Rainbow Electronics MAX686 User Manual

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-to­analog converter (DAC) for digital adjustment of the
output voltage. It comes in a small 16-pin QSOP pack­age (same size as an 8-pin SO).

The MAX686 uses a current-limited, pulse-frequency­modulation (PFM) control scheme to provide high effi­ciency 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

1

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 TA= +25°C, DC parameters only.

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

Functional Diagram appears at end of data sheet.

MAX686

V

CC

V

DD

V

OUT

22µH

V

IN

= 0.8V TO 27.5V

UP

SHDN

DN

POL

GND PGND

LX

DACOUT

LCDON

FB

REF

POK

ISET

0.1µF

R3

R2

MBR0530L

R1

ON/OFF

DAC CONTROL

V

CC

= 2.7V TO 5.5V

0.1µF

Typical Operating Circuit

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

PGND LX

N.C.
LCDON
GND

POK
FB
REF

TOP VIEW

MAX686

QSOP

UP
DN

ISET

POL

V

DD

V

CC

SHDN

DACOUT

Pin Configuration

MAX686

DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= VDD= VIN= +5V, C

REF

= 0.1µF, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Voltage

V

CC

, ISET, POK, POL, SHDN,

UP, DN, V

DD

to GND...........................................-0.3V to +6V

FB, REF, DACOUT to GND.......................-0.3V to (V

CC

+ 0.3V)

PGND to GND .....................................................-0.3V to +0.3V

LX, LCDON to GND..............................................-0.3V to +30V

Current

LX (sinking).....................................................................600mA

LCDON (sinking)...............................................................10mA

Continuous Power Dissipation (T

A

= +70°C)

QSOP (derate 8.30mW/°C above +70°C)......................667mW

Operating Temperature Ranges

MAX686C/D ..........................................................0°C to +70°C

MAX686EEE.......................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

SHDN = GND

POL = GND, VFB= 1.3V, I

DACOUT

= 0mA

Boost configuration, V

OUT

= 27.5V,

I

LOAD

= 0mA to 5mA

Boost configuration, V

OUT

= 27.5V,

I

LOAD

= 5mA, VCC= V

DD

= 2.7V to 5.5V

Rising or falling

CONDITIONS

µA

1.3 4

I

SHDN

Shutdown Current

µA

65 125

ICC+ I

DD

V

2.7 5.5

VCC, V

DD

Supply Voltage (Note 1)

Supply Current

V

28

V

LX

LX Voltage Range

%/mA

0.01

Load Regulation

%/V

0.1

Line Regulation

V

2.10 2.5 2.65

V

LOCK

VCCUndervoltage Lockout

mV

100

VCCUndervoltage Lockout
Hysteresis

V

0.5 1.5 2.1

V

RESET

VCCDAC Reset Threshold

UNITSMIN TYP MAXSYMBOLPARAMETER

ISET = V

CC

A

0.42 0.50 0.58

I

LX

LX Switch Current Limit

ISET = GND

0.21 0.25 0.29

VLX= 28V µA

1.5

I

LXLEAK

LX Leakage Current

VCC= V

DD

= 5V, ILX= 100mA

Ω

0.6 1.2

R

LX

LX On-Resistance

VCC= V

DD

= 3.3V, ILX= 100mA

0.8 1.6

µs

8 10 12

t

ON

Maximum LX On-Time

POL = GND, VFB> 1.2V

µs

0.8 1 1.2

t

OFF

Minimum LX Off-Time

POL = VCC, VFB< 0.15V

2.8 3.5 4.2

POL = GND, VFB< 0.8V

4 5 6

POL = VCC, VFB> 0.4V

4 5 6

Voltage applied to L1 V

0.8 V

OUT

V

IN

Input Voltage

LX

MAX686

DAC-Controlled Boost/Inverter

LCD Bias Supply with Internal Switch

_______________________________________________________________________________________ 3

I

REF

= 0µA to 25µA, C

REF

= 0.1µF

VCC= VDD= 2.7V to 5.5V, no load

0µA < I

DACOUT

< 20µA

-50µA < I

DACOUT

< 0µA

I

REF

= 0µA to 50µA, C

REF

= 0.47µF

CONDITIONS

mV

1 10

REF Load Regulation

V

1.225 1.250 1.275

V

REF

REF Output Voltage

mV

0 15

V

ZS

Zero-Scale Output Voltage

V

V

REF

-

V

REF

V

REF

+

0.015 0.015

V

FS

Full-Scale Output Voltage

1.5

nA

±50

I

FB

FB Input Bias Current

UNITSMIN TYP MAXSYMBOLPARAMETER

ELECTRICAL CHARACTERISTICS (continued)

