MAX1760|MAX1760H [MAXIM]
0.8A. Low-Noise. 1MHz. Step-Up DC-DC Converter ; 0.8A 。低噪声。 1MHz的。升压型DC- DC转换器\n
| 型号： | MAX1760|MAX1760H |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 0.8A. Low-Noise. 1MHz. Step-Up DC-DC Converter
|
| 文件： | 总14页 (文件大小：405K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1660; Rev 2; 1/04
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
General Description
Features
♦ Up to 94% Efficiency
♦ 0.7V to 5.5V Input Range
The MAX1760/MAX1760H are high-efficiency, low-noise,
step-up DC-DC converters intended for use in battery-
powered wireless applications. They combine low quies-
cent supply current (100µA) with a high 1MHz operating
frequency. Small external components and tiny 10-pin
TDFN and µMAX packages make this device an excel-
lent choice for small hand-held applications. The
MAX1760 is activated by a logic-low ON signal while the
MAX1760H is activated by a logic-high ON input.
♦ Up to 800mA Output
♦ Fixed 3.3V Output (or Adjustable from 2.5V to 5.5V)
♦ PWM Synchronous-Rectified Topology
♦ Low-Noise, Constant-Frequency Operation (1MHz)
♦ 0.1µA Logic-Controlled Shutdown
♦ Synchronizable Switching Frequency
♦ Adjustable Current Limit
Both devices use a synchronous-rectified pulse-width-
modulation (PWM) boost topology to generate 2.5V to
5.5V outputs from a wide range of inputs, such as 1 to 3
alkaline or NiCd/NiMH cells or a single lithium-ion (Li+)
cell. Proprietary Idle-Mode™ circuitry significantly
improves light-load efficiency and smoothly transitions to
fixed-frequency PWM operation at higher load currents.
♦ Adjustable Soft-Start
♦ 10-Pin µMAX Package
Low-noise, forced-PWM mode is available for applica-
tions requiring constant-frequency operation at all load
currents. PWM operation can also be synchronized to
an external clock to protect sensitive frequency bands
in communications equipment. Analog soft-start and
adjustable current limit permit optimization of efficiency,
external component size, and output voltage ripple.
♦ 10-Pin 3mm x 3mm TDFN Package
Ordering Information
ON
LOGIC
PART
TEMP RANGE PIN-PACKAGE
MAX1760ETB
-40°C to +85°C
-40°C to +85°C
10 TDFN
10 µMAX
10 TDFN
10 µMAX
Low
Low
High
High
Applications
PCS Phones
MAX1760EUB
Digital Cordless Phones
Wireless Handsets
Palmtop Computers
Two-Way Pagers
MAX1760HETB -40°C to +85°C
MAX1760HEUB -40°C to +85°C
Hand-Held Instruments
Personal Communicators
Typical Operating Circuit
Pin Configurations
INPUT = 0.7V
TO V
TOP VIEW
OUT
MAX1760
ISET
REF
GND
FB
1
2
3
4
5
10 ON (ON)
ISET
1
2
3
4
5
10 ON (ON)
ON
LX
9
8
7
6
POUT
LX
REF
GND
FB
9
8
7
6
POUT
LX
V
= 3.3V,
OUT
CLK/SEL
POUT
MAX1760
MAX1760H
MAX1760
MAX1760H
800mA
PGND
CLK/SEL
PGND
CLK/SEL
ISET
REF
FB
OUT
OUT
OUT
µMAX
TDFN
(3mm x 3mm)
GND PGND
(ON) FOR MAX1760H
Idle Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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.
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
Continuous Power Dissipation (T = +70°C)
A
ON, ON, OUT, CLK/SEL to GND..............................-0.3V to +6V
10-Pin µMAX (derate 5.6mW/°C above +70°C)...........444mW
10-Pin TDFN (derate 24.4mV°C above +70°C) .........1951mW
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
+ 0.3V)
POUT
POUT to OUT...................................................................... 0.3V
REF, FB, ISET, POUT to GND...................-0.3V to (V + 0.3V)
OUT
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 = FB = PGND = GND, ISET = REF, OUT = POUT, V
unless otherwise noted.)
