Rainbow Electronics MAX1677 User Manual

General Description

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. 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 oper­ating 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 con­verter also features pin-selectable pulse-frequency­modulation (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 fea­tures 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

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

LX

POUT

OUT

±28V
LCD
BOOST
OUTPUT

3.3V MAIN

BOOST OUTPUT

LCDFB

REF

FB

LCDGND

GND

LCDLX

LCDON

LBI

ON

OFF

LBO

CLK/SEL

ON

LCDPOL

PGND

PWM

PFM

ON

OFF

+VE OUT

-VE OUT

V

IN

= 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.

TOP VIEW

1

OUT POUT

FB

2

LBI

3

4

LBO

CLK/SEL

5

LCDON

6

LCDPOL

7

REF

8

MAX1677

QSOP

16

15

14

13

12

11

10

9

LX

PGND

LCDGND

LCDLX

ON

LCDFB

GND

MAX1677

Compact, High-Efficiency, Dual-Output
Step-Up and LCD Bias DC-DC Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

OUT

= 3.3V, C

REF

= 0.1µF, POUT = OUT, 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.

OUT, LCDON, ON, POUT, LBI, LBO,

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

CLK/SEL, LCDPOL, REF, LCDFB,

FB to GND .............................................-0.3V to (V

OUT

+ 0.3V)

LCDLX to GND .......................................................-0.3V to +30V

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

POUT to OUT.........................................................-0.3V to +0.3V

Continuous Power Dissipation (T

A

= +70°C)

16-Pin QSOP (derate 8.3mW/°C above +70°C)...........696mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

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

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

PARAMETER

CONDITIONS

UNITS

GENERAL

Input Voltage Range V

IN

(Note 1) 0.7 5.5 V

Minimum Startup Voltage

TA = +25°C, I

LOAD

< 1mA 0.9 1.1 V

Reference Voltage V

REF

I

REF

= 0

V

Reference Load Regulation I

REF

= 0 to 50µA (Note 2) 2 15 mV

Reference Line Rejection V

OUT

= 2.5V to 5.5V 0.2 5 mV

Supply Current
Main DC On, LCD Off

No load, current into OUT 20 40 µA

Supply Current All On,
Main DC-DC in PFM Mode

I

PFM

No load, current into OUT 35 60 µA

Supply Current All On,
Main DC-DC in PWM Mode

I

PWM

No load, current into OUT

µA

Supply Current in Shutdown 0.3 5 µA

MAIN BOOST DC-DC

Output Voltage V

OUT

FB = GND, 0 ≤ ILX ≤ 350mA,
CLK/SEL = OUT (Note 3)

V

FB Regulation Voltage

)

V

FB Input Current I

FB

VFB = 1.3V

50 nA

Output Voltage Adjustment
Range

2.5 5.5 V

Startup to Normal Mode
Transition Voltage (Note 4)

2.1 2.4 V

Line Regulation I

OUT

= 150mA, VIN = 2V to 3V 0.6 %

Load Regulation

CLK/SEL = OUT, V

IN

= 2.4V,

I

LOAD

= 10mA to 200mA

1%

Frequency in Startup Mode

V

OUT

= 15V 40

kHz

LX Leakage Current

)

0.2 5 µA

SYMBOL

V

STARTUP

MIN TYP MAX

1.23 1.25 1.27

I

LCDOFF

V

FB (REG

V

LOCKOUT

f

STARTUP

I

LX (LEAK

3.20 3.30 3.43

Adjustable mode, CLK/SEL = OUT (Note 3) 1.225 1.25 1.275

115 300

0.02

300

MAX1677

Compact, High-Efficiency, Dual-Output

Step-Up and LCD Bias DC-DC Converter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(V

OUT

= 3.3V, C

REF

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

CONDITIONS

N-channel 0.22 0.5

Ω

P-channel 0.4 1.0

LX Current Limit

I

LX(PWM)

N-channel PWM mode 550 670 800

mA

UNITSMIN TYP MAXPARAMETER

I

LX(PFM)

N-channel PFM mode 250 350 450

P-Channel Synchronous Rectifier
Turn-Off Current in PFM Mode

40 90 140 mA

Internal Oscillator f CLK/SEL = OUT 240 300 360 kHz

Oscillator Maximum Duty Cycle D 80 85 90 %

External Clock Frequency
Range

200 400 kHz

ON Input Threshold

V

ON(LOW)

