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General Description

The MAX1677 is a compact, high-efficiency, dual-out-

put boost converter for portable devices needing two

regulated supplies, typically for logic and liquid crystal

displays (LCDs). Operation with inputs as low as 0.7V

allows the MAX1677 to accept 1, 2, or 3-cell alkaline,

NiCd, or NiMH batteries as well as 1-cell lithium-ion bat-

teries. The device requires no external FETs and can

maintain regulation while consuming only 20µA, making

it ideal for hand-held pen-input and PDA devices oper-

ating with low-current “sleep” states.

The MAX1677’s primary regulator supplies up to

350mA at either a factory-preset 3.3V or an adjustable

2.5V to 5.5V output. On-chip synchronous rectification

provides efficiencies up to 95%. 300kHz (or externally

clocked) pulse-width-modulation (PWM) operation is

particularly suitable for applications needing low noise,

such as those with wireless features. The primary con-

verter also features pin-selectable pulse-frequency-

modulation (PFM) operation that consumes only 20µA.

A 1µA shutdown state also minimizes battery drain.

The MAX1677’s secondary step-up converter supplies up

to +28V or -28V for LCD bias, varactor tuning, or other

high-voltage, low-current functions. Other MAX1677 fea-

tures include precision reference, logic control inputs for

both regulators, and an uncommitted comparator for

low-battery detection or a reset function. The MAX1677

is supplied in Maxim’s compact 16-pin QSOP package,

which occupies no more space than a standard SO-8.

Applications

PDAs Portable Phones

Hand-Held Terminals Portable Instruments

Features

♦ No External FETs Required

♦ Main Output

Up to 350mA for Logic Supply

Fixed 3.3V or Adjustable (2.5V to 5.5V)

Synchronous Rectification for High Efficiency

(up to 95%)

300kHz (200kHz to 400kHz Synchronizable)

Fixed-Frequency PWM Operation

♦ Secondary Output

Up to +28V or -28V for LCD Bias

Programmable Current Limit

♦ 0.7V to 5.5V Input Voltage Range

♦ 20µA Quiescent Current

♦ 1µA Shutdown Current

♦ Low-Battery Comparator

♦ Small 16-Pin QSOP Package

MAX1677

Compact, High-Efficiency, Dual-Output

Step-Up and LCD Bias DC-DC Converter

________________________________________________________________ Maxim Integrated Products 1

OUT POUT

PGND

LCDGND

LCDLX

LCDFB

GND

TOP VIEW

MAX1677

LBI

LCDON

LBO

CLK/SEL

LCDPOL

REF

QSOP

19-1403; Rev 1; 3/01

PART

MAX1677EEE -40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT

AVAILABLE

Pin Configuration

Ordering Information

Typical Operating Circuit

MAX1677

POUT

OUT

±28V

LCD

BOOST

OUTPUT

3.3V MAIN

BOOST OUTPUT

LCDFB

REF

LCDGND

GND

LCDLX

LCDON

LBI

OFF

LBO

CLK/SEL

LCDPOL

PGND

PWM

PFM

OFF

+VE OUT

-VE OUT

= 0.7V to 5.5V

(UP TO MAIN

OUT

)

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Summary of content (16 pages)

