Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Boost, Switched-capacitor voltage converter QSOP 16

General Description

The MAX686 DAC-controlled boost/inverter IC converts

a positive input voltage to a positive or negative LCD

bias voltage up to +27.5V or -27.5V. The device features

an internal N-channel MOSFET switch, programmable

current limiting, and an internal 6-bit digital-to-

analog converter (DAC) for digital adjustment of the

output voltage. It comes in a small 16-pin QSOP pack-

age (same size as an 8-pin SO).

The MAX686 uses a current-limited, pulse-frequency-

modulation (PFM) control scheme to provide high effi-

ciency over a wide range of load conditions. Its high

switching frequency (up to 300kHz) allows the use of

small external components.

An LCDON output allows the LCD bias voltage to be

automatically disabled when the display logic voltage is

removed, protecting the display. The MAX686 has a

+2.7V to +5.5V input voltage range for the IC, and a

+0.8V to +27.5V input voltage range for the inductor.

Typical quiescent supply current is 65µA. Shutdown

current is 1.5µA.

The MAX686 offers high-level integration to save space,

reduce power consumption, and increase battery life,

making it an excellent choice for battery-powered

portable equipment. The MAX629 is similar to the

MAX686, except that it does not contain a built-in DAC.

Both devices have evaluation kits to facilitate designs.

Applications

Positive or Negative LCD Bias

Personal Digital Assistants

Notebook Computers

Portable Data-Collection Terminals

Palmtop Computers

Varactor Tuning Diode Bias

____________________________Features

♦ Internal 500mA, 28V N-Channel Switch

(no external FET required)

♦ Adjustable Output Voltage to +27.5V or -27.5V

♦ 6-Bit DAC-Controlled Output Voltage

♦ Up to 90% Efficiency

♦ Small 16-Pin QSOP Package

(Same size as 8-pin SO)

♦ Power-OK Indicator

♦ 65µA Quiescent Current

♦ 1.5µA Shutdown Current

♦ Up to 300kHz Switching Frequency

MAX686

DAC-Controlled Boost/Inverter

LCD Bias Supply with Internal Switch

________________________________________________________________

Maxim Integrated Products

19-1327; Rev 1; 2/98

PART

MAX686C/D

MAX686EEE -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*

16 QSOP

EVALUATION KIT

AVAILABLE

Ordering Information

Dice are specified at T

= +25°C, DC parameters only.

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

For small orders, phone 408-737-7600 ext. 3468.

Functional Diagram appears at end of data sheet.

MAX686

OUT

22µH

= 0.8V TO 27.5V

SHDN

POL

GND PGND

DACOUT

LCDON

REF

POK

ISET

0.1µF

MBR0530L

ON/OFF

DAC CONTROL

= 2.7V TO 5.5V

0.1µF

Typical Operating Circuit

PGND LX

N.C.

LCDON

GND

POK

REF

TOP VIEW

MAX686

QSOP

ISET

POL

SHDN

DACOUT

Pin Configuration

Summary of content (16 pages)

