MAX1763EUE+ - MAXIM INTEGRATED PRODUCTS

General Description

The MAX1763 is a high-efficiency, low-noise, step-up

DC-DC converter intended for use in battery-powered

wireless applications. This device maintains exception-

ally low quiescent supply current (110µA) despite its

high 1MHz operating frequency. Small external compo-

nents and a tiny package make this device an excellent

choice for small hand-held applications that require the

longest possible battery life.

The MAX1763 uses a synchronous-rectified pulse-

width-modulation (PWM) boost topology to generate

2.5V to 5.5V outputs from a wide range of input

sources, such as one to three alkaline or NiCd/NiMH

cells or a single Lithium-ion (Li+) cell. Maxim's propri-

etary Idle Mode™ circuitry significantly improves effi-

ciency at light load currents while smoothly transitioning

to fixed-frequency PWM operation at higher load cur-

rents to maintain excellent full-load efficiency. Low-

noise, forced-PWM mode is available for applications

that require constant-frequency operation at all load

currents. The MAX1763 may also be synchronized to

an external clock to protect sensitive frequency bands

in communications equipment.

The MAX1763 includes an on-chip linear gain block

that can be used to build a high-power external linear

regulator or as a low-battery comparator. Soft-start and

current limit functions permit optimization of efficiency,

external component size, and output voltage ripple.

The MAX1763 is available in a space-saving 16-pin

QSOP package or a high-power (1.5W) 16-pin TSSOP-

EP package.

Features

♦Up to 94% Efficiency

♦+0.7V to +5.5V Input Voltage Range

♦1.1V Guaranteed Startup Input Voltage

♦Up to 1.5A Output

♦Fixed 3.3V Output or Adjustable (2.5V to 5.5V)

♦1MHz PWM Synchronous-Rectified Topology

♦1µA Logic-Controlled Shutdown

♦Analog Gain Block for Linear-Regulator or Low-

Battery Comparator

♦Adjustable Current Limit and Soft-Start

♦1.5W TSSOP Package Available

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

19-1698; Rev 2; 4/11

Ordering Information

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad

Idle Mode is a trademark of Maxim Integrated Products.

PART TEMP RANGE PIN-PACKAGE

MAX1763EEE+ -40°C to +85°C 16 QSOP

MAX1763EUE+ -40°C to +85°C 16 TSSOP-EP*

Digital Cordless

Phones

PCS Phones

Wireless Handsets

Hand-Held

Instruments

Palmtop Computers

Personal

Communicators

Typical Operating Circuit

ON OFF

PWM

OFF ON ONB

ONA

POUT

OUT

CLK/SEL

GND PGNDFB

ISET

REF

MAX1763

OR NORMAL

AIN

LBI OR GAIN

BLOCK INPUT

1.5μH

0.7V TO 5.5V

LBO OR

GAIN BLOCK OUTPUT

OUT

3.3V AT 1.5A

________________________Applications

ONA ONB

POUT

PGND

CLK/SEL

TOP VIEW

MAX1763

QSOP

TSSOP-EP

ISET

REF

OUT

GND

AIN

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA= 0°C to +85°C, unless other-

wise 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.

ONA, ONB, AO, OUT to GND.......................................0.3V, +6V

PGND to GND.....................................................................±0.3V

LX to PGND ............................................-0.3V to (VPOUT + 0.3V)

CLK/SEL, REF, FB, ISET, POUT,

AIN to GND.........................................-0.3V to (VOUT + 0.3V)

POUT to OUT ......................................................................±0.3V

Continuous Power Dissipation

16-Pin QSOP (derate 8.7mW/°C above +70°C)...........667mW

16-Pin TSSOP-EP (derate 19mW/°C above +70°C) ...........1.5W

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

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

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

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

Soldering Temperature (reflow) .......................................+260°C

PARAMETER CONDITIONS MIN TYP MAX UNITS

DC-DC CONVERTER

Input Voltage Range (Note 1) 0.7 5.5 V

Minimum Startup Voltage

(Note 2) ILOAD < 1mA, TA = +25°C 0.9 1.1 V

Temperature Coefficient of

Startup Voltage ILOAD < 1mA -2 mV/°C

Frequency in Startup Mode VOUT = 1.5V 125 500 1000 kHz

Internal Oscillator Frequency CLK/SEL = OUT 0.8 1 1.2 MHz

Oscillator Maximum Duty Cycle

(Note 3) 80 86 90 %

External Clock Frequency Range 0.5 1.2 MHz

Output Voltage VFB < 0.1V, CLK/SEL = OUT, includes load regulation

for 0 < ILX < 1.1A 3.17 3.3 3.38 V

FB Regulation Voltage Adjustable output, CLK/SEL = OUT, includes load

regulation for 0 < ILX < 1.1A 1.215 1.245 1.270 V

FB Input Current VFB = 1.35V 0.01 100 nA

Load Regulation CLK/SEL = OUT, 0 < ILX < 1.1A -1.0 %

Output Voltage Adjust Range 2.5 5.5 V

Output Voltage Lockout

Threshold (Note 4) Rising edge 2.00 2.15 2.30 V

ISET Input Leakage Current VISET = 1.25V 0.01 50 nA

Supply Current in Shutdown V

ONB = 3.6V, VONA = 0V 1 10 µA

No-Load Supply Current, Low-

Power Mode (Note 5) CLK/SEL = GND, AIN = OUT 110 200 µA

No-Load Supply Current, Low-

Noise Mode CLK/SEL = OUT 2.5 mA

Gain Block Supply Current VAIN < (VOUT - 1.4V), gain block enabled 25 50 µA

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA= 0°C to +85°C, unless other-

wise noted. Typical values are at TA= +25°C.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

