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
LX
POUT
OUT
CLK/SEL
AO
GND PGNDFB
ISET
REF
MAX1763
OR NORMAL
AIN
LBI OR GAIN
BLOCK INPUT
1.5μH
IN
0.7V TO 5.5V
LBO OR
GAIN BLOCK OUTPUT
OUT
3.3V AT 1.5A
________________________Applications
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
ONA ONB
POUT
LX
POUT
PGND
LX
PGND
CLK/SEL
TOP VIEW
MAX1763
QSOP
TSSOP-EP
ISET
REF
OUT
GND
FB
AIN
AO
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
V
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
V
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
0.001 0.01 0.1 1 10
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 3.3V)
20
MAX1763 toc01
OUTPUT CURRENT (A)
EFFICIENCY (%)
40
60
80
70
50
30
10
90
A
B
C
A: VIN = 2.4V
B: VIN = 1.2V
C: VIN = 0.9V
= NORMAL MODE
= FPWM MODE
100
0
0.001 0.01 0.1 1 10
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 5V)
20
MAX1763 toc02
OUTPUT CURRENT (A)
EFFICIENCY (%)
40
60
80
70
50
30
10
90 A
B
C
A: VIN = 3.6V
B: VIN = 2.4V
C: VIN = 1.2V
= NORMAL MODE
= FPWM MODE
0
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)
24
= INPUT VOLTAGE INCREASING
= INPUT VOLTAGE DECREASING
10
0.1
046
1
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (μA)
2
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)
0
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
A
B
C
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
A
B
C
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
A
B
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
A
B
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
8
2
0
6
4
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
AO
N
AIN
2.15V
IC POWER
1.25V
DUAL
MODE/
FB
REFERENCE
UNDERVOLTAGE LOCKOUT
STARTUP
OSCILLATOR
1MHz
OSCILLATOR
CONTROLLER
P
N
EN D
EN
POUT
LX
PGND
OSC
MODE
FB
EN
QQ
Q
REF
FB
ISET
GND
CLK/SEL
ON RDY
REF
0.938V
ONB
ONA
OUT
MAX1763
ISET
GNDPGND
AO
POUT
OUT
AIN
LX
D1
MBR0520L
VIN
0.7V TO 5.5V
C4
2 x 100μF
OUT
3.3V
L1
1.5μH
FB
REF
CLK/SEL
ONA
ONB
ISET
C3
0.22μF
C2
1.0μF
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
R5
4.7Ω
MAX1763
C1
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
R6
150k
R3
R4
POWER-OK
OUTPUT
TO VIN OR
VOUT
GNDPGND
AO
POUT
OUT
LX
C1
47μF
BOOST
OUTPUT
COUT
47μF
LINEAR-
REGULATED
OUTPUT
RG
20k
R5
4.7Ω
C2
1.0μF
0.22μF
VIN
1.8V TO 5.5V
L1
1.5μH
FB
C4
220μF
REF
AIN
R3
R4
R2
30k
SIGNAL
GROUND
POWER
GROUND
R1
MAX1763
ISET
CLK/SEL
ONA
ONB
P
GNDPGND
POUT
OUT
LX
C4
220μF
R5
4.7Ω
C2
1μF
C3
0.22μF
VIN
1.5μH
FB
COUT
47μF
C1
47μF
REF
AIN
R3
165k
R4
100k
MAX1763
ISET
CLK/SEL
AO
ONB
ONA
MBRO520L
3.3V
2.5V
RG
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
FB
R2
R1
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
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
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