(VCC= VDD= VIN= +5V, C

REF

= 0.1µF, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

POL = GND
POL = V

CC

V

1.225 1.250 1.275

V

FB

FB Set Point

mV

-15 0 15

nA

±50

I

POK

POK Input Current

V

POK

rising V

1.100 1.125 1.150

V

POK

POK Threshold

mV

12

POK Hysteresis

V

LCDON

= 0.4V, V

POK

= 1.25V mA

2 6

I

LCDON

LCDON Sink Current

V

LCDON

= 28V, V

POK

= GND µA

0.02 1

LCDON Leakage Current

bits

6

Resolution

Mid-scale = V

REF

x 32/63 %

-2 2

MSAMid-Scale Accuracy

Guaranteed monotonic LSB

-1 1

DNLDifferential Nonlinearity

kΩ

1.5

R

DACOUT

Output Resistance in Shutdown

2.7V < VCC= VDD< 5.5V V0.7V

IL

Input Low Level

2.7V < VCC= VDD< 5.5V V2.4V

IH

Input High Level

µA±1I

BIAS

Input Bias Current

UP, DN, TA= +25°C µs1t

PWH

Pulse Width High

UP, DN, TA= +25°C µs1t

PWL

Pulse Width Low

UP, DN, TA= +25°C µs1t

PWS

Pulse Separation

REFERENCE AND FB INPUT

POWER OK COMPARATOR, LCDON OUTPUT

DAC OUTPUT (Notes 2, 3)

LOGIC INPUTS: POL, ISET, UP, DN, SHDN

MAX686

DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch

4 _______________________________________________________________________________________

ISET = V

CC

A

0.4 0.6

SHDN = GND

I

LX

LX Switch Current Limit

POL = GND, VFB = 1.3V, I

DACOUT

= 0mA

ISET = GND
VCC= VDD= 5V, ILX= 100mA

0.2 0.3

Ω

1.2

VLX= 28V

Rising or falling

µA

1.5

CONDITIONS

I

LXLEAK

LX Leakage Current

R

LX

LX On-Resistance

VCC= VDD= 3.3V, ILX= 100mA

1.6

µs

7.5 12.5

t

ON

Maximum LX On-Time

POL = GND, VFB> 1.2V

µs

0.7 1.3

t

OFF

Minimum LX Off-Time

POL = VCC, VFB< 0.15V

2.8 4.2

POL = GND, VFB< 0.8V

3.8 6.2

POL = VCC, VFB> 0.4V

3.8 6.2

µA

4

I

SHDN

Shutdown Current

µA

125

ICC+ I

DD

V

2.7 5.5

VCC, V

DD

Supply Voltage (Note 1)

Supply Current

V

28

V

LX

LX Voltage Range

V

2.10 2.65

V

LOCK

VCCUndervoltage Lockout

UNITSMIN TYP MAXSYMBOLPARAMETER

ELECTRICAL CHARACTERISTICS

(VCC= VDD= VIN= +5V, C

REF

= 0.1µF, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

Note 1: The MAX686 requires a supply voltage at V

CC

= VDDbetween +2.7V and +5.5V; however, the voltage that supplies the

inductor can vary from +0.8V to +27.5V, depending on circuit operating conditions.

Note 2: The DAC output is set to its midpoint value at power-on.
Note 3: The DAC setting is guaranteed to remain valid as long as V

CC

is greater than the V

CC

DAC Reset Threshold.

Note 4: Specifications to -40°C are guaranteed by design, not production tested.

VCC= VDD= 2.7V to 5.5V, no load V

1.22 1.28

V

REF

REF Output Voltage

I

REF

= 0µA to 25µA, C

REF

= 0.1µF mV

10

REF Load Regulation

POL = GND V

1.22 1.28

V

FB

FB Set Point

POL = V

CC

-15 15
nA

±50

I

FB

FB Input Bias Current

V

POK

rising V

1.05 1.20

V

POK

POK Threshold

nA

±50

I

POK

POK Input Current

V

LCDON

= 0.4V, V

POK

= 1.25V mA

2

I

LCDON

LCDON Sink Current

mV

Voltage applied to L1 V

0.8 V

OUT

V

IN

Input Voltage

-50µA < I

DACOUT

< 0µA V

V

REF

- V

REF

+

0.02 0.02

V

FS

Full-Scale Output Voltage

0µA < I

DACOUT

< 20µA mV

0 15

V

ZS

Zero-Scale Output Voltage

Bits

6

Resolution

Mid-scale = V

REF

x 32/63 %

-3 3

MSAMid-Scale Accuracy

2.7V < VCC= V

DD

< 5.5V V

0.7

V

IL

Input Low Level

2.7V < VCC= V

DD

< 5.5V V

2.4

V

IH

Input High Level

µA

±1

I

BIAS

Input Bias Current

LX

REFERENCE AND FB INPUT

POWER OK COMPARATOR, LCDON OUTPUT

LOGIC INPUTS: POL, ISET, UP, DN, SHDN

DAC OUTPUT (Notes 2, 3)

