MAX1763 [MAXIM]
1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter; 1.5A ，低噪声， 1MHz时，升压型DC- DC转换器
| 型号： | MAX1763 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter |
| 文件： | 总16页 (文件大小：455K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1698; Rev 1; 2/01
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
General Description
Features
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.
o Up to 94% Efficiency
o +0.7V to +5.5V Input Voltage Range
o 1.1V Guaranteed Startup Input Voltage
o Up to 1.5A Output
o Fixed 3.3V Output or Adjustable (2.5V to 5.5V)
o 1MHz PWM Synchronous-Rectified Topology
o 1µA Logic-Controlled Shutdown
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.
o Analog Gain Block for Linear-Regulator or Low-
Battery Comparator
o Adjustable Current Limit and Soft-Start
o 1.5W TSSOP Package Available
________________________Applications
Digital Cordless
Phones
Hand-Held
Instruments
PCS Phones
Palmtop Computers
Wireless Handsets
Personal
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.
Communicators
Ordering Information
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
MAX1763EEE
MAX1763EUE
*EP = Exposed pad
The MAX1763 is available in a space-saving 16-pin
QSOP package or a high-power (1.5W) 16-pin TSSOP-
EP package.
16 TSSOP-EP*
Idle Mode is a trademark of Maxim Integrated Products.
Typical Operating Circuit
Pin Configuration
1.5µH
IN
0.7V TO 5.5V
TOP VIEW
OUT
3.3V AT 1.5A
LX
POUT
ONA
ISET
REF
GND
FB
1
2
3
4
5
6
7
8
16 ONB
15 POUT
14 LX
MAX1763
OFF
ON
ONB
ONA
ON
OFF
OUT
MAX1763
13
POUT
PWM
12 PGND
11 LX
CLK/SEL
AIN
OR NORMAL
OUT
AIN
AO
LBI OR GAIN
BLOCK INPUT
10 PGND
ISET
REF
AO
9
CLK/SEL
LBO OR
GAIN BLOCK OUTPUT
FB
GND PGND
QSOP
TSSOP-EP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, AO, OUT to GND.......................................0.3V, +6V
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
PGND to GND..................................................................... 0.3V
LX to PGND ............................................-0.3V to (V
CLK/SEL, REF, FB, ISET, POUT,
+ 0.3V)
POUT
AIN to GND.........................................-0.3V to (V
+ 0.3V)
OUT
POUT to OUT...................................................................... 0.3V
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, V
= V
= V
= 3.6V, T = 0°C to +85°C, unless other-
OUT A
ONA
AIN
wise noted. Typical values are at T = +25°C.)
A
PARAMETER
DC-DC CONVERTER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range (Note 1)
0.7
0.9
5.5
1.1
V
V
Minimum Startup Voltage
(Note 2)
I
I
< 1mA, T = +25°C
A
LOAD
LOAD
Temperature Coefficient of
Startup Voltage
< 1mA
= 1.5V
-2
mV/°C
Frequency in Startup Mode
Internal Oscillator Frequency
V
125
0.8
500
1
1000
1.2
kHz
OUT
CLK/SEL = OUT
MHz
Oscillator Maximum Duty Cycle
(Note 3)
80
0.5
86
90
1.2
%
MHz
V
External Clock Frequency Range
Output Voltage
V
< 0.1V, CLK/SEL = OUT, includes load regulation
FB
3.17
1.215
3.3
3.38
for 0 < I < 1.1A
LX
Adjustable output, CLK/SEL = OUT, includes load
regulation for 0 < I < 1.1A
FB Regulation Voltage
1.245
1.270
100
V
LX
FB Input Current
V
= 1.35V
0.01
-1.0
nA
%
V
FB
Load Regulation