DC-DC SWITCHES

POUT Leakage Current VLX = 0V, VOUT = 5.5V 0.1 10 µA

LX Leakage Current VLX = V ONB = VOUT = 5.5V, VONA = 0V 0.1 10 µA

N channel 0.075 0.13

Switch On-Resistance P channel 0.13 0.25 Ω

N-Channel Current Limit 2.0 2.5 3.4 A

P-Channel Turn-Off Current CLK/SEL = GND 10 120 240 mA

REFERENCE

Reference Output Voltage IREF = 0A 1.230 1.250 1.270 V

Reference Load Regulation -1µA < IREF < 50µA 5 15 mV

Reference Supply Rejection 2.5V < VOUT < 5V 0.2 5 mV

GAIN BLOCK

AIN Reference Voltage IAO = 20µA 910 938 970 mV

AIN Input Current VAIN = 1.5V ±0.01 ±30 nA

Transconductance VAO = 1V, 10µA < IAO < 100µA 5 10 16 mS

AO Output Low Voltage VAIN = 0.5V, IAO = 100µA 0.1 0.4 V

AO Output High Leakage VAIN = 1.5V, VAO = 5.5V 0.01 1 µA

Gain-Block Enable Threshold

(VOUT - VAIN) (Note 6) 1.4 V

Gain-Block Disable Threshold

(VOUT - VAIN) (Note 6) 0.2 V

LOGIC INPUTS

CLK/SEL Input Low Level 2.5V ≤ VOUT ≤ 5.5V (0.2)

VOUT V

CLK/SEL Input High Level 2.5 V ≤ VOUT ≤ 5.5V (0.8)

VOUT V

1.1 V ≤ VOUT ≤ 1.8V 0.2

ONA and ONB Input Low Level

(Note 7) 1.8 V ≤ VOUT ≤ 5.5V 0.4 V

1.1 V ≤ VOUT ≤ 1.8V VOUT

- 0.2V

ONA and ONB Input High Level

(Note 7)

1.8 V ≤ VOUT ≤ 5.5V 1.6

Input Leakage Current CLK/SEL, ONA, ONB 0.01 1 µA

Minimum CLK/SEL Pulse Width 100 ns

Maximum CLK/SEL

Rise/Fall Time 100 ns

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA= -40°C to +85°C, unless other-

wise noted.) (Note 8)

PARAMETER CONDITIONS MIN MAX UNITS

DC-DC CONVERTER

Input Voltage Range (Note 1) 5.5 V

M i ni m um S tartup V ol tag e ( N ote 2) ILOAD < 1mA, TA = +25°C 1.1 V

Frequency in Startup Mode VOUT = 1.5V 125 1000 kHz

Internal Oscillator Frequency CLK/SEL = OUT 0.75 1.25 MHz

Oscillator Maximum Duty Cycle

(Note 3) 80 91 %

E xter nal C l ock Fr eq uency Rang e 0.6 1.2 MHz

Output Voltage VFB < 0.1V, CLK/SEL = OUT, includes load regulation

for 0 < ILX < 1.1A 3.17 3.38 V

FB Regulation Voltage Adjustable output, CLK/SEL = OUT, includes load

regulation for 0 < ILX < 1.1A

1.215 1.270 V

FB Input Current VFB = 1.35V 100 nA

Output Voltage Adjust Range 2.5 5.5 V

Output Voltage Lockout

Threshold (Note 4) Rising edge 2.00 2.30 V

ISET Input Leakage Current VISET = 1.25V 50 nA

Supply Current in Shutdown V

ONB = 3.6V, VONA = 0V 10 µA

No-Load Supply Current, Low-

Power Mode (Note 5) CLK/SEL = GND, AIN = OUT 200 µA

Gain Block Supply Current VAIN < (VOUT - 1.4V), gain block enabled 50 µA

DC-DC SWITCHES

POUT Leakage Current VLX = 0V, VOUT = 5.5V 10 µA

LX Leakage Current VLX = V ONB = VOUT = 5.5V, VONA = 0V 10 µA

N-channel 0.13

Switch On-Resistance P-channel 0.25 Ω

N-Channel Current Limit 2.0 3.4 A

P-Channel Turn-Off Current CLK/SEL = GND 10 240 mA

REFERENCE

Reference Output Voltage IREF = 0A 1.220 1.270 V

Reference Load Regulation -1µA < IREF < 50µA 15 mV

Reference Supply Rejection 2.5V < VOUT < 5V 5 mV

GAIN BLOCK

AIN Reference Voltage IAO = 20µA 910 970 mV

AIN Input Current VAIN = 1.5V ±30 nA

Transconductance VAO = 1V, 10µA < IAO < 100µA 5 16 mS

AO Output Low Voltage VAIN = 0.5V, IAO = 100µA 0.4 V

AO Output High Leakage VAIN = 1.5V, VAO = 5.5V 1 µA

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA= -40°C to +85°C, unless other-

wise noted.) (Note 8)

