Rainbow Electronics MAX8715 User Manual

General Description

The MAX1790/MAX8715 boost converters incorporate
high-performance (at 1.2MHz), current-mode, fixed-fre­quency, pulse-width modulation (PWM) circuitry with a
built-in 0.21Ω/0.15Ω n-channel MOSFET to provide a high­ly efficient regulator with fast response.

High switching frequency (640kHz or 1.2MHz selectable)
allows easy filtering and faster loop performance. An
external compensation pin provides the user flexibility in
determining loop dynamics, allowing the use of small, low
equivalent-series-resistance (ESR) ceramic output capaci­tors. The device can produce an output voltage as high as
12V from an input as low as 2.6V.

Soft-start is programmed with an external capacitor, which
sets the input-current ramp rate. In shutdown mode, cur­rent consumption is reduced to 0.1µA. The MAX1790/
MAX8715 are available in a space-saving 8-pin µMAX

®

package. The ultra-small package and high switching fre­quency allow the total solution to be less than 1.1mm high.

Applications

LCD Displays
PCMCIA Cards
Portable Applications
Hand-Held Devices

Features

♦ 90% Efficiency
♦ Adjustable Output from V

IN

to 12V

♦ 1.6A, 0.21Ω, 14V Power MOSFET (MAX1790)
♦ 2.4A, 0.15Ω, 14V Power MOSFET (MAX8715)
♦ +2.6V to +5.5V Input Range
♦ Pin-Selectable 640kHz or 1.2MHz Switching

Frequency

♦ 0.1µA Shutdown Current
♦ Programmable Soft-Start
♦ Small 8-Pin µMAX Package

MAX1790/MAX8715

Low-Noise Step-Up DC-DC Converters

________________________________________________________________ Maxim Integrated Products 1

IN

LXGND

1
2

87SS

FREQFB

COMP

µMAX

TOP VIEW

3

4

6

5

MAX1790
MAX8715

SHDN

Typical Operating Circuit

19-1563; Rev 2; 5/04

Pin Configuration

Ordering Information

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.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX1790EUA -40°C to +85°C 8 µMAX
MAX8715EUA -40°C to +85°C 8 µMAX

µMAX is a registered trademark of Maxim Integrated Products,
Inc.

V

IN

2.6V TO 5V

IN

ON/OFF

SHDN

FREQ

SS

MAX1790
MAX8715

COMP

LX

GND

FB

V

OUT

MAX1790/MAX8715

Low-Noise Step-Up DC-DC Converters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= SHDN = 3V, FREQ = GND, 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.

LX to GND ..............................................................-0.3V to +14V

IN, SHDN, FREQ, FB to GND................................-0.3V to +6.2V

SS, COMP to GND.......................................-0.3V to (V

IN

+ 0.3V)

RMS LX Pin Current ..............................................................1.2A

Continuous Power Dissipation (T

A

= +70°C)

8-Pin µMAX (derate 4.1mW/°C above +70°C).............330mW

Operating Temperature Range

MAX1790EUA/MAX8715EUA ........................-40°C to +85°C

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

Storage Temperature Range.............................-65°C to +150°C

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

PARAMETER

CONDITIONS

UNITS

Input Supply Range V

IN

2.6 5.5 V

VIN Undervoltage Lockout UVLO

V

IN

rising, typical hysteresis is 40mV,

LX remains off below this level

V

MAX1790

V

FB

= 1.0V, switching 2 5

Quiescent Current I

IN

MAX8715

V

FB

= 1.0V, switching 2.5 5.0

mA

Shutdown Supply Current I

IN

SHDN = GND 0.1 10 µA

ERROR AMPLIFIER

Feedback Voltage V

FB

Level to produce V

COMP

= 1.24V

V

MAX1790 0 40

FB Input Bias Current I

FB

VFB = 1.24V

MAX8715

nA

Feedback-Voltage Line
Regulation

Level to produce V

COMP

= 1.24V,

2.6V < V

IN

< 5.5V

%/V

MAX1790 70

Transconductance g

m

∆I = 5µA

MAX8715 70

µS

Voltage Gain A

V

V/V

OSCILLATOR

FREQ = GND

Frequency f

OSC

FREQ = IN

kHz

FREQ = GND

79 85 92

Maximum Duty Cycle DC

FREQ = IN 84

%

N-CHANNEL SWITCH

MAX1790 1.2 1.6 2.3

Current Limit I

LIM

VFB = 1V,
duty cycle =
65% (Note 1)

MAX8715 1.8 2.4 3.4

A

MAX1790

0.5

On-Resistance R

ON

MAX8715

Ω

MAX1790

20

Leakage Current I

LXOFF

VLX = 12V

MAX8715 5 30

µA

SYMBOL

MIN TYP MAX

2.25 2.38 2.52

VFB = 1.3V, not switching 0.18 0.35

VFB = 1.3V, not switching 0.21 0.35

1.222 1.24 1.258

540 640 740

1000 1220 1500

125 190

0.05 0.15
140 240

160 240
700

0.21

0.15 0.35

0.01

MAX1790/MAX8715

Low-Noise Step-Up DC-DC Converters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VIN= SHDN = 3V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

ELECTRICAL CHARACTERISTICS (continued)

