MAX856 Datasheet, PDF (1/12 Pages) Maxim Integrated Products – 3.3V/5V or Adjustable-Output, Step-Up DC-DC Converters

19-0211; Rev 4; 5/96
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3.3V/5V or Adjustable-Output,
Step-Up DC-DC Converters
_______________General Description
The MAX856–MAX859 are high-efficiency, CMOS, step-
up, DC-DC switching regulators for small, low input volt-
age or battery-powered systems. The MAX856/MAX858
accept a positive input voltage between 0.8V and VOUT
and convert it to a higher, pin-selectable output voltage of
3.3V or 5V. The MAX857/MAX859 adjustable versions
accept 0.8V to 6.0V input voltages and generate higher
adjustable output voltages in the 2.7V to 6.0V range.
Typical efficiencies are greater than 85%. Typical quies-
cent supply current is 25µA (1µA in shutdown).
The MAX856–MAX859 combine ultra-low quiescent supply
current and high efficiency to give maximum battery life. An
internal MOSFET power transistor permits high switching
frequencies. This benefit, combined with internally set peak
inductor current limits, permits the use of small, low-cost
inductors. The MAX856/MAX857 have a 500mA peak
inductor current limit. The MAX858/MAX859 have a 125mA
peak inductor current limit.
________________________Applications
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
__________Typical Operating Circuit
____________________________Features
o 0.8V to 6.0V Input Supply Voltage
o 0.8V Typ Start-Up Supply Voltage
o 85% Efficiency at 100mA
o 25µA Quiescent Current
o 1µA Shutdown Mode
o 125mA and 500mA Switch-Current Limits Permit
Use of Low-Cost Inductors
o Up to 500kHz Switching Frequency
o ±1.5% Reference Tolerance Over Temperature
o Low-Battery Detector (LBI/LBO)
o 8-Pin SO and µMAX Packages
______________Ordering Information
PART
TEMP. RANGE PIN-PACKAGE
MAX856CSA
0°C to +70°C
8 SO
MAX856CUA
0°C to +70°C
8 µMAX
MAX856C/D
0°C to +70°C
Dice*
MAX856ESA
MAX856MJA
-40°C to +85°C
-55°C to +125°C
8 SO
8 CERDIP^†
MAX857CSA
0°C to +70°C
8 SO
MAX857CUA
0°C to +70°C
8 µMAX
MAX857C/D
0°C to +70°C
Dice*
MAX857ESA
MAX857MJA
-40°C to +85°C
-55°C to +125°C
8 SO
8 CERDIP^†
Ordering Information continued at end of data sheet.
* Dice are tested at TA = +25°C only.
† _{Contact factory for availability.}
INPUT
0.8V TO V_OUT
ON/OFF
3V/5V SELECT
LOW-BATTERY
DETECTOR
INPUT
SHDN
LX
MAX856
3/5
OUT
LBI
REF _GND
LBO
OUTPUT
47µH ^{5V AT 100mA}
OR
3.3V AT 125mA
1N5817
68µF
LOW-BATTERY
DETECTOR OUTPUT
__________________Pin Configuration
TOP VIEW
SHDN 1
3/5 ²
REF ³
LBO ⁴
MAX856
MAX858
8 _LX
7 GND
6 OUT
5 _LBI
SO/µMAX
SHDN 1
FB ²
REF ³
LBO ⁴
MAX857
MAX859
8 _LX
7 GND
6 OUT
5 _LBI
SO/µMAX
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