________________General Description
The MAX1703 is a high-efficiency, low-noise, step-up
DC-DC converter intended for use in battery-powered
wireless applications. It uses a synchronous-rectified
pulse-width-modulation (PWM) boost topology to gen-
erate a 2.5V to 5.5V output from battery inputs, such as
one to three NiCd/NiMH cells or one Li-Ion cell. The
device includes a 2A, 75mΩ, N-channel MOSFET
switch and a 140mΩ, P-channel synchronous rectifier.
With its internal synchronous rectifier, the MAX1703
delivers up to 5% better efficiency than similar nonsyn-
chronous converters. It also features a pulse-frequency-
modulation (PFM) low-power mode to improve efficiency
at light loads, and a 1µA shutdown mode.
The MAX1703 comes in a 16-pin narrow SO package
and includes an uncommitted comparator that generates
a power-good or low-battery-warning output. It also
contains a linear gain block that can be used to build a
linear regulator.
For lower-power outputs and a smaller package, refer
to the MAX1700/MAX1701. For dual outputs (step-up
plus linear regulator), refer to the MAX1705/MAX1706.
For an on-board analog-to-digital converter, refer to the
MAX848/MAX849.
The MAX1703 evaluation kit is available to speed designs.
____________________________Features
♦Up to 95% Efficiency
♦Up to 1.5A Output
♦Fixed 5V or Adjustable Step-Up Output
(2.5V to 5.5V)
♦0.7V to 5.5V Input Range
♦Low-Power Mode (300µW)
♦Low-Noise, Constant-Frequency Mode (300kHz)
♦Synchronizable Switching Frequency
(200kHz to 400kHz)
♦1µA Logic-Controlled Shutdown
♦Power-Good Comparator
♦Uncommitted Gain Block
________________________Applications
Digital Cordless Phones Personal Communicators
PCS Phones Palmtop Computers
Wireless Handsets Hand-Held Instruments
Two-Way Pagers
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
________________________________________________________________
Maxim Integrated Products
1
19-1336; Rev 2; 11/98
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
Ordering Information
Typical Operating Circuit
PART TEMP. RANGE PIN-PACKAGE
MAX1703ESE -40°C to +85°C 16 Narrow SO
PGNDGNDFB
POUT
OUT
LXP, LXN
OFF
INPUT
0.7V TO 5.5V
OR
ON
SYNC
PWM
PFM
OUTPUT
5V OR ADJ
UP TO 1.5A
CLK/
SEL
ON
POKIN
POK
AO
AIN
REF
POWER-GOOD
INPUT POWER-GOOD
OUTPUT
GAIN-BLOCK INPUT
GAIN-BLOCK
OUTPUT
MAX1703
Pin Configuration
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
REF ON
POUT
LXP
POUT
PGND
LXN
PGND
CLK/SEL
TOP VIEW
MAX1703
Narrow SO
FB
POKIN
AIN
OUT
GND
AO
POK
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Switch On-Resistance
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA= 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
OUT, ON, AO, POK to GND .....................................-0.3V to +6V
PGND to GND.....................................................................±0.3V
LXP, LXN to PGND .................................-0.3V to (VPOUT + 0.3V)
POUT, CLK/SEL, AIN, REF, FB,
POKIN to GND.......................................-0.3V to (VOUT + 0.3V)
Continuous Power Dissipation (TA = +70°C)
Narrow SO (derate 8.70mW/°C above +70°C) .............696mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
ILOAD < 1mA, TA= +25°C (Note 3)
CLK/SEL = GND
CLK/SEL = GND
(Note 2)
CLK/SEL = OUT
N-channel
VON = VLXN = VOUT = 5.5V
ON = OUT
CLK/SEL = OUT, no load to full load
VLXP = 0V, VOUT = VON = 5.5V
(Note 5)
VOUT = 1.5V
VFB < 0.1V, CLK/SEL = OUT,
0 ≤ILX ≤1.1A, VBATT = 3.7V
Adjustable output, CLK/SEL = OUT,
0 ≤ILX ≤1.1A, VBATT = 2.2V, VOUT = 3.3V
CLK/SEL = OUT (Note 1)
VFB = 1.25V
CLK/SEL = GND (Note 1)
CONDITIONS
mA20 160 260P-Channel Turn-Off Current
mA500 800 1100
N-Channel Current Limit mA2200 2700 3200
0.075 0.13 Ω
0.14 0.25
µA0.1 20LXN Leakage Current
µA0.1 20POUT, LXP Leakage Current
µA150 300Supply Current in Low-Noise Mode
µA65 120Supply Current in Low-Power Mode
V0.9 1.1Minimum Start-Up Voltage
V0.7 5.5Input Supply Range
µA0.1 20Supply Current in Shutdown
%-1.6Load Regulation (Note 6)
V2.0 2.15 2.3Output Voltage Lockout Threshold
V2.5 5.5Output Voltage Adjust Range
kHz40 140 300Frequency in Start-Up Mode
V4.87 5.05 5.20
Output Voltage
(Note 4)
V1.21 1.24 1.255FB Regulation Voltage
nA0.1 20FB Input Current
UNITSMIN TYP MAXPARAMETER
P-channel 0.13 0.25
Switch On-Resistance
CLK/SEL = GND
CLK/SEL = OUT
Rising VPOKIN V1.225 1.250 1.275POKIN Trip Level
VPOKIN = 0.7V nA-20 20POKIN Input Current
ISINK(POK) = 1mA, VOUT = 3.6V or
ISINK(POK) = 20µA, VOUT = 1V V0.03 0.4POK Low Voltage
VOUT = VPOK = 5.5V µA0.01 1POK High Leakage Current
DC-DC CONVERTER
DC-DC SWITCHES
POWER-GOOD COMPARATOR
V
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA= 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.)