= 3.6V, T = 0°C to +85°C. Typical values are at T = +25°C,
A A
OUT
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC-DC CONVERTER
Input Voltage Range
(Note 1)
0.7
0.9
-2.3
500
1
5.5
1.1
V
V
Minimum Startup Voltage
I
I
< 1mA, T = +25°C (Note 2)
A
LOAD
LOAD
Temperature Coefficient of Startup Voltage
Frequency in Startup Mode
Internal Oscillator Frequency
Oscillator Maximum Duty Cycle
External Clock Frequency Range
< 1mA
= 1.5V
mV/°C
kHz
MHz
%
V
125
0.8
80
1000
1.2
90
OUT
CLK/SEL = OUT
(Note 3)
86
0.5
1.2
MHz
V
< 0.1V, CLK/SEL = OUT, includes load
FB
Output Voltage
3.17
3.3
1.240
0.01
-1.5
3.38
1.270
100
V
V
regulation for 0 < I < 0.55A
LX
Adjustable output, CLK/SEL = OUT, includes
load regulation for 0 < I < 0.55A
FB Regulation Voltage
FB Input Leakage Current
Load Regulation
1.215
LX
V
= 1.35V (T = +25°C, MAX1760ETB,
A
FB
nA
%
MAX1760HETB)
CLK/SEL = OUT, no load to full load
(0 < I < 1.0A)
LX
Output Voltage Adjust Range
2.5
5.5
V
V
Output Voltage Lockout Threshold
Rising edge (Note 4)
2.00
2.15
0.01
2.30
V
= 1.25V (T = +25°C, MAX1760ETB,
A
ISET
ISET Input Leakage Current
50
nA
MAX1760HETB)
Supply Current in Shutdown
No-Load Supply Current
V
= 3.6V, V
= 0V
ON
0.1
100
2.5
5
µA
µA
ON
CLK/SEL = GND (Note 5)
185
No-Load Supply Current Forced-PWM Mode CLK/SEL = OUT
mA
DC-DC SWITCHES
V
= 0, V
= 5.5V (T = +25°C,
LX
OUT A
POUT Leakage Current
LX Leakage Current
0.1
0.1
10
10
µA
µA
MAX1760ETB, MAX1760HETB)
= V = 5.5V, in shutdown (T =
A
V
LX
OUT
+25°C, MAX1760ETB, MAX1760HETB)
2
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, V
unless otherwise noted.)
= 3.6V, T = 0°C to +85°C. Typical values are at T = +25°C,
A A
OUT
PARAMETER
CONDITIONS
MIN
TYP
0.15
0.25
1.25
60
MAX
UNITS
N-channel
0.28
0.45
1.6
Switch On-Resistance
P-channel
Ω
N-Channel Current Limit
1.0
20
A
P-Channel Turn-Off Current
REFERENCES
CLK/SEL = GND
120
mA
Reference Output Voltage
Reference Load Regulation
Reference Supply Rejection
LOGIC INPUTS
I
= 0
1.230
1.250
5
1.270
15
V
REF
-1µA < IREF < +50µA
mV
mV
2.5V < V
< 5V
0.2
5
OUT
0.2 x
CLK/SEL Input Low Level
2.5V ≤ V
2.5V ≤ V
≤ 5.5V
≤ 5.5V
V
V
V
OUT
OUT
V
OUT
0.8 x
CLK/SEL Input High Level
ON, ON Input Low Level (Note 6)
V
OUT
1.1V ≤ V
1.8V ≤ V
≤ 1.8V
≤ 5.5V
0.2
0.4
OUT
OUT
V
- 0.2
OUT
1.1V ≤ V
≤ 1.8V
≤ 5.5V
OUT
OUT
ON, ON Input High Level (Note 6)
V
1.8V ≤ V
1.6
CLK/SEL, ON, ON (T = +25°C,
MAX1760ETB, MAX1760HETB)
A
Input Leakage Current
0.01
1
µA
Minimum CLK/SEL Pulse Width
Maximum CLK/SEL Rise/Fall Time
200
100
ns
ns
ELECTRICAL CHARACTERISTICS
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, V
