MAX756CSA+ ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersGeneral Description ________
MAX756CSA+T ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersFeaturesThe MAX756/MAX757 are CMOS step-up DC-DC switch-♦ Operates Down to 0.7V Input Supply Voltag ..
MAX756ESA ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersFeaturesThe MAX756/MAX757 are CMOS step-up DC-DC switch-' Operates Down to 0.7V Input Supply Voltag ..
MAX756ESA ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersGeneral Description ________
MAX756ESA ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersFeaturesThe MAX756/MAX757 are CMOS step-up DC-DC switch-' Operates Down to 0.7V Input Supply Voltag ..
MAX756ESA+ ,3.3V/5V/Adjustable-Output, Step-Up DC-DC ConvertersEVALUATION KIT AVAILABLEMAX756/MAX7573.3V/5V/Adjustable-Output,Step-Up DC-DC Converters____________ ..
MB6M ,MINIATURE GLASS PASSIVATED SINGLE-PHASE BRIDGE RECTIFIERThermal Characteristics (TA = 25°C unless otherwise noted)Parameter Symbol MB2M MB4M MB6M UnitDevic ..
MB6S ,Bridge RectifiersThermal Characteristics (T = 25°C unless otherwise noted)AParameter Symbol MB2S MB4S MB6S UnitDevic ..
MB7117E , Schottky TTL 2048-Bit Bipolar Programmable Read-Only Memory
MB71A38-25 , PROGRAMMABLE SCHOTTKY 16384-BIT READ ONLY MEMORY
MAX756CPA+-MAX756CSA+-MAX756CSA+T-MAX756ESA+-MAX756ESA+T-MAX757CSA+-MAX757ESA+-MAX757ESA+T
3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters
AVAILABLE
EVALUATION KIT AVAILABLE
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
_______________General DescriptionThe MAX756/MAX757 are CMOS step-up DC-DC switch-
ing regulators for small, low input voltage or battery-pow-
ered systems. The MAX756 accepts a positive input
voltage down to 0.7V and converts it to a higher pin-
selectable output voltage of 3.3V or 5V. The MAX757 is
an adjustable version that accepts an input voltage down
to 0.7Vand generates a higher adjustable output voltage
in the range from 2.7V to 5.5V. Typical full-load efficiencies
for the MAX756/MAX757 are greater than 87%.
The MAX756/MAX757 provide three improvements over
previous devices. Physical size is reduced—the high
switching frequencies (up to 0.5MHz) made possible by
MOSFET power transistors allow for tiny (<5mm diameter)
surface-mount magnetics. Efficiency is improved to 87%
(10% better than with low-voltage regulators fabricated in
bipolar technology). Supply current is reduced to 60µA
by CMOS construction and a unique constant-off-time
pulse-frequency modulation control scheme.
________________________Applications3.3V to 5V Step-Up Conversion
Palmtop Computers
Portable Data-Collection Equipment
Personal Data Communicators/Computers
Medical Instrumentation
2-Cell & 3-Cell Battery-Operated Equipment
Glucose Meters
____________________________FeaturesOperates Down to 0.7V Input Supply Voltage87% Efficiency at 200mA60µA Quiescent Current20µA Shutdown Mode with Active Reference and
LBI Detector500kHz Maximum Switching Frequency±1.5% Reference Tolerance Over TemperatureLow-Battery Detector (LBI/LBO)8-Pin DIP and SO Packages
______________Ordering Information* Dice are tested at TA= +25°C only.
GND
OUT
LBILBO
REF
3/5
SHDN
MAX756
DIP/SOTOP VIEW
GND
OUT
LBILBO
REF
SHDN
MAX757
DIP/SO
_________________Pin ConfigurationsMAX756
SHDN1
3/52
REF3
LBI
150μF
GND
OUT6
INPUT
2V to VOUT1N5817
OUTPUT
5V at 200mA
3.3V at 300mA100μF
LBO4
0.1μF
22μH
LOW-BATTERY
DETECTOR OUTPUT
__________Typical Operating Circuit
PARTTEMP. RANGEPIN-PACKAGE
MAX756CPA0°C to +70°C8 Plastic DIP
MAX756CSA0°C to +70°C8 SO
MAX756C/D0°C to +70°CDice*
MAX756EPA-40°C to +85°C8 Plastic DIP
MAX756ESA-40°C to +85°C8 SO
MAX757CPA0°C to +70°C8 Plastic DIP
MAX757CSA0°C to +70°C8 SO
MAX757C/D0°C to +70°CDice*
MAX757EPA-40°C to +85°C8 Plastic DIP
MAX757ESA-40°C to +85°C8 SO
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC ConvertersSupply Voltage (OUT to GND)....................................-0.3V, +7V
Switch Voltage (LX to GND)........................................-0.3V, +7V
Auxiliary Pin Voltages (SHDN, LBI, LBO, REF,
3/5, FB to GND)........................................-0.3V, (VOUT+ 0.3V)
Reference Current (IREF)....................................................2.5mA
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C).............727mW
SO (derate 5.88mW/°C above +70°C)..........................471mW
Operating Temperature Ranges:
MAX75_C_ _........................................................0°C to +70°C
MAX75_E_ _......................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range...............................-65°to +160°C
Lead Temperature (soldering, 10sec)...........................+300°C
ELECTRICAL CHARACTERISTICS(Circuits of Figure 1 and Typical Operating Circuit, VIN= 2.5V, ILOAD= 0mA, TA= TMINto TMAX, unless otherwise noted.)