PAGE 1
9-1403; Rev 1; 3/01 KIT ATION EVALU LE B A IL A AV Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter The MAX1677 is a compact, high-efficiency, dual-output boost converter for portable devices needing two regulated supplies, typically for logic and liquid crystal displays (LCDs). Operation with inputs as low as 0.7V allows the MAX1677 to accept 1, 2, or 3-cell alkaline, NiCd, or NiMH batteries as well as 1-cell lithium-ion batteries.
PAGE 2
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter ABSOLUTE MAXIMUM RATINGS OUT, LCDON, ON, POUT, LBI, LBO, LX to GND .............................................................-0.3V to +6V CLK/SEL, LCDPOL, REF, LCDFB, FB to GND .............................................-0.3V to (VOUT + 0.3V) LCDLX to GND .......................................................-0.3V to +30V PGND, LCDGND to GND ......................................-0.3V to +0.3V POUT to OUT..............
PAGE 3
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter MAX1677 ELECTRICAL CHARACTERISTICS (continued) (VOUT = 3.3V, CREF = 0.1µF, POUT = OUT, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER LX On-Resistance LX Current Limit SYMBOL CONDITIONS MIN TYP MAX UNITS RLX(ON)N N-channel 0.22 0.5 RLX(ON)P P-channel 0.4 1.
PAGE 4
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter ELECTRICAL CHARACTERISTICS (VOUT = 3.3V, CREF = 0.1µF, POUT = OUT, TA = -40°C to +85°C, unless otherwise noted.
PAGE 5
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter 100 D 80 EFFICIENCY (%) D B 70 1 10 100 C 500 400 VOUT = 3.3V 300 VOUT = 5V 200 PFM MODE D: VIN = 3.6V E: VIN = 2.4V F: VIN = 1.2V 100 0 0.1 1 10 100 1000 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT (mA) LOAD CURRENT (mA) INPUT VOLTAGE (V) EFFICIENCY vs. LOAD CURRENT (LCD VOUT = 12V) EFFICIENCY vs. LOAD CURRENT (LCD VOUT = 20V) REFERENCE VOLTAGE vs.
PAGE 6
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Typical Operating Characteristics (continued) (Circuits of Figures 2 and 3, TA = +25°C, unless otherwise noted.) MAIN BOOST CONVERTER SWITCHING WAVEFORMS (PFM MODE) MAIN BOOST CONVERTER SWITCHING WAVEFORMS (PWM MODE) MAX1677-11 MAX1677-10 2V/ div VLX 2V/ div VLX 100mA/ div ILX 100mA/ div ILX 50mV/ div VRIPPLE VRIPPLE 20mV/ div 2µs/div 1µs/div 1.2VIN, 3.3VOUT, 20mA IOUT 2.4VIN, 3.
PAGE 7
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter LCD LINE TRANSIENT (VLCD = +12V) MAIN BOOST CONVERTER LINE TRANSIENT MAX1677-16 1V/ div MAX1677-17 1V/ div VIN VIN 0V 0V 50mV/ div VOUT 50mV/ div 5ms/div VIN = 2V TO 3V, VOUT = 3.
PAGE 8
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Pin Description PIN NAME FUNCTION 1 OUT 2 FB Dual Mode™ Main Boost Feedback Input. Connect to GND for 3.3V output. Connect a voltage-divider from OUT to FB to adjust the output in the 2.5V to 5.5V range (Figure 5). 3 LBI Low-Battery-Comparator Input. Threshold is 614mV. Set the low-battery trip-point with an external voltage divider (Figure 7). 4 LBO Open-Drain, Low-Battery Output.
PAGE 9
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter MAX1677 OUT MAX1677 839k MAIN DC-DC CLK SUCLK STARTUP OSC OUT ON ON ON QP LX EA REF CLK/SEL POUT ON QN 501k REF PGND 90% REF REFERENCE FB LBO 2.25V 50% REF LCD ON ISET/POL SENSE POL LCDPOL LBI IN LCDON ILCDLX START-UP ILCDLX POL ON LCDLX ST LCDDRV LCDFB EA CL LCD BIAS GND LCDGND Figure 1. Functional Block Diagram Table 1.
PAGE 10
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter POUT R3 10Ω P 3.3V MAIN BOOST OUTPUT REF POUT OUT C4 0.1µF FEEDBACK C2 100µF L1 10µH MAX1677 N S VIN LX GND C1 100µF L2 10µH LCDLX LCDON REF CLK/SEL LCDGND LCDPOL PWM-MODE CURRENTLIMIT LEVEL D2 MBR0530 C5 0.1µF LCD BOOST OUTPUT C3 4.7µF R1 Figure 4. Controller Block Diagram in PWM Mode output voltage. In PWM mode, the MBC can supply up to 350mA.
PAGE 11
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Startup Oscillator The MBC employs a low-voltage startup oscillator to ensure a 1.1V (0.9V typical) startup voltage. On startup, if the output voltage is less than 2.25V, the P-channel switch stays off and the N-channel pulses at a 25% duty cycle. When the output voltage exceeds 2.25V, the normal PWM or PFM control circuitry takes over. Once the MBC is in regulation, it can operate with inputs down to 0.
PAGE 12
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Table 3. Setting LCD Output Polarity and Peak Inductor Current LCD OUTPUT POLARITY LCDPOL CONNECTED TO: LCDLX PEAK INDUCTOR CURRENT (mA) Positive OUT 350 Negative GND 350 Positive OUT through 50kΩ 225 Negative GND through 50kΩ 225 off time reduces transient input current when the LCD is activated.
PAGE 13
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter For a positive LCD output, connect LCDPOL to OUT as shown in Figure 2. This sets the threshold at LCDFB to 1.25V. Select R2 and the desired output voltage (VLCD), and calculate R1: For positive LCD output: R1 = R2 [(VLCD / 1.25V) - 1] Figure 3 shows the standard circuit for generating a negative LCD supply. This connection limits VLCD to values between -VIN and -28V.
PAGE 14
MAX1677 Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Use inductors with a ferrite core or equivalent; powder iron cores are not recommended for use with the MAX1677’s high switching frequencies. The inductor’s incremental saturation rating ideally should exceed the selected current limit, however it is generally acceptable to bias most inductors into saturation by as much as 20% (although this may reduce efficiency).
PAGE 15
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter Chip Information TRANSISTOR COUNT: 1221 Layout Considerations The MAX1677’s high-frequency operation makes PC board layout important for minimizing ground bounce and noise. Protect sensitive analog grounds by using a star ground configuration. Minimize ground noise by connecting PGND, the input bypass-capacitor ground terminal, and the output filter-capacitor ground terminal to a single point (star ground configuration).
PAGE 16
Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter MAX1677 Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.