FEATURES
General Description
The MAX1864/MAX1865 power-supply controllers are designed to address cost-conscious applications such as cable modem Consumer Premise Equipment (CPE), xDSL CPE, and set-top boxes. Operating off a low-cost, unregulated DC supply (such as a wall adapter output), the MAX1864 generates three positive outputs, and the MAX1865 generates four positive outputs and one negative output to provide a cost-effective system power supply.
The MAX1864 includes a current-mode synchronous step-down controller and two positive regulator gain blocks. The MAX1865 has one additional positive gain block and one negative regulator gain block. The main synchronous step-down controller generates a high-current output that is preset to 3.3V or adjustable from 1.236V to 0.8 ✕ VIN with an external resistive divider. The 100kHz/200kHz operating frequency allows the use of low-cost aluminum-electrolytic capacitors and low-cost power magnetics. Additionally, the MAX1864/MAX1865 step-down controllers sense the voltage across the low-side MOSFET’s on-resistance to efficiently provide the current-limit signal, eliminating the need for costly current-sense resistors.
Features
♦ 4.5V to 28V Input Voltage Range
♦ Master DC-DC Step-Down Converter
Preset 3.3V or Adjustable (1.236V to 0.8 ✕ VIN)
Output Voltage
Fixed-Frequency (100kHz/200kHz) PWM
Controller
No Current-Sense Resistor
Adjustable Current Limit
95% Efficient
♦ Two (MAX1864)/Four (MAX1865) Analog Gain Blocks
Positive Analog Blocks Drive Low-Cost PNP
Pass Transistors to Build Positive Linear
Regulators
Negative Analog Block (MAX1865) Drives a
Low-Cost NPN Pass Transistor to Build a
Negative Linear Regulator
♦ Power-Good Indicator
♦ Soft-Start Ramp for All Positive Regulators
Applications
xDSL, Cable, and ISDN Modems
Set-Top Boxes
Wireless Local Loop
Analog Devices (NASDAQ: ADI) is a world leader in the design, manufacture, and marketing of a broad portfolio of high performance analog, mixed-signal, and digital signal processing (DSP) integrated circuits (ICs) used in virtually all types of electronic equipment. Since our inception in 1965, we have focused on solving the engineering challenges associated with signal processing in electronic equipment. Used by over 100,000 customers worldwide, our signal processing products play a fundamental role in converting, conditioning, and processing real-world phenomena such as temperature, pressure, sound, light, speed, and motion into electrical signals to be used in a wide array of electronic devices.