MAXIM MAX1763EEE

19-1698; Rev 2; 4/11
KIT
ATION
EVALU
E
L
B
AVAILA
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
The MAX1763 is a high-efficiency, low-noise, step-up
DC-DC converter intended for use in battery-powered
wireless applications. This device maintains exceptionally low quiescent supply current (110µA) despite its
high 1MHz operating frequency. Small external components 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 pulsewidth-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 proprietary Idle Mode™ circuitry significantly improves efficiency at light load currents while smoothly transitioning
to fixed-frequency PWM operation at higher load currents to maintain excellent full-load efficiency. Lownoise, 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 TSSOPEP package.
Typical Operating Circuit
♦
♦
♦
♦
♦
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 LowBattery Comparator
♦ Adjustable Current Limit and Soft-Start
♦ 1.5W TSSOP Package Available
Idle Mode is a trademark of Maxim Integrated Products.
________________________Applications
Digital Cordless
Phones
Hand-Held
Instruments
PCS Phones
Palmtop Computers
Wireless Handsets
Personal
Communicators
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX1763EEE+
PART
-40°C to +85°C
16 QSOP
MAX1763EUE+
-40°C to +85°C
16 TSSOP-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad
Pin Configuration
LX
POUT
PWM
♦ Up to 94% Efficiency
♦ +0.7V to +5.5V Input Voltage Range
♦ 1.1V Guaranteed Startup Input Voltage
1.5μH
IN
0.7V TO 5.5V
OFF
ON
Features
OUT
3.3V AT 1.5A
MAX1763
ON
OFF
ONB
ONA
OUT
TOP VIEW
ONA 1
16 ONB
ISET 2
15 POUT
REF 3
14 LX
GND 4
CLK/SEL
OR NORMAL
LBI OR GAIN
BLOCK INPUT
AIN
ISET
REF
FB
MAX1763
AO
GND
PGND
LBO OR
GAIN BLOCK OUTPUT
13 POUT
12 PGND
FB 5
OUT 6
11 LX
AIN 7
10 PGND
AO 8
9
CLK/SEL
QSOP
TSSOP-EP
________________________________________________________________ Maxim Integrated Products
1
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.
MAX1763
General Description
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
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
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.
ELECTRICAL CHARACTERISTICS
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
0.7
5.5
V
1.1
V
DC-DC CONVERTER
Input Voltage Range (Note 1)
Minimum Startup Voltage
(Note 2)
ILOAD < 1mA, TA = +25°C
0.9
Temperature Coefficient of
Startup Voltage
ILOAD < 1mA
-2
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
mV/°C
2.5
V
2.15
2.30
V
0.01
50
nA
1
10
µA
200
µA
Output Voltage Lockout
Threshold (Note 4)
Rising edge
ISET Input Leakage Current
VISET = 1.25V
Supply Current in Shutdown
V ONB = 3.6V, VONA = 0V
No-Load Supply Current, LowPower Mode (Note 5)
CLK/SEL = GND, AIN = OUT
110
No-Load Supply Current, LowNoise Mode
CLK/SEL = OUT
2.5
Gain Block Supply Current
VAIN < (VOUT - 1.4V), gain block enabled
25
2.00
%
5.5
_______________________________________________________________________________________
mA
50
µA
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = 0°C to +85°C, unless otherwise 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
P channel
0.13
0.25
Switch On-Resistance
N-Channel Current Limit
P-Channel Turn-Off Current
CLK/SEL = GND
Ω
2.0
2.5
3.4
A
10
120
240
mA
1.230
1.250
1.270
V
5
15
mV
0.2
5
mV
mV
REFERENCE
Reference Output Voltage
IREF = 0A
Reference Load Regulation
