Rainbow Electronics MAX1655 - Manual

_______________General Description
The MAX1649/MAX1651 BiCMOS, step-down, DC-DC
switching controllers provide high efficiency over loads
ranging from 1mA to more than 2.5A. A unique, current-
limited pulse-frequency-modulated (PFM) control scheme
gives these devices the benefits of pulse-width-modula-
tion (PWM) converters (high efficiency at heavy loads),
while using only 100µA of supply current (vs. 2mA to
10mA for PWM converters). Dropout performance down
to 300mV is provided by a high switch duty cycle (96.5%)
and a low current-sense threshold (110mV).
A high switching frequency (up to 300kHz) allows these
devices to use miniature external components.
The MAX1649/MAX1651 have dropout voltages less
than 0.3V at 500mA and accept input voltages up to
16V. Output voltages are preset at 5V (MAX1649), or
3.3V (MAX1651). They can also be adjusted to any
voltage from 1.5V to the input voltage by using two
resistors.
These step-down controllers drive external P-channel
MOSFETs at loads greater than 12.5W. If less power is
required, use the MAX639/MAX640/MAX653 step-down
converters with on-chip FETs, which allow up to a
225mA load current.
________________________Applications
PDAs
High-Efficiency Step-Down Regulation
5V-to-3.3V Green PC Applications
Battery-Powered Applications
____________________________Features
♦ More than 90% Efficiency (10mA to 1.5A Loads)
♦ More than 12.5W Output Power
♦ Less than 0.3V Dropout Voltage at 500mA
♦ 100µA Max Quiescent Supply Current
♦ 5µA Max Shutdown Supply Current
♦ 16V Max Input Voltage
♦ 5V (MAX1649), 3.3V (MAX1651), or Adjustable
Output Voltage
♦ Current-Limited Control Scheme
♦ Up to 300kHz Switching Frequency
♦ Up to 96.5% Duty Cycle
______________Ordering Information
* Dice are tested at T
A
= +25°C.
MAX1649/MAX1651
5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers
________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
8
7
6
5
GND
EXT
CS
V+ REF
SHDN
FB
OUT
DIP/SO
TOP VIEW
MAX1649
MAX1651
__________________Pin Configuration __________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0305; Rev 2; 9/95
PART TEMP. RANGE PIN-PACKAGE
MAX1649 CPA 0°C to +70°C 8 Plastic DIP
MAX1649CSA 0°C to +70°C 8 SO
MAX1649C/D 0°C to +70°C Dice*
MAX1649EPA -40°C to +85°C 8 Plastic DIP
MAX1649ESA -40°C to +85°C 8 SO
MAX1651
V+
CS SHDN
FB GND
ON/OFF
P EXT
REF OUT
OUTPUT
3.3V
INPUT
3.6V TO 16V
MAX1651 CPA 0°C to +70°C 8 Plastic DIP
MAX1651CSA 0°C to +70°C 8 SO
MAX1651C/D 0°C to +70°C Dice*
MAX1651EPA -40°C to +85°C 8 Plastic DIP
MAX1651ESA -40°C to +85°C 8 SO