PARAMETER CONDITIONS MIN MAX UNITS

LOGIC INPUTS

Gain-Block Enable Threshold

(VOUT - VAIN) (Note 6) 1.4 V

Gain-Block Disable Threshold

(VOUT - VAIN) (Note 6) 0.2 V

CLK/SEL Input Low Level 2.5 V ≤ VOUT ≤ 5.5V (0.2)

VOUT V

CLK/SEL Input High Level 2.5 V ≤ VOUT ≤ 5.5V (0.8)

VOUT V

1.1 V ≤ VOUT ≤ 1.8V 0.2

ONA and ONB Input Low Level

(Note 7) 1.8 V ≤ VOUT ≤ 5.5V 0.4 V

1.1 V ≤ VOUT ≤ 1.8V VOUT

- 0.2V

ONA and ONB Input High Level

(Note 7) 1.8V ≤ VOUT ≤ 5.5V 1.6

Input Leakage Current CLK/SEL, ONA, ONB 1µA

Note 1: Operating voltage. Because the regulator is bootstrapped to the output, once started, the MAX1763 will operate down to

0.7V input. For conditions where VIN might exceed the set VOUT, or where VOUT is set above 4V, an external Schottky diode

must be connected from LX to POUT.

Note 2: Startup is tested with the circuit of Figure 2.

Note 3: Defines low-noise mode maximum step-up ratio.

Note 4: The regulator is in startup mode until this voltage is reached. Do not apply full load current until the output exceeds 2.3V.

Note 5: Supply current from the 3.3V output is measured between the 3.3V output and the OUT pin. This current correlates directly

to the actual battery-supply current, but is reduced in value according to the step-up ratio and efficiency. The gain block is

disabled.

Note 6: Connect AIN to OUT to disable gain block.

Note 7: ONA and ONB have hysteresis of approximately 0.15 ✕VOUT.

Note 8: Specifications to -40°C are guaranteed by design and not production tested.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

6 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.)

100

0.001 0.01 0.1 1 10

EFFICIENCY vs. OUTPUT CURRENT

(VOUT = 3.3V)

MAX1763 toc01

OUTPUT CURRENT (A)

EFFICIENCY (%)

A: VIN = 2.4V

B: VIN = 1.2V

C: VIN = 0.9V

= NORMAL MODE

= FPWM MODE

100

0.001 0.01 0.1 1 10

EFFICIENCY vs. OUTPUT CURRENT

(VOUT = 5V)

MAX1763 toc02

OUTPUT CURRENT (A)

EFFICIENCY (%)

90 A

A: VIN = 3.6V

B: VIN = 2.4V

C: VIN = 1.2V

= NORMAL MODE

= FPWM MODE

1.0

0.5

2.0

1.5

2.5

3.0

0.8 2.41.6 3.2 4.0

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

MAX1763 toc03

INPUT VOLTAGE (V)

OUTPUT CURRENT (A)

VOUT = 3.3V

VOUT = 5V

0.1

0.0001

01 3 5

NO-LOAD INPUT

vs. INPUT VOLTAGE

0.001

0.01

MAX1763 toc04

INPUT VOLTAGE (V)

INPUT CURRENT (A)

= INPUT VOLTAGE INCREASING

= INPUT VOLTAGE DECREASING

0.1

046

INPUT VOLTAGE (V)

SHUTDOWN CURRENT (μA)

SHUTDOWN CURRENT

vs. INPUT VOLTAGE

135

MAX1763 toc05

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-40 -15 10 35 60 85

INTERNAL OSCILLATOR FREQUENCY

vs. TEMPERATURE

MAX1763 toc06

TEMPERATURE (°C)

FREQUENCY (MHz)

VIN = 3.6V, VOUT = 5V

VIN = 2.4V, VOUT = 3.3V

0.6

1.6

1.1

2.6

2.1

3.6

3.1

4.1

0.001 0.10.01 1 10

STARTUP VOLTAGE

vs. OUTPUT CURRENT

MAX1763 toc07

OUTPUT CURRENT (A)

STARTUP VOLTAGE (V)

1.0

0.5

2.0

1.5

2.5

3.0

0 0.6 0.80.2 0.4 1.0 1.2 1.4

PEAK INDUCTOR CURRENT vs. VISET

MAX1763 toc08

ISET VOLTAGE (V)

PEAK INDUCTOR CURRENT (A)