CLK/SEL = OUT, 0 < I < 1.1A
LX
Output Voltage Adjust Range
2.5
5.5
Output Voltage Lockout
Threshold (Note 4)
Rising edge
2.00
2.15
2.30
V
ISET Input Leakage Current
Supply Current in Shutdown
V
V
= 1.25V
0.01
1
50
10
nA
µA
ISET
= 3.6V, V
= 0
ONB
ONA
No-Load Supply Current, Low-
Power Mode (Note 5)
CLK/SEL = GND, AIN = OUT
CLK/SEL = OUT
110
200
µA
No-Load Supply Current, Low-
Noise Mode
2.5
25
mA
µA
Gain Block Supply Current
V
< (V
- 1.4V), gain block enabled
OUT
50
AIN
2
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, V
= V
= V
= 3.6V, T = 0°C to +85°C, unless other-
OUT A
ONA
AIN
wise noted. Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC-DC SWITCHES
POUT Leakage Current
LX Leakage Current
V
V
= 0, V
= 5.5V
0.1
0.1
10
10
µA
µA
LX
LX
OUT
= V
= V
= 5.5V, V
= 0
ONB
OUT
ONA
N channel
P channel
0.075
0.13
2.5
0.13
0.25
3.4
Switch On-Resistance
Ω
N-Channel Current Limit
P-Channel Turn-Off Current
REFERENCE
2.0
10
A
CLK/SEL = GND
120
240
mA
Reference Output Voltage
Reference Load Regulation
Reference Supply Rejection
GAIN BLOCK
I
= 0
1.230
1.250
5
1.270
15
V
REF
-1µA < I
< 50µA
mV
mV
REF
2.5V < V
< 5V
0.2
5
OUT
AIN Reference Voltage
AIN Input Current
I
= 20µA
910
5
938
0.01
10
970
30
16
0.4
1
mV
nA
mS
V
AO
V
V
V
V
= 1.5V
AIN
AO
Transconductance
= 1V, 10µA < I
< 100µA
AO
AO Output Low Voltage
AO Output High Leakage
= 0.5V, I
= 100µA
0.1
AIN
AIN
AO
= 1.5V, V
= 5.5V
0.01
µA
AO
Gain-Block Enable Threshold
1.4
V
V
(V
OUT
- V ) (Note 6)
AIN
Gain-Block Disable Threshold
(V - V ) (Note 6)
0.2
OUT
AIN
LOGIC INPUTS
(0.2)
CLK/SEL Input Low Level
2.5V ≤ V
≤ 5.5V
≤ 5.5V
V
V
V
OUT
V
OUT
(0.8)
CLK/SEL Input High Level
2.5 V ≤ V
OUT
V
OUT
1.1 V ≤ V
1.8 V ≤ V
≤ 1.8V
≤ 5.5V
0.2
0.4
OUT
OUT
ONA and ONB Input Low Level
(Note 7)
V
OUT
1.1 V ≤ V
≤ 1.8V
OUT
OUT
ONA and ONB Input High Level
(Note 7)
- 0.2V
1.6
V
1.8 V ≤ V
≤ 5.5V
Input Leakage Current
CLK/SEL, ONA, ONB
0.01
100
1
µA
ns
Minimum CLK/SEL Pulse Width
Maximum CLK/SEL
Rise/Fall Time
100
ns
_______________________________________________________________________________________
3
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ELECTRICAL CHARACTERISTICS
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, V
= V
= V
= 3.6V, T = -40°C to +85°C, unless other-
OUT A
ONA
AIN
wise noted.) (Note 8)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
DC-DC CONVERTER
Input Voltage Range (Note 1)
Minimum Startup Voltage (Note 2)
Frequency in Startup Mode
Internal Oscillator Frequency
5.5
V
V
I
< 1mA, T = +25°C
1.1
LOAD
A
V
= 1.5V
125
1000
1.25
kHz
MHz
OUT
CLK/SEL = OUT
0.75
Oscillator Maximum Duty Cycle
(Note 3)
80
0.6
91
%
MHz
V
External Clock Frequency Range
Output Voltage
1.2
V
< 0.1V, CLK/SEL = OUT, includes load regulation
3.38
FB
3.17
1.215
for 0 < I < 1.1A
LX
Adjustable output, CLK/SEL = OUT, includes load
regulation for 0 < I < 1.1A
1.270
FB Regulation Voltage
V
LX
FB Input Current
V
= 1.35V
100
5.5
nA
V
FB
Output Voltage Adjust Range
2.5
Output Voltage Lockout
Threshold (Note 4)
Rising edge
2.00
2.30
V
ISET Input Leakage Current
Supply Current in Shutdown
V
V
= 1.25V
50
10
nA
µA
ISET
= 3.6V, V
= 0
ONB
ONA
No-Load Supply Current, Low-
Power Mode (Note 5)
