Rainbow Electronics MAX1708 User Manual
General Description
The MAX1708 sets a new standard of space savings for
high-power, step-up DC-DC conversion. It delivers up
to 10W at a fixed (3.3V or 5V) or adjustable (2.5V to
5.5V) output, using an on-chip power MOSFET from a
+0.7V to +5V supply.
Fixed-frequency PWM operation ensures that the
switching noise spectrum is constrained to the 600kHz
fundamental and its harmonics, allowing easy postfiltering for noise reduction. External clock synchronization
capability allows for even tighter noise spectrum control. Quiescent power consumption is less than 1mW to
extend operating time in battery-powered systems.
Two control inputs (ONA, ONB) allow simple push-on,
push-off control through a single momentary push-button switch, as well as conventional on/off logic control.
The MAX1708 also features programmable soft-start
and current limit for design flexibility and optimum performance with batteries. The maximum RMS switch current rating is 5A. For a device with a higher (10A)
switch current rating, refer to the MAX1709 data sheet.
________________________Applications
Routers, Servers, Workstations, Card Racks
Local 2.5V to 3.3V or 5V Conversion
Local 3.3V to 5V Conversion
3.6V or 5V RF PAs in Communications Handsets
Features
♦ On-Chip 5A Power MOSFET
♦ 5V, 2A Output from a 3.3V Input
♦ Fixed 3.3V or 5V Output Voltage or
Adjustable (2.5V to 5.5V)
♦ Input Voltage Range Down to 0.7V
♦ Low Power Consumption
1mW Quiescent Power
1µA Current in Shutdown Mode
♦ Low-Noise, Constant Frequency Operation
(600kHz)
♦ Synchronizable Switching Frequency
(350kHz to 1000kHz)
♦ Small QSOP Package
MAX1708
High-Frequency, High-Power, Low-Noise,
Step-Up DC-DC Converter
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
ONA
REF
SS/LIM
CLK
OUTPUT
3.3V, 5V,
OR ADJ
UP TO 2A
OUT
GND
LX
2.2µH
OFF
ON
INPUT
1V TO 5V
SYNC
OR
INTERNAL
MAX1708
Typical Operating Circuit
19-2068; Rev 0; 7/01
Ordering Information
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.
PART TEMP. RANGE PIN-PACKAGE
MAX1708EEE -40°C to +85°C 16 QSOP
TOP VIEW
1
ONB CLK
ONA
2
LX
3
4
LX
LX
5
GND
6
SS/LIM
REF
7
8
MAX1708
QSOP
16
15
3.3/5
14
PGND
13
PGND
12
PGND
FB
11
10
OUT
9
GND
MAX1708
High-Frequency, High-Power, Low-Noise,
Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
OUT
= V
CLK
= +3.6V, ONA = ONB = FB = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ONA, ONB, OUT, SS/LIM, 3.3/5 to GND ...............-0.3V to +6.0V
LX to PGND ...........................................................-0.3V to +6.0V
FB, CLK, REF to GND.............................. -0.3V to (V
OUT
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.30mW/°C above +70°C). .......667mW
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
Output Voltage VFB < 0.1V (Note 1)
Load Regulation Measured between 0.5A < ISW < 1.5A (Note 2) -0.40 -0.60 %/A
FB Regulation Voltage (VFB)ISW = 0.5A 1.215 1.240 1.265 V
FB Input Current V
Output Voltage Adjust Range 2.5 5.5 V
Output Undervoltage Lockout
(Note 3)
Frequency in Startup Mode V
Minimum Startup Voltage I
Minimum Operating Voltage (Note 5) 0.7 V
Soft-Start Pin Current V
OUT Supply Current VFB = 1.5V (Note 6) 200 300 µA
OUT Leakage Current In
Shutdown
LX Leakage Current VLX = V
N-Channel Switch
On-Resistance
N-Channel Current Limit
RMS Switch Current 5A
Reference Voltage I
Reference Load Regulation -1µA ≤ I
Reference Supply Rejection +2.5V ≤ V
Input Low Level (Note 7)
PARAMETER CONDITIONS MIN TYP MAX UNITS
= +1.5V
FB
Rising and falling 2.0 2.3 V
=1.5V 40 400 kHz
OUT
< 1mA, TA = +25°C (Note 4) 0.9 1.1 V
OUT
= 1V 3.2 4 5.0 µA
SS/LIM
V
