Rainbow Electronics MAX723 User Manual

19-0113; Rev. 2; 1/95

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters

_______________General Description

The MAX756/MAX757 are CMOS step-up DC-DC switch­ing regulators for small, low input voltage or battery-pow­ered systems. The MAX756 accepts a positive input
voltage down to 0.7V and converts it to a higher pin­selectable output voltage of 3.3V or 5V. The MAX757 is
an adjustable version that accepts an input voltage down
to 0.7V and generates a higher adjustable output voltage
in the range from 2.7V to 5.5V. Typical full-load efficiencies
for the MAX756/MAX757 are greater than 87%.

The MAX756/MAX757 provide three improvements over
previous devices. Physical size is reduced—the high
switching frequencies (up to 0.5MHz) made possible by
MOSFET power transistors allow for tiny (<5mm diameter)
surface-mount magnetics. Efficiency is improved to 87%
(10% better than with low-voltage regulators fabricated in
bipolar technology). Supply current is reduced to 60µA
by CMOS construction and a unique constant-off-time
pulse-frequency modulation control scheme.

________________________Applications

3.3V to 5V Step-Up Conversion
Palmtop Computers
Portable Data-Collection Equipment
Personal Data Communicators/Computers
Medical Instrumentation
2-Cell & 3-Cell Battery-Operated Equipment
Glucose Meters

____________________________Features

♦ Operates Down to 0.7V Input Supply Voltage
♦ 87% Efficiency at 200mA
♦ 60µA Quiescent Current
♦ 20µA Shutdown Mode with Active Reference and

LBI Detector

♦ 500kHz Maximum Switching Frequency
♦ ±1.5% Reference Tolerance Over Temperature
♦ Low-Battery Detector (LBI/LBO)
♦ 8-Pin DIP and SO Packages

______________Ordering Information

PART TEMP. RANGE PIN-PACKAGE

MAX756CPA

MAX756CSA 0°C to +70°C 8 SO
MAX756C/D 0°C to +70°C Dice*
MAX756EPA -40°C to +85°C 8 Plastic DIP
MAX756ESA -40°C to +85°C 8 SO
MAX757CPA
MAX757CSA 0°C to +70°C 8 SO
MAX757C/D 0°C to +70°C Dice*
MAX757EPA -40°C to +85°C 8 Plastic DIP
MAX757ESA -40°C to +85°C 8 SO

* Dice are tested at TA= +25°C only.

0°C to +70°C 8 Plastic DIP

0°C to +70°C 8 Plastic DIP

MAX756/MAX757

__________Typical Operating Circuit

INPUT

2V to V

OUT

0.1µF

150µF

8

6

4

22µH

LOW-BATTERY
DETECTOR OUTPUT

5

1

2

3

LBI

SHDN

MAX756

3/5

REF

________________________________________________________________

LX

OUT

LBO

GND

7

1N5817

OUTPUT

5V at 200mA

or

3.3V at 300mA

100µF

_________________Pin Configurations

TOP VIEW

1

SHDN

2

3/5

REF

LBO

SHDN

REF

LBO

MAX756

3
4

DIP/SO

1
2

FB

MAX757

3
4

DIP/SO

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

8

LX

7

GND

6

OUT

5

LBI

8

LX

7

GND

6

OUT

5

LBI

1

3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (OUT to GND) ....................................-0.3V, +7V

Switch Voltage (LX to GND)........................................-0.3V, +7V

Auxiliary Pin Voltages (SHDN

3/5

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

Reference Current (I
Continuous Power Dissipation (T

Plastic DIP (derate 9.09mW/°C above +70°C) .............727mW

, LBI, LBO, REF,

) ....................................................2.5mA

REF

= +70°C)

A

OUT

+ 0.3V)

SO (derate 5.88mW/°C above +70°C)..........................471mW

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.

Operating Temperature Ranges:

MAX75_C_ _ ........................................................0°C to +70°C

MAX75_E_ _......................................................-40°C to +85°C

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

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

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

ELECTRICAL CHARACTERISTICS

(Circuits of Figure 1 and Typical Operating Circuit, VIN= 2.5V, I

= 0mA, TA= T

LOAD

MIN

to T

, unless otherwise noted.)