-1µA < IREF < 50µA
Reference Supply Rejection
2.5V < VOUT < 5V
GAIN BLOCK
AIN Reference Voltage
IAO = 20µA
AIN Input Current
VAIN = 1.5V
Transconductance
VAO = 1V, 10µA < IAO < 100µA
AO Output Low Voltage
AO Output High Leakage
910
938
970
±0.01
±30
nA
10
16
mS
VAIN = 0.5V, IAO = 100µA
0.1
0.4
V
VAIN = 1.5V, VAO = 5.5V
0.01
1
µA
1.4
V
5
Gain-Block Enable Threshold
(VOUT - VAIN) (Note 6)
Gain-Block Disable Threshold
(VOUT - VAIN) (Note 6)
0.2
V
LOGIC INPUTS
(0.2)
VOUT
CLK/SEL Input Low Level
2.5V ≤ VOUT ≤ 5.5V
CLK/SEL Input High Level
2.5 V ≤ VOUT ≤ 5.5V
ONA and ONB Input Low Level
(Note 7)
1.1 V ≤ VOUT ≤ 1.8V
0.2
1.8 V ≤ VOUT ≤ 5.5V
0.4
ONA and ONB Input High Level
(Note 7)
Input Leakage Current
(0.8)
VOUT
1.1 V ≤ VOUT ≤ 1.8V
VOUT
- 0.2V
1.8 V ≤ VOUT ≤ 5.5V
1.6
CLK/SEL, ONA, ONB
V
V
V
V
0.01
1
µA
Minimum CLK/SEL Pulse Width
100
ns
Maximum CLK/SEL
Rise/Fall Time
100
ns
_______________________________________________________________________________________
3
MAX1763
ELECTRICAL CHARACTERISTICS (continued)
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ELECTRICAL CHARACTERISTICS
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 8)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
5.5
V
DC-DC CONVERTER
Input Voltage Range (Note 1)
Minimum Startup Voltage (Note 2)
ILOAD < 1mA, TA = +25°C
Frequency in Startup Mode
VOUT = 1.5V
125
1.1
V
kHz
0.75
1000
1.25
Internal Oscillator Frequency
CLK/SEL = OUT
MHz
Oscillator Maximum Duty Cycle
(Note 3)
80
91
%
External Clock Frequency Range
0.6
1.2
MHz
Output Voltage
VFB < 0.1V, CLK/SEL = OUT, includes load regulation
for 0 < ILX < 1.1A
FB Regulation Voltage
Adjustable output, CLK/SEL = OUT, includes load
regulation for 0 < ILX < 1.1A
FB Input Current
VFB = 1.35V
Output Voltage Adjust Range
3.17
1.215
3.38
1.270
V
V
100
nA
2.5
5.5
V
2.00
2.30
V
Output Voltage Lockout
Threshold (Note 4)
Rising edge
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, LowPower Mode (Note 5)
CLK/SEL = GND, AIN = OUT
200
µA
Gain Block Supply Current
VAIN < (VOUT - 1.4V), gain block enabled
50
µA
POUT Leakage Current
VLX = 0V, VOUT = 5.5V
10
µA
LX Leakage Current
VLX = V ONB = VOUT = 5.5V, VONA = 0V
10
µA
DC-DC SWITCHES
Switch On-Resistance
N-channel
0.13
P-channel
0.25
N-Channel Current Limit
P-Channel Turn-Off Current
CLK/SEL = GND
Ω
2.0
3.4
A
10
240
mA
1.220
REFERENCE
Reference Output Voltage
IREF = 0A
1.270
V
Reference Load Regulation
-1µA < IREF < 50µA
15
mV
Reference Supply Rejection
2.5V < VOUT < 5V
5
mV
970
mV
GAIN BLOCK
AIN Reference Voltage
IAO = 20µA
AIN Input Current
VAIN = 1.5V
Transconductance
VAO = 1V, 10µA < IAO < 100µA
AO Output Low Voltage
AO Output High Leakage
4
910
±30
nA
16
mS
VAIN = 0.5V, IAO = 100µA
0.4
V
VAIN = 1.5V, VAO = 5.5V
1
µA
5
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 8)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
1.4
V
LOGIC INPUTS
Gain-Block Enable Threshold
(VOUT - VAIN) (Note 6)
Gain-Block Disable Threshold
(VOUT - VAIN) (Note 6)
0.2
V
(0.2)
VOUT
CLK/SEL Input Low Level
2.5 V ≤ VOUT ≤ 5.5V
CLK/SEL Input High Level
2.5 V ≤ VOUT ≤ 5.5V
ONA and ONB Input Low Level
(Note 7)
1.1 V ≤ VOUT ≤ 1.8V
0.2
1.8 V ≤ VOUT ≤ 5.5V
0.4
ONA and ONB Input High Level
(Note 7)
1.1 V ≤ VOUT ≤ 1.8V
VOUT
- 0.2V
1.8V ≤ VOUT ≤ 5.5V
1.6
Input Leakage Current
CLK/SEL, ONA, ONB
(0.8)
VOUT
V
V
V
V
1
µA
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.
