MAX877 Datasheet, PDF (1/12 Pages) Maxim Integrated Products – 5V/3.3V/3V/Adjustable-Output, Step-Up/Step-Down DC-DC Converters

19-0204; Rev 1; 5/94
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5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
_______________General Description
The MAX877/MAX878/MAX879 are pulse-skipping, step-
up/step-down DC-DC converters that provide a regulated
output from inputs both above and below the output. They
require only three external components—an inductor
(typically 22µH) and two filter capacitors.
The MAX877 delivers a regulated 5V output from 2.5V to
6.2V inputs. The MAX878 generates pin-selectable volt-
ages of 3.0V or 3.3V from 1.5V to 6.2V inputs. The MAX879
output can be adjusted from 2.5V to 6V via an external
resistor divider from 2.5V to 6.2V inputs.
A unique high-power, internal, synchronous rectifier design
(Active Rectifier™) enables the devices to regulate in a
switched linear mode if the input voltage is higher than the
desired output voltage. When the input voltage falls below
the output voltage, the MAX877/MAX878/MAX879 will
smoothly switch into a pulse-skipping boost mode and
step up from input voltages as low as 1V. In shutdown, the
active rectifier disconnects the output from the source. This
stops the current drain from input to output associated with
conventional step-up converters.
High-frequency operation (up to 300kHz) allows the use of
small surface-mount inductors. Supply current is 195µA
under no load, and only 20µA in shutdown mode. For 1-cell
(1V) step-up converters with similar performance and the
same pinout, refer to the MAX777/MAX778/MAX779 data
sheet.
________________________Applications
Two or Three NiCd Cells to 3V/3.3V Conversion
Three or Four Alkaline Cells to 5V Conversion
One Lithium Cell to 3V/3.3V Conversion
Pagers
Palmtop and Notebook Computers
Battery-Powered and Hand-Held Instruments
__________________Pin Configuration
____________________________Features
o Regulates from Inputs Above & Below the Output
o 1V to 6.2V Supply-Voltage Range
o Internal 1A Active Rectifier with Input-to-Output
Disconnect in Shutdown
o Up to 210mA Load Currents, Guaranteed
o 85% Efficiency
o Only 3 External Components
o Adjustable Current Limit
o 195µA Quiescent Supply Current
o 20µA Shutdown Supply Current
o 3V/3.3V/5V and Adjustable Output Voltage Versions
o Available in 8-Pin DIP and SO Packages
______________Ordering Information
PART
MAX877CPA
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
MAX877CSA
MAX877C/D
MAX877EPA
MAX877ESA
MAX877MJA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
Ordering Information continued on last page.
* Contact factory for dice specifications.
__________Typical Operating Circuit
INPUT
1.8V TO 6.2V
TOP VIEW
ILIM 1
IN 2
AGND 3
PGND 4
MAX877
MAX878
MAX879
8 N.C. (MAX877)^*
7 SHDN
6 OUT
5 LX
DIP/SO
22µF
ON/OFF
2
IN
1 _{ILIM MAX878}
5
LX
7
SHDN
6
OUT
SEL PGND AGND
8
4
3
22µH
OUTPUT
3.3V
210mA
100µF
* SEL (MAX878), FB (MAX879)
™ Active Rectifier is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products 1
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