HEAVY-LOAD SWITCHING WAVEFORMS

MAX1763 toc09

400ns/div

VIN = 2.4V, VOUT = 3.3V, IOUT = 1.5A

A: INDUCTOR CURRENT, 500mA/div

B: VLX, 2V/div

C: VOUT, 100mV/div, AC COUPLED

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

_______________________________________________________________________________________ 7

LIGHT-LOAD SWITCHING WAVEFORMS

MAX1763 toc10

200ns/div

VIN = 1.1V, VOUT = 3.3V, IOUT = 20mA

A: LX NODE, 5V/div

B: INDUCTOR CURRENT, 0.1A/div, AC COUPLED

C: OUTPUT RIPPLE, 0.1V/div, AC COUPLED

LOAD-TRANSIENT RESPONSE

MAX1763 toc11

100μs/div

VIN = 2.4V, VOUT = 3.3V, IOUT = 0.2A TO 1.35A

A: IOUT, 0.5A/div

B: VOUT, 100mV/div, AC-COUPLED

LINE-TRANSIENT RESPONSE

MAX1763 toc12

40μs/div

VIN = 2.4V TO 1.4V, IOUT = 70mA

A: VIN, 1V/div

B: VOUT, 5mV/div, AC-COUPLED

POWER-ON DELAY

MAX1763 toc13

100μs/div

ONA

5V/div

IIN

0.5A/div

VOUT

2V/div

IL = 10mA

STARTUP WAVEFORMS

NO SOFT-START

MAX1763 toc14

2ms/div

VIN = 1.2V, VOUT = 3.3V, RLOAD = 3kΩ

VOUT

2V/div

ONA

5V/div

IIN

1A/div

STARTUP WAVEFORMS

USING SOFT-START

MAX1763 toc15

2ms/div

VIN = 1.2V, VOUT = 3.3V, RSS = 510kΩ, CSS = 0.1μF, RLOAD = 3kΩ

VOUT

2V/div

ONA

5V/div

IIN

1A/div

0.01 1010.1

NOISE SPECTRUM

MAX1763 toc16

FREQUENCY (MHz)

NOISE (mVRMS)

VIN = 2.4V

VOUT = 3.3V

Typical Operating Characteristics (continued)

(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.)

MAX1763

Detailed Description

The MAX1763 is a highly-efficient, low-noise power

supply for portable RF and hand-held instruments. It

combines a boost switching regulator, N-channel

power MOSFET, P-channel synchronous rectifier, preci-

sion reference, shutdown control, and a versatile gain

block (Figure 1).

The DC-DC converter boosts a one-cell to three-cell bat-

tery voltage input to a fixed 3.3V or adjustable voltage

between 2.5V and 5.5V. An external Schottky diode is

required for output voltages greater than 4V. The

MAX1763 guarantees startup with an input voltage as

low as 1.1V and remains operational down to an input of

just 0.7V. It is optimized for use in cellular phones and

other applications requiring low noise and low quiescent

current for maximum battery life. It features constant-fre-

quency (1MHz), low-noise PWM operation with up to

1.5A output capability. A CLK input allows frequency

synchronization to control the output noise spectrum.

See Table 1 for typical available output current.

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

8 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1 ONA On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal

operation (Table 3).

2 ISET

N-Channel Current Limit Control. For maximum current limit, connect to REF. To reduce current,

supply a voltage between REF and GND by means of a resistive voltage-divider. If soft-start is

desired, connect a capacitor from ISET to GND. When ONA = low and ONB = high, or VREF < 80% of

nominal value, an on-chip switched resistor (100kΩ typ) discharges this pin to GND.

3 REF 1.250V Voltage Reference Bypass Pin. Connect a 0.22µF ceramic bypass capacitor to GND. Up to

50µA of external REF load current is allowed.

4 GND Ground. Connect to PGND with short trace.

5FB

DC-DC Converter Feedback Input. To set fixed output voltage of +3.3V, connect FB to ground. For

adjustable output of 2.5V to 5.5V, connect to a resistive divider placed from OUT to GND. FB set

point is 1.245V (Figure 6).

6 OUT IC Power, Supplied from the Output. Bypass to GND with a 1.0µF ceramic capacitor, and connect to

POUT with a series 4.7Ω resistor (Figure 2).

7 AIN

Gain-Block Input. The nominal transconductance from AIN to AO is 10mS. An external P-channel

pass device can be used to build a linear regulator. The gain block can also be used as a low-battery

comparator with a threshold of 0.938V. The gain block and its associated quiescent current are

disabled by connecting AIN to OUT.

8AO

Gain-Block Output. This open-drain N-channel output sinks current when VAIN < (0.75)(VREF). AO is

high-Z when the device is shut down, or when AIN = OUT.

9 CLK/SEL

Clock Input for the DC-DC Converter. Also serves to program the operating mode of the switcher as

follows:

CLK/SEL = LO: Normal; operates at a fixed frequency, automatically switching to low-power mode if

load is minimized.

CLK/SEL = HI: Forced PWM mode; operates in low-noise, constant-frequency mode at all loads.

CLK/SEL = Clocked: Forced PWM mode with the internal oscillator synchronized to CLK in 500kHz

to 1200kHz range.

10, 12 PGND Source of N-Channel Power MOSFET Switch. Connect both PGND pins together close to the device.

11, 14 LX Inductor Connection. Connect the LX pins together close to the device.