PAGE 1
9-1327; Rev 1; 2/98 KIT ATION EVALU E L B A AVAIL DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch ____________________________Features ♦ Internal 500mA, 28V N-Channel Switch (no external FET required) ♦ Adjustable Output Voltage to +27.5V or -27.5V ♦ 6-Bit DAC-Controlled Output Voltage ♦ Up to 90% Efficiency ♦ Small 16-Pin QSOP Package (Same size as 8-pin SO) ♦ Power-OK Indicator ♦ 65µA Quiescent Current ♦ 1.
PAGE 2
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch ABSOLUTE MAXIMUM RATINGS Voltage VCC, ISET, POK, POL, SHDN, UP, DN, VDD to GND ...........................................-0.3V to +6V FB, REF, DACOUT to GND.......................-0.3V to (VCC + 0.3V) PGND to GND .....................................................-0.3V to +0.3V LX, LCDON to GND..............................................-0.3V to +30V Current LX (sinking) ..........................................................
PAGE 3
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch (VCC = VDD = VIN = +5V, CREF = 0.1µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 1.225 1.250 1.275 V 1 10 REFERENCE AND FB INPUT REF Output Voltage VREF VCC = VDD = 2.7V to 5.5V, no load IREF = 0µA to 25µA, CREF = 0.1µF REF Load Regulation FB Set Point VFB FB Input Bias Current IFB 1.225 1.250 1.
PAGE 4
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch ELECTRICAL CHARACTERISTICS (VCC = VDD = VIN = +5V, CREF = 0.1µF, TA = -40°C to +85°C, unless otherwise noted.
PAGE 5
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch E D F A: VIN = 12V, ISET = VCC B: VIN = 12V, ISET = GND C: VIN = 5V, ISET = VCC D: VIN = 5V, ISET = GND E: VIN = 3V, ISET = GND F: VIN = 3V, ISET = VCC 70 65 1 10 100 1 D C E 70 F C: VIN = 5V, ISET = GND D: VIN = 5V, ISET = VCC E: VIN = 3V, ISET = GND F: VIN = 3V, ISET = VCC 65 60 1000 0.1 1 10 100 LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT (VOUT = -18V) MAXIMUM OUTPUT CURRENT vs.
PAGE 6
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch _____________________________Typical Operating Characteristics (continued) (Circuits of Figures 1 and 2, VCC = VDD = VIN = +5V, L1 = 22µH, SHDN = VCC, CREF = 0.1µF, TA = +25°C, unless otherwise noted.
PAGE 7
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch POWER-DOWN RESPONSE (NEGATIVE CONFIGURATION) POWER-UP RESPONSE (NEGATIVE CONFIGURATION) MAX686 TOC14B MAX686 TOC14A ISET = VCC RL = 4.7kΩ SHDN 5V/div SHDN 5V/div 0V 0V VOUT 5V/div VOUT 5V/div -16.8V -16.8V ISET = VCC RL = 4.7kΩ 20ms/div 500µs Pin Description PIN NAME FUNCTION 1 PGND 2 UP Increment Output Voltage Input. Increments the DAC on each rising edge such that |VOUT| increases.
PAGE 8
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch D1 MBR0530L L1 22µH VOUT VIN = 0.8V TO 27.5V 15µF 4.7µF VCC = 2.7V TO 5.5V VCC LX VDD DACOUT R2 CF 22pF R3 0.1µF LCDON FB MAX686 UP R1 DAC CONTROL ON/OFF DN POK SHDN REF POL ISET GND 0.1µF PGND Figure 1. Boost Configuration: Positive Output Voltage L1 22µH R4 2Ω VIN = 0.8V TO 27.5V 15µF 2.2µF VCC = 2.7V TO 5.5V 0.
PAGE 9
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch MAX686 D2 MBR0530L R4 2Ω L1 22µH VIN = 0.8V TO 27.5V 15µF 2.2µF VCC = 2.7V TO 5.5V 0.1µF VCC LX VDD DACOUT POL LCDON D1 MBR0530L R3 CF 470pF FB UP R1 MAX686 DAC CONTROL DN ON/OFF NEGATIVE OUTPUT VOLTAGE REF POK SHDN |VOUT| ≤ (27.5V - VIN) ISET GND PGND R2 0.1µF 2.2µF Figure 3.
PAGE 10
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch Power-OK Comparator POK is the input to the power-OK comparator. The comparator drives an internal N-channel MOSFET. The MOSFET’s open-drain output, LCDON, can drive an external PNP transistor or P-channel MOSFET, switching a positive VOUT to the LCD (Figures 6 and 7). When the voltage at POK exceeds 1.125V (power OK), LCDON goes low, turning on the external PNP transistor. When the voltage at POK drops below 1.
PAGE 11
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch Setting the Minimum Negative Output Voltage For a negative output voltage, the FB threshold voltage (VFB) is 0V, and R1 is placed between FB and REF (Figures 2 and 3). Again, choose R1 to be 120kΩ so that the current in the divider is about 10µA. Then determine R2 as follows: R2 = R1 x |VOUT / VREF | For example, if VOUT(MIN) = -12.5V: R2 = 120kΩ x |(-12.5) / (1.25)| = 1.
PAGE 12
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch MBR0530L 22µH VIN = 0.8V TO 27.5V VOUT 15µF R2 VIN = 0.8V TO 27.5V MBR0530L 22µH VOUT 15µF R2 CF CF LX VCC = 2.7V TO 5.5V VCC = 2.7V TO 5.5V 0.1µF LX VCC 0.1µF MAX686 R3 REF VCC R3 MAX686 RPOT 100k POTENTIOMETER DACOUT FB FB R1 R1 Figure 4. Feed-Forward Capacitor Figure 5. Using a Potentiometer to Adjust Output Voltage Selecting Capacitors Table 1.
PAGE 13
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch R2 LX VCC VOUT R6 R2 ILCD LX VCC R3 DACOUT MBR0530L 22µH VIN = 0.8V TO 27.5V R7 VOUT R6 ILCD R3 DACOUT VOUTSW LCDON MAX686 MBR0530L 22µH VIN = 0.8V TO 27.5V R7 VOUTSW LCDON POSITIVE OUTPUT VOLTAGE FB POSITIVE OUTPUT VOLTAGE FB R4 POK MAX686 MAX686 POK R1 R5 GND R1 GND Figure 6. Using the POK for Input Voltage Monitoring Figure 7.
PAGE 14
MAX686 DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch MBR0530L 22µH VIN = 2.7V TO 5.5V 15µF R2 CF LX VDD R8 100Ω VOUT MAX686 VCC to the source through a 100Ω resistor (R8), and bypass VCC with a 1µF ceramic capacitor as shown in Figure 8. Since the supply current is very small, the voltage drop across R8 is insignificant and does not degrade performance. The RC isolates V CC from the switching noise created by the inductor and internal power switch.
PAGE 15
DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch VCC VDD GND BIAS UP DN SHDN DIGITAL INTERFACE MAX686 6-BIT DAC POL REF 1.25V DACOUT BANDGAP REFERENCE LX 1.125V ERROR AMP FB ON-TIME/ OFF-TIME CONTROL ISET 1.
PAGE 16
QSOP.