V

ON(HIGH)

LCDON, LCDPOL, CLK/SEL
Input Threshold

V

IL

V

OUT

> 2.5V

0.2V

OUT

V

V

IH

0.8V

OUT

LBI Falling Threshold V

LBI(TH)

599 614 629 mV

LBI Hysteresis 1 %
LBO Output Low Voltage

V

LBO(LO)

Sink current = 1mA 0.1 V

LBI Input Bias Current I

LBI(BIAS)

50 nA

LBO Leakage Current

I

LBO(LEAK)VLBO

= 5.5V 1 µA

LCDLX Voltage 28 V

LCDPOL connected to OUT or GND through
50kΩ

150 225 300

mA

LCDLX Switch Resistance RLCDLX V

OUT

= 3.3V 1.0 1.4 Ω

LCDLX Leakage Current V

LCDLX

= 28V 1 µA

LCDFB Set Point

Positive LCD, LCDPOL = OUT 1.225 1.25 1.275 V

Negative LCD, LCDPOL = GND -15 0 15 mV

LCDFB Input Bias Current 50 nA

LCD Line Regulation

I

LOAD

= 5mA, VIN= 1.2V to 3.6V,

Figure 2

0.1 %/V

LCD Load Regulation

I

LOAD

= 0 to 5mA, VIN= 2.4V,

Figure 2

0.5 %

Maximum LCDLX On-Time t

ON LCD

3.4 4.3 5.2 µs

1.1V < V

OUT

< 5.5V

0.8V

OUT

0.2V

OUT

V

LX On-Resistance

SYMBOL

R

LX(ON)N

R

LX(ON)P

LCDPOL = OUT or GND 300 350 450

LCDLX Switch Current Limit

Input Leakage Current ON, LCDON, LCDPOL, CLK/SEL 1 µA

Minimum LCDLX Off-Time

Operating mode 0.8 1 1.2

µs

Start-up mode (positive or negative) 3.0 4.0 5.0

LCDFB Voltage for
Startup Mode

LCDPOL = OUT 0.75

V

LCDPOL = GND 0.5

LOGIC AND CONTROL INPUTS

MAX1677

Compact, High-Efficiency, Dual-Output
Step-Up and LCD Bias DC-DC Converter

4 _______________________________________________________________________________________

Note 1: The MAX1677 operates in bootstrap mode (operates from the output voltage). Once started, it will operate down to 0.7V

input. If V

IN

exceeds the set V

OUT

, V

OUT

will follow one diode drop below VIN.

Note 2: C

REF

= 0.22µF for applications where I

REF

> 10µA.

Note 3: In low-power mode (CLK/SEL = GND), the output voltage regulates 1% higher than in low-noise mode (CLK/SEL = OUT or

synchronized).

Note 4: The device is in a startup mode when V

OUT

is below this value.

Note 5: Specifications to -40°C are guaranteed by design and not production tested.

ELECTRICAL CHARACTERISTICS

(V

OUT

= 3.3V, C

REF

= 0.1µF, POUT = OUT, TA= -40°C to +85°C, unless otherwise noted. ) (Note 5)

LBO Output Low Voltage

V

LBO(LO)

Sink current = 1mA

LCDPOL = OUT or GND 300 450

0.1 V

µA

Supply Current
Main DC On, LCD Off

Supply Current All On,
Main DC-DC in PFM Mode

I

PFM

No load, current into OUT 60 µA

VFB Regulation Voltage

µALX Leakage Current

Startup to Normal Mode Transition
Voltage (Note 4)

CONDITIONS

V

LOCKOUT

2.1 2.4 V

I

LX(LEAK)

5

Output Voltage V

OUT

FB = GND, 0 ≤ ILX≤ 350mA,
CLK/SEL = OUT (Note 3)

3.17 3.46 V

V

FB(REG)

Adjustable mode, CLK/SEL = OUT (Note 3) 1.22 1.28

µA

Supply Current All On,
Main DC-DC in PWM Mode

Supply Current in Shutdown 5 µA

I

PWM

No load, current into OUT 300

I

LCDOFF

No load, current into OUT 40

LX Current Limit

I

LX(PWM)

N-channel PWM mode 550 900

mA

UNITSMIN MAXSYMBOLPARAMETER

I

LX(PFM)