13, 15 POUT Power Output. P-channel synchronous rectifier source.

16 ONB Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal

operation (Table 3).

— EP Exposed Pad (TSSOP Only). Connect EP to a large ground plane to maximize thermal performance.

In its normal mode of operation (CLK/SEL = low), the

MAX1763 offers fixed-frequency PWM operation through

most of its load range. At light loads (less than 25% of full

load), the device automatically optimizes efficiency by

switching only as needed to supply the load. Shutdown

reduces quiescent current to just 1µA. Figure 2 shows

the standard application circuit for the MAX1763. (An

external Schottky diode is needed for output voltages

greater than 4V, or to assist low-voltage startup.)

Additional features include synchronous rectification for

high efficiency and increased battery life, and a gain

block that can be used to build a linear regulator using

an external P-channel MOSFET pass device. This gain

block can also function as a voltage-monitoring com-

parator. The MAX1763 is available in a 16-pin QSOP

package or a 1.5W 16-pin TSSOP-EP package for high-

temperature or high-dissipation applications.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

_______________________________________________________________________________________ 9

Figure 1. Functional Diagram

Figure 2. PFM/PWM Automode Connection

GAIN

BLOCK

AIN

2.15V

IC POWER

1.25V

DUAL

MODE/

REFERENCE

UNDERVOLTAGE LOCKOUT

STARTUP

OSCILLATOR

1MHz

OSCILLATOR

CONTROLLER

EN D

POUT

PGND

OSC

MODE

REF

ISET

GND

CLK/SEL

ON RDY

REF

0.938V

ONB

ONA

OUT

MAX1763

ISET

GNDPGND

POUT

OUT

AIN

MBR0520L

VIN

0.7V TO 5.5V

2 x 100μF

OUT

3.3V

1.5μH

REF

CLK/SEL

ONA

ONB

ISET

0.22μF

1.0μF

NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.

4.7Ω

MAX1763

47μF

Table 1. Typical Available Output Current

NUMBER

OF CELLS

INPUT

VOLTAGE

(V)

OUTPUT

VOLTAGE

(V)

OUTPUT

CURRENT

(mA)

1 NiCd/NiMH 1.2 3.3 675

2.4 3.3 1500

2 NiCd/NiMH

2.4 5.0 950

1 Li+ 2.7 (min) 3.3 1300

1 Li+ 2.7 (min) 5.0 1100

3 NiCd/NiMH 3.6 5.0 1600

MAX1763

Step-Up Converter

During DC-DC converter operation, the internal N-chan-

nel MOSFET switch turns on for the first part of each

cycle, allowing current to ramp up in the inductor and

store energy in a magnetic field. During the second

part of each cycle, the MOSFET turns off and inductor

current flows through the synchronous rectifier to the

output filter capacitor and the load. As the energy

stored in the inductor is depleted, the current ramps

down and the synchronous rectifier turns off, the N-

channel FET turns on, and the cycle repeats. At light

loads, depending on the CLK/SEL pin setting, output

voltage is regulated using either PWM or by switching

only as needed to service the load (Table 2).

Normal Operation

Pulling CLK/SEL low selects the MAX1763’s normal

operating mode. In this mode, the device operates in

PWM when driving medium to heavy loads, and at light

loads only, switches as needed. This optimizes efficien-

cy over the widest range of load conditions. In normal

operation mode, the output voltage regulates 1% higher

than in forced-PWM mode. See Efficiency vs. Load

Current in the Typical Operating Characteristics section.

Forced-PWM Operation

When CLK/SEL is high, the MAX1763 operates in a low-

noise forced-PWM mode. During forced-PWM opera-

tion, the MAX1763 switches at a constant frequency

(1MHz) and modulates the MOSFET switch pulse width

to control the power transferred per cycle and regulate

the output voltage. Switching harmonics generated by

fixed-frequency operation are consistent and easily fil-

tered. See the Noise Spectrum plot in the Typical

Operating Characteristics.

Synchronized-PWM Operation

In a variation of forced-PWM mode, the MAX1763 can

be synchronized to an external frequency by applying

a clock signal to CLK/SEL. This allows the user to

choose an operating frequency (from 500kHz to

1.2MHz) to avoid interference in sensitive applications.

For the most noise-sensitive applications, limit the

external synchronization signal duty cycle to less than

10% or greater than 90%. This eliminates the possibility

that noise from the power switching will coincide with

the synchronization signal. If the synchronization signal

edge falls on the power switching edge, a slight fre-

quency jitter may occur.

Synchronous Rectifier

The MAX1763 features an internal 130mΩP-channel syn-

chronous rectifier to enhance efficiency. Synchronous

rectification provides a 5% efficiency improvement over

similar boost regulators that rely on diode rectifiers. In

PWM mode, the synchronous rectifier is turned on during

the second half of each switching cycle. In low-power

mode, an internal comparator turns on the synchronous

rectifier when the voltage at LX exceeds the boost regula-

tor output and turns it off when the inductor current drops

below 120mA. When setting output voltages greater than

4V, an external 0.5A Schottky diode must be connected

in parallel with the on-chip synchronous rectifier.