CLK/SEL = OUT, VFB = 0.5V
CLK/SEL = OUT, VFB = 0.5V
ON, CLK/SEL
CLK/SEL, VOUT = 5.5V
CLK/SEL, VOUT = 2.5V
ON, 1.2V < VOUT < 5.5V (Note 7)
VAIN = 1.5V, VAO = 5.5V
VAIN = 0.5V, IAO = 100µA
2.5V < VOUT < 5.5V
-1µA < IREF < 50µA
10µA < IAO < 100µA
VAIN = 1.5V
IREF = 0µA
IAO = 20µA
CONDITIONS
kHz200 400External Clock Frequency Range
%80 86 90Oscillator Maximum Duty Cycle
kHz260 300 340Internal Oscillator Frequency
µA-1 0.01 1Logic Input Current
V
0.8VOUT
Input High Voltage
V
0.2VOUT
Input Low Voltage 0.2VOUT
mV0.2 5REF Supply Rejection
mV515REF Load Regulation
V1.237 1.250 1.263Reference Output Voltage
µA0.01 1AO Output High Leakage
V0.1 0.4AO Output Low Voltage
mmho51016Transconductance
nA-30 30AIN Input Current
V1.237 1.25 1.263AIN Reference Voltage
UNITSMIN TYP MAXPARAMETER
ns100Maximum CLK/SEL Rise/Fall Time
ns200Minimum CLK/SEL Pulse Width
ELECTRICAL CHARACTERISTICS
(CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA= -40°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.) (Note 8)
ON = OUT
(Note 5)
VFB < 0.1V, CLK/SEL = OUT,
0 ≤ILX ≤1.1A, VBATT = 3.7V
Adjustable output, CLK/SEL = OUT,
0 ≤ILX ≤1.1A, VOUT = 3.3V, VBATT = 2.2V
CLK/SEL = OUT (Note 1)
CLK/SEL = GND (Note 1)
CONDITIONS
µA300Supply Current in Low-Noise Mode
µA120Supply Current in Low-Power Mode
µA20Supply Current in Shutdown
V2.0 2.3Output Voltage Lockout Threshold
V4.87 5.20Output Voltage (Note 4)
V1.20 1.27FB Regulation Voltage
UNITSMIN TYP MAXPARAMETER
DC-DC CONVERTER
ON, 1.2V < VOUT < 5.5V 0.8VOUT
GAIN BLOCK
REFERENCE
LOGIC INPUTS
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA= -40°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.) (Note 8)
CLK/SEL = GND
CLK/SEL = OUT
CLK/SEL = GND
CLK/SEL = OUT
N-channel
CONDITIONS
P-channel
Rising VPOKIN V1.225 1.275POKIN Trip Level
0.25
Switch On-Resistance
mA500 1100
N-Channel Current Limit mA2200 3600
0.13
IAO = 20µA
Ω
0.25
V1.23 1.27AIN Reference Voltage
UNITSMIN TYP MAXPARAMETER
Note 1: Supply current from the 5.05V output is measured between the 5.05V 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. Set
VOUT = 5.3V to keep the internal switch open when measuring the device operating current.
