General Description The MAX1864/MAX1865 power supply controllers are designed to meet cost-sensitive applications such as consumer end equipment (CPE) cable modems, xDSL customer premises equipment, and set-top boxes. Operating off a low-cost, unregulated DC power source (such as a wall adapter output), the MAX1864 produces three positive outputs, while the MAX1865 produces positive outputs and one four negative outputs to provide a cost-effective system power supply. The MAX1864 includes a current-mode synchronous buck controller and two positive-regulating gain blocks. The MAX1865 has an additional positive gain cap and 1 negative trim gain block. The main synchronous buck controller produces a high current output, preset to 3.3V or adjustable from 1.236V to 0.8✕ VIN with an external resistivedivider. The 100kHz/200kHz operating frequency allows the use of low-cost aluminum electrolytic capacitors and low-cost power magnetics. In addition, the MAX1864/MAX1865 buck controllers sense the voltage across the low-side MOSFET's on-resistance to effectively provide a current-limiting signal, eliminating the need for expensive current-sense resistors. Low-cost MAX1864/MAX1865 rails to generate additional supplies. Positively regulated gain blocks use external PNP transistors to generate low voltages directly from the main buck converter rails (eg up to 2.5V or 1.8V from the main 3.3V output) or higher buck converters with coupled winding voltages (eg 5V, 12V or 15V). The negative gain block of the MAX1865 uses an external NPN transistor with coupled windings to generate a combination of -5V and -12V or -15V. All output voltages are externally adjustable for maximum flexibility. In addition, the MAX1864/MAX1865 have soft step-down converter startup and all positive linear regulators, and have power-good output voltage monitoring on all outputs.