(VIN= SHDN = 3V, FREQ = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

CONDITIONS

UNITS

MAX1790

Current-Sense Transresistance R

CS

MAX8715

V/A

SOFT-START

Reset Switch Resistance

Ω

Charge Current VSS = 1.2V 1.5 4 7.0 µA

CONTROL INPUTS

Input Low Voltage V

IL

SHDN, FREQ

V

Input High Voltage V

IH

SHDN, FREQ

V

Hysteresis SHDN, FREQ

V

FREQ Pulldown Current I

FREQ

1.8 5 9.0 µA

SHDN Input Current I

SHDN

1µA

SYMBOL

MIN TYP MAX

0.30 0.45 0.65

0.20 0.30 0.43

0.3 x V

0.7 x V

IN

0.1 x V

IN

0.001

Input Supply Range V
VIN Undervoltage Lockout UVLO

Quiescent Current I

Shutdown Supply Current I

ERROR AMPLIFIER

Feedback Voltage V
FB Input Bias Current I

Feedback-Voltage Line
Regulation

Transconductance g

OSCILLATOR

Frequency f
Maximum Duty Cycle DC FREQ = GND 78 92 %

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IN

V

rising, typical hysteresis is 40mV,

IN

LX remains off below this level

MAX1790

IN

MAX8715

IN

FB

FB

OSC

SHDN = GND 10 µA

Level to produce V
VFB = 1.24V

Level to produce V

2.6V < V

∆I = 5µA

m

FREQ = GND
FREQ = IN 900 1500

< 5.5V

IN

VFB = 1.3V, not switching 0.35
V

= 1.0V, switching 5

FB

VFB = 1.3V, not switching 0.35
V

= 1.0V, switching 5

FB

= 1.24V 1.215 1.24 1.260 V

COMP

MAX1790 40
MAX8715 190

= 1.24V,

COMP

MAX1790 70 260
MAX8715 70 260

2.6 5.5 V

2.25 2.52 V

490 770

100

IN

mA

nA

0.15 %/V

µS

kHz

MAX1790/MAX8715

Low-Noise Step-Up DC-DC Converters

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VIN= SHDN = 3V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

PARAMETER

CONDITIONS

UNITS

N-CHANNEL SWITCH

MAX1790 1.2 2.3

Current Limit I

LIM

VFB = 1V,
duty cycle =
65% (Note 1)

MAX8715 1.8 3.0

A

MAX1790 0.5

On-Resistance R

ON

MAX8715

Ω

MAX1790

Current-Sense Transresistance R

CS

MAX8715

V/A

CONTROL INPUTS

Input Low Voltage V

IL

SHDN, FREQ

V

Input High Voltage V

IH

SHDN, FREQ

V

Note 1: Current limit varies with duty cycle due to slope compensation. See the Output-Current Capability section.
Note 2: Specifications to -40°C are guaranteed by design and not production tested.

SYMBOL

MIN TYP MAX

0.30 0.65

0.20 0.43

0.7 x V

0.35

0.3 x V

IN

IN

Typical Operating Characteristics

(Circuit of Figure 1, VIN= 3.3V, f

OSC

= 640kHz, TA= +25°C, unless otherwise noted.)

MAX1790 toc01

50

1100010010

MAX1790 EFFICIENCY

vs. OUTPUT CURRENT

65

55

85

75

95

70

60

90

80

OUTPUT CURRENT (mA)

EFFICIENCY (%)

f

OSC

= 1.2MHz

L

= 2.7µH

V

IN

= 3.3V

V

OUT

= 5V

f

OSC

= 640kHz

L

= 5.4µH

50

1 100010010

MAX1790 EFFICIENCY
vs. OUTPUT CURRENT

65

55

85

75

95

70

60

90

80

MAX1790 toc02

OUTPUT CURRENT (mA)

EFFICIENCY (%)

f

OSC

= 1.2MHz

L

= 5.4µH

V

IN

= 3.3V

V

OUT

= 12V

f

OSC

= 640kHz

L

= 10µH

OUTPUT CURRENT (mA)

50

1 100010010

MAX1790 EFFICIENCY

vs. OUTPUT CURRENT

65

55

85

75

95

70

60

90

80

MAX1790 toc03

EFFICIENCY (%)

f

OSC

= 1.2MHz

L

= 5.4µH

V

IN

= 5V

V

OUT

= 12V

f

OSC

= 640kHz

L

= 10µH

0

0.2

0.1

0.4

0.3

0.6

0.5

0.7

2.5 3.5 4.03.0 4.5 5.0 5.5

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE

MAX1790 toc04

INPUT VOLTAGE (V)

NO-LOAD SUPPLY CURRENT (mA)

V

OUT

= 12V

f

OSC

= 1.2MHz

f

OSC

= 640kHz

11.60

11.70

11.65

11.80

11.75

11.90

11.85

11.95

12.05

12.00

12.10

040608020 100 120 140 180160 200

MAX1790 OUTPUT VOLTAGE

vs. OUTPUT CURRENT

MAX1790 toc05

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE (V)

f

OSC

= 640kHz

TA = +85°C

TA = +25°C

TA = -40°C

MAX8715 EFFICIENCY

vs. OUTPUT CURRENT

MAX1790 toc06

OUTPUT CURRENT (mA)

EFFICIENCY (%)

10010

50

55

60

65

70

75

80

85

90

95

45

1 1000

VIN = 5.0V

VIN = 3.3V

V

OUT

= 9V

f

OSC

= 1.2MHz

L = 6.8µH

MAX1790/MAX8715

Low-Noise Step-Up DC-DC Converters

_______________________________________________________________________________________ 5