Note 2: Minimum operating voltage. Since the regulator is bootstrapped to the output, once started it will operate down to a 0.7V
input.
Note 3: Start-up is tested with the circuit of Figure 2.
Note 4: In low-power mode (CLK/SEL = GND) the output voltage regulates 1% higher than low-noise mode (CLK/SEL = OUT or
synchronized).
Note 5: The regulator is in start-up mode until this voltage is reached. Do not apply full-load current below this voltage.
Note 6: Load regulation is measured from no-load to full load, where full load is determined by the N-channel switch current limit.
Note 7: The ON input has a total hysteresis of approximately 0.15 x VOUT.
Note 8: Specifications to -40°C are guaranteed by design and not production tested.
10µA < IAO < 100µA mmho516Transconductance
IREF = 0µA V1.23 1.27Reference Output Voltage
CLK/SEL = OUT, VFB = 0.5V kHz260 340Internal Oscillator Frequency
CLK/SEL = OUT, VFB = 0.5V %80 92Oscillator Maximum Duty Cycle
DC-DC SWITCHES
POWER-GOOD COMPARATOR
GAIN BLOCK
REFERENCE
LOGIC INPUTS
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
_______________________________________________________________________________________
5
100
40
0.1 1 10 100 1000 10,000
EFFICIENCY vs. LOAD CURRENT
(VOUT = 5V)
50
MAX1703-01
LOAD CURRENT (mA)
EFFICIENCY (%)
60
80
70
90
VIN = 3.6V
VIN = 2.4V
VIN = 1.2V
PFM
PWM
100
40
0.1 1 10 100 1000 10,000
EFFICIENCY vs. LOAD CURRENT
(VOUT = 3.3V)
50
MAX1703-02
LOAD CURRENT (mA)
EFFICIENCY (%)
60
80
70
90
VIN = 2.4V
VIN = 1.2V
VIN = 0.9V
PFM
PWM
0
1
2
3
4
03412 56
NO-LOAD BATTERY CURRENT
vs. INPUT VOLTAGE
MAX1703-03
INPUT VOLTAGE (V)
BATTERY CURRENT (mA)
TA = +85°C
LOW-POWER MODE
TA = +25°C
TA = -40°C
0
0.5
1.0
2.0
1.5
2.5
0.5 3.0 3.5 4.01.0 1.5 2.0 2.5 4.5 5.0 5.5
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1703-04
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
TA = +85°C
INCLUDES ALL EXTERNAL
COMPONENT LEAKAGES.
CAPACITOR LEAKAGE
DOMINATES AT TA = +85°C
TA = +25°C,
TA = -40°C
1.2460
1.2470
1.2490
1.2480
1.2500
1.2510
1.2520
0 4050 607010 20 30 80 90
REFERENCE VOLTAGE
vs. REFERENCE CURRENT
MAX1703-07
REFERENCE CURRENT (µA)
REFERENCE VOLTAGE (V)
VIN = 3.6V
VOUT = 5V
LOW-POWER MODE
2.0
0.6
0.01 0.1 1 10 100 1000
START-UP VOLTAGE vs. LOAD CURRENT
0.8
MAX1703-05
LOAD CURRENT (mA)
START-UP VOLTAGE (V)
1.0
1.2
1.6
1.4
1.8
VOUT = 5V
PWM MODE
1.2450
1.2490
1.2470
1.2510
1.2530
1.2550
-40 20 40 60-20 0 80 100
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX1703-06
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
9
100 1k 10k 100k 1M 10M
NOISE SPECTRUM
1
0
-1
MAX1703-14
FREQUENCY (Hz)
NOISE (mVRMS)
2
6
7
5
4
3
8VOUT = 5V
VIN = 3.6V
ILOAD = 500mA
__________________________________________Typical Operating Characteristics
(VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.)
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
6 _______________________________________________________________________________________
_________________________________Typical Operating Characteristics (continued)
(VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.)