CLK/SEL = GND, AIN = OUT
200
50
µA
µA
Gain Block Supply Current
DC-DC SWITCHES
V
< (V
- 1.4V), gain block enabled
= 5.5V
OUT
AIN
OUT
POUT Leakage Current
LX Leakage Current
V
V
= 0, V
10
10
µA
µA
LX
LX
= V
= V
= 5.5V, V
= 0
ONB
OUT
ONA
N-channel
P-channel
0.13
0.25
3.4
Switch On-Resistance
Ω
N-Channel Current Limit
P-Channel Turn-Off Current
REFERENCE
2.0
10
A
CLK/SEL = GND
= 0
240
mA
Reference Output Voltage
Reference Load Regulation
Reference Supply Rejection
GAIN BLOCK
I
1.220
1.270
15
V
REF
-1µA < I
< 50µA
mV
mV
REF
2.5V < V
< 5V
5
OUT
AIN Reference Voltage
AIN Input Current
I
= 20µA
910
5
970
30
16
0.4
1
mV
nA
mS
V
AO
V
V
V
V
= 1.5V
AIN
AO
Transconductance
= 1V, 10µA < I
< 100µA
AO
AO Output Low Voltage
AO Output High Leakage
= 0.5V, I
= 100µA
AIN
AIN
AO
= 1.5V, V
= 5.5V
µA
AO
4
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, V
= V
= V
= 3.6V, T = -40°C to +85°C, unless other-
OUT A
ONA
AIN
wise noted.) (Note 8)
PARAMETER
LOGIC INPUTS
Gain-Block Enable Threshold
(V - V ) (Note 6)
CONDITIONS
MIN
MAX
UNITS
1.4
V
V
V
V
V
OUT
AIN
Gain-Block Disable Threshold
(V - V ) (Note 6)
0.2
OUT
AIN
(0.2)
CLK/SEL Input Low Level
CLK/SEL Input High Level
2.5 V ≤ V
2.5 V ≤ V
≤ 5.5V
≤ 5.5V
OUT
OUT
V
OUT
(0.8)
V
OUT
1.1 V ≤ V
1.8 V ≤ V
≤ 1.8V
≤ 5.5V
0.2
0.4
OUT
OUT
ONA and ONB Input Low Level
(Note 7)
V
OUT
1.1 V ≤ V
≤ 1.8V
OUT
ONA and ONB Input High Level
(Note 7)
- 0.2V
V
1.8V ≤ V
≤ 5.5V
1.6
OUT
Input Leakage Current
CLK/SEL, ONA, ONB
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.
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
V
OUT
.
Note 8: Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Typical Operating Characteristics
(Circuit of Figure 2, V = +3.6V, V
= +5V, T = +25°C, unless otherwise noted.)
A
IN
OUT
EFFICIENCY vs. OUTPUT CURRENT
(V = 3.3V)
EFFICIENCY vs. OUTPUT CURRENT
(V = 5V)
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
OUT
OUT
100
100
3.0
2.5
2.0
1.5
1.0
0.5
0
90
80
70
60
50
40
30
20
90
80
70
60
50
40
30
20
A
B
A
B
V
= 3.3V
C
OUT
C
V
OUT
= 5V
A: V = 3.6V
A: V = 2.4V
IN
IN
B: V = 2.4V
B: V = 1.2V
IN
IN
C: V = 1.2V
C: V = 0.9V
IN
IN
= NORMAL MODE
= FPWM MODE
= NORMAL MODE
= FPWM MODE
10
0
10
0
0.001
0.01
0.1
1
10
0.001
0.01
0.1
1
10
0.8
1.6
2.4
INPUT VOLTAGE (V)
3.2
4.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
NO-LOAD INPUT
vs. INPUT VOLTAGE
10
0.1
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
= INPUT VOLTAGE INCREASING
= INPUT VOLTAGE DECREASING
0.01
V
= 3.6V, V
= 5V
OUT
IN
1
V
= 2.4V, V
= 3.3V
OUT
IN
0.001
0.1
0.0001
3
1
0
2
4
5
6
-40
-15
10
35
60
85
0
1
2
3
4
5
INPUT VOLTAGE (V)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
STARTUP VOLTAGE
vs. OUTPUT CURRENT
PEAK INDUCTOR CURRENT vs. V
ISET
HEAVY-LOAD SWITCHING WAVEFORMS
4.1
3.0
3.6
3.1
2.6
2.1
1.6
1.1
0.6
2.5
2.0
1.5
1.0
0.5
0
A
B
C
0.001
0.01
0.1
1
10
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
ISET VOLTAGE (V)
400ns/div
V
= 2.4V, V
= 3.3V, I
= 1.5A
OUTPUT CURRENT (A)
IN
OUT
OUT
A: INDUCTOR CURRENT, 500mA/div
B: V , 2V/div
LX
OUT
C: V , 100mV/div, AC COUPLED
6
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 2, V = +3.6V, V
= +5V, T = +25°C, unless otherwise noted.)