Low-Voltage Startup Oscillator

The MAX1763 uses a CMOS low-voltage startup oscil-

lator for a 1.1V guaranteed minimum startup input volt-

age. At startup, the low-voltage oscillator switches the

N-channel MOSFET until the output voltage reaches

2.15V. Above this level, the normal feedback and con-

trol circuitry take over. Once the device is in regulation,

it can operate down to 0.7V input because internal

power for the IC is derived from the output through the

OUT pin. Do not apply full system load until the output

exceeds 2.3V.

Shutdown, ONA,

ONB

ONA and ONB turn the MAX1763 on or off. When ONA =

1 or ONB = 0, the device is on. When ONA = 0 and

ONB = 1, the device is off (Table 3). Logic high ON

control can be implemented by connecting ONB high

and using ONA for the control input. Momentary one-

pushbutton ON/OFF control is described in the

Applications Information section. Both ONA and ONB

have approximately (0.15 ✕VOUT)V of hysteresis.

Reference

The MAX1763 has an internal 1.250V reference.

Connect a 0.22µF ceramic bypass capacitor to GND

within 0.2in (5mm) of the REF pin. REF can source up

to 50µA of external load current.

Gain Block

The MAX1763 gain block can function as a power-OK

comparator or can be used to build a linear regulator

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

10 ______________________________________________________________________________________

Table 2. Selecting the Operating Mode

CLK/SEL MODE FEATURES

0Normal

operation

High efficiency at all

loads. Fixed

frequency at all but

light loads.

1 Forced PWM Low noise, fixed

frequency at all loads.

External clock

500kHz to 1.2MHz

S ynchr oni zed

P WM

Low noise, fixed

frequency at all loads.

using an external P-channel MOSFET pass device. The

gain-block output is a single-stage transconductance

amplifier that drives an open-drain N-channel MOSFET.

The transconductance (GM) of the entire gain-block

stage is 10mS. The internal gain block amplifies the dif-

ference between AIN and the internal 0.938V reference.

To provide a power-OK signal, connect the gain-block

input, AIN, to an external resistor-divider (Figure 3). The

input bias current into AIN is less than 30nA, allowing

large-value divider resistors without sacrificing accura-

cy. Connect the resistor voltage-divider as close to the

IC as possible, within 0.2in (5mm) of AIN. Choose an

R4 value of 270kΩor less, then calculate R3 using:

R3 = R4((VTRIP / VAIN ) - 1)

where VAIN is 0.938V.

Figures 4 and 5 show the gain block used in a linear-

regulator application. The output of an external P-chan-

nel pass element is compared to an internal 0.938V

reference. The difference is amplified and drives the

gate of the pass element. Use a logic-level PFET, such

as Fairchild’s NDS336P (RDS(ON) = 270mΩ). When the

linear-regulator output voltage is in regulation, the

MOSFET will not be full on; thus, the on-resistance will

not be important. However, if the linear regulator is used

in dropout, the MOSFET on-resistance will determine

the dropout voltage (VDROPOUT = IOUT ✕RDS(ON)). If a

lower RDS(ON) PFET is used, increase the linear-regula-

tor output filter capacitance to maintain stability.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

______________________________________________________________________________________ 11

Figure 3. Using the Gain Block as a Power-OK Comparator

Table 3. On/Off Logic Control

ONA ONB MAX1763

00On

0 1 Off

10On

11On

MAX1763

POUT

AOAIN

150k

POWER-OK

OUTPUT

TO VIN OR

VOUT

GNDPGND

POUT

OUT

47μF

BOOST

OUTPUT

COUT

47μF

LINEAR-

REGULATED

OUTPUT

20k

4.7Ω

1.0μF

0.22μF

VIN

1.8V TO 5.5V

1.5μH

220μF

REF

AIN

30k

SIGNAL

GROUND

POWER

GROUND

MAX1763

ISET

CLK/SEL

ONA

ONB

GNDPGND

POUT

OUT

220μF

4.7Ω

1μF

0.22μF

VIN

1.5μH

COUT

47μF

REF

AIN

165k

100k

MAX1763

ISET

CLK/SEL

ONB

ONA

MBRO520L

3.3V

2.5V

20k

Figure 4. Using the Gain Block as a Linear Regulator from the

Boosted Output Voltage

Figure 5. Powering a Gain-Block Linear Regulator from the

Input Voltage

MAX1763

The output capacitance can be determined by the

function:

COUT ≥[ (VREF / VOUT) ✕GM✕GFS ✕CG✕(RG ✕2) ]

and

COUT ≥10 ✕[ (VREF / [VOUT ✕GBP]) ✕GM✕GFS ✕RG]

where VREF is the 0.983V reference voltage, GMis the

10mS internal amplifier transconductance, GFS is the

external MOSFET transconductance, RGis the gate-

source resistor, and GBP is the gain-bandwidth prod-

uct of the internal gain block, 63Mrad/s.

__________________

Design Procedure

Setting the Output Voltage

For a fixed 3.3V output, connect FB to GND. To set the

output voltage between 2.5V and 5.5V, connect a resis-

tor voltage-divider to FB from OUT to GND (Figure 6).