260
290
280
270
310
300
320
330
340
-40 20 40 60-20 0 80 100
FREQUENCY vs. TEMPERATURE
MAX1703-15
TEMPERATURE (°C)
FREQUENCY (kHz)
VOUT = 5V
VOUT = 3.3V
0.5
1.5
1.0
2.5
2.0
3.0
3.5
2.5 4.0 4.53.0 3.5 5.0 5.5
PEAK INDUCTOR CURRENT LIMIT
vs. OUTPUT VOLTAGE
MAX1703-16
OUTPUT VOLTAGE (V)
CURRENT LIMIT(A)
PWM
LOW POWER (PFM)
2µs/div
ILOAD = 1.5A, C7 = 0.47µF
HEAVY LOAD SWITCHING
MAX1703-08
2ms/div
VOUT IS AC COUPLED
LOAD CURRENT = 0A TO 1.5A
VOUT
(50mV/div)
1.0A
0.5A
0A
LOAD-TRANSIENT RESPONSE
MAX1703-10
2ms/div
VIN = 2.6V TO 3.6V, VOUT IS AC COUPLED
VOUT
(50mV/div)
VIN
4V
2V
0V
LINE-TRANSIENT RESPONSE
MAX1703-09
1ms/div
VIN = 2.6V TO 3.6V, VOUT IS AC COUPLED
VON
VOUT
(2V/div)
IIN
(0.2A/div)
POWER-ON DELAY
(PFM MODE)
MAX1703-11
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
_______________________________________________________________________________________ 7
Pin Description
_________________________________Typical Operating Characteristics (continued)
(VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.)
1ms/div
VIN = 3.6V, VOUT = 5V, COUT = 470µF,
PULSE WIDTH = 577µs, LOAD CURRENT = 100mA TO 1A
VOUT
(100mV/div)
ILOAD
(0.5A/div)
GSM LOAD-TRANSIENT RESPONSE
MAX1703-12
2ms/div
VIN = 1.2V, VOUT = 3.3V, COUT = 470µF,
PULSE WIDTH = 416µs, LOAD CURRENT = 50mA TO 400mA
VOUT
(100mV/div)
ILOAD
(0.2A/div)
DECT LOAD-TRANSIENT RESPONSE
MAX1703-13
PIN
Dual-Mode™ Feedback Input. Connect FB to ground to set a fixed output voltage of +5V. Connect a
divider between the output voltage and GND to set the output voltage from 2.5V to 5.5V.
FB2
Reference Output. Bypass with a 0.22µF bypass capacitor to GND.REF1
FUNCTIONNAME
DC-DC Converter Output. Power source for the IC.OUT4
Power-Good Comparator Input. Threshold is 1.250V, with 1% hysteresis on the threshold’s rising edge.POKIN3
Power-Good Comparator Output. This open-drain N-channel output is low when VPOKIN < 1.250V.POK8
Gain-Block Output. This open-drain output sinks current when VAIN < VREF.AO7
Gain-Block Input. When AIN is low, AO sinks current. The nominal transconductance from AIN to AO is
10mmhos.
AIN6
GroundGND5
Source of P-Channel Synchronous Rectifier MOSFET Switch. Connect an external Schottky diode from LXN
and LXP to POUT.
POUT13, 15
Source of N-Channel Power MOSFET SwitchPGND10, 12
On/Off Input. When ON is low, the IC turns on.ON
16
Switch-Mode Selection and External-Clock Synchronization Input:
•CLK/SEL = Low: Low-power, low-quiescent-current PFM mode. Delivers up to 10% of full load current.
•CLK/SEL = High: High-power PWM mode. Full output power available. Operates in low-noise, constant-
frequency mode.
•CLK/SEL = External Clock: High-power PWM mode with the internal oscillator synchronized to the exter-
nal CLK
Turning on with CLK/SEL = 0V also serves as a soft-start function, since peak inductor current is limited to
25% of that allowed in PWM mode.
CLK/SEL9
Dual Mode is a trademark of Maxim Integrated Products.
Drain of N-Channel Power Switch. Connect LXP to LXN.LXN11
Drain of P-Channel Synchronous Rectifier. Connect LXP to LXN.LXP14
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
8 _______________________________________________________________________________________
_______________Detailed Description
The MAX1703 is a highly efficient, low-noise power
supply for portable RF and data-acquisition instru-
ments. It combines a boost switching regulator, N-
channel power MOSFET, P-channel synchronous
rectifier, precision reference, shutdown control, versa-
tile gain block, and power-good (POK) comparator
(Figure 1) in a 16-pin narrow SO package.
The switching DC-DC converter boosts a 1- to 3-cell
input to a fixed 5V or an adjustable output between
2.5V and 5.5V. Typically the MAX1703 starts from a
low, 0.9V input and remains operational down to 0.7V.
The MAX1703 is optimized for use in cellular phones
and other applications requiring low noise during full-
power operation, as well as low quiescent current for
maximum battery life in low-power mode and shut-
down. It features constant-frequency (300kHz), low-
noise PWM operation with up to 1.5A output capability.