= 3.6V 0.1 2 µA
ONB
= V
ONB
SS/LIM = open
SS/LIM = 150kΩ to GND
= 0 1.245 1.260 1.275 V
REF
≤ 50µA 4 10 mV
REF
OUT
ONA, ONB, 3.3/5, 1.2V < V
CLK, 2.7V < V
= +5.5V 1 25 µA
OUT
≤ +5.5V 0.2 5 mV
< 5.5V 0.2 ✕ V
OUT
3.3/5 = GND, ISW = 0.5A 3.26 3.34 3.42
3.3/5 = OUT, I
< 5.5V 0.2 ✕ V
OUT
= 0.5A 4.90 5.05 5.20
SW
1
30 80 mΩ
4.5
1.80
5.3
3.00
200 nA
7.0
3.85
OUT
OUT
V
A
RMS
V
MAX1708
High-Frequency, High-Power, Low-Noise,
Step-Up DC-DC Converter
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V
OUT
= V
CLK
= +3.6V, ONA = ONB = FB = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS
(V
OUT
= V
CLK
= +3.6V, ONA = ONB = FB = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 9)
Input High Level
Logic Input Current ONA, ONB, CLK, 3.3/5 = 0, 5.5V -1 1 µA
Internal Oscillator Frequency 520 600 680 kHz
Maximum Duty Cycle 82 88 94 %
External Clock Frequency
Range
CLK Pulse Width (Note 8) 100 ns
CLK Rise/Fall Time (Note 8) 50 ns
PARAMETER CONDITIONS MIN TYP MAX UNITS
ONA, ONB, 3.3/5, 1.2V < V
CLK, 2.7 V< V
< 5.5V 0.8 ✕ V
OUT
<5.5V 0.8 ✕ V
OUT
OUT
OUT
350 1000 kHz
Output Voltage
FB Regulation Voltage I
FB Input Current (VFB)V
Load Regulation Measured between 0.5A < ISW < 1.5A (Note 2) -0.60 %/A
Soft-Start Pin Current SS/LIM = 1V 3.2 5.2 µA
OUT Leakage Current in
Shutdown
OUT Supply Current V
N-Channel Switch
On-Resistance
N-Channel Current Limit
Reference Voltage I
PARAMETER CONDITIONS MIN MAX UNITS
V
< 0.1V, VIN = +2.4V
FB
(Note 1)
= 0.5A 1.20 1.28 V
SW
= +1.5V 200 nA
FB
V
= 3.6V 2 µA
ONB
= 1.5V (Note 6) 300 µA
FB
SS/LIM = open 4.5 7.5
SS/LIM = 150kΩ to GND 1.8 4.0
= 0 1.24 1.28 V
REF
3.3/5 = GND, I
3.3/5 = OUT, I
= 0.5A 3.24 3.45
SW
= 0.5A 4.90 5.22
SW
80 mΩ
V
V
A
Note 1: Output voltage is specified at 0.5A switch current ISW, which is equivalent to approximately 0.5A ✕(VIN/ V
OUT
) of load cur-
rent.
Note 2: Load regulation is measured by forcing specified switch current and straight-line calculation of change in output voltage in
external feedback mode. Note that the equivalent load current is approximately I
SW
✕
(VIN/ V
OUT
).
Note 3: Until undervoltage lockout is reached, the device remains in startup mode. Do not apply full load until this voltage is
reached.
Note 4: Startup is tested with Figure 1’s circuit. Output current is measured when both the input and output voltages are applied.
Note 5: Minimum operating voltage. The MAX1708 is bootstrapped and will operate down to a 0.7V input once started.
Note 6: Supply current is measured from the output voltage (+3.3V) to the OUT pin. This correlates directly with actual input supply
current but is reduced in value according to the step-up ratio and efficiency.
Note 7: ONA and ONB inputs have approximately 0.15V hysteresis.
Note 8: Guaranteed by design, not production tested.
Note 9: Specifications to -40°C are guaranteed by design, not production tested.
MAX1708
High-Frequency, High-Power, Low-Noise,
Step-Up DC-DC Converter
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V
OUT
= V
CLK
= +3.6V, ONA = ONB = FB = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 9)
Input Low Level (Note 7)
Input High Level
Logic Input Current ONA, ONB, CLK, 3.3/5 = 0, 5.5V -1 1 µA
Internal Oscillator Frequency 500 700 kHz
Maximum Duty Cycle 80 95 %
External Clock Frequency Range 350 1000 kHz
CLK Pulse Width (Note 8) 100 ns
CLK Rise/Fall Time (Note 8) 50 ns
PARAMETER CONDITIONS MIN MAX UNITS
ONA, ONB, 3.3/5, 1.2V < V
CLK, 2.7V < V
ONA, ONB, 3.3/5, 1.2V < V
CLK, 2.7V < V
< 5.5V 0.2 ✕ V
OUT
< 5.5V 0.8 ✕ V
OUT
< 5.5V 0.2 ✕ V
OUT
< 5.5V 0.8 ✕ V
OUT
OUT
OUT
OUT
OUT
V
V
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