_______________________________________________________________________________________
5
MAX1763
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 5V)
70
80
A
B
EFFICIENCY (%)
C
60
50
40
A: VIN = 2.4V
B: VIN = 1.2V
C: VIN = 0.9V
= NORMAL MODE
= FPWM MODE
30
20
10
B
70
C
60
50
40
A: VIN = 3.6V
B: VIN = 2.4V
C: VIN = 1.2V
= NORMAL MODE
= FPWM MODE
30
20
10
0
3.0
2.5
0.01
0.1
1
10
VOUT = 3.3V
2.0
1.5
VOUT = 5V
1.0
0.5
0
0
0.001
0.01
0.1
1
10
0.8
1.6
2.4
3.2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
INPUT VOLTAGE (V)
NO-LOAD INPUT
vs. INPUT VOLTAGE
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
0.001
4.0
MAX1763 toc06
1.20
1.15
1.10
FREQUENCY (MHz)
0.01
10
MAX1763 toc05
= INPUT VOLTAGE INCREASING
= INPUT VOLTAGE DECREASING
SHUTDOWN CURRENT (μA)
0.1
MAX1763 toc04
0.001
INPUT CURRENT (A)
A
MAX1763 toc03
80
90
MAX1763 toc02
90
EFFICIENCY (%)
100
MAX1763 toc01
100
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 3.3V)
1
VIN = 3.6V, VOUT = 5V
1.05
1.00
VIN = 2.4V, VOUT = 3.3V
0.95
0.90
0.85
0.80
0.1
0
1
3
2
4
0
5
1
3.1
2.6
2.1
1.6
-15
10
35
0.1
1
10
85
PEAK INDUCTOR CURRENT vs. VISET
HEAVY-LOAD SWITCHING WAVEFORMS
2.5
A
2.0
B
1.5
1.0
C
0
60
TEMPERATURE (°C)
0
0.01
OUTPUT CURRENT (A)
6
-40
0.5
1.1
0.6
0.001
6
MAX1763 toc08
3.6
5
3.0
PEAK INDUCTOR CURRENT (A)
MAX1763 toc07
4.1
4
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
STARTUP VOLTAGE
vs. OUTPUT CURRENT
3
2
MAX1763 toc09
0.0001
STARTUP VOLTAGE (V)
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
0.2
0.4
0.6
0.8
ISET VOLTAGE (V)
1.0
1.2
1.4
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
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
LIGHT-LOAD SWITCHING WAVEFORMS
LINE-TRANSIENT RESPONSE
MAX1763 toc12
MAX1763 toc11
MAX1763 toc10
LOAD-TRANSIENT RESPONSE
A
A
A
B
B
C
B
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
40μs/div
VIN = 2.4V TO 1.4V, IOUT = 70mA
A: VIN, 1V/div
B: VOUT, 5mV/div, AC-COUPLED
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
MAX1763 toc13
ONA
5V/div
VOUT
2V/div
VOUT
2V/div
IIN
1A/div
ONA
5V/div
IL = 10mA
2ms/div
VIN = 1.2V, VOUT = 3.3V, RLOAD = 3kΩ
100μs/div
STARTUP WAVEFORMS
USING SOFT-START
NOISE SPECTRUM
MAX1763 toc15
8
ONA
5V/div
2ms/div
VIN = 1.2V, VOUT = 3.3V, RSS = 510kΩ, CSS = 0.1μF, RLOAD = 3kΩ
VIN = 2.4V
VOUT = 3.3V
6
NOISE (mVRMS)
IIN
1A/div
MAX1763 toc16
IIN
0.5A/div
VOUT
2V/div
MAX1763 toc14
STARTUP WAVEFORMS
NO SOFT-START
POWER-ON DELAY
4
2
0
0.01
0.1
1
10
FREQUENCY (MHz)
_______________________________________________________________________________________
7
MAX1763
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.)