See Table 1 for typical outputs. A low-quiescent-cur-
rent, low-power mode offers an output up to 150mA
and reduces quiescent power consumption to 300µW.
In shutdown mode, the quiescent current is further
reduced to just 1µA. Figure 2 shows the standard appli-
cation circuit for the MAX1703.
2.15V
IC POWER
1.25V
DUAL
MODE/
FB
OUT
REFERENCE
UNDERVOLTAGE LOCKOUT
START-UP
OSCILLATOR
300kHz
OSCILLATOR
PFM/PWM
CONTROLLER
PFM/PWM
P
N
EN D
EN
POUT
LXN
LXP
PGND
COMPARATOR
OSC
MODE
FB
EN
QQ
Q
OUT
REF
FB
POKIN
GND
CLK/SEL
ON RDY
REF
REF
ON
OUT
MAX1703
POK
N
GAIN
BLOCK
REF
AO
N
AIN
Figure 1. Functional Block Diagram
Table 1. Typical Available Output Current
Additional features include synchronous rectification for
high efficiency and improved battery life, and an
uncommitted comparator (POK) for monitoring the reg-
ulator’s output or battery voltage. The MAX1703 also
includes 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 second
comparator. A CLK input allows frequency synchro-
nization to reduce interference.
Table 2. Selecting the Operating Mode
Step-Up Converter
The step-up switching DC-DC converter generates an
adjustable output from 2.5V to 5.5V. The internal N-
channel MOSFET switch is turned on during 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, when the MOSFET is
turned off, the voltage across the inductor reverses and
forces current through the diode and synchronous rec-
tifier to the output filter capacitor and load. As the ener-
gy stored in the inductor is depleted, the current ramps
down and the output diode and synchronous rectifier
turn off. Depending on the CLK/SEL pin setting, voltage
across the load is regulated using either low-noise
PWM or low-power operation (Table 2).
Low-Noise PWM Operation
When CLK/SEL is pulled high, the MAX1703 operates
in a high-power, low-noise PWM mode. During PWM
operation, the MAX1703 switches at a constant fre-
quency (300kHz), and modulates the MOSFET-switch
pulse width to control the power transferred per cycle
and regulate the voltage across the load. In PWM mode
the device can output up to 1.5A. Switching harmonics
generated by fixed-frequency operation are consistent
and easily filtered. See the Noise Spectrum plot in the
Typical Operating Characteristics
.
During PWM operation, each of the internal clock’s ris-
ing edges sets a flip-flop, which turns on the N-channel
MOSFET switch (Figure 3). The switch turns off when
the sum of the voltage-error, slope-compensation, and
current-feedback signals trips a multi-input comparator
and resets the flip-flop; the switch remains off for the
rest of the cycle. When a change occurs in the output
voltage error signal, the comparator shifts the level to
which the inductor current ramps during each cycle. A
second comparator enforces an inductor current limit of
2.7A (typical).
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
_______________________________________________________________________________________ 9
2.4
2 NiCd/NiMH 2.4
3.63 NiCd/NiMH
NO. OF CELLS
1.21 NiCd/NiMH
INPUT
VOLTAGE
(V)
5.0
3.3
5.0
3.3
OUTPUT
VOLTAGE
(V)
950
1400
1600
600
OUTPUT
CURRENT
(mA)
GNDPGND
AO
POUT
OUT
LXP, LXN
D1
C1
100µF
MBR0520L
VBATT
C4
2 x 220µF
L1
4.7µH
POK
FB
REF
CLK/SEL
ON
AIN
POKIN
C3
0.22µF
R3
R4
C2
0.22µF
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
C5
0.22µF
R5
10Ω
MAX1703
SIGNAL GROUND
POWER GROUND
Figure 2. MAX1703 in High-Power PWM Mode
Synchronized
PWM
External Clock
(200kHz to 400kHz)
PWM1
Low power
MODE
0
CLK/SEL
Low noise,
high output current
Low noise,
high output current
Low supply current
FEATURES
MAX1703
Synchronized PWM Operation
The MAX1703 can be synchronized in PWM mode to a
200kHz to 400kHz frequency by applying an external
clock to CLK/SEL. This allows the user to set the har-
monics to avoid IF bands in wireless applications. The
synchronous rectifier is also active during synchronized
PWM operation.