N-channel PFM mode 250 500

Internal Oscillator f CLK/SEL = OUT 240 360 kHz

External Clock Frequency Range 200 400 kHz

ON Input Threshold

V

ON(LOW)

1.1V < V

OUT

< 5.5V

0.2V

OUT

V

V

ON(HIGH)

0.8V

OUT

LCDON, LCDPOL, CLK/SEL
Input Threshold

V

IL

0.2V

OUT

V

V

IH

0.8V

OUT

LBI Falling Threshold V

LBI(TH)

599 629 mV

LCD BIAS DC-DC

LCDLX Switch Current Limit

LCDPOL connected to OUT or GND
through 50kΩ

150 300

mA

LCDFB Set Point

Positive LCD, LCDPOL = OUT 1.22 1.28 V

-20 +20Negative LCD, LCDPOL = GND mV

GENERAL

MAIN

LCD BIAS DC-DC

LOGIC

MAX1677

Compact, High-Efficiency, Dual-Output

Step-Up and LCD Bias DC-DC Converter

_______________________________________________________________________________________ 5

0.1 101 100 1000

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 3.3V)

MAX1677-01

LOAD CURRENT (mA)

EFFICIENCY (%)

100

60

70

80

90

PWM MODE
C = 2.4V
D = 1.2V

PFM MODE
A = VIN = 2.4V
B = VIN = 1.2V

C

D

B

A

100

80

60

40

20

0

0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 5V)

MAX1677-02

LOAD CURRENT (mA)

EFFICIENCY (%)

PWM MODE
A: V

IN

= 3.6V
B: VIN = 2.4V
C: VIN = 1.2V

A

D

E
F

B

C

PFM MODE
D: VIN = 3.6V
E: VIN = 2.4V
F: VIN = 1.2V

0

100

300

200

500

600

400

700

01.01.50.5 2.0 2.5 3.0 3.5 4.0

MAXIMUM LOAD CURRENT

vs. BATTERY INPUT VOLTAGE

(PWM MODE)

MAX1677-03

INPUT VOLTAGE (V)

LOAD CURENT (mA)

V

OUT

= 3.3V

V

OUT

= 5V

40

0.1 100101

EFFICIENCY vs. LOAD CURRENT

(LCD V

OUT

= 12V)

100

60

50

80

90

70

MAX1677-04

LOAD CURRENT (mA)

EFFICIENCY (%)

CIRCUIT OF FIGURE 2
A: VIN = 3.6V
B: VIN = 2.4V
C: VIN = 1.2V

A

B

C

50

0.1 100101

EFFICIENCY vs. LOAD CURRENT

(LCD V

OUT

= 20V)

100

70

60

90

80

MAX1677-05

LOAD CURRENT (mA)

EFFICIENCY (%)

CIRCUIT OF FIGURE 2
A: VIN = 3.6V
B: V

IN

= 2.4V

C: V

IN

= 1.2V

A

B

C

1.2450

1.2475

1.2525

1.2500

1.2550

0 20406080100

REFERENCE VOLTAGE

vs. REFERENCE CURRENT

MAX1677-06

REFERENCE CURRENT (µA)

REFERENCE VOLTAGE (V)

Typical Operating Characteristics

(Circuits of Figures 2 and 3, TA = +25°C, unless otherwise noted.)

0

100

50

250

200

150

400

350

300

450

01.00.5 1.5 2.0 2.5 3.0

LOAD CURRENT

vs. STARTUP VOLTAGE

MAX1677-07

START-UP VOLTAGE (V)

LOAD CURRENT (mA)

PWM

PFM

V

OUT

= 3.3V
TESTED WITH
RESISTIVE LOAD

0

0.06

0.04

0.02

0.10

0.08

0.18

0.16

0.14

0.12

0.20

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

NO-LOAD SUPPLY CURRENT vs.

INPUT VOLTAGE (LCD OFF)

MAX1677-08

INPUT VOTAGE (V)

SUPPLY CURRENT (mA)

V

OUT

= 3.3V
PFM MODE
LCD OFF

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

NO-LOAD SUPPLY CURRENT vs.

INPUT VOLTAGE (LCD ON)

MAX1677-09

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

V

OUT

= 3.3V
PFM MODE
V

LCD

= -20V