The input bias current into FB is less than 100nA, allow-

ing large-value divider resistors without sacrificing

accuracy. Connect the resistor voltage-divider as close

to the IC as possible, within 0.2in (5mm) of FB. Choose

R2 of 30kΩor less, then calculate R1 using:

R1 = R2((VOUT / VFB ) - 1)

where VFB, the boost-regulator feedback set point, is

1.245V.

Setting the Switch Current Limit

and Soft-Start

The ISET pin adjusts the inductor peak current and can

also be used to implement soft-start. With ISET con-

nected to REF, the inductor current limits at 2.5A. With

ISET connected to a resistive divider set from REF to

GND, the current limit is reduced according to:

ILIM = 2.5(VISET / 1.25) [A]

Implement soft-start by placing a resistor from ISET to

REF (>300kΩ) and a capacitor from ISET to GND. In

shutdown, ISET is discharged to GND through an inter-

nal 100kΩresistor. As the capacitor voltage rises, the

output current is allowed to increase, and the output

voltage rises. The speed at which the output rises is

determined by the soft-start time constant:

tSS = RSS CSS

where RSS ≥300k.

Both features may be implemented simultaneously by

placing a capacitor across the lower resistor of the cur-

rent-limiting resistive divider (Figures 7 and 8).

Package Selection

The MAX1763 is available in two packages, a 16-pin

QSOP and a 16-pin TSSOP-EP. Since the MAX1763

has excellent efficiency, most applications are well

served by the QSOP package. If the application

requires high power dissipation, or operation in a high

ambient temperature, choose the TSSOP-EP package.

The TSSOP-EP is equipped with an exposed metal pad

on its underside for soldering to grounded circuit board

copper. This reduces the junction-to-case thermal

resistance of the package from +115°C/W for QSOP to

+53°C/W for the TSSOP-EP.

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

12 ______________________________________________________________________________________

MAX1763

OUT

R1 = R2 ( - 1)

VOUT

VFB , VFB = 1.245V, R2 ≤ 30k

MAX1763

REF

ISET

RSS

CSS

0.22μF

ILIM = 2.5A

tSS = RSS CSS

MAX1763

REF

ISET

RSS1

CSS

0.22μF

ILIM = 2.5A( )

RSS2

RSS1 + RSS2

tSS = (RSS1 RSS2)CSS

RSS2

Figure 7. Soft-Start with Maximum Switch Limit Current

Figure 8. Soft-Start with Reduced Switch Limit Current

Figure 6. Connecting Resistors for External Feedback

At an ambient temperature of +70°C, continuous power

dissipation for the QSSOP package is 667mW, while

the TSSOP-EP can dissipate 1.5W. A first-order esti-

mate of power dissipation can be determined by calcu-

lating the output power delivered to the load (e.g., 3.3V

✕1A = 3.3W). At the input voltage used, find the effi-

ciency from the Typical Operating Characteristics

graphs (e.g., 87%). The estimated power dissipation in

the MAX1763 is then: (100% - %Efficiency) ✕Output

Power. The example would have: 13% ✕3.3W = 0.43W,

allowing the QSOP package (667mW) to be used. For

higher ambient temperature, higher output power, or a

lower-efficiency operating point, the TSSOP-EP pack-

age (1.5W) may be necessary. For detailed package

mechanical information, see the package outline draw-

ings at the end of this data sheet.

Inductor Selection

The MAX1763’s high switching frequency allows the

use of a small 1.5µH surface-mount inductor. The cho-

sen inductor should generally have a saturation current

rating exceeding the N-channel switch current limit;

however, it is acceptable to bias the inductor current

into saturation by as much as 20% if a slight reduction

in efficiency is acceptable. Inductors rated for lower

peak current may be used if ISET is employed to

reduce the peak inductor current (see Setting the

Switch Current Limit and Soft-Start). For high efficiency,

choose an inductor with a high-frequency ferrite core

material to reduce core losses. To minimize radiated

noise, use a toroid or shielded inductor. See Table 4 for

suggested components and Table 5 for a list of compo-

nent suppliers. Connect the inductor from the battery to

the LX pins as close to the IC as possible.

External Diode

For conditions where VIN might exceed the set VOUT, or

where VOUT is set above 4V, an external Schottky diode

must be connected from LX to POUT in parallel with the

on-chip synchronous rectifier. See D1 in Figure 2. The

diode should be rated for 0.5A. Representative devices

are Motorola MBR0520L, Nihon EP05Q03L, or generic

1N5817. This external diode is also recommended for

applications that must start with input voltages at or

below 1.8V. The Schottky diode carries current during

both startup and after the synchronous rectifier turns

off. Thus, its current rating only needs to be 500mA

even if the inductor current is higher. Connect the

diode as close to the IC as possible. Do not use ordi-

nary rectifier diodes; their slow switching speeds and

long reverse-recovery times render them unacceptable.

For circuits that do not require startup with inputs below

1.8V, and have an output of 4V or less, no external

diode is needed.