= 3.6V, T = -40°C to +85°C, unless otherwise noted.) (Note 7)
A
OUT
PARAMETER
CONDITIONS
MIN
MAX
UNITS
DC-DC CONVERTER
V
< 0.1V, CLK/SEL = OUT, includes load
FB
Output Voltage
3.17
3.38
V
V
regulation for 0 < I < 0.55A
LX
Adjustable output, CLK/SEL = OUT, includes
load regulation for 0 < I < 0.55A
LX
FB Regulation Voltage
1.215
1.270
Internal Oscillator Frequency
Oscillator Maximum Duty Cycle
Output Voltage Lockout Threshold
Supply Current in Shutdown
No-Load Supply Current
CLK/SEL = OUT
(Note 3)
0.75
80
1.2
90
MHz
%
Rising edge (Note 4)
2.00
2.30
5
V
V
= 3.6V
µA
µA
ON
CLK/SEL = GND (Note 5)
185
DC-DC SWITCHES
N-channel
P-channel
0.28
0.45
Switch On-Resistance
Ω
_______________________________________________________________________________________
3
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, V
= 3.6V, T = -40°C to +85°C, unless otherwise noted.) (Note 7)
A
OUT
PARAMETER
N-Channel Current Limit
REFERENCE
CONDITIONS
MIN
MAX
UNITS
1.0
1.6
A
Reference Output Voltage
I
= 0
1.230
0.8 x
1.270
V
REF
LOGIC INPUTS
0.2 x
CLK/SEL Input Low Level
2.5V ≤ V
2.5V ≤ V
≤ 5.5V
≤ 5.5V
V
V
V
OUT
OUT
V
OUT
CLK/SEL Input High Level
ON, ON Input Low Level (Note 6)
V
OUT
1.1V ≤ V
1.8V ≤ V
1.1V ≤ V
1.8V ≤ V
≤ 1.8V
≤ 5.5V
≤ 1.8V
≤ 5.5V
0.2
0.4
OUT
OUT
OUT
OUT
V
+ 0.2
OUT
1.6
ON, ON Input High Level (Note 6)
V
Input Leakage Current
CLK/SEL, ON, ON
1
µA
Note 1: Operating voltage—since the regulator is bootstrapped to the output, once started, the MAX1760 operates down
to 0.7V input.
Note 2: Startup is tested with the circuit shown in Figure 6.
Note 3: Defines 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 into 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.
Note 6: ON (MAX1760) and ON (MAX1760H) have a hysteresis of approximately 0.15 × V
Note 7: Specifications to -40°C are guaranteed by design and not production tested.
.
OUT
Typical Operating Characteristics
(Circuit of Figure 2, V = 2.4V, V
= 3.3V, T = +25°C, unless otherwise noted.)
A
IN
OUT
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
EFFICIENCY vs. OUTPUT CURRENT
= 5V
EFFICIENCY vs. OUTPUT CURRENT
= 3.3V
V
V
OUT
OUT
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
A
A
B
V
OUT
= 3.3V
C
B
C
V
OUT
= 5V
= AUTO MODE
= FPWM MODE
= AUTO MODE
= FPWM MODE
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
0.0001
0.001
0.01
0.1
1
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
INPUT VOLTAGE (V)
0.0001
0.001
0.01
0.1
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
4
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 2, V = 2.4V, V
= 3.3V, T = +25°C, unless otherwise noted.)