MAX686

DAC-Controlled Boost/Inverter

LCD Bias Supply with Internal Switch

_______________________________________________________________________________________ 5

95

60

0.1 1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= +24V)

70

65

75

80

85

90

MAX686 TOC01

LOAD CURRENT (mA)

EFFICIENCY (%)

A: VIN = 12V, ISET = V

CC

B: VIN = 12V, ISET = GND
C: V

IN

= 5V, ISET = V

CC

D: VIN = 5V, ISET = GND
E: V

IN

= 3V, ISET = GND

F: V

IN

= 3V, ISET = V

CC

C

D

E

F

A

B

95

90

60

0.1 101 1000100

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= +12V)

65

MAX686 TOC02

LOAD CURRENT (mA)

EFFICIENCY (%)

70

75

80

85

A: VIN = 9V, ISET = V

CC

B: VIN = 9V, ISET = GND
C: V

IN

= 5V, ISET = V

CC

D: VIN = 5V, ISET = GND
E: V

IN

= 3V, ISET = GND

F: V

IN

= 3V, ISET = V

CC

D

C

F

B

A

E

85

60

0.1 1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= -12V)

65

70

75

80

MAX686 TOC03

LOAD CURRENT (mA)

EFFICIENCY (%)

A

F

E

B

D

C: V

IN

= 5V, ISET = GND

D: V

IN

=

5V, ISET = V

CC

E: V

IN

=

3V, ISET = GND

F: V

IN

= 3V, ISET = V

CC

A: V

IN

= 9V, ISET = GND

B: V

IN

= 9V, ISET = V

CC

C

__________________________________________Typical Operating Characteristics

(Circuits of Figures 1 and 2, VCC= VDD= VIN= +5V, L1 = 22µH, SHDN = VCC, C

REF

= 0.1µF, TA= +25°C, unless otherwise noted.)

85

50

0.1 1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= -18V)

60

55

65

70

75

80

MAX686 TOC04

LOAD CURRENT (mA)

EFFICIENCY (%)

C

D

A: VIN = 9V, ISET = GND
B: V

IN

= 9V, ISET = V

CC

C: VIN = 5V, ISET = GND
D: V

IN

= 5V, ISET = V

CC

E: VIN = 3V, ISET = GND
F: V

IN

= 3V, ISET = V

CC

E
F

A

B

1000

1

0 4 62 10 128 14

MAXIMUM OUTPUT CURRENT vs.

INPUT VOLTAGE (V

OUT

= +12V, +24V)

10

100

MAX686 TOC05

INPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

A: V

OUT

= 12V, ISET = V

CC

B: V

OUT

= 12V, ISET = GND

C: V

OUT

= 24V, ISET = V

CC

D: V

OUT

= 24V, ISET = GND

A

C

D

B

1

10

100

0 4 6 82 10 12 14 16 18

MAXIMUM OUTPUT CURRENT vs.

INPUT VOLTAGE (V

OUT

= -12V, -18V)

MAX686 TOC06

INPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

B

D

C

A: V

OUT

= -12V, ISET = V

CC

B: V

OUT

= -18V, ISET = V

CC

C: V

OUT

= -12V, ISET = GND

D: V

OUT

= -18V, ISET = GND

A

B & D

A & C

V

OUT

50mV/div

AC-COUPLED

V

OUT

50mV/div

AC-COUPLED

ISET = V

CC

ISET = GND

OUTPUT VOLTAGE RIPPLE

MAX686 TOC09

20µs/div

V

OUT

= 24V

I

LOAD

= 5mA

1000

1

0 21 4 53 6

INPUT CURRENT

vs. INPUT VOLTAGE

10

100

MAX686 TOC07

INPUT VOLTAGE (V)

INPUT CURRENT (µA)

VCC = V

IN

= V

DD

INPUT CURRENT = ICC + I

DD

V

OUT

= 18V, NO LOAD

1.244

1.246

1.245

1.248

1.247

1.251

1.250

1.249

1.252

0 4020 60 80 100 120 140

REFERENCE VOLTAGE

vs. LOAD CURRENT

MAX686 TOC08

LOAD CURRENT (µA)

REFERENCE VOLTAGE (V)

VIN = VCC = 5V
C

REF

= 0.1µF