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.
ABSOLUTE MAXIMUM RATINGS
Note 1:Supply current from the 3.3V output is measured with an ammeter between the 3.3V output and OUT pin. This current
correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency.
Note 2:Minimum value is production tested. Maximum value is guaranteed by design and is not production tested.
LBO Output Leakage Current
SHDN, 3/5, FB, LBI Input Current2.75.5MAX757, ILOAD= 0mA (Note 2)Output Voltage Range1.221.251.28MAX757FB Voltage±100LBI = 1.25V, FB = 1.25V, SHDN= 0V or 3V,
3/5= 0V or 3V1.6SHDN, 3/5Input Voltage High0.4SHDN, 3/5Input Voltage Low
Shutdown Quiescent Current
(Note 1)
Battery Quiescent Current
Measured at VINin Figure 11.221.251.28With falling edgeLBI Input Threshold25LBI Input Hysteresis0.4ISINK= 2mALBO Output Voltage Low1LBO = 5V2040SHDN= 0V, LBI = 1.25V, 3/5= 3V, VOUT= 3.47V,
FB = 1.3V (MAX757 only)Quiescent Supply Current in
3.3V Mode (Note 1)
MAX757, VOUT= 5V, 0mA < ILOAD< 200mA
MAX756, 3/5= 0V, 0mA < ILOAD< 200mA
MAX756, 3/5= 3V, 0mA < ILOAD< 300mA0.82.03/5= 3V, -20µA < REF load < 250µA, CREF= 0.22µFReference-Voltage Regulation1.231.251.27No REF load, CREF= 0.1µFILOAD= 0mA, 3/5= 3V, LBI = 1.25V, VOUT= 3.47V,
FB = 1.3V (MAX757 only)Output set for 3.3V
1.11.8ILOAD= 10mAMinimum Start-Up Supply Voltage
2V < VIN< 3V
Reference Voltage
3.173.303.43V
Output Voltage
UNITSMINTYPMAXCONDITIONSPARAMETER0.7ILOAD= 20mAMinimum Operating Supply
Voltage (once started)
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
MINIMUM START-UP INPUT VOLTAGE
vs. LOAD CURRENTMAX756-7
LOAD CURRENT (mA)
START-UP INPUT VOLTAGE (V)10010001
3.3V MODE
EFFICIENCY vs. LOAD CURRENT
3.3V OUTPUT MODE
MAX756-1
LOAD CURRENT (mA)
EFFICIENCY (%)60100
VIN = 2.0V
VIN = 1.2V
EFFICIENCY vs. LOAD CURRENT
5V OUTPUT MODE
MAX756-2
LOAD CURRENT (mA)
EFFICIENCY (%)60100
VIN = 3.3V
VIN = 2.5V
VIN = 1.25V
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX756-3
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
3.3V MODE5V MODE
10μ10m1
SWITCHING FREQUENCY
vs. LOAD CURRENTMAX756-4
LOAD CURRENT (A)
SWITCHING FREQUENCY (Hz)
10k
100k
100μ1m100m
5V MODE
3.3V MODE
VIN= 2.5V
QUIESCENT CURRENT
vs. INPUT VOLTAGEMAX756-5
INPUT VOLTAGE (V)
QUIESCENT CURRENT (
VOUT = 3.3V
VOUT = 5V
CURRENT MEASURED AT VIN5
SHUTDOWN QUIESCENT CURRENT
vs. INPUT VOLTAGEMAX756-6
INPUT VOLTAGE (V)
SHUTDOWN QUIESCENT CURRENT (
CURRENT MEASURED AT VIN
REFERENCE VOLTAGE
LOAD REGULATIONMAX756-8
LOAD CURRENT (μA)
VREF LOAD REGULATION (mV)100150200250
VOUT = 3.3V
__________________________________________Typical Operating Characteristics(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
______________________________________________________________Pin Description
NAMEFUNCTIONSHDN3/5Selects the main output voltage setting; 5V when low, 3.3V when high.FBREFLBOLBIOUTGNDPower Ground. Must be low impedance; solder directly to ground plane.LX1A, 0.5ΩN-Channel Power MOSFET Drain
PIN
MAX756MAX757Shutdown Input disables SMPS when low, but the voltage reference and low-battery com-
parator remain active.