Low-Power PFM Operation
Pulling CLK/SEL low places the MAX1703 in a low-
power mode. During low-power mode, PFM operation
regulates the output voltage by transferring a fixed
amount of energy during each cycle, and then modulat-
ing the pulse frequency to control the power delivered
to the output. The devices switch only as needed to
service the load, resulting in the highest possible effi-
ciency at light loads. Output current capability in PFM
mode is 150mA (max). The output voltage is typically
1% higher than in PWM mode.
During PFM operation, the error comparator detects the
output voltage falling out of regulation and sets a flip-
flop, which turns on the N-channel MOSFET switch
(Figure 4). When the inductor current ramps to the PFM
mode current limit (800mA typical) and stores a fixed
amount of energy, the current-sense comparator resets
a flip-flop. The flip-flop turns off the N-channel switch
and turns on the P-channel synchronous rectifier. A
second flip-flop, previously reset by the switch’s “on” sig-
nal, inhibits the error comparator from initiating another
cycle until the energy stored in the inductor is transferred
to the output filter capacitor and the synchronous rectifier
current has ramped down to 80mA. This forces operation
with a discontinuous inductor current.
Synchronous Rectifier
The MAX1703 features an internal 140mΩ, P-channel
synchronous rectifier to enhance efficiency. Synchro-
nous rectification provides a 5% efficiency improve-
ment over similar nonsynchronous boost regulators. In
PWM mode, the synchronous rectifier is turned on dur-
ing 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 regulator output, and then turns it off when
the inductor current drops below 80mA.
Low-Voltage Start-Up Oscillator
The MAX1703 uses a CMOS, low-voltage start-up oscil-
lator for a 1.1V guaranteed minimum start-up input volt-
age at +25°C. On start-up, the low-voltage oscillator
switches the N-channel MOSFET until the output volt-
age reaches 2.15V. Above this level, the normal boost-
converter feedback and control circuitry take over.
Once the device is in regulation, it can operate down to
a 0.7V input, since internal power for the IC is boot-
strapped from the output via the OUT pin. Do not apply
full load until the output exceeds 2.3V (max).
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
10 ______________________________________________________________________________________
2.7A TYP
CURRENT
LIMIT
OSC
FB
RQ
S
REF
LXP
LXN
POUT
PGND
P
N
Figure 3. Simplified PWM Controller Block Diagram
ERROR
COMPARATOR
FB
REF
800mA TYP
CURRENT
LIMIT
LOGIC HIGH
POUT
P
N
PGND
S
S
Q
R
D
Q
R
LXP
LXN
Figure 4. Controller Block Diagram in Low-Power PFM Mode
Shutdown
The MAX1703 shuts down to reduce quiescent current
to 1µA. During shutdown (ON = VOUT), the reference,
low-battery comparator, gain block, and all feedback
and control circuitry are off. The boost converter’s out-
put drops to one Schottky diode drop below the input.
Power-Good (POK) Comparator
The MAX1703 features an uncommitted POK compara-
tor. The internal POK comparator has an open-drain
output (POK) capable of sinking 1mA. When the input
(POKIN) rises above the 1.25V reference, the POK
open-drain output turns off. The POKIN input has 10mV
of hysteresis.
To provide a power-good signal, connect the POKIN
input to an external resistor-divider between OUT and
GND (Figure 5). Calculate the resistor values as follows:
R3 = R4(VTH / VREF - 1)
where VTH is the desired input voltage trip threshold.
Since the input bias current into POKIN is less than
20nA, R4 can be a large value (such as 270kΩor less)
without sacrificing accuracy. Connect the resistor volt-
age-divider as close to the IC as possible, within 0.2in.
(5mm) of POKIN.
Reference
The MAX1703 has an internal 1.250V, 1% bandgap ref-
erence. Connect a 0.22µF 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 MAX1703 gain block can function as a second
comparator, or can be used to build a linear regulator
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 gmof the entire gain-block stage is 10mmho.
Figure 6 shows the gain block used in a linear-regulator
application. The output of an external P-channel pass
element is compared to the internal reference. The dif-
ference is amplified and used to drive the gate of the
pass element. Use a logic-level PFET, such as an
NDS336P (RDS(ON) = 270mΩ) from Fairchild. This con-
figuration allows ripple reduction at the output. If a
lower RDS(ON) PFET is used, then the linear regulator
output filter capacitance may need to be increased.
To use the gain block as a comparator, refer to the
Power-Good (POK) Comparator
section.
