12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC
Controller
♦ 90% Efficiency for 30mA to 2A Load Currents
♦ Up to 24W Output Power
♦ 110µA Max Supply Current
♦ 5µA Max Shutdown Current
♦ 2V to 16.5V Input Range
♦ Preset 12V or Adjustable Output Voltage
♦ Current-Limited PFM Control Scheme
♦ Up to 300kHz Switching Frequency
♦ Evaluation Kit Available
General Description
The MAX1771 step-up switching controller provides 90% efficiency
over a 30mA to 2A load. A unique current-limited
pulse-frequency-modulation (PFM) control scheme gives this device
the benefits of pulse-widthmodulation (PWM) converters (high
efficiency at heavy loads), while using less than 110µA of supply
current (vs. 2mA to 10mA for PWM converters).
This controller uses miniature external components. Its high
switching frequency (up to 300kHz) allows surface-mount magnetics
of 5mm height and 9mm diameter. It accepts input voltages from 2V
to 16.5V. The output voltage is preset at 12V, or can be adjusted
using two resistors.
The MAX1771 optimizes efficiency at low input voltages and reduces
noise by using a single 100mV current-limit threshold under all
load conditions. A family of similar devices, the MAX770–MAX773,
trades some full-load efficiency for greater current-limit
accuracy; they provide a 200mV current limit at full load, and
switch to 100mV for light loads.
The MAX1771 drives an external N-channel MOSFET switch, allowing it
to power loads up to 24W. If less power is required, use the
MAX756/MAX757 or MAX761/MAX762 step-up switching regulators with
on-board MOSFETs. An evaluation kit is available. Order the
MAX1771EVKIT-SO.
Applications
► Positive LCD-Bias Generators
► Flash Memory Programmers
► High-Power RF Power-Amplifier Supply
► Palmtops/Hand-Held Terminals
► Battery-Powered Applications
► Portable Communicators
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V+ to GND
...............................................................-0.3V,
17V
EXT, CS, REF, SHDN, FB to GND ...................-0.3V, (V+ + 0.3V)
GND to
AGND.............................................................0.1V,
-0.1V
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
CERDIP (derate 8.00mW/°C above +70°C).................640mW
Operating Temperature Ranges
MAX1771C_A .....................................................0°C
to +70°C
MAX1771E_A ..................................................-40°C
to +85°C
MAX1771MJA ................................................-55°C to
+125°C
Junction Temperatures
MAX1771C_A/E_A.......................................................+150°C
MAX1771MJA
..............................................................+175°C
Storage Temperature Range .............................-65°C to
+160°C
Lead Temperature (soldering, 10sec)
.............................+300°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.