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
MAX1763
Pin Description
PIN
NAME
FUNCTION
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
1
Ground. Connect to PGND with short trace.
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).
5
FB
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.
8
AO
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
11, 14
LX
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.
Source of N-Channel Power MOSFET Switch. Connect both PGND pins together close to the device.
Inductor Connection. Connect the LX pins together close to the device.
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, precision reference, shutdown control, and a versatile gain
block (Figure 1).
The DC-DC converter boosts a one-cell to three-cell battery voltage input to a fixed 3.3V or adjustable voltage
between 2.5V and 5.5V. An external Schottky diode is
8
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-frequency (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
MAX1763
UNDERVOLTAGE LOCKOUT
OUT
IC POWER
POUT
CONTROLLER
2.15V
EN
STARTUP
OSCILLATOR
D
Q
P
Q
LX
ONA
ON
ONB
REF
1.25V
RDY
EN
REFERENCE
OSC
EN
REF
GND
CLK/SEL
N
Q
1MHz
OSCILLATOR
MODE
DUAL
MODE/
FB
FB
FB
PGND
ISET
ISET
AIN
AO
MAX1763
GAIN
BLOCK
N
0.938V
Figure 1. Functional Diagram
Table 1. Typical Available Output Current
NUMBER
OF CELLS
1 NiCd/NiMH
INPUT
VOLTAGE
(V)
OUTPUT
VOLTAGE
(V)
OUTPUT
CURRENT
(mA)
1.2
3.3
675
VIN
0.7V TO 5.5V
MBR0520L
CLK/SEL
2.4
3.3
D1
2 NiCd/NiMH
5.0
950
1 Li+
2.7 (min)
3.3
1300
1 Li+
2.7 (min)
5.0
1100
3.6
5.0
1600
ONA
POUT
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
OUT
AIN
ISET
C3
0.22μF
REF
PGND
OUT
3.3V
C4
2 x 100μF
R5
4.7Ω
MAX1763
ONB
3 NiCd/NiMH
LX
1500
2.4
C1
47μF
L1
1.5μH
C2
1.0μF
AO
FB
GND
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
Figure 2. PFM/PWM Automode Connection
block can also function as a voltage-monitoring comparator. The MAX1763 is available in a 16-pin QSOP
package or a 1.5W 16-pin TSSOP-EP package for hightemperature or high-dissipation applications.
_______________________________________________________________________________________
9
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Table 2. Selecting the Operating Mode
CLK/SEL
MODE
FEATURES
0
Normal
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
Synchronized
PWM
Low noise, fixed
frequency at all loads.
Step-Up Converter
During DC-DC converter operation, the internal N-channel 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 Nchannel 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 efficiency 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 lownoise forced-PWM mode. During forced-PWM operation, 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 filtered. 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
10
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 frequency jitter may occur.
Synchronous Rectifier
The MAX1763 features an internal 130mΩ P-channel synchronous 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 regulator 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 oscillator for a 1.1V guaranteed minimum startup input voltage. 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 control 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 onepushbutton 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
ONA
0
ONB
0
MAX1763
On
0
1
Off
1
0
On
1
1
On
RG
20k
VIN
2.5V
1.5μH
AO
CLK/SEL
LX
3.3V
MBRO520L
TO VIN OR
VOUT
ONB
POUT
MAX1763
AIN
POWER-OK
OUTPUT
AO
POUT
R3
165k
ONA
C4
220μF
R5
4.7Ω
MAX1763
R6
150k
R3
COUT
47μF
C1
47μF
OUT
C2
1μF
AIN
R4
R4
100k
Figure 3. Using the Gain Block as a Power-OK Comparator
ISET
REF
C3
0.22μF
PGND
FB
GND
VIN
1.8V TO 5.5V
CLK/SEL
ONA
ONB
0.22μF
R5
4.7Ω
C4
220μF
RG
20k
OUT
C2
1.0μF
ISET
AO
REF
FB
PGND
LINEARREGULATED
OUTPUT
COUT
47μF
POUT
AIN
R4
P
LX
MAX1763
R3
BOOST
OUTPUT
C1
47μF
L1
1.5μH
GND
R1
R2
30k
SIGNAL
GROUND
POWER
GROUND
Figure 4. Using the Gain Block as a Linear Regulator from the
Boosted Output Voltage
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
Figure 5. Powering a Gain-Block Linear Regulator from the
Input Voltage
stage is 10mS. The internal gain block amplifies the difference 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 accuracy. Connect the resistor voltage-divider as close to the
IC as possible, within 0.2in (5mm) of AIN. Choose an
R4 value of 270kΩ or 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 linearregulator application. The output of an external P-channel 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-regulator output filter capacitance to maintain stability.