IN
OUT
A
LIGHT-LOAD SWITCHING WAVEFORMS
LINE-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
A
B
A
A
B
C
B
200ns/div
40µs/div
100µs/div
V
= 1.1V, V
= 3.3V, I
= 20mA
V
= 2.4V, V
OUT
OUT
= 3.3V, I
= 0.2A TO 1.35A
V
= 2.4V TO 1.4V, I
IN
OUT
= 70mA
IN
OUT
OUT
IN
OUT
OUT
IN
OUT
A: LX NODE, 5V/div
A: I , 0.5A/div
A: V , 1V/div
B: INDUCTOR CURRENT, 0.1A/div, AC COUPLED
C: OUTPUT RIPPLE, 0.1V/div, AC COUPLED
B: V , 100mV/div, AC-COUPLED
B: V , 5mV/div, AC-COUPLED
STARTUP WAVEFORMS
NO SOFT-START
POWER-ON DELAY
V
OUT
2V/div
ONA
5V/div
V
OUT
2V/div
I
IN
1A/div
ONA
5V/div
I
IN
0.5A/div
I = 10mA
L
2ms/div
OUT
100µs/div
V
IN
= 1.2V, V
= 3.3V, R
= 3kΩ
LOAD
STARTUP WAVEFORMS
USING SOFT-START
NOISE SPECTRUM
8
6
4
2
0
V
V
= 2.4V
OUT
IN
= 3.3V
V
OUT
2V/div
I
IN
1A/div
ONA
5V/div
2ms/div
0.01
0.1
1
10
V
IN
= 1.2V, V
= 3.3V, R = 510kΩ, C = 0.1µF, R
= 3kΩ
LOAD
OUT
SS
SS
FREQUENCY (MHz)
_______________________________________________________________________________________
7
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Pin Description
PIN
NAME
FUNCTION
On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal
operation (Table 3).
1
ONA
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
2
ISET
desired, connect a capacitor from ISET to GND. When ONA = low and ONB = high, or V
nominal value, an on-chip switched resistor (100kΩ typ) discharges this pin to GND.
< 80% of
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.
3
4
REF
GND
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
6
FB
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).
OUT
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.
7
8
AIN
AO
Gain-Block Output. This open-drain N-channel output sinks current when V
high-Z when the device is shut down, or when AIN = OUT.
< (0.75)(V
). AO is
AIN
REF
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.
9
CLK/SEL
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
11, 14
13, 15
PGND
LX
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.
Power Output. P-channel synchronous rectifier source.
POUT
Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal
operation (Table 3).
16
ONB
age between 2.5V and 5.5V. An external Schottky
Detailed Description
diode is required for output voltages greater than 4V.