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
______________________________________________________________________________________ 11
GNDPGND
AO
POUT
OUT
LXP, LXN
D1
MBR0520L OUTPUT
C1
100µF
VIN
C4
2 x 220µF
L1
4.7µH
POK
FB
REF
CLK/SEL
ON
AIN
POKIN
C3
0.22µF
R3
R4
C2
0.22µF
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
C5
0.22µF
R5
10Ω
R2
R1
MAX1703
SIGNAL GROUND
POWER GROUND
Figure 5. Adjustable Output (PWM Mode)
GNDPGND
AO
POUT
OUT
LXP, LXN
C1
100µF
MBR0520L
BOOST
OUTPUT
47µF
LINEAR
REGULATED
OUTPUT
R6
20k
C5
0.22µF
C4
330µF
R5
10Ω
C2
0.22µF
VIN
L1
4.7µH
POK
FB
REF
CLK/SEL
ON
AIN
POKIN
R3
R4
R2
100k
R1
MAX1703
P
SIGNAL GROUND
POWER GROUND
Figure 6. Using the Gain Block as a Linear Regulator
MAX1703
__________________Design Procedure
Setting the Output Voltages
Set the output voltage between 2.5V and 5.5V by con-
necting a resistor voltage-divider to FB from OUT to
GND, as shown in Figure 2. The resistor values are then
as follows:
R1 = R2(VOUT / VFB - 1)
where VFB, the boost-regulator feedback setpoint, is
1.24V. Since the input bias current into FB is less than
20nA, R2 can have a large value (such as 270kΩor
less) without sacrificing accuracy. Connect the resistor
voltage-divider as close to the IC as possible, within
0.2in. (5mm) of the FB pin.
Inductor Selection
The MAX1703’s high switching frequency allows the
use of a small surface-mount inductor. A 4.7µH induc-
tor should have a saturation-current rating that exceeds
the N-channel switch current limit. However, it is gener-
ally acceptable to bias the inductor current into satura-
tion by as much as 20%, although this will slightly
reduce efficiency. For high efficiency, choose an induc-
tor with a high-frequency core material, such as ferrite,
to reduce core losses. To minimize radiated noise, use
a toroid, pot core, or shielded bobbin inductor. See
Table 3 for suggested components and Table 4 for a
list of component suppliers. Connect the inductor from
the battery to the LX pins as close to the IC as possible.
Output Diode
Use a Schottky diode such as a 1N5817, MBR0520L, or
equivalent. The Schottky diode carries current during
both start-up and PFM mode after the synchronous recti-
fier turns off. Thus, its current rating only needs to be
500mA. Connect the diode between LXN/LXP and
POUT, as close to the IC as possible. Do not use ordi-
nary rectifier diodes, since slow switching speeds and
long reverse recovery times will compromise efficiency
and load regulation.
Input and Output Filter Capacitors
Choose input and output filter capacitors that will ser-
vice the input and output peak currents with accept-
able voltage ripple. Choose input capacitors with
working voltage ratings over the maximum input volt-
age, and output capacitors with working voltage ratings
higher than the output.
A 330µF, 100mΩ, low-ESR tantalum capacitor is recom-
mended for a 5V output. For full output load current,
one 470µF or two 220µF, 100mΩlow-ESR tantalum
capacitors are recommended for a 3.3V output. The
input filter capacitor (CIN) also reduces peak currents
drawn from the input source and reduces input switch-
ing noise. The input voltage source impedance deter-
mines the required size of the input capacitor.
When operating directly from one or two NiCd cells
placed close to the MAX1703, use a 100µF, low-ESR
input filter capacitor.
Sanyo OS-CON and Panasonic SP/CB-series ceramic
capacitors offer the lowest ESR. Low-ESR tantalum
capacitors are a good choice and generally offer a
good tradeoff between price and performance. Do not
exceed the ripple current ratings of tantalum capaci-
tors. Avoid most aluminum-electrolytic capacitors,
because their ESR is often too high.
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
12 ______________________________________________________________________________________
Sanyo OS-CON series
Sumida RCH654 seriesThrough Hole
Matsuo 267 series
CAPACITORS
1N5817
DIODESPRODUCTION INDUCTORS
Table 3. Component Selection Guide
Table 4. Component Suppliers
(714) 960-6492USA: (714) 969-2491Matsuo
(847) 639-1469USA: (847) 639-6400Coilcraft
(803) 626-3123
FAXSUPPLIER
USA: (803) 946-0690
(800) 282-4975
AVX
PHONE
Nichicon PL series
Sprague 595D series
(602) 994-6430USA: (602) 303-5454Motorola
(619) 661-1055
81-7-2070-1174
USA: (619) 661-6835
Japan: 81-7-2070-6306
Sanyo
(847) 956-0702
81-3-3607-5144
USA: (847) 956-0666
Japan: 81-3-3607-5111
Sumida
Sumida CDR125
AVX TPS series
Surface Mount Motorola MBR0520L
Coilcraft DO3316
Bypass Capacitors
A few ceramic bypass capacitors are required for proper
operation. Bypass REF with a 0.22µF capacitor to GND.