A
IN
OUT
NO-LOAD BATTERY CURRENT
vs. INPUT VOLTAGE
TOTAL SHUTDOWN CURRENT
(I + I ) vs. INPUT VOLTAGE
INTERNAL OSCILLATOR
FREQUENCY vs. TEMPERATURE
LX OUT
10
2.5
2.0
1.5
1.0
0.5
0.0
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
1
V
OUT
= 5V
V
= 3.3V
1
OUT
0.1
0
1
2
3
4
5
6
0
2
3
4
5
-40
-15
10
35
60
85
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
STARTUP VOLTAGE
vs. OUTPUT CURRENT
PEAK INDUCTOR CURRENT vs. V
HEAVY-LOAD SWITCHING WAVEFORMS
ISET
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
A = +85°C
B = +25°C
C = -40°C
A
B
C
B
A
C
0V
CIRCUIT OF FIGURE 6
0.001 0.01
OUTPUT CURRENT (A)
0.1
1
0.1
0.3
0.5
0.7
0.9
1.1
1.3
A = LX PIN, 5V/div
B = INDUCTOR CURRENT, 200mA/div
C = OUTPUT RIPPLE, 50mV/div AC-COUPLED
t = 400ns/div
V
(V)
ISET
LOAD-TRANSIENT RESPONSE
LIGHT-LOAD SWITCHING WAVEFORMS
LINE-TRANSIENT RESPONSE
A
B
A
B
A
B
C
t = 200ms/div
400µs/div
t = 400ns/div
V
= 1.1V, V = 3.3V, I = 0 AND 0.2A
OUT
OUT
V
IN = 2.4V TO 1.4V, IOUT = 70mA
IN
A = LX PIN, 5V/div
B = INDUCTOR CURRENT, 200mA/div
C = OUTPUT RIPPLE, 50mV/div, AC-COUPLED
IN
OUT
OUT
A = I , 100mA/div
B = V , 50mV/div, AC-COUPLED
A = V , 1V/div
B = V , 5mA/div, AC-COUPLED
OUT
_______________________________________________________________________________________
5
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 2, V = 2.4V, V
IN
= 3.3V, T = +25°C, unless otherwise noted.)
A
OUT
TURN-ON WAVEFORMS
NO SOFT-START COMPONENTS
SOFT-START WAVEFORMS
NOISE SPECTRUM
R
SS
= 500kΩ, C = 0.1µF
SS
16
A
B
A
B
12
8
4
C
0
C
0V
OV
0.1
1
10
t = 2ms/div
A = ON, 5V/div
2.00ms/div
FREQUENCY (MHz)
A = ON, 5V/div
B = INPUT CURRENT, 100mA/div
B = INPUT CURRENT, 500mA/div
C = V , 2V/div
C = V , 2V/div
OUT
OUT
Pin Description
PIN
NAME
FUNCTION
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
1
ISET
capacitor from ISET to GND. When ON = high, or V
<80% of nominal value, an on-chip 100kΩ switched
REF
resistor discharges this pin to GND.
1.250V Voltage Reference Bypass. Connect a 0.22µF ceramic bypass capacitor to GND. Up to 50µA of
external load current is allowed.
2
3
4
REF
GND
FB
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 from OUT to GND. FB set point = 1.24V.
IC Power, Supplied from the Output. Bypass to GND with a 0.68µF ceramic capacitor, and connect to POUT
with a series 4.7Ω resistor (Figure 2).
5
OUT
Clock Input for the DC-DC Converter. Also serves to program operating mode of switcher as follows:
CLK/SEL = LO: Normal operation—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.
6
CLK/SEL
7
8
9
PGND
LX
Source of N-Channel Power MOSFET Switch
Inductor Connection
POUT
ON
Power Output. P-channel synchronous-rectifier source.
MAX1760 Enable Input. When ON is low, the IC is on. Connect to GND for normal operation.
MAX1760H Enable Input. When ON is high, the IC is on. Connect to OUT for normal operation.
10
ON
6
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
UNDERVOLTAGE LOCKOUT
OUT
IC POWER
2.15V
CONTROLLER
POUT
STARTUP
OSCILLATOR
PCH
NCH
D
EN
Q
ON
(MAX1760H)
ON
(MAX1760)
LX
ON
RDY
EN
REFERENCE
EN
OSC
OSC
1.25V
REF
REF GND
OSCILLATOR
1MHz
GND
MODE
FB
MODE
CLK/SEL
PGND
CLK/SEL
FB
ISET
ISET
MAX1760
Figure 1. Functional Diagram
Detailed Description
The MAX1760 is a highly efficient, low-noise power sup-
ply for portable RF and hand-held instruments. It com-
bines a boost switching regulator, N-channel power
MOSFET, P-channel synchronous rectifier, precision
reference, and shutdown control (Figure 1).
