24V and down to -9V

(up to 45V and down to -16V with added

components)

♦ Internal Switches in a Small 24-Pin 4mm x 4mm

Thin QFN Package

♦ 220kHz/400kHz Fixed-Frequency PWM Operation

♦ Frequency Can Be Synchronized to External

Clock

♦ Power-OK Indicator

♦ Selectable Power-On Sequencing

♦ 0.1µA Logic-Controlled Shutdown

MAX685

Dual-Output (Positive and Negative),

DC-DC Converter for CCD and LCD

________________________________________________________________ Maxim Integrated Products 1

MAX685

OFF

INPUT

2.7V TO 5.5V

LXN

FBP

LXP

FBN

REFGND

NEGATIVE

OUTPUT

DOWN TO -9V,

10mA

POSITIVE

OUTPUT

UP TO 24V,

10mA

SHDN

SYNC

SEQ

POK

POS

NEG

OPTIONAL

POWER-OK

INDICATOR

MAX685

24-TQFN (4mm x 4mm)

TOP VIEW

N.C.

POK

SEQ

SHDN

I.C.

LXP

LXN

I.C.

N.C.

PGND

FBP

REF

FBN

GND

N.C.

SYNC

Typical Operating Circuit

19-1353; Rev 1; 6/03

PART

MAX685EEE -40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

Pin Configuration

Ordering Information

MAX685ETG -40°C to +85°C 24 TQFN

Summary of content (11 pages)

PAGE 1
9-1353; Rev 1; 6/03 L MANUA ION KIT HEET T A U L EVA TA S WS DA FOLLO Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD Features ♦ Dual Output Using a Single Inductor ♦ Low-Noise Output, 30mVp-p Ripple ♦ Output Voltages up to 24V and down to -9V (up to 45V and down to -16V with added components) ♦ Internal Switches in a Small 24-Pin 4mm x 4mm Thin QFN Package ♦ 220kHz/400kHz Fixed-Frequency PWM Operation ♦ Frequency Can Be Synchronized to External Clock ♦ Power-OK Indicator ♦ Selectabl
PAGE 2
MAX685 Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD ABSOLUTE MAXIMUM RATINGS VDD, VP to GND........................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V VDD to VP...............................................................-0.3V to +0.3V LXN, POK to GND ..................................................-0.3V to +30V LXP to VDD..............................................................
PAGE 3
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD (VDD = VP = 5V, TA = 0°C to +85°C unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 480 kHz SYNC INPUT Sync Frequency Range (external) Oscillator Frequency (internal) 200 SYNC = GND 175 220 265 SYNC = VDD 320 400 480 kHz POK COMPARATORS FBP POK Threshold FBP rising 1.090 1.122 1.
PAGE 4
Typical Operating Characteristics (Circuit of Figure 3, VOUT+ = 15V, VOUT- = -7.5V, TA = +25°C, unless otherwise noted.) VIN = 5.0V VIN = 5.0V 80 70 80 70 65 60 2 4 6 8 10 1 2 3 4 5 6 7 8 9 10 2 4 6 8 LOAD CURRENT (mA) REFERENCE LOAD REGULATION REFERENCE VOLTAGE (V) 1.5 1.0 MAX685-06 1.250 MAX685-04 2.0 1.249 0.5 1.248 0 2.5 3.0 3.5 4.0 4.5 5.0 0 5.5 5 10 15 20 25 30 35 40 45 50 INPUT VOLTAGE (V) LOAD CURRENT (µA) LX SWITCHING FREQUENCY vs.
PAGE 5
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD 11mA IOUT+ MAX685-09 VOUT- LOAD-TRANSIENT RESPONSE MAX685-08 VOUT+ LOAD-TRANSIENT RESPONSE -1mA 5mA/div 1mA 5mA/div IOUT-11mA 100mV/div 100mV/div VOUT+ VOUT- 2ms/div 2ms/div MAX685-10 LINE-TRANSIENT RESPONSE VOUT+ 100mV/div VOUT- 100mV/div VDD, VP 2V/div 1ms/div INPUT 4V TO 5V, +15V AT 10mA, -7.
PAGE 6
MAX685 Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD Pin Description PIN PIN 16-QSOP 24-TQFN NAME FUNCTION 1 22, 23 LXP P-Channel Switching Inductor Node. LXP turns off when the part enters shutdown. 2, 15 19, 24 I.C. Internally Connected. Do not externally connect. 3 2, 3 VP Power Input. Connect to VDD. 4 4 POK Open-Drain Power-OK Output. POK is high when both outputs are in regulation. Connect POK to VDD with a 100kΩ pull-up resistor to VDD.
PAGE 7
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD VDD MAX685 POK TO VOUT- VP MAX685 FBN NEGATIVE ERROR AMP P TO VOUT+ FBP POSITIVE ERROR AMP LXP D1 LXN D2 VOUT- CONTROL LOGIC VOUT+ N REF 1.25V REF GND PGND SYNC SEQ SHDN Figure 1. Functional Diagram +15V LXN 0V +5V LXP 0V -7.5V Figure 2. LXN and LXP Waveforms (see also Figure 5) The current into the LXN pin is sensed to measure the inductor current.
PAGE 8
MAX685 Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD Applications Information Figure 3 shows the standard application circuit for the MAX685. The values shown in Table 1 will work well for output currents up to 10mA. However, this circuit can be optimized to a particular application by using different capacitors and a different inductor. Higher Output Voltages If the application requires output voltages greater than -7.5V or +24V, use the circuit of Figure 4.
PAGE 9
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD REF DESCRIPTION MANUFACTURER PART NUMBER C1 10µF, 10V tantalum cap Sprague 595D106X0010A2T or AVX TAJA106K010R C2 0.22µF ceramic capacitor Any manufacturer C3, C4 2.2µF ceramic capacitor Any manufacturer 47pF ceramic cap Any manufacturer 0.1A, 20V Schottky rectifier Motorola MBR0520LT1 (0.5A) or Central Semiconductor CMPSH-3 22µH, 0.
PAGE 10
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages. 24L QFN THIN.EPS MAX685 Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.
PAGE 11
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD Package Information (continued) QSOP.EPS (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH 21-0055 E 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.