______________________________________________________________________________________
11
MAX1763
Table 3. On/Off Logic Control
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
The output capacitance can be determined by the
function:
OUT
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, GM is the
10mS internal amplifier transconductance, GFS is the
external MOSFET transconductance, RG is the gatesource resistor, and GBP is the gain-bandwidth product of the internal gain block, 63Mrad/s.
FB
R2
R1 = R2
Setting the Output Voltage
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 connected 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 internal 100kΩ resistor. 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 current-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
12
( VV - 1), V
OUT
FB = 1.245V, R2 ≤ 30k
FB
___________________Design Procedure
For a fixed 3.3V output, connect FB to GND. To set the
output voltage between 2.5V and 5.5V, connect a resistor voltage-divider to FB from OUT to GND (Figure 6).
The input bias current into FB is less than 100nA, allowing 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 30kΩ or less, then calculate R1 using:
R1 = R2((VOUT / VFB ) - 1)
where VFB, the boost-regulator feedback set point, is
1.245V.
R1
MAX1763
Figure 6. Connecting Resistors for External Feedback
REF
0.22μF
MAX1763
RSS
ISET
CSS
ILIM = 2.5A
tSS = RSS CSS
Figure 7. Soft-Start with Maximum Switch Limit Current
REF
0.22μF
MAX1763
RSS1
ISET
RSS2
CSS
ILIM = 2.5A
(R
RSS2
SS1 + RSS2
)
tSS = (RSS1 RSS2) CSS
Figure 8. Soft-Start with Reduced Switch Limit Current
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
INDUCTORS
CAPACITORS
Coilcraft LPT3305
Motorola
MBR0520L
Kemet T510 series
Sanyo POSCAP series
Sumida
Panasonic SP/CB
Table 5. Component Suppliers
DIODES
AVX TPS series
Nihon
EP10QY03
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 estimate of power dissipation can be determined by calculating the output power delivered to the load (e.g., 3.3V
✕ 1A = 3.3W). At the input voltage used, find the efficiency 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 package (1.5W) may be necessary. For detailed package
mechanical information, see the package outline drawings 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 chosen 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 component 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
MAX1763
Table 4. Component Selection Guide
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.
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 ordinary 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 ratings over the maximum input voltage, and output capacitors with working voltage ratings higher than the output. A
220µF, low equivalent-series-resistance (ESR) (less than
100mΩ) capacitor is recommended for most applications. 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 capacitor. 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). LowESR tantalum capacitors offer a good trade-off between
price and performance. Do not exceed the ripple current ratings of tantalum capacitors. Avoid aluminum
electrolytic capacitors; their high ESR typically results
in higher output ripple voltage.
______________________________________________________________________________________
13
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Bypass Components
A few ceramic bypass capacitors are required for proper 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 4.7Ω resistor. 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.
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.
Layout Considerations
Step-Up/Step-Down Applications
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.
In some battery-powered applications, the battery voltage 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 stepup/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 increasing the efficiency when the battery voltage is close to,
but slightly above, the regulation voltage.
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.
14
Chip Information
SUBSTRATE CONNECTED TO GND
______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
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
Note: The MAX1763EEE is a 16-pin QSOP and does not have a heat slug. Use the MAX1763EUE for higher power dissipation.
______________________________________________________________________________________
15
MAX1763
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 pertains to the package regardless of RoHS status.
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
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 pertains to the package regardless of RoHS status.
16
______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
______________________________________________________________________________________
17
MAX1763
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 pertains to the package regardless of RoHS status.
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
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
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.