Feedback Input for adjustable output operation. Connect to an external voltage divider
between OUT and GND.
1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external
reference load). Maximum load capability is 250µA source, 20µA sink.
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at
LBI drops below +1.25V.
Low-Battery Input. When the voltage on LBI drops below +1.25V, LBO sinks current.
Connect to VINif not used.
Connect OUT to the regulator output. It provides bootstrapped power to both devices,
and also senses the output voltage for the MAX756.
OUTPUT
VOLTAGE
50mV/div
VIN = 2.5V
HORIZONTAL = 50μs/div
5V Mode
LOAD-TRANSIENT RESPONSEOUTPUT
CURRENT
0mA to 200mA
_____________________________Typical Operating Characteristics (continued)(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
VSHDN
2V/div
VIN = 2.5V
HORIZONTAL = 5ms/div
5V Mode
START-UP DELAYVOUT
2V/div
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
_______________Detailed Description
Operating PrincipleThe MAX756/MAX757 combine a switch-mode regulator
with an N-channel MOSFET, precision voltage reference,
and power-fail detector in a single monolithic device.
The MOSFET is a “sense-FET” type for best efficiency,
and has a very low gate threshold voltage to ensure
start-up under low-battery voltage conditions (1.1V typ).
Pulse-Frequency
Modulation Control SchemeA unique minimum off time, current-limited, pulse-frequen-
cy modulation (PFM) control scheme is a key feature of
the MAX756/MAX757. This PFM scheme combines the
advantages of pulse-width modulation (PWM) (high output
power and efficiency) with those of a traditional PFM
pulse-skipper (ultra-low quiescent currents). There is no
oscillator; at heavy loads, switching is accomplished
through a constant peak-current limit in the switch, which
allows the inductor current to self-oscillate between this
peak limit and some lesser value. At light loads, switching
frequency is governed by a pair of one-shots, which set a
minimum off-time (1µs) and a maximum on-time (4µs).
The switching frequency depends on the load and the
input voltage, and can range as high as 500kHz.
The peak switch current of the internal MOSFET power
switch is fixed at 1A ±0.2A. The switch's on resistance
is typically 0.5Ω, resulting in a switch voltage drop
(VSW) of about 500mV under high output loads. The
value of VSWdecreases with light current loads.
Conventional PWM converters generate constant-fre-
quency switching noise, whereas this architecture pro-
duces variable-frequency switching noise. However,
the noise does not exceed the switch current limit times
the filter-capacitor equivalent series resistance (ESR),
unlike conventional pulse-skippers.
Voltage ReferenceThe precision voltage reference is suitable for driving
external loads such as an analog-to-digital converter.
It has guaranteed 250µA source-current and 20µA
sink-current capability. The reference is kept alive
even in shutdown mode. If the reference drives an
external load, bypass it with 0.22µF to GND. If the ref-
erence is unloaded, bypass it with at least 0.1µF.
Control-Logic InputsThe control inputs (3/5, SHDN) are high-impedance
MOS gates protected against ESD damage by normally
reverse-biased clamp diodes. If these inputs are dri-
ven from signal sources that exceed the main supply
voltage, the diode current should be limited by a series
resistor (1MΩsuggested). The logic input threshold
level is the same (approximately 1V) in both 3.3V and
5V modes. Do not leave the control inputs floating.
__________________Design Procedure
Output Voltage SelectionThe MAX756 output voltage can be selected to 3.3V or
5V under logic control, or it can be left in one mode or
the other by tying 3/5to GND or OUT. Efficiency varies
depending upon the battery and the load, and is typi-
cally better than 80% over a 2mA to 200mA load range.
The device is internally bootstrapped, with power
derived from the output voltage (via OUT). When the
output is set at 5V instead of 3.3V, the higher internal
supply voltage results in lower switch-transistor on
resistance and slightly greater output power.
Bootstrapping allows the battery voltage to sag to less
than 1V once the system is started. Therefore, the bat-
tery voltage range is from VOUT+ VDto less than 1V
(where VDis the forward drop of the Schottky rectifier).
If the battery voltage exceeds the programmed output
voltage, the output will follow the battery voltage. In
many systems this is acceptable; however, the output
voltage must not be forced above 7V.
The output voltage of the MAX757 is set by two resis-
tors, R1 and R2 (Figure 1), which form a voltage divider
between the output and the FB pin. The output voltage
is set by the equation:
VOUT= (VREF) [(R2 + R1) / R2]
where VREF= 1.25V.