3.3µH
V
IN
= 2.4V
33µF
ON
LX
CLK/SEL
MAX1760
The DC-DC converter boosts a 1-cell to 3-cell battery
voltage input to a fixed 3.3V or adjustable voltage
between 2.5V and 5.5V. An external Schottky diode is
required for output voltages greater than 4V. The
MAX1760 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 qui-
escent current for maximum battery life. It features
fixed-frequency operation at medium and heavy loads,
but at light loads, switches only as needed for optimum
efficiency. This device is also capable of constant-fre-
quency (1MHz), low-noise PWM operation at all load
currents, or frequency-synchronized PWM operation
when connected to an external clock. Table 1 lists
some typical outputs. Shutdown reduces quiescent cur-
rent to just 1µA. Figure 2 shows the standard applica-
tion circuit for the MAX1760.
V
= 3.3V,
OUT
ꢀ
POUT
800mA
ISET
REF
4.7Ω
100µF
OUT
0.68µF
0.22µF
FB
GND PGND
Figure 2. Standard Application Circuit
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
_______________________________________________________________________________________
7
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Table 1. Typical Available Output Current
NUMBER OF NiCd/NiMH
CELLS
INPUT VOLTAGE
(V)
OUTPUT VOLTAGE
(V)
OUTPUT CURRENT
(mA)
1
2
3
1.2
2.4
2.4
3.6
3.3
3.3
5.0
5.0
350
800
500
750
Table 2. Selecting the Operating Mode
CLK/SEL
MODE
FEATURES
0
1
Normal operation
Forced PWM
High efficiency at all loads. Fixed frequency at all but light loads.
Low noise, fixed frequency at all loads.
External clock
500kHz to 1.2MHz
Synchronized PWM
Low noise, fixed frequency at all loads.
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. At light
loads, the device operates at fixed frequency or only as
needed to maintain regulation, depending on the
CLK/SEL setting (Table 2).
Synchronous Rectifier
The MAX1760 features an internal, P-channel synchro-
nous rectifier to enhance efficiency. Synchronous recti-
fication provides 5% improved efficiency over similar
nonsynchronous boost regulators. 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 60mA. When setting output voltages greater than
4V, an external 0.5A Schottky diode must be connected
in parallel with the on-chip synchronous rectifier.
Normal Operation
Pulling CLK/SEL low selects the MAX1760’s normal
operating mode. In this mode, the device operates in
PWM when driving medium-to-heavy loads, and auto-
matically switches to PFM if the load requires less
power. PFM operation allows higher efficiency than
PWM under light-load conditions.
Low-Voltage Startup Oscillator
The MAX1760 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 boost-converter
feedback and control circuitry take over. Once the
device is in regulation, it can operate down to 0.7V
input since internal power for the IC is bootstrapped
from the output through OUT. Do not apply full load
until the output exceeds 2.3V.
Forced-PWM Operation
When CLK/SEL is high, the MAX1760 operates in a low-
noise PWM-only mode. During forced-PWM operation,
the MAX1760 switches at a constant frequency (1MHz)
and modulates the MOSFET switch pulse width to con-
trol the power transferred per cycle to regulate the out-
put voltage. Switching harmonics generated by
fixed-frequency operation are consistent and easily fil-
tered. See the Noise Spectrum plot in the Typical
Operating Characteristics.
Synchronized-PWM Operation
The MAX1760 can be synchronized in PWM mode to an
external frequency of 500kHz to 1.2MHz by applying an
external clock signal to CLK/SEL. This allows interfer-
ence to be minimized in wireless applications. The syn-
chronous rectifier is active during synchronized-PWM
operation.
Shutdown
The MAX1760 has a shutdown mode that reduces qui-
escent current to 0.1µA. During shutdown (ON = high
on MAX1760, ON = low on MAX1760H), the reference
and all feedback and control circuitry are off. During
shutdown, the output voltage is one diode drop below
the input voltage.