Connect a 0.22µF ceramic capacitor from OUT to GND.
Each of these should be placed as close to their respec-
tive pins as possible, within 0.2in. (5mm) of the DC-DC
converter IC. See Table 4 for suggested suppliers.
__________ Applications Information
Intermittent Supply/Battery Connections
When boosting an input supply connected via a
mechanical switch, or a battery connected via spring
contacts, input power may sometimes be intermittent
as a result of contact bounce. When operating in PFM
mode with input voltages greater than 2.5V, restarting
after such dropouts may initiate high current pulses that
interfere with the MAX1703’s internal MOSFET switch
control. If contact or switch bounce is anticipated in the
design, use one of the following solutions:
1) Connect a capacitor (CON) from ON to VIN and a
1MΩresistor (RON) from ON to GND, as shown in
Figure 7. This resistor-capacitor network differenti-
ates fast input edges at VIN and momentarily holds
the IC off until VIN settles. The appropriate value of
CON is 10-5 times the total output filter capacitance
(COUT), so a COUT of 440µF results in CON = 4.7nF.
2) Use the system microcontroller to hold the MAX1703
in shutdown from the time when power is applied (or
reapplied) until COUT has charged to at least the
input voltage. Standard power-on-reset times
accomplish this.
3) Ensure that the IC operates, or at least powers up, in
PWM mode (CLK/SEL = high). Activate PFM mode
only after the output voltage has settled and all of
the system’s power-on-reset flags are cleared.
Use in a Typical Wireless
Phone Application
The MAX1703 is ideal for use in digital cordless and
PCS phones. The power amplifier (PA) is connected
directly to the boost-converter output for maximum volt-
age swing (Figure 8). Low-dropout linear regulators are
used for post-regulation to generate low-noise power
for DSP, control, and RF circuitry. Typically, RF phones
spend most of their life in standby mode with only short
periods in transmit/receive mode. During standby, max-
imize battery life by setting CLK/SEL = 0; this places
the IC in low-power mode (for the lowest quiescent
power consumption). See
Gain Block
section for infor-
mation on configuring an external MOSFET as a linear
regulator.
Designing a PC Board
High switching frequencies and large peak currents
make PC board layout an important part of design.
Poor design can cause excessive EMI and ground
bounce, both of which can cause instability or regula-
tion errors by corrupting the voltage and current feed-
back signals.
Power components—such as the inductor, converter
IC, filter capacitors, and output diode—should be
placed as close together as possible, and their traces
should be kept short, direct, and wide. A separate low-
noise ground plane containing the reference and signal
grounds should only connect to the power-ground
plane at one point. This minimizes the effect of power-
ground currents on the part.
Keep the voltage feedback network very close to the
IC, within 0.2in. (5mm) of the FB pins. Keep noisy
traces, such as from the LX pin, away from the voltage
feedback networks and separated from them using
grounded copper. Consult the MAX1703 EV kit for a full
PC board example.
Soft-Start
To implement soft-start, set CLK/SEL low on power-up;
this forces PFM operation and reduces the peak
switching current to 800mA max. Once the circuit is in
regulation and start-up transients have settled,
CLK/SEL can be set high for full-power operation.
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
______________________________________________________________________________________ 13
OUT
POUT
LXP, LXN
COUT
2 x 220µF
11, 14
16
4
15, 13
CON
4.7nF
RON
1M
ON
MAX1703
Figure 7. Connecting CON and RON when Switch or Battery-
Contact Bounce is Anticipated
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
14 ______________________________________________________________________________________
___________________Chip Information
TRANSISTOR COUNT: 554
SUBSTRATE CONNECTED TO GND
LX POUT
LDOs
MAX8865/MAX8866
RADIOµC
PA
MAX1703
Figure 8. Typical Phone Application
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
______________________________________________________________________________________ 15
________________________________________________________Package Information
SOICN.EPS
MAX1703
1-Cell to 3-Cell, High-Power (1.5A),
Low-Noise, Step-Up DC-DC Converter
16 ______________________________________________________________________________________
NOTES