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 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 fea-
tures constant-frequency (1MHz), low-noise PWM oper-
ation with up to 1.5A output capability. A CLK input
allows frequency synchronization to control the output
The DC-DC converter boosts a one-cell to three-cell
battery voltage input to a fixed 3.3V or adjustable volt-
8
_______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
UNDERVOLTAGE LOCKOUT
OUT
IC POWER
2.15V
POUT
LX
CONTROLLER
STARTUP
OSCILLATOR
P
D
EN
Q
Q
ONA
ONB
REF
ON
RDY
REFERENCE
EN
OSC
EN
1.25V
REF
N
Q
1MHz
OSCILLATOR
GND
CLK/SEL
MODE
FB
PGND
AO
DUAL
MODE/
FB
FB
ISET
ISET
AIN
MAX1763
GAIN
BLOCK
N
0.938V
Figure 1. Functional Diagram
V
Table 1. Typical Available Output Current
IN
0.7V TO 5.5V
INPUT
VOLTAGE
(V)
OUTPUT
VOLTAGE
(V)
OUTPUT
CURRENT
(mA)
NUMBER
OF CELLS
C1
47µF
L1
1.5µH
1 NiCd/NiMH
2 NiCd/NiMH
1 Li+
1.2
2.4
3.3
3.3
5.0
3.3
675
1500
950
MBR0520L
D1
OUT
3.3V
CLK/SEL
LX
C4
2 x 100µF
ONA
POUT
2.4
R5
4.7Ω
MAX1763
2.7 (min)
1300
ONB
OUT
AIN
1 Li+
2.7 (min)
3.6
5.0
5.0
1100
1600
C2
1.0µF
3 NiCd/NiMH
ISET
REF
AO
FB
noise spectrum. See Table 1 for typical available output
current.
PGND
GND
C3
0.22µF
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.)
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
Figure 2. PFM/PWM Automode Connection
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
_______________________________________________________________________________________
9
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Synchronized-PWM Operation
Table 2. Selecting the Operating Mode
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.
CLK/SEL
MODE
FEATURES
High efficiency at all
loads. Fixed
frequency at all but
light loads.
Normal
operation
0
Low noise, fixed
frequency at all loads.
1
Forced PWM
Synchronized
External clock
500kHz to 1.2MHz PWM
Low noise, fixed
frequency at all loads.
Synchronous Rectifier
The MAX1763 features an internal 130mΩ P-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.
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.
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).
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.
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.
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
✕
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.
have approximately (0.15
V
OUT
)V of hysteresis.
Reference
The MAX1763 has an internal 1.250V reference.
Connect a 0.22µF ceramic bypass capacitor to GND
10 ______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Table 3. On/Off Logic Control
ONA
ONB
MAX1763
R
G
0
0
On
Off
On
20k
V
IN
2.5V
0
1
1
0
C
47µF
C1
47µF
OUT
1.5µH
AO
CLK/SEL
1
1
On
LX
3.3V
MBRO520L
C4
220µF
TO V OR
IN
ONB
POUT
V
OUT
POUT
AO
R5
4.7Ω
R6
150k
MAX1763
R3
ONA
OUT
R3
165k
MAX1763
POWER-OK
OUTPUT
C2
1µF
AIN
AIN
R4
R4
100k
ISET
REF
FB
Figure 3. Using the Gain Block as a Power-OK Comparator
C3
0.22µF
PGND
GND
V
IN
1.8V TO 5.5V
BOOST
OUTPUT
Figure 5. Powering a Gain-Block Linear Regulator from the
Input Voltage
C1
47µF
L1
1.5µH
LINEAR-
REGULATED
OUTPUT
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.
P
CLK/SEL
ONA
LX
C
OUT
47µF
POUT
The transconductance (G ) of the entire gain-block
M
R
G
C4
220µF
R5
4.7Ω
stage is 10mS. The internal gain block amplifies the dif-
ference between AIN and the internal 0.938V reference.
20k
MAX1763
R3
R4
ONB
OUT
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 270kΩ or less, then calculate R3 using:
C2
AIN
1.0µF
ISET
REF
AO
FB
R1
0.22µF
PGND
GND
SIGNAL
GROUND
R2
30k
R3 = R4((V
/ V
) - 1)
TRIP
AIN
POWER
GROUND
where V
is 0.938V.