To simplify resistor selection:
R1 = (R2) [(VOUT/ VREF) - 1]
Since the input bias current at FB has a maximum
value of 100nA, large values (10kΩto 200kΩ) can be
used for R1 and R2 with no significant loss of accuracy.
For 1% error, the current through R1 should be at least
100 times FB’s bias current.
Low-Battery DetectionThe MAX756/MAX757 contain on-chip circuitry for low-
battery detection. If the voltage at LBI falls below the reg-
ulator’s internal reference voltage (1.25V), LBO (an open-
drain output) sinks current to GND. The low-battery mon-
itor's threshold is set by two resistors, R3 and R4 (Figure
1), which forms a voltage divider between the input volt-
age and the LBI pin. The threshold voltage is set by R3
and R4 using the following equation:
R3 = [(VIN/ VREF) - 1] (R4)
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converterswhere VINis the desired threshold of the low-battery
detector, R3 and R4 are the input divider resistors at
LBI, and VREFis the internal 1.25V reference.
Since the LBI current is less than 100nA, large resistor
values (typically 10kΩto 200kΩ) can be used for R3
and R4 to minimize loading of the input supply.
When the voltage at LBI is below the internal threshold,
LBO sinks current to GND. A pull-up resistor of 10kΩ
or more connected from LBO to VOUTcan be used
when driving CMOS circuits. Any pull-up resistor con-
nected to LBO should not be returned to a voltage
source greater than VOUT. When LBI is above the
threshold, the LBO output is off. The low-battery com-
parator and reference voltage remain active when the
MAX756/MAX757 is in shutdown mode.
If the low-battery comparator is not used, connect LBI
to VINand leave LBO open.
Inductor SelectionThe inductors should have a saturation (incremental)
current rating equal to or greater than the peak switch-
current limit, which is 1.2A worst-case. However, it’s
generally acceptable to bias the inductor into satura-
tion by 20%, although this will reduce the efficiency.
The 22µH inductor shown in the typical applications cir-
cuit is sufficient for most MAX756/MAX757 application
circuits. Higher input voltages increase the energy
transferred with each cycle, due to the reduced
input/output differential. Minimize excess ripple due to
increased energy transfer by reducing the inductor
The inductor’s DC resistance significantly affects effi-
ciency. For highest efficiency, limit L1’s DC resistance
to 0.03Ωor less. See Table 1 for a list of suggested
inductor suppliers.
Table 1. Component SuppliersAVXUSA:(207) 282-5111, FAX (207) 283-1941
(800) 282-9975
CoilCraftUSA:(708) 639-6400, FAX (708) 639-1969
CoiltronicsUSA:(407) 241-7876, FAX (407) 241-9339
Collmer
SemiconductorUSA:(214) 233-1589
MotorolaUSA:(602) 244-3576, FAX (602) 244-4015
NichiconUSA:(708) 843-7500, FAX (708) 843-2798
Japan:+81-7-5231-8461, FAX (+81-) 7-5256-4158
NihonUSA:(805) 867-2555, FAX (805) 867-2556
Japan:+81-3-3494-7411, FAX (+81-) 3-3494-7414
Sanyo OS-CONUSA:(619) 661-6835
Japan:+81-720-70-1005, FAX (+81-720-) 70-1174
SpragueUSA:(603) 224-1961, FAX (603) 224-1430
SumidaUSA:(708) 956-0666
Japan:+81-3-3607-5111, FAX (+81-3-) 3607-5428
United
Chemi-ConUSA:(708) 696-2000, FAX (708) 640-6311
Capacitor SelectionA 100µF, 10V surface-mount (SMT) tantalum capacitor
typically provides 50mV output ripple when stepping
up from 2V to 5V at 200mA. Smaller capacitors, down
to 10µF, are acceptable for light loads or in applica-
tions that can tolerate higher output ripple.
MAX757
REF3
150μF
GND
OUT6
VIN
1N5817VOUT
LBO4
0.1μF
22μH
LBI5
100μF
SHDN1FB2
Figure 1. Standard Application Circuit
PRODUCTION
METHOD
INDUCTORSCAPACITORSSurface-MountAVX
TPS series
Sprague
595D series
Miniature
Through-Hole
Sumida
RCH654-220
Low-Cost
Through-Hole
Sumida
CD54-220 (22µH)
CoilCraft
DT3316-223
Coiltronics
CTX20-1
Sanyo OS-CON
OS-CON series
low-ESR organic
semiconductor
CoilCraft
PCH-27-223
Nichicon
PL series
low-ESR
electrolyic
United Chemi-Con
LXF series
MAX756/MAX757