Input and Output Capacitors

Choose input and output capacitors that will service the

input and output peak currents with acceptable voltage

ripple. Choose input capacitors with working voltage rat-

ings over the maximum input voltage, and output capaci-

tors with working voltage ratings higher than the output. A

220µF, low equivalent-series-resistance (ESR) (less than

100mΩ) capacitor is recommended for most applica-

tions. Alternatively, two 100µF capacitors in parallel will

reduce the effective ESR for even better performance.

The input capacitor reduces peak currents drawn from

the input source and also reduces input switching noise.

The input voltage source impedance determines the

required size of the input capacitor. When operating

directly from one or two NiMH cells placed close to the

MAX1763, use a single 47µF low-ESR input filter capac-

itor. With higher impedance batteries, such as alkaline

and Li+, a higher value input capacitor may improve

efficiency.

Sanyo POSCAP, Panasonic SP/CB, and Kemet T510

are good low-ESR capacitors (Tables 4 and 5). Low-

ESR tantalum capacitors offer a good trade-off between

price and performance. Do not exceed the ripple cur-

rent ratings of tantalum capacitors. Avoid aluminum

electrolytic capacitors; their high ESR typically results

in higher output ripple voltage.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

______________________________________________________________________________________ 13

Table 5. Component Suppliers

SUPPLIER PHONE

AVX USA: 843-448-9411

Coilcraft USA: 847-639-6400

Kemet USA: 810-287-2536

Motorola USA: 408-629-4789

Japan: 81-45-474-7030

Sumida USA: 847-956-0666

Japan: 011-81-3-3667-3302

Note: Please indicate that you are using the MAX1763 when

contacting these component suppliers.

Table 4. Component Selection Guide

INDUCTORS CAPACITORS DIODES

AVX TPS series

Kemet T510 series

Coilcraft LPT3305

Sanyo POSCAP series

Motorola

MBR0520L

Sumida Panasonic SP/CB Nihon

EP10QY03

MAX1763

Bypass Components

A few ceramic bypass capacitors are required for prop-

er operation. Bypass REF to GND with 0.22µF. Also,

bypass OUT to GND with a 1µF ceramic capacitor, and

connect OUT to POUT with a 4.7Ωresistor. Each of

these components should be placed as close to their

respective IC pins as possible, within 0.2in (5mm).

Table 5 lists suggested suppliers.

Layout Considerations

High switching frequencies and large peak currents

make PC board layout a critical part of design. Poor

design will cause excessive EMI and ground bounce,

both of which can cause instability or regulation errors

by corrupting the voltage and current feedback signals.

Power components, such as the inductor, converter IC,

and filter capacitors, should be placed as close together

as possible, and their traces should be kept short, direct,

and wide. Keep the voltage feedback network very close

to the IC, within 0.2in (5mm) of the FB pins. Keep noisy

traces, such as those from the LX pin, away from the

voltage feedback networks and guarded from them

using grounded copper. If an external rectifier is used,

its traces must be kept especially short and use an

absolute minimum of copper area to avoid excess

capacitance that can slow the operation of the on-chip

synchronous rectifier and actually reduce efficiency.

Refer to the MAX1763 EV kit for a full PC board example.

The MAX1763 TSSOP-EP package features an

exposed thermal pad on its underside. This pad lowers

the package’s thermal resistance by providing a direct

thermal heat path from the die to the PC board.

Additionally, the ground pin (GND) also channels heat.

Connect the exposed thermal pad and GND to circuit

ground by using a large pad or multiple vias to the

ground plane.

Step-Up/Step-Down Applications

In some battery-powered applications, the battery volt-

age range overlaps the output voltage. In this case,

depending on the battery voltage, the regulator will

have to step the voltage up or down. To make a step-

up/step-down regulator, use the gain block to make a

linear regulator that follows the step-up converter. In

this case, if the battery voltage is low, then the circuit

will step up, and when the battery voltage is high, the

linear regulator will drop the voltage. See the Gain

Block section on how to use the gain block to make a

linear regulator. When the output voltage is greater than

the regulation voltage, then the synchronous rectifier

will be held on, reducing the dropout, and thus increas-

ing the efficiency when the battery voltage is close to,

but slightly above, the regulation voltage.

Chip Information

SUBSTRATE CONNECTED TO GND

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

14 ______________________________________________________________________________________

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

______________________________________________________________________________________ 15

Note: The MAX1763EEE is a 16-pin QSOP and does not have a heat slug. Use the MAX1763EUE for higher power dissipation.

Package Information

For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or

“-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing per-

tains to the package regardless of RoHS status.

PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.

16 QSOP E16+1 21-0055 90-0167

16 TSSOP-EP U16E+3 21-0108 90-0120

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

16 ______________________________________________________________________________________

Package Information (continued)

For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or

“-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing per-

tains to the package regardless of RoHS status.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

______________________________________________________________________________________ 17

Package Information (continued)

For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or

“-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing per-

tains to the package regardless of RoHS status.

MAX1763

1.5A, Low-Noise, 1MHz, Step-Up

DC-DC Converter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

2 4/11 Added lead-free designation, added conditions for use when VIN > VOUT, updated

Pin Description section 1, 5, 8, 13