8
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
3.3µH
V
= 2.4V
IN
33µF
CLK/SEL
ON
LX
MAX1760
POUT
V
OUT
100µF
ISET
REF
4.7Ω
OUT
FB
0.68µF
0.22µF
PGND GND
R1
R2
V
OUT
-
1
R1 = R2
(V )
FB
= 1.24V
V
FB
Figure 3. Connecting Resistors for External Feedback
REF
REF
R
SS2
I
= 1.25A
LIM
0.22µF
0.22µF
I
= 1.25A
(R )
+ R
LIM
SS1
SS2
R
SS1
R
SS
t
SS
= R C
SS SS
MAX1760
MAX1760
t
SS
= (R
R ) C
SS2 SS
SS1
II
ISET
ISET
R
SS2
C
SS
C
SS
R
SS1
≥ 470kΩ
R
SS
≥ 470kΩ
Figure 4. Soft-Start with Maximum Switch Limit Current
Figure 5. Soft-Start with Reduced Switch Current Limit
Reference
The MAX1760 has an internal 1.250V 1% reference.
Connect a 0.22µF ceramic bypass capacitor from REF
to GND within 0.2in (5mm) of the REF pin. REF can
source up to 50µA of external load current.
where V , the boost-regulator feedback set point, is
FB
1.24V.
Setting the Switch Current Limit
and Soft-Start
The ISET pin adjusts the inductor current limit and
implements soft-start. With ISET connected to REF, the
inductor current limits at 1.25A. With ISET connected to
a resistive divider set from REF to GND, the current limit
is reduced according to:
Design Procedure
Setting the Output Voltages
For a fixed 3.3V output, connect FB to GND. To set
other output voltages between 2.5V and 5.5V, connect
a resistor voltage-divider to FB from OUT to GND
(Figure 3). The input bias current into FB is <20nA,
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 270kΩ or less, then calculate R1 using:
V
ISET
ILIM = 1.25A
1.25V
Implement soft-start by placing a resistor from ISET to
REF and a capacitor from ISET to GND. In shutdown,
ISET is discharged to GND through an on-chip 100kΩ
resistor. At power-up, ISET is 0V and the LX current is
zero. As the capacitor voltage rises, the current
increases and the output voltage rises. The soft-start
VOUT
VFB
R1 = R2
− 1
_______________________________________________________________________________________
9
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Table 3. Component Selection Guide
PRODUCTION METHOD
INDUCTORS
CAPACITORS
AVX TPS series
Kemet T510 series
Sanyo POSCAP series
—
DIODES
TOKO type D52LC
TOKO type D518LC
Sumida CDRH5D18
Sumida CDRH4D28
EIC SB series
Motorola MBR0520L
Surface mount
—
—
External Diode
Table 4. Component Suppliers
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
6). The diode should be rated for 0.5A. Representative
devices are Motorola MBR0520L, Nihon EP05Q03L, or
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 startup and after the synchronous rectifi-
er turns off; thus, its current rating only needs to be
500mA. Connect the diode as close to the IC as possi-
ble. Do not use ordinary rectifier diodes; their slow
switching speeds and long reverse-recovery times ren-
der 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.
SUPPLIER
PHONE
AVX
EIC
USA: 843-448-9411
USA: 916-941-0712
USA: 810-287-2536
Kemet
USA: 408-629-4789
Japan: 81-45-474-7030
Motorola
USA: 847-956-0666
Japan: 011-81-3-3667-3302
Sumida
TOKO
USA: 847-297-0070
Note: Please indicate that you are using the MAX1760 when
contacting these component suppliers.
time constant is:
Input and Output Filter Capacitors
tSS = RSSCSS
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-
where R ≥ 470kΩ.
SS
Placing a capacitor across the lower resistor of the cur-
rent-limiting resistive divider provides both current-limit
and soft-start features simultaneously (Figures 4 and 5).
Inductor Selection
The MAX1760’s high switching frequency allows the
use of a small 3.3µH 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. Lower current-rated induc-
tors may be used if ISET is employed to reduce the
peak inductor current (see the Setting the Switch
Current Limit and Soft-Start section). For high efficien-
cy, choose an inductor with a high-frequency ferrite
core material to reduce core losses. To minimize radiat-
ed noise, use a toroid or shielded 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 pin as close to the IC as possible.
