MAX757 Maxim Integrated Products, MAX757 Datasheet

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MAX757

Manufacturer Part Number
MAX757
Description
Manufacturer
Maxim Integrated Products
Datasheet

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The 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 0.7V and 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.
________________________Applications
19-0113; Rev. 2; 1/95
Call toll free 1-800-998-8800 for free samples or literature.
__________Typical Operating Circuit
_______________General Description
0.1 F
3.3V 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
2
1
3
SHDN
3/5
REF
________________________________________________________________ Maxim Integrated Products
MAX756
7
5
GND
LBI
150 F
OUT
LBO
LX
8
6
4
2V to V
INPUT
OUT
22 H
LOW-BATTERY
DETECTOR OUTPUT
1N5817
3.3V at 300mA
5V at 200mA
OUTPUT
100 F
or
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
____________________________Features
* Dice are tested at T
_________________Pin Configurations
______________Ordering Information
MAX756CPA
MAX756CSA
MAX756C/D
MAX756EPA
MAX756ESA
MAX757CPA
MAX757CSA
MAX757C/D
MAX757EPA
MAX757ESA
Operates Down to 0.7V Input Supply Voltage
87% Efficiency at 200mA
60µA Quiescent Current
20µA Shutdown Mode with Active Reference and
LBI Detector
500kHz Maximum Switching Frequency
±1.5% Reference Tolerance Over Temperature
Low-Battery Detector (LBI/LBO)
8-Pin DIP and SO Packages
TOP VIEW
PART
SHDN
SHDN
LBO
REF
LBO
REF
3/5
FB
A
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
1
2
3
4
1
2
3
4
TEMP. RANGE
= +25°C only.
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
MAX756
DIP/SO
MAX757
DIP/SO
8
7
6
5
8
7
6
5
8 Plastic DIP
8 SO
Dice*
8 Plastic DIP
8 SO
8 Plastic DIP
8 SO
Dice*
8 Plastic DIP
8 SO
LX
GND
OUT
LBI
LX
GND
OUT
LBI
PIN-PACKAGE
1

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MAX757 Summary of contents

Page 1

... The MAX756 accepts a positive input voltage down to 0.7V and converts higher pin- selectable output voltage of 3.3V or 5V. The MAX757 is an adjustable version that accepts an input voltage down to 0.7V and generates a higher adjustable output voltage in the range from 2 ...

Page 2

... I = 20mA LOAD Voltage (once started 0mA, 3/5 = 3V, LBI = 1.25V, V Quiescent Supply Current in LOAD 3.3V Mode (Note 1.3V (MAX757 only) Battery Quiescent Current Output set for 3.3V Measured Figure 1 IN Shutdown Quiescent Current SHDN = 0V, LBI = 1.25V, 3/5 = 3V, V (Note 1.3V (MAX757 only) ...

Page 3

Operating Characteristics (Circuit of Figure +25°C, unless otherwise noted.) A EFFICIENCY vs. LOAD CURRENT 3.3V OUTPUT MODE 100 1000 ...

Page 4

... V = 2.5V IN HORIZONTAL = 50 s/div 5V Mode ______________________________________________________________Pin Description PIN NAME MAX756 MAX757 Shutdown Input disables SMPS when low, but the voltage reference and low-battery com SHDN parator remain active. 2 – 3/5 Selects the main output voltage setting; 5V when low, 3.3V when high. ...

Page 5

... 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 ...

Page 6

... 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 ...

Page 7

The ESR of both bypass and filter capacitors affects efficiency. Best performance is obtained by using spe- cialized low-ESR capacitors, or connecting two or more filter capacitors in parallel. The smallest low-ESR SMT tantalum capacitors currently available are Sprague 595D ...

Page 8

... All connections to the FB and LX pins should also be kept as short as possible. To obtain maximum output power and efficiency and mini- mum output ripple voltage, use a ground plane and solder the MAX756/MAX757 GND (pin 7) directly to the ground plane. ________________________________________________________Package Information E ...

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