AIN
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
Figure 4. Using the Gain Block as a Linear Regulator from the
Boosted Output Voltage
within 0.2in (5mm) of the REF pin. REF can source up
to 50µA of external load current.
as Fairchild’s NDS336P (R
= 270mΩ). When the
DS(ON)
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
Gain Block
The MAX1763 gain block can function as a power-OK
comparator or can be used to build a linear regulator
______________________________________________________________________________________ 11
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
in dropout, the MOSFET on-resistance will determine
✕
the dropout voltage (V
= I
R
). If a
DROPOUT
OUT
DS(ON)
OUT
FB
lower R
PFET is used, increase the linear-regula-
tor output filter capacitance to maintain stability.
DS(ON)
R1
R2
MAX1763
The output capacitance can be determined by the
function:
✕
✕
✕
✕
✕
C
OUT
≥ [ (V
/ V
)
G
M
G
FS
C
G
(R
G
2) ]
REF
OUT
and
✕
✕
✕
✕
✕
C
OUT
≥ 10 [ (V
/ [V
GBP])
G
M
G
FS
R ]
G
REF
OUT
V
where V
is the 0.983V reference voltage, G is the
M
OUT
REF
R1 = R2
- 1 , V = 1.245V, R2 ≤ 30k
FB
( V )
FB
10mS internal amplifier transconductance, G is the
FS
external MOSFET transconductance, R is the gate-
source resistor, and GBP is the gain-bandwidth prod-
uct of the internal gain block, 63Mrad/s.
G
Figure 6. Connecting Resistors for External Feedback
REF
__________________
_
Design Procedure
0.22µF
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 30kΩ or less, then calculate R1 using:
MAX1763
R
SS
ISET
C
SS
I
= 2.5A
LIM
t
= R
C
SS SS
SS
Figure 7. Soft-Start with Maximum Switch Limit Current
R1 = R2((V
/ V ) - 1)
FB
OUT
where V , the boost-regulator feedback set point, is
FB
1.245V.
REF
0.22µF
Setting the Switch Current Limit
and Soft-Start
MAX1763
R
SS1
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:
ISET
C
SS
R
SS2
R
SS2
+ R
I
= 2.5A
LIM
(
)
R
SS1
SS2
I
= 2.5(V
/ 1.25) [A]
ISET
LIM
t
= (R
R )C
SS2 SS
SS
SS1
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 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:
Figure 8. Soft-Start with Reduced Switch Limit Current
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
t
SS
= R
C
SS SS
where R ≥ 300k.
SS
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).
12 ______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Table 4. Component Selection Guide
Table 5. Component Suppliers
INDUCTORS
Coilcraft LPT3305
Sumida
CAPACITORS
AVX TPS series
DIODES
SUPPLIER
PHONE
AVX
USA: 843-448-9411
USA: 847-639-6400
USA: 810-287-2536
Motorola
MBR0520L
Kemet T510 series
Sanyo POSCAP series
Panasonic SP/CB
Coilcraft
Kemet
Nihon
EP10QY03
USA: 408-629-4789
Japan: 81-45-474-7030
Motorola
Sumida
USA: 847-956-0666
resistance of the package from +115°C/W for QSOP to
+53°C/W for the TSSOP-EP.
Japan: 011-81-3-3667-3302
Note: Please indicate that you are using the MAX1763 when
contacting these component suppliers.
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
generic 1N5817. This external diode is also recom-
mended for applications that must start with input volt-
ages 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 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.
✕
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.
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 par-
allel will reduce the effective ESR for even better perfor-
mance.
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.
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 capaci-
tor. With higher impedance batteries, such as alkaline
and Li+, a higher value input capacitor may improve effi-
ciency.
External Diode
For output voltages greater than 4V, an external
Schottky diode must be connected from LX to POUT, in
parallel with the on-chip synchronous rectifier (Figure
2). The diode should be rated for 0.5A. Representative
devices are Motorola MBR0520L, Nihon EP05Q03L, or
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
______________________________________________________________________________________ 13
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
electrolytic capacitors; their high ESR typically results
in higher output ripple voltage.
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.
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 4.7Ω 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.
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.
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.
Chip Information
TRANSISTOR COUNT: 1530
SUBSTRATE CONNECTED TO GND
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.
14 ______________________________________________________________________________________
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Package Information
Note: The MAX1763EEE is a 16-pin QSOP and does not have a heat slug. Use the MAX1763EUE for higher power dissipation.
______________________________________________________________________________________ 15
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Package Information (continued)
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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