MAX

MAX756/MAX757

Output Voltage

Minimum Start-Up Supply Voltage
Minimum Operating Supply

Voltage (once started)

Quiescent Supply Current in

3.3V Mode (Note 1)

Battery Quiescent Current
Measured at V

in Figure 1

IN

Shutdown Quiescent Current

(Note 1)
Reference Voltage
Reference-Voltage Regulation

LBO Output Voltage Low

LBO Output Leakage Current

SHDN, 3/5, FB, LBI Input Current

Output Voltage Range

MAX756, 3/5 = 0V, 0mA < I

2V < VIN< 3V

I

LOAD

I

LOAD

I

= 0mA, 3/5 = 3V, LBI = 1.25V, V

LOAD

FB = 1.3V (MAX757 only)

SHDN = 0V, LBI = 1.25V, 3/5 = 3V, V
FB = 1.3V (MAX757 only)

MAX756, 3/5 = 3V, 0mA < I
MAX757, V

= 10mA
= 20mA

= 0.1µF

REF

= 5V, 0mA < I

OUT

OUT

OUT

3/5 = 3V, -20µA < REF load < 250µA, C

I

= 2mA

SINK

LBI = 1.25V, FB = 1.25V, SHDN = 0V or 3V,
3/5 = 0V or 3V

MAX757, I

= 0mA (Note 2)

LOAD

LOAD
LOAD

LOAD

= 3.47V,

= 3.47V,

= 0.22µF

REF

< 200mA
< 300mA

< 200mA

4.8 5.0 5.2

3.17 3.30 3.43 V

4.8 5.0 5.2

1.1 1.8

60

60Output set for 3.3V

UNITSMIN TYP MAXCONDITIONSPARAMETER

V
V0.7

µA

µA

µA20 40

V1.23 1.25 1.27No REF load, C

%0.8 2.0

V1.22 1.25 1.28With falling edgeLBI Input Threshold

mV25LBI Input Hysteresis

V0.4

µA1LBO = 5V

V0.4SHDN, 3/5 Input Voltage Low
V1.6SHDN, 3/5 Input Voltage High

nA±100

V1.22 1.25 1.28MAX757FB Voltage
V2.7 5.5

Note 1: Supply current from the 3.3V output is measured with an ammeter between the 3.3V output and OUT pin. This current

correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency.

Note 2: Minimum value is production tested. Maximum value is guaranteed by design and is not production tested.

2 _______________________________________________________________________________________

3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)

EFFICIENCY vs. LOAD CURRENT

90

80

70

60

EFFICIENCY (%)

50

40

1M

100k

10k

1k

SWITCHING FREQUENCY (Hz)

100

10

3.3V OUTPUT MODE

VIN = 2.0V

VIN = 1.2V

0.1 10 1000

1 100

LOAD CURRENT (mA)

SWITCHING FREQUENCY

vs. LOAD CURRENT

5V MODE

10µ 10m 1

100µ 1m 100m

LOAD CURRENT (A)

MINIMUM START-UP INPUT VOLTAGE

1.8

1.6

3.3V MODE

V

= 2.5V

IN

vs. LOAD CURRENT

MAX756-1

EFFICIENCY (%)

MAX756-4

EFFICIENCY vs. LOAD CURRENT

90

80

70

60

50

40

500

400

300

200

QUIESCENT CURRENT (µA)

100

0

5V OUTPUT MODE

VIN = 3.3V

VIN = 1.25V

0.1 10 1000

1 100

LOAD CURRENT (mA)

QUIESCENT CURRENT

vs. INPUT VOLTAGE

CURRENT MEASURED AT V

V

= 5V

OUT

V

1

2

3

INPUT VOLTAGE (V)

MAX756-7

OUT

VIN = 2.5V

IN

= 3.3V

4

10

8

MAX756-2

MAXIMUM OUTPUT CURRENT (mA)

MAX756-5

SHUTDOWN QUIESCENT CURRENT (µA)

5

REFERENCE VOLTAGE

LOAD REGULATION

MAXIMUM OUTPUT CURRENT

800
700

600
500
400
300
200
100

0

50

40

30

20

10

0

vs. INPUT VOLTAGE

3.3V MODE

02

13

INPUT VOLTAGE (V)

SHUTDOWN QUIESCENT CURRENT

vs. INPUT VOLTAGE

CURRENT MEASURED AT V

12 5

3

INPUT VOLTAGE (V)

5V MODE

4

IN

4

MAX756-8

MAX756/MAX757

MAX756-3

5

MAX756-6

1.4

1.2

START-UP INPUT VOLTAGE (V)

1.0

0.8
1

10 100

LOAD CURRENT (mA)

3.3V MODE

1000

6

4

VREF LOAD REGULATION (mV)

2

0

0

50 100 150 200

LOAD CURRENT (µA)

V

= 3.3V

OUT

250

_________________________________________________________________________________________________

3