3.3µH
V
= 0.7V
IN
TO VOUT
33µF
CLK/SEL
ON
MRB0520L
LX
V
OUT
100µF
MAX1760
POUT
ISET
REF
4.7Ω
OUT
FB
0.68µF
0.22µF
PGND GND
Figure 6. Connection with External Schottky Diode for Output
Voltages Greater than 4V, or to Assist Low-Voltage Startup
10 ______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
age, and output capacitors with working voltage ratings
higher than the output.
bypass OUT to GND with a 0.68µF ceramic capacitor,
and connect OUT to POUT with a 4.7Ω resistor. Each of
these components should be placed as close to its
respective IC pins as possible, within 0.2in (5mm).
Table 4 lists suggested suppliers.
The input filter capacitor reduces peak currents drawn
from the input source and also reduces input switching
noise. The input voltage source impedance determines
the required value of the input capacitor. When operat-
ing directly from one or two NiMH cells placed close to
the MAX1760, use a single 33µF low-ESR input filter
capacitor. With higher impedance batteries, such as
alkaline and Li+, a higher value input capacitor may
improve efficiency.
Layout Considerations
High switching frequencies and large peak currents
make PC board layout a critical part of design. Poor
design causes excessive EMI and ground bounce,
both of which can cause instability or regulation errors
by corrupting the voltage and current feedback signals.
The output filter capacitor reduces output ripple voltage
and provides the load with transient peak currents
when necessary. For the output, a 100µF, low-equiva-
lent-series-resistance (ESR) capacitor is recommended
for most applications.
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. Keep the voltage feed-
back network very close to the IC, within 0.2in (5mm) of
the FB pin. Keep noisy traces, such as those from the
LX pin, away from the voltage feedback network and
guarded from them using grounded copper. Refer to the
MAX1760 evaluation kit for a full PC board example.
Sanyo POSCAP, Panasonic SP/CB, and Kemet T510
are good low-ESR capacitors. Low-ESR tantalum
capacitors offer a good tradeoff 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.
Chip Information
TRANSISTOR COUNT: 1361
Other External Components
Two ceramic bypass capacitors are required for proper
operation. Bypass REF to GND with 0.22µF. Also,
______________________________________________________________________________________ 11
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
e
4X S
10
10
INCHES
DIM MIN
MAX
MILLIMETERS
MIN
-
MAX
1.10
0.15
0.95
3.05
3.00
3.05
3.00
5.05
0.70
A
-
0.043
0.006
0.037
0.120
0.118
0.120
0.118
0.199
A1
A2
D1
D2
E1
E2
H
0.002
0.030
0.116
0.114
0.116
0.114
0.187
0.05
0.75
2.95
2.89
2.95
2.89
4.75
0.40
H
ÿ 0.50±0.1
0.6±0.1
L
0.0157 0.0275
0.037 REF
L1
b
0.940 REF
0.007
0.0106
0.177
0.090
0.270
1
1
e
0.0197 BSC
0.500 BSC
0.6±0.1
c
0.0035 0.0078
0.0196 REF
0.200
BOTTOM VIEW
0.498 REF
S
TOP VIEW
α
0∞
6∞
0∞
6∞
D2
E2
GAGE PLANE
A2
c
A
E1
b
L
α
A1
D1
L1
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0061
I
1
12 ______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
L
A
D2
D
A2
PIN 1 ID
1
N
1
C0.35
b
[(N/2)-1] x e
REF.
E
E2
PIN 1
INDEX
AREA
DETAIL A
e
k
A1
C
L
C
L
L
L
e
e
A
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
1
2
21-0137
D
______________________________________________________________________________________ 13
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS
SYMBOL
MIN.
0.70
2.90
2.90
0.00
0.20
MAX.
0.80
3.10
3.10
0.05
0.40
A
D
E
A1
L
k
0.25 MIN.
0.20 REF.
A2
PACKAGE VARIATIONS
PKG. CODE
T633-1
N
6
D2
E2
e
JEDEC SPEC
MO229 / WEEA
MO229 / WEEC
b
[(N/2)-1] x e
1.90 REF
1.95 REF
2.00 REF
1.50±0.10 2.30±0.10 0.95 BSC
1.50±0.10 2.30±0.10 0.65 BSC
0.40±0.05
0.30±0.05
T833-1
8
T1033-1
10
1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
2
2
21-0137
D
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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